Biology subjects

Brul, S.

Publications and source records attributed to Brul, S..

At least 19 recordsLinked to original sources

bioRxiv2026

GerAB Residues Predicted to Interact with Water Based on MD Simulations Mediate Germinosome Stability in Bacillus subtilis spores

Some species in the Bacillales and Clostridiales orders form spores under unfavourable environmental conditions. These spores are metabolically dormant and highly resistant to extreme stress. The spore core--analogous to the protoplast of vegetative cells--contains only 25-45% water by wet weight, compared to ~80% in vegetative cells. Upon activation by small-molecule nutrients, spores germinate, restoring their core water content, restoring metabolism and becoming easy to kill, while progressing through outgrowth to vegetative growth. GerAB is the B subunit of the prototypical Bacillus subtilis GerA GR (germinant receptor), a membrane protein belonging to the Amino Acid--Polyamine-Organocation (APC) superfamily of transporters. It functions as the L-alanine sensor that initiates germination and was previously predicted, based on molecular dynamics (MD) simulations, to contain a putative water channel. Using MD simulations, we identified low amount of water permeating through GerAB (ranging from 1-121 water molecule/{micro}s in 10 parallel MD simulations), thus revealing a water pathway in GerAB that diverges from the L-alanine binding pocket, suggesting that water transport may play roles in germination beyond facilitating ligand binding. Analysis of water-residue contact frequencies identified eight hydrophilic residues lining this path. Individual substitution of high-contact residues with similarly sized non-polar residues impaired L-alanine germination and disrupted GerAB structural integrity as assessed by Western Blotting. These mutants also respond to the AGFK germinant mixture (L-asparagine, D-glucose, D-fructose and potassium) in slower, yet individually distinct kinetics compared to that of wt spores. These findings prove that water contact residues in GerAB predicted by MD simulations are crucial for the stability of this protein and thus the germinosome complex with all GRs.

microbiology↗

bioRxiv2025

A mathematical kinetic model of memory in Bacillus subtilis spore germination

Dormant Bacillus subtilis spores germinate through interaction of germinants with germinant receptors (GRs). Subsequently, the activated GR signal is transduced to SpoVA proteins that constitute transport channels. The opening of the SpoVA channel then leads to calcium dipicolinic acid (CaDPA) release and then completion of spore germination. Spores are known to exhibit memory in germination, as spores given an initial short germinant pulse respond more readily to a second pulse. We have developed a mathematical model to identify a minimal reconstructed molecular network that is crucial for germination kinetics leading to memory of germinant exposure; the model reproduces experimental double germinant pulse germination curves. Analysis of the reconstructed network indicates that a minimal set of inactive and active GRs and a SpoVA channel in three states - closed inactive, closed active and open - is needed to reproduce memory. Spore germination memory is introduced in the network by the activation and deactivation rates of GRs, and by the interplay between activation of closed SpoVA channels and their rate of opening and closing. Author summaryDormant bacterial spores return to life in germination when exposed to germinants which are recognized by germinant receptors (GRs). Spores have memory of germinant exposure, such that more spores germinate after a 2nd germinant pulse than after the 1st one, if intervals between pulses are short. In this work, a mathematical model has been developed that reproduces experimental memory behavior. Computer simulations of the model reveal the crucial factors in spore memory of germinant exposure as: i) active and inactive GR states and ii) a membrane channel for a major spore core molecule, Ca-dipicolinic acid (CaDPA), with the channel existing in closed inactive, closed active and open states, all of which are indispensable for spore memory. The model will be part of an iterative cycle of modelling of network dynamics and generating hypotheses for further experimentation.

microbiology↗

bioRxiv2025

Driving factors for beta-lactam resistance gene amplification during de novo resistance evolution in E. coli

Long-term exposure of E. coli to non-lethal step-wise increasing concentrations of beta-lactam antibiotics induces high levels of resistance that can be accompanied by amplification of a chromosomal fragment around the ampC gene. We compared the amplification of the ampC fragment in the wildtype, an ampC knockout mutant, a mutant in which the ampC gene was replaced by a tetracycline resistance gene tet(B)and a strain in which the ampC has been translocated. When ampC was removed, no amplification occurred at the original ampC location, but DNA fragments were amplified around the genes coding for efflux pump AcrAB and the multiple antibiotic resistance operon MarRAB. When tet(B) replaced ampC, exposure to tetracycline induced amplification of comparable fragments, while exposure to amoxicillin induced duplication of a larger fragment elsewhere. When ampC was translocated, a fragment around it at the new location was amplified. The importance of the presence but not of the location within the chromosome of the resistance genes for the amplification process indicates that the mechanisms are neither gene nor location specific. Without the relatively efficient resistance gene ampC, duplication and amplification occur around acrAB and marRAB that code for amoxicillin and tetracycline resistance factors. These duplications and amplifications are prevented by ampC amplification.

microbiology↗

bioRxiv2024

Candida albicans and Staphylococcus aureus reciprocally promote secretion of virulence factors

Co-infections of Candida albicans and Staphylococcus aureus can significantly increase morbidity and mortality. This synergism is linked to the interactions between C. albicans and S. aureus that allow for staphylococcal co-invasion and dissemination. While it is known that extracellular virulence factors (ECVFs) contribute to this process, the effects of C. albicans-S. aureus co-culturing on ECVF composition remain unknown. In this study we used mass spectrometry-based proteomics to investigate the effect of co-culturing on the extracellular proteins released by the S. aureus and C. albicans. Co- culturing of C. albicans and S. aureus promoted the secretion of 7 cytolytic, 11 proteolytic, and 3 lipolytic ECVFs. Interestingly, co-culturing of C. albicans Als1p/Als3p mutant alleviated the increase for the majority of the differentially changed C. albicans ECVFs, but not for S. aureus ECVFs, highlighting the importance of Als1p/Als3p in the secretion of C. albicans ECVFs. Of 27 detected S. aureus ECVFs, 17 were significantly increased in co-culturing. Among these, maintenance of pH alone in S. aureus monoculture increased five haemolytic proteins, i.e., alpha haemolysin (Hly/Hla), beta haemolysin (Hlb), and gamma haemolysin (HlgA-C) to a similar extent as the co-culture. In contrast, maintenance of pH diminished the increase of protease-like proteins, (phospho)lipases, delta hemolysin, and leukotoxin, suggesting that both pH-dependent and pH-independent C. albicans factors affect S. aureus ECVFs. A cytotoxicity assay demonstrated that the secretome from co-culture has higher cytotoxicity towards human oral cells (Ca 9-22 and HO1N1) than monoculture. Finally, co-culturing increased the levels of non-extracellular virulence factors from both C. albicans and S. aureus. Taken together, the co-culturing of C. albicans and S. aureus reciprocally promotes their virulence potential, which may provide insights into the synergistic lethality during their co-infection in vivo.

microbiology↗

bioRxiv2024

Modelling interactions that determine core gut microbiome stability to predict microbiome perturbation by opportunistic pathogens

The gut microbiome plays a crucial role in host homeostasis, with implications for nutrition, immune development, metabolism, and protection against pathogens. Disturbance of the microbiome by microbial invasion can be negative or positive: invasions of opportunistic pathogens can cause disease while dysbiotic states need invasions to recover. However, the complexity of the microbiome challenges our understanding of what factors determine the ability of microbes to invade. In this study we measure interactions between members of a SynCom of prominent gut bacteria with supernatant assays. We measure relative abundances of growth of co-cultures up to four species to validate a generalised Lotka-Volterra model parameterized with these supernatant assays. We predict differential invasion profiles of the opportunistic pathogens Escherichia coli and Bacteroides ovatus based on their monoculture growth profiles and interactions with other species. With experimental data of both predicted invasion and resistant communities we confirm model predictions of invasion success. Our model shows that both negative interactions within a community and neutral to positive interactions with the invading species promote invasion success, but the interactions towards the invading species dominate. Our validated approach opens the way for testing of interactions of human gut microbiome species, thereby developing inventions to avoid pathogenic overgrowth and therapies to enhance health-benefitting invasions. ImportanceThe stability of the human gut microbiome is crucial for host health, with opportunistic pathogen invasions causing diseases and healthy strain replacements needed for recovery. The microbiotas complexity complicates understanding its stabilizing mechanisms. This study uses a 10-species synthetic community of common gut microbiota to predict stable communities and invasion success. We employ supernatant experiments to parameterize a computational model, accurately predicting community composition and invasion success of Escherichia coli and Bacteroides ovatus. Our findings show that interactions within the resident community and with the invader are important, but the latter dominate. These results pave the way for larger-scale studies to characterize gut microbiome interactions and properties that resist invasions, potentially benefiting health through improved probiotics and faecal microbiota transplants.

microbiology↗

bioRxiv2024

De novo acquisition of antibiotic resistance in six species of bacteria

Bacteria can become resistant to antibiotics in two ways, by acquiring resistance genes through horizontal gene transfer and by de novo development of resistance upon exposure to non-lethal concentrations. The importance of the second process, de novo build-up, has not been investigated systematically over a range of species and may be underestimated as a result. To investigate the DNA mutation patterns accompanying the de novo antibiotic resistance acquisition process, six bacterial species encountered in the food chain were exposed to step-wise increasing sublethal concentrations of six antibiotics to develop high levels of resistance. Phenotypic and mutational landscapes were constructed based on whole genome sequencing (WGS) sequencing at two time points of the evolutionary trajectory. In this study, we found: 1) all of the six strains can develop high levels of resistance against most antibiotics. 2) increased resistance is accompanied by different mutations for each bacterium-antibiotic combination. 3) the number of mutations varies widely, with Y. enterocolitica having by far the most. 4) in the case of fluoroquinolone resistance, a mutational pattern of gyrA combined with parC is conserved in five of six species. 5) mutations in genes coding for efflux pumps are widely encountered in gram-negative species. The overall conclusion is that very similar phenotypic outcomes are instigated by very different genetic changes. IMPORTANCEThe significance of this study lies in the comparison of how six species of distinct genomic background under uniform conditions develop high levels of antibiotic resistance against six antibiotics. The mutational patterns in these six species of bacteria identify common target mutations and reveal how they acquire mutations from various pathways to survive and grow when exposed to sub-lethal levels of antibiotics. In addition to providing insights in microbial genetics, outcome of this study will assist policymakers when formulating practical strategies to prevent development of antimicrobial resistance in human and veterinary health care.

microbiology↗

bioRxiv2024

Identification of key residues in water channel formation in the Bacillus subtilis germinant receptor protein GerAB

Some Bacillales and Clostridiales bacteria form spores in unfavorable environments. These spores are dormant but can rapidly resume metabolism in response to certain small molecule nutrients. This process is termed germination and can be initiated by a variety of low molecular wt nutrients termed germinants. Structural modeling and mutagenesis studies showed that GerAB, an inner membrane (IM) protein of the Bacillus subtilis spore germinant receptor (GR) GerA, is involved in L-alanine-initiated spore germination. A previous molecular simulation study also suggested there is a water channel in GerAB. In the current work, Steered Molecular Dynamics (SMD) simulations were employed to force a single water molecule through GerAB, identifying three key amino acid residues, Y97, L199 and F342, that interfere with water passage. When these residues were altered to alanine, L-alanine germination was minimal in spores with L199A, F342A and triA (Y97A, L199A and F342A triple mutant), while Y97A mutant spores germinated [~]61%. And besides Y97A, all other mutants showed compromised germination triggered by AGFK mixture. Western blotting found reduced levels of the GerA GR in the Y97A mutant, and an absence of the GerA GR in all other mutants. This proved that all three identified residues are crucial to the structural integrity of the GerAB protein and therefore probably the formation of the GR complex, the germinosome.

microbiology↗

bioRxiv2024

Non-mechanical disruption of Bacillus subtilis spores allows sensitive and deep characterization of the minimal proteome for resuming a cellular lifestyle.

In response to extreme conditions, Bacillus subtilis generates highly resilient spores characterized by a unique multilayered structure. This confers resistance against various chemicals and enzymes yet adding complexity to the analysis of the spore proteome. As the first step in bottom-up proteomics, sample preparation poses a significant challenge. We assessed how an optimized protocol for sample preparation by easy extraction and digestion (SPEED) performed compared to previously established methods "One-pot" (OP) and single-pot, solid phase-enhanced sample-preparation (SP3) for the proteomic analysis of B. subtilis cell and spore samples. We found that SPEED outperformed both OP and SP3 in terms of peptides and proteins identified, moreover SPEED highly reproducibly quantified over 1000 proteins in limited input samples as low as 1 OD600 of B. subtilis cells and spores. SPEED was applied to analyze spore samples of different purity by applying sequential purification following harvesting of spores. Comparison of the differential abundance of proteins revealed clusters likely partially stemming from remaining vegetative cells in less purified spore samples. We show that ranking of absolute protein abundance in cellular and spore samples further enables us to rationally differentiate integral spore proteins from vegetative remnants. This is of importance in applications and organisms where highly homogenous spore samples are difficult to obtain. A deep proteomic analysis of spore and vegetative cell samples with the new approach led to the identification of 2447 proteins, 2273 of which were further quantified and compared between B. subtilis spores and cells. Our findings indicate that pathways related to peptidoglycan biosynthesis, glycolysis, carbon metabolism, and biosynthesis of secondary metabolites are shared between cells and spores. This corroborates and extends earlier work stressing that despite marked differences in their physiological states, spores preserve vegetative cell (core) proteins, essential for revival under conditions conducive to growth. O_FIG O_LINKSMALLFIG WIDTH=200 HEIGHT=126 SRC="FIGDIR/small/584050v2_ufig1.gif" ALT="Figure 1"> View larger version (36K): org.highwire.dtl.DTLVardef@9ac7b1org.highwire.dtl.DTLVardef@1ac35c6org.highwire.dtl.DTLVardef@fe73a4org.highwire.dtl.DTLVardef@15a24e8_HPS_FORMAT_FIGEXP M_FIG C_FIG

microbiology↗

bioRxiv2023

Isolation and characterization of persisters of the pathogenic microorganism Staphylococcus aureus

Staphylococcus aureus is a notorious pathogen responsible for significant morbidity and mortality in both human society and animal husbandry. The presence of S. aureus persisters is also one of the leading causes of recurrent and chronic diseases. Persisters are a subset of growth-arrested bacteria within a susceptible bacterial population that are able to tolerate antibiotic treatment and resuscitate after stress removal. Consequently, investigating their formation and characteristics is of crucial importance to provide mechanism-based options for their eradication. However, one challenge in mechanistic research on persisters is the enrichment of pure persisters. In this work, we validated a proposed method to isolate persisters from vancomycin and enrofloxacin generated persistent populations. With this, we analyzed the proteome profile of pure persisters and revealed the distinct mechanisms associated with vancomycin and enrofloxacin induced persisters. Furthermore, morphological and metabolic characterizations were performed, indicating further differences between these two persister populations. Finally, we assessed the effect of ATP repression, protein synthesis inhibition and reactive oxygen species (ROS) level on persister formation. In conclusion, this work provides a comprehensive understanding of S. aureus vancomycin and enrofloxacin induced persisters at the molecular, single cell and population levels, facilitating a better understanding of persisters and the development of effective strategies to combat them.

microbiology↗

bioRxiv2023

Reactive oxygen species accelerate de novo acquisition of antibiotic resistance in E. coli

Reactive oxygen species (ROS) produced as a secondary effect of bactericidal antibiotics are hypothesized to play a role in killing bacteria. However, the role of ROS in the development of de novo resistance as a result of sublethal levels of bactericidal antibiotics has barely been investigated. Here, we report that single-gene knockout strains with reduced ROS scavenging exhibited enhanced ROS accumulation and more rapid acquisition of resistance when exposed to sublethal levels of bactericidal antibiotics. Consistent with this observation, the ROS scavenger thiourea in the medium decelerated resistance development. Thiourea downregulated the transcriptional level of error-prone DNA polymerase and DNA glycosylase MutM, which counters the incorporation and accumulation of 8-hydroxy-2-deoxyguanosine (8-HOdG) in the genome. The level of 8-HOdG significantly increased following incubation with bactericidal antibiotics but decreased after treatment with the ROS scavenger thiourea. These observations suggest that in E. coli sublethal levels of ROS stimulate de novo development of resistance, providing a mechanistic basis for hormetic responses induced by antibiotics. ImportanceExposure to sublethal concentrations of antimicrobials is known to result in de novo resistance development against the specific compound. Particularly, the use of antibiotics as feed additives to enhance productivity may result in the development of drug resistance in environmental and veterinary microorganisms, which could subsequently transfer to human populations. Nevertheless, the mechanisms underlying de novo resistance development have not been extensively explored. In this study, we indicate the role of ROS in promoting the formation of resistance to bactericidal antibiotics and show the potential of ROS scavengers to reduce mutation rates and slow down resistance formation under long-term selection. Thus, the supplementary use of antioxidants during prolonged antibiotic administration potentially contributes to mitigating the emergence of antimicrobial resistance.

microbiology↗

bioRxiv2023

Molecular physiological characterization of the dynamics of persister formation in Staphylococcus aureus.

Bacteria possess the ability to enter a growth arrested state known as persistence in order to survive antibiotic exposure. Clinically, persisters are regarded as the main causative agents for chronic and recurrent infectious diseases. To combat this antibiotic-tolerant population, a better understanding of the molecular physiology of persisters is required. In this study, we collected samples at different stages of the biphasic kill curve to reveal the dynamics of the cellular molecular changes that occur in the process of persister formation. After exposure to antibiotics with different modes of action, namely vancomycin and enrofloxacin, similar persister levels were obtained. Both shared and distinct stress responses were enriched for the respective persister populations. However, the dynamics of the presence of proteins linked to the persister phenotype throughout the biphasic kill curve and the molecular profiles in a stable persistent population did show large differences depending on the antibiotic used. This suggests that persisters at the molecular level are highly stress specific, emphasizing the importance of characterizing persisters generated under different stress conditions. Additionally, although generated persisters exhibited cross-tolerance toward tested antibiotics, combined therapies were demonstrated to be a promising approach to reduce persister levels. In conclusion, this investigation sheds light on the stress-specific nature of persisters, highlighting the necessity of tailored treatment approaches and the potential of combined therapy. ImportanceBy monitoring proteome and metabolites during Staphylococcus aureus persister formation under vancomycin and enrofloxacin exposure, we revealed the dynamic information of the molecular physiology of persister formation upon exposure to two different antibiotics with different modes of action. The data shows that cells that phenotypically are similarly classified as persisters, do have several molecular characteristics in common but, remarkably so, differ substantially in a significant number of other aspects of their molecular makeup. These contrasts provided valuable insights into persister eradication, which holds considerable clinical relevance.

microbiology↗

bioRxiv2023

Multi-omics analysis of Bacillus. subtilis spores formed at different environmental temperatures reveal differences at the morphological and molecular level.

Spore-forming bacteria play an essential role in the food industry and public health. Through sporulation, bacteria can withstand extreme environmental conditions that vegetative cells cannot survive. Although it is well established that the same environmental factors that affect the growth of vegetative cells also profoundly influence sporulation, the mechanisms of how growth conditions affect spore structure and function remain unknown. Prior research has shown that spores prepared at higher temperatures are more heat resistant than those prepared at lower temperatures. The present study examines, both at metabolomic and proteomic levels, the effect of different sporulation temperatures (25, 37 and 42{degrees}C) on the small molecule and protein composition of spores (strain PY79) of the model organism B. subtilis. Through differential harvesting times, spores of the same developmental stage were obtained for each temperature regime. The heat resistance, dipicolinic acid content, germination kinetics and spore morphology were assayed to compare spore properties. Metabolome and proteome analysis yielded unparalleled broad molecular detail of the spores formed at different environmental temperatures. Our findings indicate that peptidoglycan biosynthesis and 28 outer-layer proteins play a crucial role in the functional diversity of spores produced by B. subtilis under varying temperatures.

microbiology↗

bioRxiv2023

Integrative metabolomics and proteomics allow the global intracellular characterization of Bacillus subtilis cells and spores.

Reliable and comprehensive multi-omics analysis is essential for researchers to understand and explore complex biological systems more completely. Bacillus subtilis is a model organism for Gram-positive spore-forming bacteria, and in-depth insight into the physiology and molecular basis of spore formation and germination in this organism requires advanced multilayer molecular datasets generated from the same sample. In this study, we evaluated two monophasic methods for polar and nonpolar compound extraction (acetonitrile/methanol/water; isopropanol/water, and 60% ethanol), and two biphasic methods (chloroform/methanol/water, and methyl tert-butyl ether/methanol/water) on coefficients of variation of analytes, identified metabolite composition and the quality of proteomics profiles. The analytical workflow comprises (1) parallel metabolite and protein extraction, (2) monophasic or biphasic sample extraction, (3) proteomics comparison and (4) multi-omics-based data visualization. The 60% EtOH protocol proved to be the easiest in sample processing and more amenable to automation. Collectively, we annotated 505 and 484 metabolites and identified 1665 and 1562 proteins in B. subtilis vegetative cells and spores, respectively. We also show differences between vegetative cells and spores from a multi-omics perspective and demonstrated that an integrative multi-omics analysis can be implemented from one sample using the 60% EtOH protocol. Correlation analysis further demonstrated that the metabolome and proteome datasets were highly correlated in content for components annotated to be part of the pyrimidine metabolism pathway. The results obtained by the 60% EtOH protocol provide a comprehensive insight into differences in the metabolic and protein makeup of B. subtilis vegetative cells and spores. O_FIG O_LINKSMALLFIG WIDTH=200 HEIGHT=122 SRC="FIGDIR/small/545067v1_ufig1.gif" ALT="Figure 1"> View larger version (41K): org.highwire.dtl.DTLVardef@18b0206org.highwire.dtl.DTLVardef@1321433org.highwire.dtl.DTLVardef@cc5e6eorg.highwire.dtl.DTLVardef@14bac12_HPS_FORMAT_FIGEXP M_FIG C_FIG

microbiology↗

bioRxiv2023

Exploring the potential of Bacillus subtilis as cell factory for food ingredients and special chemicals

BackgroundBacillus subtilis has been established as model microorganism for fundamental research in the laboratory on protein production/secretion and sporulation and as model bacterium for controlling spoilage in the food industry. It has also been used for production of (commercial) enzymes and several secondary metabolites such as vitamins. However, this doesnt fully reflect the potential of B. subtilis as a cell-factory. Here, various strains of B. subtilis, including food-grade, spore-deficient strains and industrially used strains, were compared for their growth and metabolic potential. Industry-relevant parameters were analyzed for all strains under various aeration regimes, under anaerobic conditions, in various nutritious and nutrient-limited cultivation media, with and without organic nitrogen sources, and with and without sugar. ResultsPractical experiments were conducted to compare industrial relevant properties like growth rates, intracellular components and extracellular metabolite profile of different B. subtilis strains. Based on growth flexibility in different media, we found that some strains like NCIB3610 and DSM1092 are adapted to inorganic or organic nitrogen source utilization, which is highly relevant when considering a biorefinery approach using various cheap and abundant waste/sidestreams. Secondly, spore-deficient strains such as 3NA, 168S and PY79S, showed advantages in microbial protein and acetolactate pathway expression, which is associated with applications in food industry for protein supplement and diacetyl production. Lastly, WB800 and PY79S exhibited potential for fermentative production of Dipicolinic acid, 2,3-Butanediol and Lactic acid that could serve as precursors for biopolymers. ConclusionThis study demonstrates the broad potential for more extensive industrial use of Bacillus subtilis in the (bio-based) chemical industry for use of sidestreams, in the personal care industry, in the food industry for food additive production, and in the bio-sustainable industry for biofuel and bio-degradable plastic precursors production. In addition, selecting different B. subtilis strains for specific purposes makes full use of the diversity of this species and increases the potential of B. subtilis in its contribution to the bio-based economy.

microbiology↗

bioRxiv2022

Model-driven approach for the production of butyrate from CO2/H2 by a novel co-culture of C. autoethanogenum and C. beijerinckii.

One-carbon (C1) compounds are promising feedstocks for sustainable production of commodity chemicals. CO2 is a particularly advantageous C1-feedstock since it is an unwanted industrial off-gas that can be converted to valuable products while reducing its atmospheric levels. Acetogens are known microorganisms that can grow on CO2/H2 and syngas converting these substrates into ethanol and acetate. Co-cultivation of acetogens with microbes that can further process such products can expand the variety of products to, for example, medium chain fatty acids (MCFA) and longer chain alcohols. Solventogens are microorganisms known to produce MCFA and alcohols via the acetone, butanol and ethanol (ABE) fermentation in which acetate is a key metabolite. Thus, co-cultivation of a solventogen and acetogen in a consortium provides a potential platform to produce valuable chemicals from CO2. In this study, metabolic modelling was implemented to design a new co-culture of an acetogen and a solventogen to produce butyrate from CO2/H2 mixtures. The model-driven approach suggested the ability of the studied solventogenic species to grow on lactate/glycerol with acetate as co-substrate. This ability was confirmed experimentally by cultivation of Clostridium beijerinckii on these substrates in serum bottles and subsequently in pH-controlled bioreactors. Community modelling also suggested that a novel microbial consortium consisting of the acetogen Clostridium autoethanogenum, and the solventogen C. beijerinckii would be feasible and stable. On the basis of this prediction, a co-culture was experimentally established. C. autoethanogenum grew on CO2/H2 producing acetate and traces of ethanol. Acetate was in turn, consumed by C. beijerinckii together with lactate, producing butyrate. These results show that community modelling of metabolism is a valuable tool to guide the design of microbial consortia for the tailored production of chemicals from renewable resources.

microbiology↗

bioRxiv2021

Heat activation and inactivation of bacterial spores. Is there an overlap?

Heat activation at a sublethal temperature is widely applied to promote Bacillus species spore germination. This treatment also has potential to be employed in food processing to eliminate undesired bacterial spores by enhancing their germination, and then inactivating the less heat resistant germinated spores at a milder temperature. However, incorrect heat treatment could also generate heat damage in spores, and lead to more heterogeneous spore germination. Here, the heat activation and heat damage profile of Bacillus subtilis spores was determined by testing spore germination and outgrowth at both population and single spore levels. The heat treatments used were 40-80{degrees}C, and for 0-300 min. The results were as follows. 1) Heat activation at 40-70{degrees}C promoted L-valine and L-asparagine-glucose-fructose-potassium (AGFK) induced germination in a time dependent manner. 2) The optimal heat activation temperatures for AGFK and L-valine germination via the GerB plus GerK or GerA germinant receptors were 65 and 50-65{degrees}C, respectively. 3) Heat inactivation of dormant spores appeared at 70{degrees}C, and the heat damage of molecules essential for germination and growth began at 70 and 65{degrees}C, respectively. 4) Heat treatment at 75{degrees}C resulted in both activation of germination and damage to the germination apparatus, and 80{degrees}C treatment caused more pronounced heat damage. 5) For the spores that should withstand adverse environmental temperatures in nature, heat activation seems functional for a subsequent optimal germination process, while heat damage affected both germination and outgrowth.

microbiology↗

bioRxiv2021

Organization and dynamics of the SpoVAEa protein, and its surrounding inner membrane lipids upon germination of Bacillus subtilis spores

The SpoVA proteins make up a channel in the inner membrane (IM) of B. subtilis spore. This channel responds to signals from activated germinant receptors (GRs), and allows release of Ca2+-DPA from the spore core during germination. In the current work, we studied the location and dynamics of SpoVAEa in dormant spores. Notably, the SpoVAEa-SGFP2 proteins were present in a single spot in spores, similar to the complex formed by all GRs. However, while the GRs spot remains in one location, the SpoVAEa-SGFP2 spot in the IM moved randomly with high frequency. The dynamics of the SpoVAEa-SGFP2 and its surrounding IM region as stained by fluorescent dyes were also tracked during spore germination, as the dormant spore IM appeared to have an immobile germination related functional microdomain. This microdomain disappeared around the time of appearance of a germinated spore, the loss of fluorescence of the IM by fluorescent dyes, as well as the appearance of SpoVAEa-SGFP2 peak fluorescent intensity occurred in parallel. These observed events were highly related to the rapid phase darkening, which is considered as the Ca2+DPA rapid release. We also tested the response of SpoVAEa and the IM to thermal treatments at 40-80{degrees}C. Heat treatment triggered an increase of green autofluorescence, which is speculated to be due to coat protein denaturation, and 80{degrees}C treatments induce the appearance of phase-grey-like spores. These spores presumably have a similar intracellular physical state as the phase grey spores detected in the germination but lack the functional proteins for further germination events.

microbiology↗

bioRxiv2021

The role of the gut microbiota in the effects of early-life stress and dietary fatty acids on later-life central and metabolic outcomes in mice

Early-life stress (ELS) leads to increased vulnerability for mental and metabolic disorders. We have previously shown that dietary low {omega}-6/{omega}-3 polyunsaturated fatty acid (PUFA) ratio is able to protect against ELS-induced cognitive impairments. Due to the importance of the gut microbiota as determinants of long-term health, we here study the impact of ELS and dietary PUFAs on the gut microbiota, and how this relates to the previously described cognitive, metabolic and fatty acid profiles. Male mice were exposed to ELS via the limited bedding and nesting paradigm (postnatal day (P)2 - P9) and to an early diet (P2 - P42) with either high (15) or low (1) {omega}-6 linoleic acid to {omega}-3 alpha-linolenic acid ratio. 16S ribosomal RNA was sequenced and analyzed from fecal samples at P21, P42 and P180. ELS increased {beta}-diversity at P42, which persisted into adulthood. The low {omega}-6/{omega}-3 diet prevented the ELS-induced increase in {beta}-diversity, at P42. At the level of taxa abundance, for example, the abundance of the phyla Bacteroidetes increased while Actinobacteria and Verrucomicrobia decreased with age; ELS reduced the relative abundance of the genera RC9 gut group and Rikenella into adulthood and the low {omega}-6/{omega}-3 diet reduced the abundance of the Firmicutes Erysipelotrichia. At P42, species abundance correlated with body fat mass and circulating leptin (e.g. Bacteroidetes and Proteobacteria taxa) and fatty acid profiles (e.g. Firmicutes taxa). This study gives novel insights into the impact of age, ELS and dietary PUFAs on microbiota composition, providing potential targets for non-invasive (nutritional) modulation of the ELS-induced deficits. ImportanceEarly-life stress (ELS) leads to increased vulnerability to develop mental and metabolic disorders, however the biological mechanisms leading to such programming are not fully clear. Increased attention has been given to the importance of the gut microbiota as determinant of long term health and as potential target for non-invasive nutritional strategies to protect against the negative impact of ELS. Here we give novel insights in the complex interaction between ELS, early dietary {omega}-3 availability and the gut microbiota across ages and provides new potential targets for (nutritional) modulation of the long-term effects of the early-life environment via the microbiota.

microbiology↗