Biology subjects

Hertweck, C.

Publications and source records attributed to Hertweck, C..

14 recordsLinked to original sources

bioRxiv2026

Viral infection and virophage co-infection induce distinct remodeling of host lipidome

Virophages are small double-stranded DNA viruses that co-infect eukaryotic cells along with giant viruses. They are widespread in aquatic ecosystems and can influence microbial population dynamics by acting as an adaptive antiviral defense system, limiting production of giant virus progeny. Giant viruses extensively reprogram host metabolism to support their replication, yet little is known about how this process is altered by virophages. Characterizing these alterations may reveal the metabolic mechanisms underlying virophage-mediated changes in infection outcomes. Here, we used one of the few established host-giant virus-virophage experimental systems, consisting of the marine heterotrophic flagellate Cafeteria burkhardae, its giant virus CroV, and the virophage mavirus, to investigate lipid remodeling during viral infection and virophage co-infection. We found that infection by the giant virus strongly induced triacylglycerols containing furan fatty acids (FuFAs), a class of potent antioxidants that may protect infected cells and newly formed virions from oxidative damage. These lipids were also detected in purified giant virus particles, linking their accumulation to virus production. Co-infection with the virophage reduced the FuFA response and was instead characterized by pronounced accumulation of the betaine lipid diacylglyceryltrimethylhomoserine (DGTS). Most of the induced DGTS species were also present in the giant virus particles, suggesting that their accumulation during co-infection may be associated with altered giant virus production and lipid utilization. Together, these findings show that virophage co-infection reshapes giant virus-induced remodeling of the host lipidome, revealing a potential metabolic basis for their effects on virus production and infection outcomes.

microbiology↗

bioRxiv2026

Ovothiol A mediates singlet oxygen resistance and acclimation in Chlamydomonas

Light is essential for photosynthetic organisms, but excess light can generate toxic levels of reactive oxygen species (ROS). To neutralize these ROS, plants and algae produce a variety of antioxidants like carotenoids, tocopherols, and glutathione. However, the role of alternative ROS scavengers, such as ovothiols, has not been studied in the context of oxidative stress in photosynthetic organisms. Here, we report that many algal groups have the potential for the biosynthesis of ovothiols, a group of thiohistidines. We discovered that the model green microalga Chlamydomonas reinhardtii produces millimolar concentrations of ovothiol A, whose biosynthesis is mediated by the ovothiol synthase OVOA1. Using CRISPR-generated ovoa1 knockout mutants, we found that ovothiol production is essential for resistance and acclimation to singlet oxygen, a prominent ROS in photosynthetic organisms. Finally, we demonstrated that OVOA1 expression is activated by singlet oxygen and light signaling pathways in which we identified the major regulatory factors. Overall, our results show that ovothiol A is a major, previously overlooked antioxidant in Chlamydomonas. This work broadens our understanding of cellular mechanisms that combat the damaging effects of oxidative stress. Graphical abstract O_FIG O_LINKSMALLFIG WIDTH=200 HEIGHT=200 SRC="FIGDIR/small/702910v2_ufig1.gif" ALT="Figure 1"> View larger version (54K): org.highwire.dtl.DTLVardef@cddb9corg.highwire.dtl.DTLVardef@10d0a43org.highwire.dtl.DTLVardef@11cc087org.highwire.dtl.DTLVardef@a40cc5_HPS_FORMAT_FIGEXP M_FIG C_FIG

plant biology↗

bioRxiv2025

The give and take in photosymbiosis unraveled by metabolomics of Radiolaria

Marine planktonic Radiolaria harboring symbiotic microalgae are ubiquitous in the oceans and abundant in oligotrophic areas. In these low-nutrient environments they are among the most important primary producers. Systematic studies of radiolarian biology are limited because Radiolaria are non-culturable and prone to damage during sampling. To obtain insight into the mechanistic basis of radiolarian photosymbiosis we address here the metabolic contributions of the partners to the performance of the holobiont. Therefore, we describe the metabolic inventory of two highly abundant photosymbiotic Radiolaria - colony-forming Collodaria and single-celled Acantharia and compare their metabolomes to metabolomes of respective free-living algae. Most of the metabolites detected in the symbiosis are not present in the free-living algae, suggesting a significant transformation of symbionts metabolites by the host. The metabolites identified in both the holobiont and the free-living algae encompass molecules of primary metabolism and a number of osmolytes, including dimethylsulfoniopropionate. Mass spectrometry imaging revealed the presence of dimethylsulfoniopropionate in both the symbionts and host cells, indicating that the algae provide osmolytic protection to the host. Furthermore, our findings suggest a possible dependence of Collodaria on symbiotic vitamin B3. Distinctive differences in phospholipid composition between free-living and symbiotic stages indicate that the algal cell membrane may undergo rearrangement in the symbiosis. Our results demonstrate a strong interdependence and rewiring of the algal metabolism underlying Radiolaria-microalgae photosymbioses.

microbiology↗

bioRxiv2025

Dual-use virulence factors of the opportunistic pathogen Chromobacterium haemolyticum mediate haemolysis and colonization

Chromobacterium haemolyticum is an environmental bacterium that can cause severe and fatal opportunistic infections in humans and animals. Although C. haemolyticum is characterized by its strong {beta}-haemolytic activity, the molecular basis of this phenotype has remained elusive over the more than fifteen years since the species was first described. Here, we report the discovery of a family of cyclic lipodepsipeptides that are responsible for the potent haemolytic activity of C. haemolyticum. Comparative genomics of Chromobacterium spp. isolated from different environments revealed a completely conserved gene locus (chl) encoding a non-ribosomal peptide synthetase (NRPS). Metabolic profiling of C. haemolyticum DSM 19808 identified a suite of cyclic lipodepsipeptides as the products of the chl locus, with the three main congeners (jagaricin, chromolysin A and B) being elucidated by a combination of tandem mass spectrometry, chemical derivatization, and NMR spectroscopy. Significantly, a C. haemolyticum chl deletion mutant is devoid of haemolytic activity. Moreover, purified jagaricin, chromolysin A and B are haemolytic at low- micromolar concentrations in an erythrocyte lysis assay. Further bioassays demonstrated that the cyclic lipodepsipeptides are crucial for biofilm-forming and swarming behavior of C. haemolyticum. MALDI mass spectrometry imaging showed that primarily chromolysin A and B are involved in these processes in vitro. Our data shed light on the bioactivities of chromolysin A and B, specialized metabolites that likely contribute to both successful colonization of new niches and virulence potential of C. haemolyticum. ImportanceDespite the rising incidence of Chromobacterium haemolyticum as a serious opportunistic pathogen, there is limited information on whether the competitive traits that ensure its survival in its freshwater niche contribute to host infection. We present a case where bacterially produced specialized metabolites act as lynchpin chemical mediators that are not only responsible for the pronounced haemolytic phenotype of C. haemolyticum but are crucial for biofilm formation and swarming motility. These results exemplify a case of coincidental evolution, wherein the selective pressures encountered in a primary environmental niche drive the evolution of a trait impacting virulence. This knowledge provides a foundation for the development of antivirulence therapies against the emerging pathogen C. haemolyticum.

microbiology↗

bioRxiv2022

Ubiquitous bacterial polyketides induce cross-kingdom microbial interactions

Although the interaction of prokaryotic and eukaryotic microorganisms is critical for the functioning of ecosystems, knowledge of the processes driving microbial interactions within communities is in its infancy. We previously reported that the soil bacterium Streptomyces iranensis specifically triggers the production of natural products in the fungus Aspergillus nidulans. Here, we discovered that arginine-derived polyketides serve as the bacterial signals for this induction. Arginine-derived polyketide-producing bacteria occur world wide. These producer bacteria and the fungi that decode and respond to this signal can be co-isolated from the same soil sample. Arginine-derived polyketides impact surrounding microorganisms both directly as well as indirectly, by inducing the production of natural products in fungi that further influence the composition of microbial consortia. One-Sentence SummaryUbiquitous bacterial polyketides are universal components of the chemical network for microbial communication

microbiology↗

bioRxiv2022

Toxin-producing endosymbionts shield pathogenic fungus against micropredators

The phytopathogenic fungus Rhizopus microsporus harbours a bacterial endosymbiont (Mycetohabitans rhizoxinica) for the production of the toxin rhizoxin, the causative agent of rice seedling blight. This toxinogenic bacterial-fungal alliance is, however, not restricted to the plant disease, but has been detected in numerous environmental isolates from geographically distinct sites covering all five continents. Yet, the ecological role of rhizoxin beyond rice seedling blight has been unknown. Here we show that rhizoxin serves the fungal host in fending off protozoan and metazoan predators. Fluorescence microscopy and co-culture experiments with the fungivorous amoeba Protostelium aurantium revealed that ingestion of R. microsporus spores is toxic to P. aurantium. This amoebicidal effect is caused by the bacterial rhizoxin congener rhizoxin S2, which is also lethal towards the model nematode Caenorhabditis elegans. By combining stereomicroscopy, automated image analyses, and quantification of nematode movement we show that the fungivorous nematode Aphelenchus avenae actively feeds on R. microsporus that is lacking endosymbionts, while worms co-incubated with symbiotic R. microsporus are significantly less lively. This work uncovers an unexpected ecological role of rhizoxin as shield against micropredators. This finding suggests that predators may function an evolutionary driving force to maintain toxin-producing endosymbionts in non-pathogenic fungi.

microbiology↗

bioRxiv2021

A polyyne toxin produced by an antagonistic bacterium blinds and lyses a green microalga

Microalgae are key contributors to global carbon fixation and the basis of many food webs. In nature, their growth is often supported or suppressed by other microorganisms. The bacterium Pseudomonas protegens Pf-5 arrests the growth of the green alga Chlamydomonas reinhardtii, deflagellates the alga by the cyclic lipopeptide orfamide A, and alters its morphology. Using a combination of Raman microspectroscopy, genome mining and mutational analysis, we discovered a novel polyyne toxin we name protegencin that is secreted by P. protegens and penetrates algal cells to destroy their primitive visual system, the eyespot. Together with secreted orfamide A, protegencin prevents the phototactic behavior of C. reinhardtii needed to perform optimal photosynthesis. A protegencin-deficient biosynthetic mutant of P. protegens does not affect growth or eyespot carotenoids of C. reinhardtii. Thus, protegencin acts in a direct and destructive way, and reveals at least a two-pronged molecular strategy used by algicidal bacteria.

plant biology↗

bioRxiv2021

Exploration of polyyne biosynthetic gene cluster diversity in bacteria leads to the discovery of the Pseudomonas polyyne protegencin

Natural products that possess alkyne or polyyne moieties have been isolated from a variety of biological sources. In bacteria their biosynthesis has been defined, however, the distribution of polyyne biosynthetic gene clusters (BGCs), and their evolutionary relationship to alkyne biosynthesis, have not been addressed. We explored the distribution of alkyne biosynthesis gene cassettes throughout bacteria, revealing evidence of multiple horizontal gene transfer events. Investigating the evolutionary connection between alkyne and polyyne biosynthesis identified a monophyletic clade possessing a conserved seven-gene cassette for polyyne biosynthesis. Mapping the diversity of these conserved genes revealed a phylogenetic clade representing a polyyne BGC in Pseudomonas, pgn, and subsequent pathway mutagenesis and analytical chemistry characterised the associated metabolite, protegencin. In addition to unifying and expanding our knowledge of polyyne diversity, our results show that alkyne and polyyne biosynthetic gene clusters are promiscuous within bacteria. Systematic mapping of conserved biosynthetic genes across bacterial genomic diversity has proven to be a successful method for discovering natural products.

microbiology↗

bioRxiv2020

Food-Poisoning Bacteria Employ a Citrate Synthase and a Type II NRPS to Synthesize Bolaamphiphilic Lipopeptide Antibiotics

Mining the genome of the food-spoiling bacterium Burkholderia gladioli pv. cocovenenans revealed five non-ribosomal peptide synthetase (NRPS) gene clusters, including an orphan gene locus (bol). Gene inactivation and metabolic profiling linked the bol gene cluster to novel bolaamphiphilic lipopeptides with antimycobacterial activity. A combination of chemical analyses and bioinformatics elucidated the structures of bolagladin A and B, lipocyclopeptides featuring an unusual dehydro-{beta}-alanine enamide linker fused to an unprecedented tricarboxylic fatty acid tail. Through a series of targeted gene deletions we proved the involvement of a designated citrate synthase (CS), priming ketosynthases (KS III), a type II NRPS including a novel desaturase for enamide formation, and a multimodular NRPS generating the cyclopeptide. Network analyses revealed the evolutionary origin of the CS and identified cryptic CS/NRPS gene loci in various bacterial genomes.

microbiology↗

bioRxiv2020

Secreted TAL effectors protect symbiotic bacteria from entrapment within fungal hyphae

The association of the agriculturally significant phytopathogenic fungus Rhizopus microsporus with the bacterial endosymbiont Burkholderia rhizoxinica is a remarkable example of bacteria controlling host physiology and reproduction. Here, we show that a group of transcription activator-like effectors (TALEs) called Burkholderia TALE-like proteins (BATs) from B. rhizoxinica are essential for the establishment of the symbiosis. Mutants lacking BAT proteins are unable to induce host sporulation. Utilising novel microfluidic devices in combination with fluorescence microscopy we observed the accumulation of BAT-deficient mutants in specific fungal side-hyphae with accompanying increased fungal re-infection. High-resolution live imaging revealed septa biogenesis at the base of infected hyphae leading to compartmental trapping of BATdeficient endobacteria. Trapped endosymbionts showed reduced intracellular survival, suggesting a protective response from the fungal host against bacteria lacking specific effectors. These findings underscore the involvement of BAT proteins in maintaining a balance between mutualism and antagonism in bacterial-fungal interactions and provide deeper insights into the dynamic interactions between bacteria and eukaryotes.

microbiology↗

bioRxiv2019

Highly parallelized microfluidic droplet cultivation and prioritization on antibiotic producers from complex natural microbial communities

To investigate the overwhelming part of the bacterial diversity still evading standard cultivation for its potential use in antibiotic synthesis, we have compiled a microscale-cultivation and screening system. We devised a strategy based on droplet-microfluidics taking advantage of the inherent miniaturization and high throughput. Single cells of natural samples were confined in 9 x 106 aqueous droplets and subjected to long-term incubation under controlled conditions. Subsequent a high-throughput screening for antimicrobial natural products was implemented, employing a whole cell reporting system using the viability of reporter strains as a probe for antimicrobial activity. Due to the described microscale cultivation a novel subset of bacterial strains was made available for the following screening for antimicrobials. We demonstrate the merits of the in-droplet cultivation by comparing the cultivation outcome in microfluidic droplets and on conventional agar plates for a bacterial community derived from soil by 16S rRNA gene amplicon sequencing. In-droplet cultivation resulted in a significantly higher bacterial diversity without the common overrepresentation of Firmicutes. Natural strains able to inhibit either a Gram-positive or a Gram-negative reporter strain were isolated from the microscale system and further cultivated. Thereby a variety of rare isolates was obtained. The natural products with antimicrobial activity were elucidated for the most promising candidate. Our method combines a new cultivation approach with a high-throughput search for antibiotic producers to increase the chances of finding new lead substances.

microbiology↗

bioRxiv2019

Horizontal gene transfer to a defensive symbiont with a reduced genome amongst a multipartite beetle microbiome

The loss of functions required for independent life when living within a host gives rise to reduced genomes in obligate bacterial symbionts. Although this phenomenon can be explained by existing evolutionary models, its initiation is not well understood. Here, we describe the microbiome associated with eggs of the beetle Lagria villosa, containing multiple bacterial symbionts related to Burkholderia gladioli including a reduced-genome symbiont thought to produce the defensive compound lagriamide. We find that the putative lagriamide producer is the only symbiont undergoing genome reduction, and that it has already lost most primary metabolism and DNA repair pathways. The horizontal acquisition of the lagriamide biosynthetic gene cluster likely preceded genome reduction, and unexpectedly we found that the symbiont accepted additional genes horizontally during genome reduction, even though it lacks the capacity for homologous recombination. These horizontal gene transfers suggest that absolute genetic isolation is not a requirement for genome reduction.

evolutionary biology↗

bioRxiv2019

Metabolic pathway rerouting in Paraburkholderia rhizoxinica evolved long-overlooked derivatives of coenzyme F420

Coenzyme F420 is a specialized redox cofactor with a highly negative redox potential. It supports biochemical processes like methanogenesis, degradation of xenobiotics or the biosynthesis of antibiotics. Although well-studied in methanogenic archaea and actinobacteria, not much is known about F420 in Gram-negative bacteria. Genome sequencing revealed F420 biosynthetic genes in the Gram-negative, endofungal bacterium Paraburkholderia rhizoxinica, a symbiont of phytopathogenic fungi. Fluorescence microscopy, high-resolution LC-MS, and structure elucidation by NMR demonstrated that the encoded pathway is active and yields unexpected derivatives of F420 (3PG-F420). Further analyses of a biogas-producing microbial community showed that these derivatives are more widespread in nature. Genetic and biochemical studies of their biosynthesis established that a specificity switch in the guanylyltransferase CofC re-programmed the pathway to start from 3-phospho-D-glycerate, suggesting a rerouting event during the evolution of F420 biosynthesis. Furthermore, the cofactor activity of 3PG-F420 was validated, thus opening up perspectives for its use in biocatalysis. The 3PG-F420 biosynthetic gene cluster is fully functional in Escherichia coli, enabling convenient production of the cofactor by fermentation.

biochemistry↗

bioRxiv2017

Bacterium-triggered remodeling of chromatin identifies BasR, a novel regulator of fungal natural product biosynthesis

The eukaryotic epigenetic machinery is targeted by bacteria to reprogram the response of eukaryotes during their interaction with microorganisms. In line, we discovered that the bacterium Streptomyces rapamycinicus triggered increased chromatin acetylation and thus activation of the silent secondary metabolism ors gene cluster leading to the production of orsellinic acid in the fungus Aspergillus nidulans. Using this model we aim at understanding molecular mechanisms of communication between bacteria and eukaryotic microorganisms based on bacteria-triggered chromatin modification. By genome-wide ChIP-seq analysis of acetylated histone H3 (H3K9ac, H3K14ac) we uncovered the unique chromatin landscape in A. nidulans upon co-cultivation with S. rapamycinicus. Genome-wide acetylation of H3K9 correlated with increased gene expression, whereas H3K14 appears to function in transcriptional initiation by providing a docking side for regulatory proteins. In total, histones belonging to six secondary metabolism gene clusters showed higher acetylation during co-cultivation including the ors, aspercryptin, cichorine, sterigmatocystin, anthrone and 2,4-dihydroxy-3-methyl-6-(2-oxopropyl)benzaldehyde gene cluster with the emericellamide cluster being the only one with reduced acetylation and expression. Differentially acetylated histones were also detected in genes involved in amino acid and nitrogen metabolism, signaling, and genes encoding transcription factors. In conjunction with LC-MS/MS and MALDI-MS imaging, molecular analyses revealed the cross-pathway control and Myb-like transcription factor BasR as regulatory nodes for transduction of the bacterial signal in the fungus. The presence of basR in other fungal species allowed forecasting the inducibility of ors-like gene clusters by S. rapamycinicus in these fungi, and thus their effective interaction with activation of otherwise silent gene clusters.

microbiology↗