Biology subjects

Hunter, R. C.

Publications and source records attributed to Hunter, R. C..

18 recordsLinked to original sources

bioRxiv2025

Anaerobic microbiota facilitate pathogen access to the airway epithelium in a novel co-culture model of colonization

Chronic rhinosinusitis (CRS) is a prevalent condition characterized by mucus stasis, persistent inflammation, and infection of the paranasal sinuses. It often involves the bacterium Pseudomonas aeruginosa, especially in individuals with cystic fibrosis or a history of antibiotic use. While P. aeruginosa is a known opportunistic pathogen that employs a diverse array of virulence factors to cause airway infections, its ability to thrive in the sinonasal environment is also likely influenced by its local microbial ecology. For instance, anaerobic bacterial genera, such as Streptococcus, Veillonella, and Prevotella, are also commonly found in CRS and may contribute to P. aeruginosa persistence. Here we sought to test the hypothesis that anaerobes promote P. aeruginosa colonization of the upper airways, specifically through degradation of mucin glycoproteins that decorate the epithelial surface. Using a novel dual oxic-anoxic culture platform termed DOAC, we co-cultured Calu-3 epithelial cells with a CRS-derived anaerobic microbial community. We observed increased expression of inflammatory marker genes and degradation of mucin glycoproteins, along with enhanced P. aeruginosa colonization of the epithelial surface after anaerobe pre-treatment. Furthermore, mucins isolated from anaerobe-treated Calu-3 cells promoted greater P. aeruginosa attachment to microtiter plates in vitro compared to intact mucins. These results suggest that anaerobic microbiota may shape the sinonasal environment in a way that favors P. aeruginosa persistence, offering new insights into CRS pathogenesis and potential therapeutic targets to disrupt detrimental bacterial interactions in chronic airway disease. IMPORTANCEThe prevalence and abundance of strict and facultative anaerobic bacteria in chronic sinusitis as detected by culture-independent sequencing has renewed interest in their potential role(s) in disease onset, progression, and treatment. However, reductionist study of interactions between anaerobic microbiota and the host has been limited by the lack of laboratory models compatible with their conflicting oxygen demands. The significance of this work lies in the use of a novel co-culture platform, termed DOAC, to interrogate anaerobe interactions with the airway epithelium. We use this platform to show that anaerobic CRS microbiota elicit a pro-inflammatory response, degrade mucin glycoproteins, and promote mucosal colonization by the canonical CRS pathogen, Pseudomonas aeruginosa. This work highlights highlight a potential role of anaerobic microbiota in conditioning the sinonasal environment to favor pathogen colonization.

microbiology↗

bioRxiv2025

Cross-feeding interactions between Fusobacterium nucleatum and the glycan forager Segatella oris

Fusobacterium nucleatum is a common member of the oral microbiota frequently associated with extra-oral infections and diverse polymicrobial environments, including chronic airway diseases and colorectal tumors. Yet, its interactions with co-colonizing microbiota remain poorly defined. Here, we investigate cross-feeding interspecies dynamics between F. nucleatum and Segatella oris, a glycan-foraging anaerobe enriched in airways and gastrointestinal tumors. Using broth cultures, cell-free supernatants, and co-culture on primary human airway epithelial cells, we identify bidirectional interactions that shape nutrient acquisition, biofilm formation, gene expression, and host responses. While mucin or S. oris supernatants modestly enhanced F. nucleatum growth, both conditions triggered transcriptional remodeling, including induction of the nan operon for sialic acid catabolism, suggesting reliance on glycan degradation by S. oris. Conversely, S. oris exhibited differential expression of multiple polysaccharide utilization loci (PULs) when exposed to F. nucleatum or its metabolites. Biofilm formation by F. nucleatum was strongly inhibited by S. oris, indicative of antagonistic interactions. Dual and triple RNA-seq revealed that epithelial responses were predominately shaped by F. nucleatum, with enrichment of inflammatory and cancer-associated pathways; however, co-colonization with S. oris modulated the magnitude and specificity of host gene expression. These findings demonstrate that glycan-mediated cross-feeding and microbial interactions shape the physiology and pathogenic potential of F. nucleatum in mucosal environments. This work underscores the importance of modeling polymicrobial communities under host-relevant conditions to better understand pathobiont behavior at the epithelial interface. ImportanceFusobacterium nucleatum is increasingly recognized as a pathobiont in mucosal diseases, including colorectal cancers and chronic airway infections, yet its functional interactions with co-colonizing microbiota remain poorly understood. Here, we demonstrate that F. nucleatum engages in bidirectional interactions with Segatella oris, a glycan-foraging anaerobe also enriched in mucin-rich environments. Through nutrient cross-feeding, antagonism, and transcriptional modulation, these interactions shape bacterial behavior and the host epithelial response. Notably, glycan degradation by S. oris enables F. nucleatum access to sialic acids, while F. nucleatum suppresses expression of multiple polysaccharide utilization loci in S. oris, revealing a reciprocal ecological influence. Co-colonization of the airway epithelial surface also modulates gene expression linked to inflammation and cancer. These findings advance our understanding of polymicrobial dynamics at mucosal interfaces and highlight the importance of incorporating microbe-microbe-host interactions into reductionist models of infection and disease.

microbiology↗

bioRxiv2025

Host- and microbial-mediated mucin degradation differentially shape Pseudomonas aeruginosa physiology and gene expression

Pseudomonas aeruginosa is a hallmark pathogen of cystic fibrosis (CF) airway infections, capable of reaching high cell densities despite its limited ability to directly utilize mucin glycoproteins as a nutrient source. In the CF lung, however, P. aeruginosa may access preferred carbon sources (e.g., amino acids and short-chain fatty acids) through metabolic cross-feeding with co-colonizing mucin-degrading microbes. Although host-derived enzymes such as neutrophil elastase can also degrade mucins, the extent to which host-mediated mucin breakdown supports P. aeruginosa growth remains unclear. Thus, here we compared the nutritional impact of microbial versus host mucolytic activity on P. aeruginosa physiology. Analyses of CF sputum revealed patient-specific variability in mucin integrity that is shaped by both host and microbial factors. We demonstrate that mucin degradation by anaerobic bacteria through proteolysis, glycolysis, and fermentation, promotes robust P. aeruginosa growth, unlike mucin processed by neutrophil elastase alone. Targeted metabolomics identified acetate and propionate as key metabolites driving this cross-feeding, while transcriptomic and phenotypic analyses revealed that P. aeruginosa engages in diauxic growth on a broader set of mucin-derived substrates. Unexpectedly, cross-feeding with anaerobes triggered the induction of P. aeruginosa denitrification and fermentation pathways, suggesting redox remodeling despite being cultured under oxygen-replete conditions. Finally, the transcriptional profile of P. aeruginosa grown on anaerobe-conditioned mucins more closely resembled its in vivo gene expression, more so than when grown on intact or neutrophil-degraded mucins. Together, these findings provide new insight into the potential role of interspecies metabolic interactions in shaping pathogen physiology in the inflammatory, polymicrobial, and mucus-rich environment of the CF airways. Author SummaryCystic fibrosis (CF) airways contain viscous mucus that traps both pathogens and commensals. The major pathogen, P. aeruginosa thrives in these mucus-rich, inflamed environments, but how it acquires nutrients to sustain growth is poorly understood. We demonstrate that while host neutrophil enzymes degrade mucin polymers, this degradation alone does not provide substantial nutrients to support P. aeruginosa proliferation. In contrast, co-colonizing anaerobic microbiota extensively degrade mucins and generate short-chain fatty acids and other metabolites that strongly promote P. aeruginosa growth. We show that anaerobe-degraded mucins not only support faster growth but also trigger redox remodeling and gene expression changes that closely resemble P. aeruginosa behavior in CF patient sputum. This work highlights the important role of interspecies metabolic interactions in shaping CF airway infections and suggests new consideration for therapeutic strategies targeting airway microbiomes.

microbiology↗

bioRxiv2025

Evaluating the Link Between Efflux Pump Expression and Motility Phenotypes in Pseudomonas aeruginosa Treated with Virulence Inhibitors

Antibiotic resistance continues to rise as a global health threat. Novel anti-virulence strategies diminish the drive for evolutionary pressure, but still hinder a pathogens ability to infect a host. Treatment of the highly virulent Pseudomonas aeruginosa strain PA14 with virulence inhibitors (R-2 and R-6) elicited widely varying transcriptional profiles. Of interest, expression of a family of resistance-nodulation-division (RND) efflux pumps implicated in the intrinsic drug resistance of P. aeruginosa, was significantly altered by R-2 and R-6 treatment. While structurally similar, these inhibitors caused differential expression of various RND efflux pumps within the Mex family--R-2 treatment stimulated expression of mexEF-oprN while R-6 treatment led to increased mexAB-oprM expression. Further expansion into a small library of virulence inhibitors revealed chemical motifs that trigger increases in RND efflux pump expression. Additionally, activation of these efflux pumps suggests low accumulation of virulence inhibitors in WT PA14. Treatment of an efflux pump-deficient strain with R-2 or R-6 resulted in inhibition of several virulence factors, for example R-2 was found to abolish swimming motility. Collectively, treatment with either R-2 or R-6 gives rise to a convoluted transcriptomic response, confounded by the impact of efflux pump expression on the system. However, understanding the moieties that lead to high expression of the efflux pumps enables further rational design of novel virulence inhibitors that do not cause RND efflux pump activation. SummaryAntibiotic resistance continues to rise across the world. The continued failure of antibiotics to treat infectious disease clearly demonstrates the need for new therapeutics. Small molecule inhibitors of virulence, or the ability of a bacteria to establish and maintain an infection, have showed promise in this area. By reducing virulence, the host immune system can clear the infection on its own and there is less selective pressure on the bacteria, reducing the emergence of resistance. Our work demonstrates a clear link between virulence inhibitors and efflux pump expression. Efflux pumps are critical for bacteria to extrude toxic compounds from their interior. Interestingly, the changes in efflux pump expression can be quite large even with similar molecular structures. Additionally, the repression of efflux expression caused by our virulence inhibitors results in synergy with current antibiotics. This work will allow the future design of virulence inhibitors that do not activate efflux pump expression and therefore, enable high intracellular concentrations.

microbiology↗

bioRxiv2024

Commensal-derived short-chain fatty acids disrupt lipid membrane homeostasis in Staphylococcus aureus

The role of commensal anaerobic bacteria in chronic respiratory infections is unclear, yet they can exist in abundances comparable to canonical pathogens in vivo. Their contributions to the metabolic landscape of the host environment may influence pathogen behavior by competing for nutrients and creating inhospitable conditions via toxic metabolites. Here, we reveal a mechanism by which the anaerobe-derived short chain fatty acids (SCFAs) propionate and butyrate negatively affect Staphylococcus aureus physiology by disrupting branched chain fatty acid (BCFA) metabolism. In turn, BCFA impairment results in impaired growth, diminished expression of the agr quorum sensing system, as well as increased sensitivity to membrane-targeting antimicrobials. Altered BCFA metabolism also reduces S. aureus fitness in competition with Pseudomonas aeruginosa, suggesting that airway microbiome composition and the metabolites they produce and exchange directly impact pathogen succession over time. The pleiotropic effects of these SCFAs on S. aureus fitness and their ubiquity as metabolites in animals also suggests that they may be effective as sensitizers to traditional antimicrobial agents when used in combination.

microbiology↗

bioRxiv2023

Mutualism reduces the severity of gene disruptions in predictable ways across microbial communities.

Predicting evolution in microbial communities is critical for problems from human health to global nutrient cycling. Understanding how species interactions impact the distribution of fitness effects for a focal population would enhance our ability to predict evolution. Specifically, it would be useful to know if the type of ecological interaction, such as mutualism or competition, changes the average effect of a mutation (i.e., the mean of the distribution of fitness effects). Furthermore, how often does increasing community complexity alter the impact of species interactions on mutant fitness? To address these questions, we created a transposon mutant library in Salmonella enterica and measured the fitness of loss of function mutations in 3,550 genes when grown alone versus competitive co-culture or mutualistic co-culture with Escherichia coli and Methylorubrum extorquens. We found that mutualism reduces the average impact of mutations, while competition had no effect. Additionally, mutant fitness in the 3-species communities can be predicted by averaging the fitness in each 2-species community. Finally, the fitness effects of several knockouts in the mutualistic communities were surprising. We discovered that S. enterica is obtaining a different source of carbon and more vitamins and amino acids than we had expected. Our results suggest that species interactions can predictably impact fitness effect distributions, in turn suggesting that evolution may ultimately be predictable in multi-species communities.

microbiology↗

bioRxiv2023

Evaluation of Expanded 2-Aminobenzothiazole Library for Inhibition of Pseudomonas aeruginosa Virulence Phenotypes

Bacterial resistance to antibiotics is a rapidly increasing threat to human health. New strategies to combat resistant organisms are desperately needed. One potential avenue is targeting two-component systems, which are the main bacterial signal transduction pathways used to regulate development, metabolism, virulence, and antibiotic resistance. These systems consist of a homodimeric membrane-bound sensor histidine kinase, and a cognate effector, the response regulator. The high sequence conservation in the catalytic and adenosine triphosphate-binding (CA) domain of histidine kinases and their essential role in bacterial signal transduction could enable broad-spectrum antibacterial activity. Through this signal transduction, histidine kinases regulate multiple virulence mechanisms including toxin production, immune evasion, and antibiotic resistance. Targeting virulence, as opposed to development of bactericidal compounds, could reduce evolutionary pressure for acquired resistance. Additionally, compounds targeting the CA domain have the potential to impair multiple two-component systems that regulate virulence in one or more pathogens. We conducted structure-activity relationship studies of 2-aminobenzothiazole-based inhibitors designed to target the CA domain of histidine kinases. We found these compounds have anti-virulence activities in Pseudomonas aeruginosa, reducing motility phenotypes and toxin production associated with the pathogenic functions of this bacterium.

microbiology↗

bioRxiv2022

Outside-in: intracellular vesicles in giant sulfur bacteria contain peptidoglycan

Until recently, the cellular envelopes of bacteria were regarded as static and rigid relative to those of eukaryotes. While investigating peptidoglycan synthesis in populations of giant sulfur bacteria, Candidatus Thiomargarita spp., we observed internal vesicle-like features (VLFs). VLFs, as imaged following the active incorporation of D-amino acids, appear to begin as invaginations and delaminations of the cellular envelope. Staining with wheat germ agglutinin confirmed the presence of peptidoglycan in VLFs, while polymyxin B revealed that the outer membrane is present in some VLFs. Transmission electron microscopy revealed a complex network of interconnected VLFs. Genomes of Ca. Thiomargarita nelsonii lack a canonical divisome, while possessing homologs to genes such as actin, membrane scaffolding proteins, and dynamins that are associated with phagocytosis in eukaryotes. The physiological role of VLFs remains unclear, but the presence of sulfur globules in some suggests compartmentalization of metabolism and energy production. This is the first report of peptidoglycan and outer membrane bound intracellular vesicles within prokaryotic cells. These findings transform the canonical view of the inflexible bacterial cell envelope and further narrow the divide between prokaryotes and eukaryotes.

microbiology↗

bioRxiv2022

Staphylococcus aureus overcomes anaerobe-derived short-chain fatty acid stress via FadX and the CodY regulon

Chronic rhinosinusitis (CRS) is characterized by immune dysfunction, mucus hypersecretion, and persistent infection of the paranasal sinuses. While Staphylococcus aureus is a primary CRS pathogen, recent sequence-based surveys have found increased relative abundances of anaerobic bacteria, suggesting that S. aureus may experience altered metabolic landscapes in CRS relative to healthy airways. To test this possibility, we characterized the growth kinetics and transcriptome of S. aureus in supernatants of the abundant CRS anaerobe Fusobacterium nucleatum. While growth was initially delayed, S. aureus ultimately grew to similar levels as in the control medium. The transcriptome was significantly affected by F. nucleatum metabolites, with the agr quorum sensing system notably repressed. Conversely, expression of fadX, encoding a putative propionate coA-transferase, was significantly increased, leading to our hypothesis that short chain fatty acids (SCFAs) produced by F. nucleatum could mediate S. aureus growth behavior and gene expression. Supplementation with propionate and butyrate, but not acetate, recapitulated delayed growth phenotypes observed in F. nucleatum supernatants. A fadX mutant was found to be more sensitive than wild type to propionate, suggesting a role for FadX in the S. aureus SCFA stress response. Interestingly, spontaneous resistance to butyrate, but not propionate, was frequently observed. Whole genome sequencing and targeted mutagenesis identified codY mutants as resistant to butyrate inhibition. Together, these data show that S. aureus physiology is dependent on its co-colonizing microbiota and metabolites they exchange, and indicate that propionate and butyrate may act on different targets in S. aureus to suppress its growth. ImportanceS. aureus is an important CRS pathogen, yet is found in the upper airways of 30-50% of people without complications. The presence of strict and facultative anaerobic bacteria in CRS sinuses has recently spurred research into bacterial interactions and how they influence S. aureus physiology and pathogenesis. We show here that propionate and butyrate produced by one such CRS anaerobe, F. nucleatum, alter the growth and gene expression of S. aureus. We show that fadX is important for S. aureus to resist propionate stress, and that the CodY regulon mediates growth in inhibitory concentrations of butyrate. This work highlights the possible complexity of S. aureus-anaerobe interactions, and implicates membrane stress as a possible mechanism influencing S. aureus behavior in CRS sinuses.

microbiology↗

bioRxiv2021

Anaerobic microbiota facilitate P. aeruginosa access to airway epithelia in a novel co-culture model of colonization

Strict and facultative anaerobic bacteria are widely associated with both acute and chronic airway disease. However, their potential role(s) in disease pathophysiology remain poorly understood due to inherent limitations of existing models and conflicting oxygen demands between anaerobes and host cells. To overcome these limitations, we optimized a dual oxic-anoxic culture (DOAC) platform that maintains an oxygen-limited microenvironment at the epithelial interface while host cells are oxygenated basolaterally. This approach enables host-bacterial co-culture for [~]24h, and here we demonstrate its utility via two applications. First, we show that anaerobe challenge results in epithelial mucus degradation, inflammatory marker gene expression, and enhanced pathogen colonization. Second, we combine DOAC with single cell RNA sequencing (scRNAseq) to reveal a cell type-specific transcriptional response of the airway epithelium to anaerobe infection. Together, these data illustrate the versatility of DOAC while revealing new insights into anaerobe-host interactions and their mechanistic contributions to airway disease pathophysiology.

microbiology↗

bioRxiv2020

Single cell resolution of SARS-CoV-2 tropism, antiviral responses, and susceptibility to therapies in primary human airway epithelium

The human airway epithelium is the initial site of SARS-CoV-2 infection. We used flow cytometry and single cell RNA-sequencing to understand how the heterogeneity of this diverse cell population contributes to elements of viral tropism and pathogenesis, antiviral immunity, and treatment response to remdesivir. We found that, while a variety of epithelial cell types are susceptible to infection, ciliated cells are the predominant cell target of SARS-CoV-2. The host protease TMPRSS2 was required for infection of these cells. Importantly, remdesivir treatment effectively inhibited viral replication across cell types, and blunted hyperinflammatory responses. Induction of interferon responses within infected cells was rare and there was significant heterogeneity in the antiviral gene signatures, varying with the burden of infection in each cell. We also found that heavily infected secretory cells expressed abundant IL-6, a potential mediator of COVID-19 pathogenesis.

microbiology↗

bioRxiv2019

A putative enoyl-CoA hydratase contributes to biofilm formation and the antibiotic tolerance of Achromobacter xylosoxidans

Achromobacter xylosoxidans has attracted increasing attention as an emerging pathogen in patients with cystic fibrosis. Intrinsic resistance to several classes of antimicrobials and the ability to form robust biofilms in vivo contribute to the clinical manifestations of persistent A. xylosoxidans infection. Still, much of A. xylosoxidans biofilm formation remains uncharacterized due to the scarcity of existing genetic tools. Here we demonstrate a promising genetic system for use in A. xylosoxidans; generating a transposon mutant library which was then used to identify genes involved in biofilm development in vitro. We further described the effects of one of the genes found in the mutagenesis screen, encoding a putative enoyl-CoA hydratase, on biofilm structure and tolerance to antimicrobials. Through additional analysis, we find that a cis-2 fatty acid signaling compound is essential to A. xylosoxidans biofilm ultrastructure and maintenance. This work describes methods for the genetic manipulation of A. xylosoxidans and demonstrated their use to improve our understanding of A. xylosoxidans pathophysiology.

microbiology↗

bioRxiv2019

Bioorthogonal non-canonical amino acid tagging reveals translationally active subpopulations of the cystic fibrosis lung microbiota

Culture-independent studies of cystic fibrosis lung microbiota have provided few mechanistic insights into the polymicrobial basis of disease. Deciphering the specific contributions of individual taxa to CF pathogenesis requires a comprehensive understanding of their in situ ecophysiology. We applied bioorthogonal non-canonical amino acid tagging (BONCAT), a click chemistry-based metabolic labeling approach, to quantify and visualize translational activity among CF microbiota. Using BONCAT-based fluorescent imaging on sputum collected from stable CF subjects, we reveal that only a subset of bacteria are translationally active. We also combined BONCAT with fluorescent activated cell sorting (FACS) and 16S rRNA gene sequencing to assign taxonomy to the active subpopulation and found that the most dominant taxa are indeed translationally active. On average, only [~]12-18% of bacterial cells were BONCAT labeled, suggesting a heterogeneous growth strategy widely employed by most airway microbiota. Differentiating translationally active populations from those that are dormant adds to our evolving understanding of the polymicrobial basis of CF lung disease and may help guide patient-specific therapeutic strategies targeting active bacterial populations that are most likely to be susceptible.

microbiology↗

bioRxiv2018

Refinement of metabolite detection in cystic fibrosis sputum reveals heme negatively correlates with lung function

Pseudomonas aeruginosa lung infections are a leading cause of morbidity and mortality in cystic fibrosis (CF) patients (1, 2). Our laboratory has studied a class of small molecules produced by P. aeruginosa known as phenazines, including pyocyanin and its biogenic precursor phenazine-1-carboxylic acid (PCA). As phenazines are known virulence factors (3), we and others have explored the possibility of using phenazine concentrations as a marker for disease progression (4-6). Previously, we reported that sputum concentrations of pyocyanin and PCA negatively correlate with lung function in cystic fibrosis patients (6). Our study used high performance liquid chromatography (HPLC) to quantify phenazines by UV-vis absorbance after extraction from lung sputum. Since our initial study, methods for metabolite analysis have advanced considerably, aided in large part by usage of mass spectrometry (LC-MS) and tandem mass spectrometry (LC-MS/MS). Because a more recent study employing LC-MS/MS revealed a surprising decoupling of P. aeruginosa metabolites in sputum and the detection of P. aeruginosa through culturing or microbiome profiles (4), we decided to check whether we could reproduce our previous findings by analyzing sputum samples from a different patient cohort with a new LC-MS instrument in our laboratory. Our new samples were provided by the Mountain West CF Consortium Sputum Biomarker study (7). In the course of performing our new analyses, comparison of our old HPLC data to our new LC-MS data led us to realize that the peak previously assigned to PCA instead originates from heme, and the peak assigned to pyocyanin originates from an as-yet unknown compound. This correction only affects the measurements of phenazines in sputum, and we are confident in the phenazine measurements from isolated cultures and the 16S rRNA gene sequencing data from that study (6). Here we outline the basis for our correction and present additional data showing that heme concentration negatively correlates with lung function in cystic fibrosis patients.

microbiology↗

bioRxiv2018

Agmatine accumulation by Pseudomonas aeruginosa clinical isolates confers antibiotic tolerance and dampens host inflammation.

In the cystic fibrosis (CF) airways, Pseudomonas aeruginosa undergoes diverse physiological changes in response to inflammation, antibiotic pressure, oxidative stress and a dynamic bioavailable nutrient pool. These include loss-of-function mutations that result in reduced virulence, altered metabolism and other phenotypes that are thought to confer a selective advantage for long-term persistence. Recently, clinical isolates of P. aeruginosa that hyperproduce agmatine (decarboxylated arginine) were cultured from individuals with CF. Sputum concentrations of this metabolite were also shown to correlate with disease severity. This raised the question of whether agmatine accumulation might also confer a selective advantage for P. aeruginosa in vivo during chronic colonization of the lung. Here, we screened a library of P. aeruginosa CF clinical isolates and found that ~5% of subjects harbored isolates with an agmatine hyperproducing phenotype. Agmatine accumulation was a direct result of mutations in aguA, encoding the arginine deiminase that catalyzes the conversion of agmatine into various polyamines. We also found that agmatine hyperproducing isolates (aguA-) had increased tolerance to the cationic antibiotics gentamicin, tobramycin and colistin relative to their chromosomally complemented strains (aguA+). Finally, we revealed that agmatine diminishes IL-8 production by airway epithelial cells in response to bacterial infection, with a consequent decrease in neutrophil recruitment to the murine airways in an acute pneumonia model. These data highlight a potential new role for bacterial-derived agmatine that may have important consequences for the long-term persistence of P. aeruginosa in the CF airways.

microbiology↗

bioRxiv2018

Cross-feeding modulates antibiotic tolerance in bacterial communities

Microbes frequently rely on metabolites excreted by other bacterial species, but little is known about how this cross-feeding influences the effect of antibiotics. We hypothesized that when species rely on each other for essential metabolites, the minimum inhibitory concentration (MIC) for all species will drop to that of the \"weakest link\" - the species least resistant in monoculture. We tested this hypothesis in an obligate cross-feeding system that was engineered between Escherichia coli, Salmonella enterica, and Methylobacterium extorquens. The effect of tetracycline and ampicillin were tested on both liquid and solid media. In all cases, resistant species were inhibited at significantly lower antibiotic concentrations in the cross-feeding community than in monoculture or a competitive community. However, deviation from the \"weakest link\" hypothesis was also observed in cross-feeding communities apparently as result of changes in the timing of growth and cross-protection. Comparable results were also observed in a clinically relevant system involving facultative cross-feeding between Pseudomonas aeruginosa and an anaerobic consortium found in the lungs of cystic fibrosis patients. P. aeruginosa was inhibited by lower concentrations of ampicillin when cross-feeding than when grown in isolation. These results suggest that cross-feeding significantly alters tolerance to antibiotics in a variety of systems.

microbiology↗

bioRxiv2017

16S rRNA Gene Sequencing Reveals Site-Specific Signatures Of The Upper And Lower Airways Of Cystic Fibrosis Patients

RationaleChronic rhinosinusitis (CRS) is an inflammatory disorder of the sinonasal mucosa associated with microbial colonization. Metastasis of sinus microbiota into the lower airways is thought have significant implications in the development of chronic respiratory disease. However, this dynamic has not been thoroughly investigated in cystic fibrosis (CF) patients, where lower airway infections are the primary driver of patient mortality. Given the high prevalence of CRS in CF patients and the proposed infection dynamic between the upper and lower airways, a better understanding of sinus-lung continuum is warranted.\n\nObjectiveTo compare the microbiome of matched sinus mucus and lung sputum samples from CF subjects undergoing functional endoscopic sinus surgery (FESS) for treatment of CRS.\n\nMethodsMucus was isolated from the sinuses and lungs of twelve CF patients undergoing FESS. 16S ribosomal RNA gene sequencing was then performed to compare bacterial communities of the CF lung and sinus niches. Finally, functional profiling was performed to predict bacterial metagenomes from the 16S dataset, and was used to compare pathogenic bacterial phenotypes between the upper and lower airways.\n\nMeasurements and Main ResultsBacterial richness was comparable between airway sites, though sinus and lung environments differed in community evenness, with the sinuses harboring a higher prevalence of dominant microorganisms. Beta diversity metrics also revealed that samples clustered more consistently by airway niche rather than by individual. Finally, predicted metagenomes showed that anaerobic metabolism was enriched in the lung environment, while genes associated with both biofilm formation and Gram identity were not variable between sites.\n\nConclusionsSinus and lung microbiomes are distinct with respect to richness and evenness, while sinus communities have a higher incidence of a dominant taxon. Additionally, ordination analyses point to sinus and lung environments as being stronger determinants of microbial community structure than the individual patient. Finally, BugBase-predicted metagenomes revealed anaerobic phenotypes to be in higher abundance in the lung relative to the sinuses. Our findings indicate that while the paranasal sinuses and lungs may still comprise a unified airway in which lower airways are seeded by sinus microbiota, these discrete airway microenvironments harbor distinct bacterial communities.

microbiology↗

bioRxiv2016

Genome-wide survey of Pseudomonas aeruginosa PA14 reveals a role for the glyoxylate pathway and extracellular proteases in the limited utilization of mucin

Chronic airway infections by the opportunistic pathogen Pseudomonas aeruginosa are major cause of mortality in cystic fibrosis (CF) patients. While this bacterium has been extensively studied for its virulence mechanisms, biofilm growth and immune evasion within the CF airways, comparatively little is known about the nutrient sources that sustain its growth in vivo. Respiratory mucins represent a potentially abundant bioavailable nutrient source, though we have recently shown that canonical pathogens inefficiently use these host glycoproteins as a growth substrate. Yet, given that P. aeruginosa, particularly in its biofilm mode of growth is thought to grow slowly in vivo, the inefficient use of mucin glycoproteins may have relevance to its persistence within the CF airways. To this end, here we use whole genome fitness analysis combining transposon mutagenesis with high throughput sequencing (TnSeq) to identify genetic determinants required for P. aeruginosa growth using intact purified mucins as a sole carbon source. Our analysis reveals a biphasic growth phenotype, during which the glyoxylate pathway and amino acid biosynthetic machinery are required for mucin utilization. Secondary analyses confirmed the simultaneous liberation and consumption of acetate during mucin degradation and revealed a central role for the extracellular proteases LasB and AprA. Together, these studies identified the P. aeruginosa genes required for mucin-based nutrient acquisition and reveal a host-pathogen dynamic that may contribute to its persistence within the CF airways.

microbiology↗