Reciprocal regulation of enterococcal cephalosporin resistance by products of the autoregulated yvcJ-glmR-yvcL operon enhances fitness during cephalosporin exposure.

Enterococci are commensal members of the gastrointestinal tract and also major nosocomial pathogens. They possess both intrinsic and acquired resistance to many antibiotics, including intrinsic resistance to cephalosporins that target bacterial cell wall synthesis. These antimicrobial resistance traits make enterococcal infections challenging to treat. Moreover, prior therapy with antibiotics, including broad-spectrum cephalosporins, promotes enterococcal proliferation in the gut, resulting in dissemination to other sites of the body and subsequent infection. As a result, a better understanding of mechanisms of cephalosporin resistance is needed to enable development of new therapies to treat or prevent enterococcal infections. We previously reported that flow of metabolites through the peptidoglycan biosynthesis pathway is one determinant of enterococcal cephalosporin resistance. One factor that has been implicated in regulating flow of metabolites into cell wall biosynthesis pathways of other Gram-positive bacteria is GlmR. In enterococci, GlmR is encoded as the middle gene of a predicted 3-gene operon along with YvcJ and YvcL, whose functions are poorly understood. Here we use genetics and biochemistry to investigate the function of the enterococcal yvcJ-glmR-yvcL gene cluster. Our results reveal that YvcL is a DNA-binding protein that regulates expression of the yvcJ-glmR-yvcL operon in response to cell wall stress. YvcJ and GlmR bind UDP-GlcNAc and reciprocally regulate cephalosporin resistance in E. faecalis, and binding of UDP-GlcNAc by YvcJ appears essential for its activity. Reciprocal regulation by YvcJ/GlmR is essential for fitness during exposure to cephalosporin stress. Additionally, our results indicate that enterococcal GlmR likely acts by a different mechanism than the previously studied GlmR of Bacillus subtilis, suggesting that the YvcJ/GlmR regulatory module has evolved unique targets in different species of bacteria.

A serum-induced gene signature in hepatocytes is associated with pediatric nonalcoholic fatty liver disease.

OBJECTIVE: Pediatric nonalcoholic fatty liver disease (NAFLD) is a growing problem, but its underlying mechanisms are poorly understood. We used transcriptomic reporter cell assays to investigate differences in transcriptional signatures induced in hepatocyte reporter cells by the sera of children with and without NAFLD. METHODS: We studied serum samples from 45 children with NAFLD and 28 children without NAFLD. The sera were used to induce gene expression in cultured HepaRG cells and RNA-sequencing was used to determine gene expression. Computational techniques were used to compare gene expression patterns. RESULTS: Sera from children with NAFLD induced the expression of 195 genes that were significantly differentially expressed in hepatocytes compared to controls with obesity. NAFLD was associated with increased expression of genes promoting inflammation, collagen synthesis, and extracellular matrix remodeling. Additionally, there was lower expression of genes involved in endobiotic and xenobiotic metabolism, and downregulation of peroxisome function, oxidative phosphorylation, and xenobiotic, bile acid, and fatty acid metabolism. A 13-gene signature, including upregulation of TREM1 and MMP1 and downregulation of CYP2C9, was consistently associated with all diagnostic categories of pediatric NAFLD. CONCLUSION: The extracellular milieu of sera from children with NAFLD induced specific gene profiles distinguishable by a hepatocyte reporter system. Circulating factors may contribute to inflammation and extracellular matrix remodeling and impair xenobiotic and endobiotic metabolism in pediatric NAFLD.

The intestinal microbiome of children with initial and recurrent nephrolithiasis: A pilot study and exploratory analysis.

INTRODUCTION: Kidney stone disease in children is rising disproportionate to the general population, representing a disease population with a distinct biological mechanism as compared to adults. Factors influencing recurrent kidney stone disease in children are poorly characterized and the associations of the intestinal microbiome within sub-populations of kidney stone formers, however, are not well described. We evaluated a pilot cohort of children with nephrolithiasis comparing patients based on recurrent kidney stone episodes and abnormal 24-h urinary parameters, with dual aims to compare the microbiome signal in children with initial and recurrent nephrolithiasis and to explore additional associations in microbiome composition and diversity within this population. METHODS: Children aged 6-18 with a history of nephrolithiasis, without an active ureteral calculus or antibiotic exposure within 30 days of study entry were eligible to participate. All participants had a 24-h urine study within 6 months of study entry and provided a fecal sample. Microbiome samples were analyzed using 16S ribosomal DNA sequencing techniques for alpha and beta diversity comparing initial and recurrent stone formers as well as microbiome multivariate association (MaAsLin2) to determine differentially abundant taxa. Shotgun sequencing reads were aligned to custom oxidase degradation and butyrate production gene databases (5 databases total). Comparisons for MaAsLin2 and shotgun metagenomics, normalized to sequencing depth, were based on stone recurrence, sex, hypercalcuria (≤4 mg/kg/day), hyperoxaluria (≥45 mg/1.73 m2), and hypocitraturia (<310 mg/1.73 m2 [females] or < 365 mg/1.73 m2 [males]). RESULTS: A total of 16 enrolled children provided samples sufficient for analyses, including 9 girls and 7 boys, of whom 5 had experienced recurrent kidney stone events. Three participants had hypercalcuria, 2 had hyperoxaluria, and 4 had hypocitraturia. Comparisons of Formyl-CoA transferase between index and recurrent urinary stone disease revealed a trend towards higher mean abundance of the gene in initial stone formers (0.166% vs 0.0343%, p = 0.2847) (Summary Figure), while trends toward lower biodiversity were also noted in the recurrent stone cohort on both Faith (p = 0.06) and Shannon (p = 0.05) indices. Exploratory analyses found Eubacterium siraeum to be significantly greater in relative abundance in children with documented hypercalciuria (p = 0.001). DISCUSSION: Our pilot study demonstrates possible signals in both microbial diversity and oxalate gene expression, both of which are lower in recurrent pediatric kidney stone patients. These findings warrant further investigation as a potential diagnostic marker for future kidney stone events.

Thiocillin contributes to the ecological fitness of Bacillus cereus ATCC 14579 during interspecies interactions with Myxococcus xanthus.

The soil-dwelling delta-proteobacterium Myxococcus xanthus is a model organism to study predation and competition. M. xanthus preys on a broad range of bacteria mediated by lytic enzymes, exopolysaccharides, Type-IV pilus-based motility, and specialized metabolites. Competition between M. xanthus and prey bacterial strains with various specialized metabolite profiles indicates a range of fitness, suggesting that specialized metabolites contribute to prey survival. To expand our understanding of how specialized metabolites affect predator-prey dynamics, we assessed interspecies interactions between M. xanthus and two strains of Bacillus cereus. While strain ATCC 14579 resisted predation, strain T was found to be highly sensitive to M. xanthus predation. The interaction between B. cereus ATCC 14579 and M. xanthus appears to be competitive, resulting in population loss for both predator and prey. Genome analysis revealed that ATCC 14579 belongs to a clade that possesses the biosynthetic gene cluster for production of thiocillins, whereas B. cereus strain T lacks those genes. Further, purified thiocillin protects B. cereus strains unable to produce this specialized metabolite, strengthening the finding that thiocillin protects against predation and contributes to the ecological fitness of B. cereus ATCC 14579. Lastly, strains that produce thiocillin appear to confer some level of protection to their own antibiotic by encoding an additional copy of the L11 ribosomal protein, a known target for thiopeptides. This work highlights the importance of specialized metabolites affecting predator-prey dynamics in soil microenvironments.

Impact of auricular percutaneous electrical nerve field stimulation on gut microbiome in adolescents with irritable bowel syndrome: A pilot study.

OBJECTIVES: Percutaneous electrical nerve field stimulation (PENFS) has documented efficacy for irritable bowel syndrome (IBS) via plausible vagal neuromodulation effects. The vagus nerve may affect gut microbiome composition via brain-gut-microbiome signaling. We aimed to investigate gut microbiome alterations by PENFS therapy in adolescent IBS patients. METHODS: A prospective study of females with IBS aged 11-18 years receiving PENFS therapy for 4 weeks with pre- and post-intervention stool sampling was conducted. Outcome surveys completed pre-therapy, weekly, and post-therapy included IBS-Severity Scoring System (IBS-SSS), Visceral Sensitivity Index (VSI), Functional Disability Inventory (FDI), and the global symptom response scale (SRS). Bacterial DNA was extracted from stool samples followed by 16S rRNA amplification and sequencing. QIIME 2 (version 2022.2) was used for analyses of α and ß diversity and differential abundance by group. RESULTS: Twenty females aged 15.6 ± 1.62 years were included. IBS-SSS, VSI, and FDI scores decreased significantly after PENFS therapy (P < 0.0001, P = 0.0003, P = 0.0004, respectively). No intra- or interindividual microbiome changes were noted pre- versus post-therapy or between responders and non-responders. When response was defined by 50-point IBS-SSS score reduction, α diversity was higher in responders compared with non-responders at week 4 (P = 0.033). There was higher abundance of Blautia in excellent responders versus non-responders. CONCLUSIONS: There were no substantial microbial diversity alterations with PENFS. Subjects with excellent therapeutic response showed an enrichment of relative abundance of Blautia, which may indicate that patients with specific microbial signature have a more favorable response to PENFS.

Gut microbiota and metabolites drive chronic sickle cell disease pain.

Pain is a debilitating symptom and leading reason for hospitalization of individuals with sickle cell disease. Chronic sickle cell pain is poorly managed because the biological basis is not fully understood. Using transgenic sickle cell mice and fecal material transplant, we determined that the gut microbiome drives persistent sickle cell pain. In parallel patient and mouse analyses, we identified bilirubin as one metabolite that induces sickle cell pain by altering vagus nerve activity. Furthermore, we determined that decreased abundance of the gut bacteria Akkermansia mucinophila is a critical driver of chronic sickle cell pain. These experiments demonstrate that the sickle cell gut microbiome drives chronic widespread pain and identify bacterial species and metabolites that should be targeted for chronic sickle cell disease pain management.

Tuft cells mediate commensal remodeling of the small intestinal antimicrobial landscape.

Succinate produced by the commensal protist Tritrichomonas musculis (T. mu) stimulates chemosensory tuft cells, resulting in intestinal type 2 immunity. Tuft cells express the succinate receptor SUCNR1, yet this receptor does not mediate antihelminth immunity nor alter protist colonization. Here, we report that microbial-derived succinate increases Paneth cell numbers and profoundly alters the antimicrobial peptide (AMP) landscape in the small intestine. Succinate was sufficient to drive this epithelial remodeling, but not in mice lacking tuft cell chemosensory components required to detect this metabolite. Tuft cells respond to succinate by stimulating type 2 immunity, leading to interleukin-13-mediated epithelial and AMP expression changes. Moreover, type 2 immunity decreases the total number of mucosa-associated bacteria and alters the small intestinal microbiota composition. Finally, tuft cells can detect short-term bacterial dysbiosis that leads to a spike in luminal succinate levels and modulate AMP production in response. These findings demonstrate that a single metabolite produced by commensals can markedly shift the intestinal AMP profile and suggest that tuft cells utilize SUCNR1 and succinate sensing to modulate bacterial homeostasis.

A single, peri-operative antibiotic can persistently alter the post-operative gut microbiome after Roux-en-Y gastric bypass.

INTRODUCTION: Roux-en-Y gastric bypass (RYGB) significantly alters the gut microbiome and may be a mechanism for post-operative cardiovascular disease improvement. We have previously found an association between the class of peri-operative, intravenous antibiotic administered at the time of RYGB and the resolution rate of hypertension suggesting the gut microbiome as a mechanism. In this study, we performed a prospective study of RYGB to determine if a single intravenous antibiotic could alter the gastrointestinal microbial composition. METHODS: Patients undergoing RYGB were randomized to a single, peri-operative antibiotic of intravenous cefazolin (n = 8) or clindamycin (n = 8). Stool samples were collected from four-time points: 2 weeks pre-op (- 2w), 2 days pre-op (- 2d), 2 weeks post-op (+ 2w) and 3 months post-op (+ 3m). Stool samples were processed for genomic DNA followed by Illumina 16S rRNA gene sequencing and shotgun metagenomic sequencing (MGS). RESULTS: A total of 60 stool samples (- 2w, n = 16; - 2d, n = 15; + 2w, n = 16; + 3m, n = 13) from 16 patients were analyzed. 87.5% of patients were female with an average age of 48.6 ± 12.2 years and pre-operative BMI of 50.9 ± 23.3 kg/m2. RYGB induced statistically significant differences in alpha and beta diversity. There were statistically significant differences in alpha diversity at + 2w and beta diversity at + 3m due to antibiotic treatment. MGS revealed significantly distinct gut microbiota with 11 discriminatory metagenomic assembled genomes driven by antibiotic treatment at 3 months post-op, including increased Bifidobacterium spp. with clindamycin. CONCLUSION: RYGB induces significant changes in the gut microbiome at 2 weeks that are maintained 3 months after surgery. However, the single peri-operative dose of antibiotic administered at the time of RYGB induces unique and persisting changes to the gut microbiome that are antibiotic-specific. Increased Bifidobacterium spp. with clindamycin administration may improve the metabolic efficacy of RYGB when considering gut-microbiome driven mechanisms for blood pressure resolution.

Lactiplantibacillus plantarum 299v supplementation modulates ß-cell ER stress and antioxidative defense pathways and prevents type 1 diabetes in gluten-free BioBreeding rats.

The increasing incidence of Type 1 diabetes has coincided with the emergence of the low-fiber, high-gluten Western diet and other environmental factors linked to dysbiosis. Since Lactiplantibacillus plantarum 299 v (Lp299v) supplementation improves gut barrier function and reduces systemic inflammation, we studied its effects in spontaneously diabetic DRlyp/lyp rats provided a normal cereal diet (ND) or a gluten-free hydrolyzed casein diet (HCD). All rats provided ND developed diabetes (62.5±7.7 days); combining ND with Lp299v did not improve survival. Diabetes was delayed by HCD (72.2±9.4 days, p = .01) and further delayed by HCD+Lp299v (84.9±14.3 days, p < .001). HCD+Lp299v pups exhibited increased plasma propionate and butyrate levels, which correlated with enriched fecal Bifidobacteriaceae and Clostridiales taxa. Islet transcriptomic and histologic analyses at 40-days of age revealed that rats fed HCD expressed an autophagy profile, while those provided HCD+Lp299v expressed ER-associated protein degradation (ERAD) and antioxidative defense pathways, including Nrf2. Exposing insulinoma cells to propionate and butyrate promoted the antioxidative defense response but did not recapitulate the HCD+Lp299v islet ERAD transcriptomic profile. Here, both diet and microbiota influenced diabetes susceptibility. Moreover, Lp299v supplement modulated antioxidative defense and ER stress responses in ß-cells, potentially offering a new therapeutic direction to thwart diabetes progression and preserve insulin secretion.

CroR Regulates Expression of pbp4(5) to Promote Cephalosporin Resistance in Enterococcus faecalis.

Enterococcus faecalis is an opportunistic pathogen and a major cause of severe nosocomial infections. Treatment options against enterococcal infections are declining due to the resistance of enterococci to numerous antibiotics. A key risk factor for developing enterococcal infections is treatment with cephalosporin antibiotics, to which enterococci are intrinsically resistant. For susceptible organisms, cephalosporins inhibit bacterial growth by acylating the active site of penicillin-binding proteins (PBPs), key enzymes that catalyze peptidoglycan cross-linking. Two specific PBPs of enterococci, Pbp4(5) and PbpA(2b), exhibit low reactivity toward cephalosporins, allowing these PBPs to cross-link peptidoglycan in the presence of cephalosporins to drive resistance in enterococci, but the mechanisms by which these PBPs are regulated are poorly understood. The CroS/R two-component signal transduction system (TCS) is also required for cephalosporin resistance. Activation of CroS/R by cephalosporins leads to CroR-dependent changes in gene expression. However, the specific genes regulated by CroS/R that are responsible for cephalosporin resistance remain largely unknown. In this study, we characterized CroR-dependent transcriptome remodeling by RNA-seq, identifying pbp4(5) as a CroR regulon member in multiple, diverse lineages of E. faecalis. Through genetic analysis of the pbp4(5) and croR promoters, we uncovered a CroR-dependent regulatory motif. Mutations in this motif to disrupt CroR-dependent upregulation of pbp4(5) in the presence of cell wall stress resulted in a reduction of resistance to cephalosporins in E. faecalis, demonstrating that enhanced production of Pbp4(5) and likely other proteins involved in peptidoglycan biogenesis by the CroS/R system drives enterococcal cephalosporin resistance. IMPORTANCE Investigation into molecular mechanisms used by enterococci to subvert cephalosporin antibiotics is imperative for preventing and treating life-threatening infections. In this study, we used genetic means to investigate the functional output of the CroS/R TCS required for enterococcal resistance to cephalosporins. We found that enhanced production of the penicillin-binding protein Pbp4(5) upon exposure to cell wall stress was mediated by CroS/R and was critical for intrinsic cephalosporin resistance of E. faecalis.

Probiotic normalization of systemic inflammation in siblings of type 1 diabetes patients: an open-label pilot study.

The incidence of type 1 diabetes (T1D) has increased, coinciding with lifestyle changes that have likely altered the gut microbiota. Dysbiosis, gut barrier dysfunction, and elevated systemic inflammation consistent with microbial antigen exposure, have been associated with T1D susceptibility and progression. A 6-week, single-arm, open-label pilot trial was conducted to investigate whether daily multi-strain probiotic supplementation could reduce this familial inflammation in 25 unaffected siblings of T1D patients. Probiotic supplementation was well-tolerated as reflected by high participant adherence and no adverse events. Community alpha and beta diversity were not altered between the pre- and post-supplement stool samplings. However, LEfSe analyses identified post-supplement enrichment of the family Lachnospiraceae, producers of the anti-inflammatory short chain fatty acid butyrate. Systemic inflammation was measured by plasma-induced transcription and quantified with a gene ontology-based composite inflammatory index (I.I.com). Post-supplement I.I.com was significantly reduced and pathway analysis predicted inhibition of numerous inflammatory mediators and activation of IL10RA. Subjects with the greatest post-supplement reduction in I.I.com exhibited significantly lower CD4+ CD45RO+ (memory):CD4+ CD45RA+ (naïve) T-cell ratios after supplementation. Post-supplement IL-12p40, IL-13, IL-15, IL-18, CCL2, and CCL24 plasma levels were significantly reduced, while post-supplement butyrate levels trended 1.4-fold higher. Probiotic supplementation may modify T1D susceptibility and progression and warrants further study.

Nicotinamide Riboside-Conditioned Microbiota Deflects High-Fat Diet-Induced Weight Gain in Mice.

The gut microbiome plays an essential role in host energy homeostasis and influences the development of obesity and related conditions. Studies demonstrate that nicotinamide riboside (NR) supplementation for diet-induced obesity (DIO) reduces weight gain and increases energy expenditure in mice. NR is a vitamin B3 derivative and an NAD+ precursor with potential for treating human diseases arising from mitochondrial degeneration, including obesity and type 2 diabetes. Gut bacteria produce vitamin B3 in the colon and are capable of salvaging and metabolizing vitamin B3 and its derivatives. However, it is unknown how dietary supplementation of NR alters the microbiome and if those alterations contribute to deflection of weight gain. In this study, we fed C57BL/6J male mice a high-fat diet (HFD) supplemented with or without NR and performed a fecal material transfer (FMT) to establish a link between NR-conditioned microbiota and NR-induced deflection of weight gain. FMT from NR-treated donors to naive mice fed a HFD was sufficient to deflect weight gain by increasing energy expenditure. We also investigated the effects of NR on the microbiome by using metagenomics sequencing. We found that NR-treated mice displayed an altered gut microbial composition relative to controls and that fecal transplant resulted in a distinct functional metabolic profile characterized by enrichment of butyrate-producing Firmicutes. NR-treated donors and subsequent FMT recipients share a similar enrichment of metagenomic biomarkers relative to controls. These findings suggest that microbial factors contribute to the beneficial effects of dietary NR supplementation, which may be useful to enhance the therapeutic effects of NR. IMPORTANCE With obesity and type 2 diabetes (T2D) at epidemic levels, we need to understand the complex nature of these diseases to design better therapeutics. The underlying causes of both obesity and T2D are complex, but both are thought to develop, in part, based on contributions from the gut microbiota. Nicotinamide riboside is a gut-derived vitamin B3 derivative and NAD+ precursor which has the potential to treat and prevent metabolic disorders by ameliorating mitochondrial dysfunction. Understanding how NR affects the gut microbiome and whether NR-conditioned microbiota contributes to weight loss in the host would (i) improve diagnosis and treatments for obesity and other metabolic pathologies, (ii) tailor treatments to satisfy the needs of each individual moving toward the future of precision medicine, and (iii) benefit other scientific fields that currently investigate the effects of NR in other disease pathologies.

Retinoic Acid Signaling Modulates Recipient Gut Barrier Integrity and Microbiota After Allogeneic Hematopoietic Stem Cell Transplantation in Mice.

Graft-versus-host disease (GVHD) remains a major complication after allogeneic hematopoietic stem cell transplantation (HSCT). An impaired intestinal epithelial barrier is an important component of GVHD pathogenesis. However, contributing host factors that modulate mucosal barrier integrity during GVHD are poorly defined. We hypothesized that vitamin A and retinoic acid (RA) exert positive impacts on maintaining intestinal barrier function after HSCT, thus preventing or dampening GVHD severity. Unexpectedly, we found that exogenous RA increased intestinal permeability of recipient mice after allogeneic HSCT. Serum bacterial endotoxin levels were significantly higher in GVHD mice fed a vitamin A-high (VAH) diet compared to those fed a vitamin A-normal (VAN) diet, indicating a more compromised intestinal barrier function. Furthermore, VAH mice showed more severe lung GVHD with increased donor T cell infiltration in this tissue and died significantly faster than VAN recipients. 16S rRNA sequencing of fecal samples revealed significant differences in the diversity and composition of gut microbiota between VAN and VAH transplant recipients. Collectively, we show that retinoic acid signaling may negatively impact intestinal barrier function during GVHD. Mild vitamin A supplementation is associated with increased lung GVHD and more profound gut dysbiosis. Micronutrients such as vitamin A could modulate complications of allogeneic HSCT, which may be mediated by shaping gut microbiota.

Sleeve gastrectomy prevents hypertension associated with unique shifts in the gut microbiome.

INTRODUCTION: Bariatric surgery results in resolution of hypertension in over 50% of patients. While weight loss is a critical component to hypertension resolution after bariatric surgery, there may also be weight loss-independent mechanisms. OBJECTIVES: We hypothesized that sleeve gastrectomy (SG) initiates changes in the gut microbiome which reduce postoperative blood pressure. METHODS: Male, obese Zucker rats underwent SG, pair-fed sham, or ad-lib-fed sham surgery. Blood pressure measurements were performed 1 week pre-operatively, and at 2 and 6 weeks post-operatively. The stool microbiome composition was determined by 16S rDNA gene at 6 weeks post-operatively. Regression Random Forest modeling was performed to determine an association of the microbial composition with blood pressure. RESULTS: SG and pair-fed rats weighed significantly less than ad-lib-fed sham rats throughout the post-surgical period. At 6 weeks after surgery, SG rats had a significantly lower systolic blood pressure (149.2 ± 1.99 mmHg) than pair-fed (164.7 ± 7.87, p < 0.001) or ad-lib-fed sham rats (167.1 ± 2.41 mmHg, p < 0.001). There was a significant difference in multiple measures of beta diversity between SG rats and pair-fed and ad-lib-fed sham rats. 45.11% of the difference in blood pressure variability between samples was explained with the regression Random Forest model. CONCLUSION: SG in a rat model prevented hypertension progression independent of weight loss with changes in beta diversity and gut bacterial composition associated with the blood pressure outcome. These findings further support the metabolic efficacy of SG in treating hyperglycemia, cardiac dysfunction, and now hypertension, independent of obesity class.

Suppressor mutations reveal an NtrC-like response regulator, NmpR, for modulation of Type-IV Pili-dependent motility in Myxococcus xanthus.

Two-component signaling systems (TCS) regulate bacterial responses to environmental signals through the process of protein phosphorylation. Specifically, sensor histidine kinases (SK) recognize signals and propagate the response via phosphorylation of a cognate response regulator (RR) that functions to initiate transcription of specific genes. Signaling within a single TCS is remarkably specific and cross-talk between TCS is limited. However, regulation of the flow of information through complex signaling networks that include closely related TCS remains largely unknown. Additionally, many bacteria utilize multi-component signaling networks which provide additional genetic and biochemical interactions that must be regulated for signaling fidelity, input and output specificity, and phosphorylation kinetics. Here we describe the characterization of an NtrC-like RR that participates in regulation of Type-IV pilus-dependent motility of Myxococcus xanthus and is thus named NmpR, NtrC Modulator of Pili Regulator. A complex multi-component signaling system including NmpR was revealed by suppressor mutations that restored motility to cells lacking PilR, an evolutionarily conserved RR required for expression of pilA encoding the major Type-IV pilus monomer found in many bacterial species. The system contains at least four signaling proteins: a SK with a protoglobin sensor domain (NmpU), a hybrid SK (NmpS), a phospho-sink protein (NmpT), and an NtrC-like RR (NmpR). We demonstrate that ΔpilR bypass suppressor mutations affect regulation of the NmpRSTU multi-component system, such that NmpR activation is capable of restoring expression of pilA in the absence of PilR. Our findings indicate that pilus gene expression in M. xanthus is regulated by an extended network of TCS which interact to refine control of pilus function.

Association of Mycobacterium Proteins with Lipid Droplets.

Mycobacterium tuberculosis is a global pathogen of significant medical importance. A key aspect of its life cycle is the ability to enter into an altered physiological state of nonreplicating persistence during latency and resist elimination by the host immune system. One mechanism by which M. tuberculosis facilitates its survival during latency is by producing and metabolizing intracytoplasmic lipid droplets (LDs). LDs are quasi-organelles consisting of a neutral lipid core such as triacylglycerol surrounded by a phospholipid monolayer and proteins. We previously reported that PspA (phage shock protein A) associates with LDs produced in Mycobacterium In particular, the loss or overproduction of PspA alters LD homeostasis in Mycobacterium smegmatis and attenuates the survival of M. tuberculosis during nonreplicating persistence. Here, M. tuberculosis PspA (PspAMtb) and a ΔpspA M. smegmatis mutant were used as model systems to investigate the mechanism by which PspA associates with LDs and determine if other Mycobacterium proteins associate with LDs using a mechanism similar to that for PspA. Through this work, we established that the amphipathic helix present in the first α-helical domain (H1) of PspA is both necessary and sufficient for the targeting of this protein to LDs. Furthermore, we identified other Mycobacterium proteins that also possess amphipathic helices similar to PspA H1, including a subset that localize to LDs. Altogether, our results indicate that amphipathic helices may be an important mechanism by which proteins target LDs in prokaryotes.IMPORTANCEMycobacterium spp. are one of the few prokaryotes known to produce lipid droplets (LDs), and their production has been linked to aspects of persistent infection by M. tuberculosis Unfortunately, little is known about LD production in these organisms, including how LDs are formed, their function, or the identity of proteins that associate with them. In this study, an established M. tuberculosis LD protein and a surrogate Mycobacterium host were used as model systems to study the interactions between proteins and LDs in bacteria. Through these studies, we identified a commonly occurring protein motif that is able to facilitate the association of proteins to LDs in prokaryotes.

The Gut Microbiome, Energy Homeostasis, and Implications for Hypertension.

PURPOSE OF REVIEW: The influence of gut bacteria upon host physiology is increasingly recognized, but mechanistic links are lacking. Diseases of energetic imbalance such as obesity and diabetes represent major risk factors for cardiovascular diseases such as hypertension. Thus, here, we review current mechanistic contributions of the gut microbiota to host energetics. RECENT FINDINGS: Gut bacteria generate a multitude of small molecules which can signal to host tissues within and beyond the gastrointestinal tract to influence host physiology, and gut bacteria can also influence host digestive efficiency by altering the bioavailability of polysaccharides, yet the quantitative energetic effects of these processes remain unclear. Recently, our team has demonstrated that gut bacteria constitute a major anaerobic thermogenic biomass, which can quantitatively account for obesity. Quantitative understanding of the mechanisms by which gut bacteria influence energy homeostasis may ultimately inform the relationship between gut bacteria and cardiovascular dysfunction.

Type IV-pili dependent motility is co-regulated by PilSR and PilS2R2 two-component systems via distinct pathways in Myxococcus xanthus.

Myxococcus xanthus is an environmental bacterium with two forms of motility. One type, known as social motility, is dependent on extension and retraction of Type-IV pili (T4P) and production of extracellular polysaccharides (EPS). Several signaling systems have been linked to regulation of T4P-dependent motility. In particular, expression of the pilin subunit pilA requires the PilSR two-component signaling system (TCS). A second TCS, PilS2R2, encoded within the same locus that encodes PilSR, has also been linked to M. xanthus T4P-dependent motility. We demonstrate that PilSR and PilS2R2 regulate M. xanthus T4P-dependent motility through distinct pathways. Consistent with known roles of PilSR, our results indicate that the primary function of PilSR is to regulate expression of pilA. In contrast, PilS2 and PilR2 have little to no affect on PilA protein levels. However, deletion of pilR2 resulted in a reduction of assembled pili, significant decreases in EPS production and loss of T4P-dependent motility. Furthermore, the pilR2 mutation led to increased production of outer membrane vesicles (OMV). Collectively, we propose that PilS2R2 is required for proper assembly of T4P and regulation of OMV production, and hypothesize that production of these vesicles is related to M. xanthus motility.