Influence of oipA Phase Variation on Virulence Phenotypes Related to Type IV Secretion System in Helicobacter pylori.

BACKGROUND: oipA, an outer membrane protein of Helicobacter pylori, is linked to IL-8 induction and gastric inflammation, but its role is debated due to inconsistent findings. This study aims to explore the role of oipA phase variation in modulating the virulence traits of H. pylori, a bacterium strongly associated with the development of gastric cancer. MATERIAL AND METHODS: American clinical isolate AH868 strain for naturally occurring phase variations of the oipA gene, and G27 strain for in vitro-induced phase variations were used to elucidate oipA's impact on key virulence phenotypes, including cell elongation, CagA phosphorylation, and IL-8 induction. RESULTS: Using AH868 strain, natural oipA phase variation does not affect cell elongation and IL-8 induction. Interestingly, however, in vitro-induced oipA phase variations in G27 strain uncovered that 9.4% of oipA "Off" transformants exhibit reduced cell elongation while all maintaining consistent IL-8 induction levels. Additionally, complementation of oipA "Off to On" status restores the cell elongation phenotype in 12.5% of transformants, highlighting the importance of oipA in maintaining normal cell morphology. Crucially, these variations in cell elongation are not linked to changes in bacterial adherence capabilities. Furthermore, the study shows a correlation among oipA phase variation, cell elongation, and CagA phosphorylation, suggesting that oipA influences the functionality of the Type IV secretion system. Whole-genome sequencing of selected transformants reveals genetic variations in bab paralogue, cagY gene, and other genomic regions, underscoring the complex genetic interactions that shape H. pylori's virulence. CONCLUSIONS: Our research provides new insights into the subtle yet significant role of oipA phase variation in H. pylori pathogenicity, emphasizing the need for further studies to explore the intricate molecular mechanisms involved. This understanding could pave the way for targeted therapeutic strategies to mitigate the impact of H. pylori on human health.

Metformin increases gut multidrug resistance genes in type 2 diabetes, potentially linked to Escherichia coli.

Metformin is the most commonly prescribed medication for treating type 2 diabetes (T2D). It is known that metformin can alter the gut microbiome, which influences the effectiveness of metformin treatment. We posited that if the gut microbiome, a reservoir of the resistome, is altered, then the resistome should change as well. To test this hypothesis, we reanalyzed microbiome data generated by Wu et al. (Nat Med 23(7):850-858, 2017), identifying antibiotic resistance genes (ARGs) and bacterial species. Through read-based analysis, we observed that the abundance of ARGs indeed changed in many samples treated with metformin. Moreover, the altered pattern was sufficiently heterogeneous across individual samples to allow subcategorization. We also found a strong correlation between the abundance of multidrug-resistant ARGs (MDR-ARGs) and the presence of E. coli. The contig-based analysis led to the same conclusion: an increase in MDR-ARGs due to metformin was associated with an increase in E. coli. In relation to this, we were able to confirm that the majority of MDR-ARGs are likely to originate from E. coli. These results suggest that metformin may have the potential side effect of increasing E. coli carrying ARGs, particularly MDR-ARGs, which could be a concern in T2D therapy that relies on metformin.

Ctr9 promotes virulence of Candida albicans by regulating methionine metabolism.

Candida albicans, a part of normal flora, is an opportunistic fungal pathogen and causes severe health issues in immunocompromised patients. Its pathogenicity is intricately linked to the transcriptional regulation of its metabolic pathways. Paf1 complex (Paf1C) is a crucial transcriptional regulator that is highly conserved in eukaryotes. The objective of this study was to explore the role of Paf1C in the metabolic pathways and how it influences the pathogenicity of C. albicans. Paf1C knockout mutant strains of C. albicans (ctr9Δ/Δ, leo1Δ/Δ, and cdc73Δ/Δ) were generated using the CRISPR-Cas9 system. To investigate the effect of Paf1C on pathogenicity, macrophage interaction assays and mouse survival tests were conducted. The growth patterns of the Paf1C knockout mutants were analyzed through spotting assays and growth curve measurements. Transcriptome analysis was conducted under yeast conditions (30°C without serum) and hyphal conditions (37°C with 10% FBS), to further elucidate the role of Paf1C in the pathogenicity of C. albicans. CTR9 deletion resulted in the attenuation of C. albicans virulence, in macrophage and mouse models. Furthermore, we confirmed that the reduced virulence of the ctr9Δ/Δ mutant can be attributed to a decrease in C. albicans cell abundance. Moreover, transcriptome analysis revealed that metabolic processes required for cell proliferation are impaired in ctr9Δ/Δ mutant. Notably, CTR9 deletion led to the downregulation of methionine biosynthetic genes and the cAMP-PKA signaling pathway-related hypha essential genes, which are pivotal for virulence. Our results suggest that Ctr9-regulated methionine metabolism is a crucial factor for determining C. albicans pathogenicity.

N-terminal acetylation of Set1-COMPASS fine-tunes H3K4 methylation patterns.

H3K4 methylation by Set1-COMPASS (complex of proteins associated with Set1) is a conserved histone modification. Although it is critical for gene regulation, the posttranslational modifications of this complex that affect its function are largely unexplored. This study showed that N-terminal acetylation of Set1-COMPASS proteins by N-terminal acetyltransferases (NATs) can modulate H3K4 methylation patterns. Specifically, deleting NatA substantially decreased global H3K4me3 levels and caused the H3K4me2 peak in the 5' transcribed regions to shift to the promoters. NatA was required for N-terminal acetylation of three subunits of Set1-COMPASS: Shg1, Spp1, and Swd2. Moreover, deleting Shg1 or blocking its N-terminal acetylation via proline mutation of the target residue drastically reduced H3K4 methylation. Thus, NatA-mediated N-terminal acetylation of Shg1 shapes H3K4 methylation patterns. NatB also regulates H3K4 methylation, likely via N-terminal acetylation of the Set1-COMPASS protein Swd1. Thus, N-terminal acetylation of Set1-COMPASS proteins can directly fine-tune the functions of this complex, thereby substantially shaping H3K4 methylation patterns.

A shared mechanism of multidrug resistance in laboratory-evolved uropathogenic Escherichia coli.

The emergence of multidrug-resistant bacteria poses a significant threat to human health, necessitating a comprehensive understanding of their underlying mechanisms. Uropathogenic Escherichia coli (UPEC), the primary causative agent of urinary tract infections, is frequently associated with multidrug resistance and recurrent infections. To elucidate the mechanism of resistance of UPEC to beta-lactam antibiotics, we generated ampicillin-resistant UPEC strains through continuous exposure to low and high levels of ampicillin in the laboratory, referred to as Low AmpR and High AmpR, respectively. Whole-genome sequencing revealed that both Low and High AmpR strains contained mutations in the marR, acrR, and envZ genes. The High AmpR strain exhibited a single additional mutation in the nlpD gene. Using protein modeling and qRT-PCR analyses, we validated the contributions of each mutation in the identified genes to antibiotic resistance in the AmpR strains, including a decrease in membrane permeability, increased expression of multidrug efflux pump, and inhibition of cell lysis. Furthermore, the AmpR strain does not decrease the bacterial burden in the mouse bladder even after continuous antibiotic treatment in vivo, implicating the increasing difficulty in treating host infections caused by the AmpR strain. Interestingly, ampicillin-induced mutations also result in multidrug resistance in UPEC, suggesting a common mechanism by which bacteria acquire cross-resistance to other classes of antibiotics.

Preserved structure and function of human serum albumin self-folded in the oxidative cytoplasm of Escherichia coli.

Human serum albumin (HSA), a polypeptide featuring 17 disulfide bonds, acts as a crucial transport protein in human blood plasma. Its extended circulation half-life, mediated by FcRn (neonatal Fc receptor)-facilitated recycling, positions HSA as an excellent carrier for long-acting drug delivery. However, the conventional method of obtaining HSA from human blood faces limitations due to availability and potential contamination risks, such as blood-borne diseases. This study introduced SHuffle, an oxidative Escherichia coli (E. coli) expression system, for the production of recombinant HSA (rHSA) that spontaneously self-folds into its native conformation. This system ensures precise disulfide bond formation and correct folding of cysteine-rich rHSA, eliminating the need for chaperone co-expression or domain fusion of a folding enhancer. The purified rHSA underwent thorough physicochemical characterization, including mass spectrometry, circular dichroism spectroscopy, intrinsic fluorescence spectroscopy, esterase-like activity assay, and size exclusion chromatography, to assess critical quality attributes. Importantly, rHSA maintained native binding affinity to FcRn and the albumin-binding domain. Collectively, our analyses demonstrated a high comparability between rHSA and plasma-derived HSA. The expression of rHSA in E. coli with an oxidizing cytosol provides a secure and cost-effective approach, enhancing the potential of rHSA for diverse medical applications.

Swd2/Cps35 determines H3K4 tri-methylation via interactions with Set1 and Rad6.

BACKGROUND: Histone H3K4 tri-methylation (H3K4me3) catalyzed by Set1/COMPASS, is a prominent epigenetic mark found in promoter-proximal regions of actively transcribed genes. H3K4me3 relies on prior monoubiquitination at the histone H2B (H2Bub) by Rad6 and Bre1. Swd2/Cps35, a Set1/COMPASS component, has been proposed as a key player in facilitating H2Bub-dependent H3K4me3. However, a more comprehensive investigation regarding the relationship among Rad6, Swd2, and Set1 is required to further understand the mechanisms and functions of the H3K4 methylation. RESULTS: We investigated the genome-wide occupancy patterns of Rad6, Swd2, and Set1 under various genetic conditions, aiming to clarify the roles of Set1 and Rad6 for occupancy of Swd2. Swd2 peaks appear on both the 5' region and 3' region of genes, which are overlapped with its tightly bound two complexes, Set1 and cleavage and polyadenylation factor (CPF), respectively. In the absence of Rad6/H2Bub, Set1 predominantly localized to the 5' region of genes, while Swd2 lost all the chromatin binding. However, in the absence of Set1, Swd2 occupancy near the 5' region was impaired and rather increased in the 3' region. CONCLUSIONS: This study highlights that the catalytic activity of Rad6 is essential for all the ways of Swd2's binding to the transcribed genes and Set1 redistributes the Swd2 to the 5' region for accomplishments of H3K4me3 in the genome-wide level.

Model for end-stage liver disease-3.0 vs. model for end-stage liver disease-sodium: mortality prediction in Korea.

BACKGROUND/AIMS: The model for end-stage liver disease (MELD) serves as an indicator for short-term mortality among patients diagnosed with liver cirrhosis (LC) and is used to prioritize patients for liver transplantation. In 2021, the updated version of MELD, MELD-3.0, was introduced to improve the accuracy of the mortality prediction of MELD. Therefore, this study aimed to compare the efficacy of MELD 3.0 and MELD-Na in predicting mortality among Korean patients with LC. METHODS: A retrospective review was conducted using the medical records of patients diagnosed with LC who were admitted to Konkuk University Hospital From 2011 to 2021. The study calculated the predictive values of MELD-Na and MELD-3.0 for 3- and 6-months mortality using the area under the receiver operating curve (AUROC) and compared the results using the DeLong test. RESULTS: Of the 3,034 patients enrolled in the study, 339 (11.2%) died within 3 months and 421 (14.4%) died within 6 months. The AUROCs values for predicting 3 months mortality were 0.846 for MELD-Na and 0.851 for MELD-3.0. The corresponding AUROC values for predicting 6 months mortality were 0.843 for MELD-Na and 0.848 for MELD-3.0. MELD-3.0 exhibited better discrimination ability than MELD-Na for both 3 (p = 0.03) and 6 months mortality (p = 0.01). CONCLUSION: Our study found a significant difference between the performance of MELD-3.0 and MELD-Na in Korean patients with LC.

Assessment of DNA extraction methods for human gut mycobiome analysis.

The gut mycobiome plays an important role in the health and disease of the human gut, but its exact function is still under investigation. While there is a wealth of information available on the bacterial community of the human gut microbiome, research on the fungal community is still relatively limited. In particular, technical methodologies for mycobiome analysis, especially the DNA extraction method for human faecal samples, varied in different studies. In the current study, two commercial kits commonly used in DNA extraction, the QIAamp® Fast DNA Stool Mini Kit and DNeasy PowerSoil Pro Kit, and one manual method, the International Human Microbiome Standards Protocol Q, were compared. Furthermore, the effectiveness of two different bead-beating machines, the Mini-Beadbeater-16 and FastPrep-24TM 5G, was compared in parallel. A mock fungal community with a known composition of fungal strains was also generated and included to compare different DNA extraction methods. Our results suggested that the method using the DNeasy PowerSoil Pro Kit and Mini-Beadbeater-16 provides the best results to extract DNA from human faecal samples. Based on our data, we propose a standard operating procedure for DNA extraction from human faecal samples for mycobiome analysis.

Highly Efficient Nitrogen-Fixing Microbial Hydrogel Device for Sustainable Solar Hydrogen Production.

Conversion of sunlight and organic carbon substrates to sustainable energy sources through microbial metabolism has great potential for the renewable energy industry. Despite recent progress in microbial photosynthesis, the development of microbial platforms that warrant efficient and scalable fuel production remains in its infancy. Efficient transfer and retrieval of gaseous reactants and products to and from microbes are particular hurdles. Here, inspired by water lily leaves floating on water, a microbial device designed to operate at the air-water interface and facilitate concomitant supply of gaseous reactants, smooth capture of gaseous products, and efficient sunlight delivery is presented. The floatable device carrying Rhodopseudomonas parapalustris, of which nitrogen fixation activity is first determined through this study, exhibits a hydrogen production rate of 104 mmol h-1  m-2 , which is 53 times higher than that of a conventional device placed at a depth of 2 cm in the medium. Furthermore, a scaled-up device with an area of 144 cm2 generates hydrogen at a high rate of 1.52 L h-1  m-2 . Efficient nitrogen fixation and hydrogen generation, low fabrication cost, and mechanical durability corroborate the potential of the floatable microbial device toward practical and sustainable solar energy conversion.

Environmental Adaptation of Psychrophilic Bacteria Subtercola spp. Isolated from Various Cryospheric Habitats.

Subtercola boreus K300T is a novel psychrophilic strain that was isolated from permanently cold groundwater in Finland and has also been found in several places in Antarctica including lake, soil, and rocks. We performed genomic and transcriptomic analyses of 5 strains from Antarctica and a type strain to understand their adaptation to different environments. Interestingly, the isolates from rocks showed a low growth rate and smaller genome size than strains from the other isolation sources (lake, soil, and groundwater). Based on these habitat-dependent characteristics, the strains could be classified into two ecotypes, which showed differences in energy production, signal transduction, and transcription in the clusters of orthologous groups of proteins (COGs) functional category. In addition, expression pattern changes revealed differences in metabolic processes, including uric acid metabolism, DNA repair, major facilitator superfamily (MFS) transporters, and xylose degradation, depending on the nutritional status of their habitats. These findings provide crucial insights into the environmental adaptation of bacteria, highlighting genetic diversity and regulatory mechanisms that enable them to thrive in the cryosphere.

Regulation of acetate tolerance by small ORF-encoded polypeptides modulating efflux pump specificity in Methylomonas sp. DH-1.

BACKGROUND: Methanotrophs have emerged as promising hosts for the biological conversion of methane into value-added chemicals, including various organic acids. Understanding the mechanisms of acid tolerance is essential for improving organic acid production. WatR, a LysR-type transcriptional regulator, was initially identified as involved in lactate tolerance in a methanotrophic bacterium Methylomonas sp. DH-1. In this study, we investigated the role of WatR as a regulator of cellular defense against weak organic acids and identified novel target genes of WatR. RESULTS: By conducting an investigation into the genome-wide binding targets of WatR and its role in transcriptional regulation, we identified genes encoding an RND-type efflux pump (WatABO pump) and previously unannotated small open reading frames (smORFs), watS1 to watS5, as WatR target genes activated in response to acetate. The watS1 to watS5 genes encode polypeptides of approximately 50 amino acids, and WatS1 to WatS4 are highly homologous with one predicted transmembrane domain. Deletion of the WatABO pump genes resulted in decreased tolerance against formate, acetate, lactate, and propionate, suggesting its role as an efflux pump for a wide range of weak organic acids. WatR repressed the basal expression of watS genes but activated watS and WatABO pump genes in response to acetate stress. Overexpression of watS1 increased tolerance to acetate but not to other acids, only in the presence of the WatABO pump. Therefore, WatS1 may increase WatABO pump specificity toward acetate, switching the general weak acid efflux pump to an acetate-specific efflux pump for efficient cellular defense against acetate stress. CONCLUSIONS: Our study has elucidated the role of WatR as a key transcription factor in the cellular defense against weak organic acids, particularly acetate, in Methylomonas sp. DH-1. We identified the genes encoding WatABO efflux pump and small polypeptides (WatS1 to WatS5), as the target genes regulated by WatR for this specific function. These findings offer valuable insights into the mechanisms underlying weak acid tolerance in methanotrophic bacteria, thereby contributing to the development of bioprocesses aimed at converting methane into value-added chemicals.

Protective role of colitis in inflammatory arthritis via propionate-producing Bacteroides in the gut.

Objectives: To investigate whether and how inflammatory disease in the intestine influences the development of arthritis, considering that organ-to-organ communication is associated with many physiological and pathological events. Methods: First, mice were given drinking water containing dextran sodium sulfate (DSS) and then subjected to inflammatory arthritis. We compared the phenotypic symptoms between the cohoused and separately-housed mice. Next, donor mice were divided into DSS-treated and untreated groups and then cohoused with recipient mice. Arthritis was then induced in the recipients. The fecal microbiome was analyzed by 16S rRNA amplicon sequencing. We obtained type strains of the candidate bacteria and generated propionate-deficient mutant bacteria. Short-chain fatty acids were measured in the bacterial culture supernatant, serum, feces, and cecum contents using gas chromatography-mass spectrometry. Mice fed with candidate and mutant bacteria were subjected to inflammatory arthritis. Results: Contrary to expectations, the mice treated with DSS exhibited fewer symptoms of inflammatory arthritis. Intriguingly, the gut microbiota contributes, at least in part, to the improvement of colitis-mediated arthritis. Among the altered microorganisms, Bacteroides vulgatus and its higher taxonomic ranks were enriched in the DSS-treated mice. B. vulgatus, B. caccae, and B. thetaiotaomicron exerted anti-arthritic effects. Propionate production deficiency further prevented the protective effect of B. thetaiotaomicron on arthritis. Conclusions: We suggest a novel relationship between the gut and joints and an important role of the gut microbiota as communicators. Moreover, the propionate-producing Bacteroides species examined in this study may be a potential candidate for developing effective treatments for inflammatory arthritis.

Transcriptional Interplay between Malassezia restricta and Staphylococcus Species Co-Existing in the Skin Environment.

Malassezia and Staphylococcus are the most dominant genera in human skin microbiome. To explore the inter-kingdom interactions between the two genera, we examined the transcriptional changes in Malassezia and Staphylococcus species induced upon co-culturing. RNA-seq analyses revealed that genes encoding ribosomal proteins were upregulated, while those encoding aspartyl proteases were downregulated in M. restricta after co-culturing with Staphylococcus species. We identified MRET_3770 as a major secretory aspartyl protease coding gene in M. restricta through pepstatin-A affinity chromatography followed by mass spectrometry and found that the expression of MRET_3770 was significantly repressed upon co-culturing with Staphylococcus species or by incubation in media with reduced pH. Moreover, biofilm formation by Staphylococcus aureus was inhibited in the spent medium of M. restricta, suggesting that biomolecules secreted by M. restricta such as secretory aspartyl proteases may degrade the biofilm structure. We also examined the transcriptional changes in S. aureus co-cultured with M. restricta and found co-cultured S. aureus showed increased expression of genes encoding ribosomal proteins and downregulation of those involved in riboflavin metabolism. These transcriptome data of co-cultured fungal and bacterial species demonstrate a dynamic interplay between the two co-existing genera.

Mycobacterium potentiates protection from colorectal cancer by gut microbial alterations.

Not only are many Mycobacteria pathogens, but they can act as strong non-specific immunopotentiators, generating beneficial effects on the pathogenesis of some diseases. However, there has been no direct evidence of the effect of mycobacterial species on colorectal cancer (CRC). Herein, we showed that there may be a meaningful inverse correlation between the incidence of tuberculosis and CRC based on global statistics and that heat-killed Mycobacterial tuberculosis and live Mycobacterium bovis (Bacillus Calmette-Guérin strain) could ameliorate CRC development. In particular, using a faecal microbiota transplantation and a comparison between separate housing and cohousing, we demonstrated that the gut microbiota is involved in the protective effects. The microbial alterations can be elucidated by the modulation of antimicrobial activities including those of the Reg3 family genes. Furthermore, interleukin-22 production by T helper cells contributed to the anti-inflammatory activity of Mycobacteria. Our results revealed a novel role of Mycobacteria involving gut microbial alterations in dampening inflammation-associated CRC and an immunological mechanism underlying the interaction between microbes and host immunity.

A mannose-sensing AraC-type transcriptional activator regulates cell-cell aggregation of Vibrio cholerae.

In addition to catalyzing coupled transport and phosphorylation of carbohydrates, the phosphoenolpyruvate:carbohydrate phosphotransferase system (PTS) regulates various physiological processes in most bacteria. Therefore, the transcription of genes encoding the PTS is precisely regulated by transcriptional regulators depending on substrate availability. As the distribution of the mannose-specific PTS (PTSMan) is limited to animal-associated bacteria, it has been suggested to play an important role in host-bacteria interactions. In Vibrio cholerae, mannose is known to inhibit biofilm formation. During host infection, the transcription level of the V. cholerae gene encoding the putative PTSMan (hereafter referred to as manP) significantly increases, and mutations in this gene increase host survival rate. Herein, we show that an AraC-type transcriptional regulator (hereafter referred to as ManR) acts as a transcriptional activator of the mannose operon and is responsible for V. cholerae growth and biofilm inhibition on a mannose or fructose-supplemented medium. ManR activates mannose operon transcription by facilitating RNA polymerase binding to the promoter in response to mannose 6-phosphate and, to a lesser extent, to fructose 1-phosphate. When manP or manR is impaired, the mannose-induced inhibition of biofilm formation was reversed and intestinal colonization was significantly reduced in a Drosophila melanogaster infection model. Our results show that ManR recognizes mannose and fructose in the environment and facilitates V. cholerae survival in the host.

Genome of Malassezia arunalokei and Its Distribution on Facial Skin.

Malassezia is a fungal genus found on the skin of humans and warm-blooded animals, with 18 species reported to date. In this study, we sequenced and annotated the genome of Malassezia arunalokei, which is the most recently identified Malassezia species, and compared it with Malassezia restricta, the predominant isolate from human skin. Additionally, we reanalyzed previously reported mycobiome data sets with a species-level resolution to investigate M. arunalokei distribution within the mycobiota of human facial skin. We discovered that the M. arunalokei genome is 7.24 Mbp in size and encodes 4,117 protein-coding genes, all of which were clustered with M. restricta. We also found that the average nucleotide identity value of the M. arunalokei genome was 93.5, compared with the genomes of three M. restricta strains, including M. restricta KCTC 27527. Our findings demonstrate that they indeed belong to different species and that M. arunalokei may have experienced specific gene loss events during speciation. Furthermore, our study showed that M. arunalokei was diverged from M. restricta approximately 7.1 million years ago and indicated that M. arunalokei is the most recently diverged species in the Malassezia lineage to date. Finally, our analysis of the facial mycobiome of previously recruited cohorts revealed that M. arunalokei abundance is not associated with seborrheic dermatitis/dandruff or acne, but was revealed to be more abundant on the forehead and cheek than on the scalp. IMPORTANCEMalassezia is the fungus predominantly residing on the human skin and causes various skin diseases, including seborrheic dermatitis and dandruff. To date, 18 species have been reported, and among them, M. restricta is the most predominant on human skin, especially on the scalp. In this study, we sequenced and analyzed the genome of M. arunalokei, which is the most recently identified Malassezia species, and compared it with M. restricta. Moreover, we analyzed the fungal microbiome to investigate the M. arunalokei distribution on human facial skin. We found that M. arunalokei may have experienced specific gene loss events during speciation. Our study also showed that M. arunalokei was diverged from M. restricta approximately 7.1 million years ago and indicated that M. arunalokei is the most recently diverged species in the Malassezia lineage. Finally, our analysis of the facial mycobiome revealed that M. arunalokei has higher relative abundance on the forehead and cheek than the scalp.

A mucin-responsive hybrid two-component system controls Bacteroides thetaiotaomicron colonization and gut homeostasis.

The mammalian intestinal tract contains trillions of bacteria. However, the genetic factors that allow gut symbiotic bacteria to occupy intestinal niches remain poorly understood. Here, we identified genetic determinants required for Bacteroides thetaiotaomicron colonization in the gut using transposon sequencing analysis. Transposon insertion in BT2391, which encodes a hybrid two-component system, increased the competitive fitness of B. thetaiotaomicron. The BT2391 mutant showed a growth advantage in a mucin-dependent manner and had an increased ability to adhere to mucus-producing cell lines. The increased competitive advantage of the BT2391 mutant was dependent on the BT2392-2395 locus containing susCD homologs. Deletion of BT2391 led to changes in the expression levels of B. thetaiotaomicron genes during gut colonization. However, colonization of the BT2391 mutant promoted DSS colitis in low-fiber diet-fed mice. These results indicate that BT2391 contributes to a sustainable symbiotic relationship by maintaining a balance between mucosal colonization and gut homeostasis.

The human symbiont Bacteroides thetaiotaomicron promotes diet-induced obesity by regulating host lipid metabolism.

The gut microbiome plays an important role in lipid metabolism. Consumption of a high-fat diet (HFD) alters the bacterial communities in the gut, leading to metabolic disorders. Several bacterial species have been associated with diet-induced obesity, nonalcoholic fatty liver disease, and metabolic syndrome. However, the mechanisms underlying the control of lipid metabolism by symbiotic bacteria remain elusive. Here, we show that the human symbiont Bacteroides thetaiotaomicron aggravates metabolic disorders by promoting lipid digestion and absorption. Administration of B. thetaiotaomicron to HFD-fed mice promoted weight gain, elevated fasting glucose levels, and impaired glucose tolerance. Furthermore, B. thetaiotaomicron treatment upregulated the gene expression of the fatty acid transporter and increased fatty acid accumulation in the liver. B. thetaiotaomicron inhibits expression of the gene encoding a lipoprotein lipase inhibitor, angiopoietin-like protein 4 (ANGPTL4), thereby increasing lipase activity in the small intestine. In particular, we found that B. thetaiotaomicron induced the expression of hepcidin, the master regulator of iron metabolism and an antimicrobial peptide, in the liver. Hepcidin treatment resulted in a decrease in ANGPTL4 expression in Caco-2 cells, whereas treatment with an iron chelator restored ANGPTL4 expression in hepcidin-treated cells. These results indicate that B. thetaiotaomicron-mediated regulation of iron storage in intestinal epithelial cells may contribute to increased fat deposition and impaired glucose tolerance in HFD-fed mice.

Regulation of iron homeostasis by peroxide-sensitive CatR, a Fur-family regulator in Streptomyces coelicolor.

CatR, a peroxide-sensing transcriptional repressor of Fur family, can de-repress the transcription of the catA gene encoding catalase upon peroxide stress in Streptomyces coelicolor. Since CatR-regulated genes other than catA and its own gene catR have not been identified in detail, the understanding of the role of CatR regulon is very limited. In this study, we performed transcriptomic analysis to identify genes influenced by both ΔcatR mutation and hydrogen peroxide treatment. Through ChIP-qPCR and other analyses, a new consensus sequence was found in CatR-responsive promoter region of catR gene and catA operon for direct regulation. In addition, vtlA (SCO2027) and SCO4983 were identified as new members of the CatR regulon. Expression levels of iron uptake genes were reduced by hydrogen peroxide and a DmdR1 binding sequence was identified in promoters of these genes. The increase in free iron by hydrogen peroxide was thought to suppress the iron import system by DmdR1. A putative exporter protein VtlA regulated by CatR appeared to reduce intracellular iron to prevent oxidative stress. The name vtlA (VIT1-like transporter) was proposed for iron homeostasis related gene SCO2027.