Vibrio cholerae VC1741 (PsrA) enhances the colonization of the pathogen in infant mice intestines in the presence of the long-chain fatty acid, oleic acid

Long-chain fatty acids as nutrients for Gram-negative bacteria: stress, proliferation, and virulence

Bacteria use host-derived long-chain fatty acids (LCFAs) as nutrients, signals, and membrane building blocks. Although the impact of LCFAs on the pathogenesis of Gram-negative bacteria via membrane remodeling or signaling is well-documented, their importance as a nutrient source for bacterial proliferation and virulence is an emerging research area with definitive studies reported only for Salmonella Typhimurium, Vibrio cholerae, and Pseudomonas aeruginosa. Moreover, recent studies in Escherichia coli have shown that LCFA degradation confers redox stress. Here, we review the known role of LCFAs as nutrients during infection in Gram-negative human pathogens and the association of LCFA degradation with redox stress and stress response mechanisms. We suggest that for understanding how, as nutrients, LCFAs influence host-bacterial interactions, it is necessary to resolve whether LCFA utilization also causes redox stress in pathogens, with defense mechanisms preconditioning them for challenging host environments, or if pathogens have pre-existing mechanisms that prevent LCFA-induced stress.

The effects of PstR, a PadR family transcriptional regulatory factor, in Plesiomonas shigelloides are revealed by transcriptomics

BACKGROUND

Plesiomonas shigelloides is a gram-negative opportunistic pathogen associated with gastrointestinal and extraintestinal diseases in humans. There have been reports of specific functional genes in the study of P. shigelloides, but there are also many unknown genes that may play a role in P. shigelloides pathogenesis as global regulatory proteins or virulence factors.

RESULTS

In this study, we found a transcriptional regulator of the PadR family in P. shigelloides and named it PstR (GenBank accession number: EON87311.1), which is present in various pathogenic bacteria but whose function has rarely been reported. RNA sequencing (RNA-Seq) was used to analyze the effects of PstR on P. shigelloides, and the results indicated that PstR regulates approximately 9.83% of the transcriptome, which includes impacts on motility, virulence, and physiological metabolism. RNA-seq results showed that PstR positively regulated the expression of the flagella gene cluster, which was also confirmed by quantitative Real-Time Polymerase Chain Reaction (qRT-PCR) and Luminescence screening assay. Meanwhile, the ΔpstR mutant strains lacked flagella and were non-motile, as confirmed by motility assays and transmission electron microscopy (TEM). Additionally, PstR also positively regulates T3SS expression, which aids in P. shigelloides' capacity to infect Caco-2 cells. Meanwhile, we also revealed that PstR negatively regulates fatty acid degradation and metabolism, as well as the regulatory relationship between PsrA, a regulator of fatty acid degradation and metabolism, and its downstream genes in P. shigelloides.

CONCLUSIONS

Overall, we revealed the effects of PstR on motility, virulence, and physiological metabolism in P. shigelloides, which will serve as a foundation for future research into the intricate regulatory network of PstR in bacteria.

Exploring Fatty Acid β-Oxidation Pathways in Bacteria: From General Mechanisms to DSF Signaling and Pathogenicity in Xanthomonas

Fatty acids (FAs) participate in extensive physiological activities such as energy metabolism, transcriptional control, and cell signaling. In bacteria, FAs are degraded and utilized through various metabolic pathways, including β-oxidation. Over the past ten years, significant progress has been made in studying FA oxidation in bacteria, particularly in E. coli, where the processes and roles of FA β-oxidation have been comprehensively elucidated. Here, we provide an update on the new research achievements in FAs β-oxidation in bacteria. Using Xanthomonas as an example, we introduce the oxidation process and regulation mechanism of the DSF-family quorum sensing signal. Based on current findings, we propose the specific enzymes required for β-oxidation of several specific FAs. Finally, we discuss the future outlook on scientific issues that remain to be addressed. This paper supplies theoretical guidance for further study of the FA β-oxidation pathway with particular emphasis on its connection to the pathogenicity mechanisms of bacteria.

An essential host dietary fatty acid promotes TcpH inhibition of TcpP proteolysis promoting virulence gene expression in Vibrio cholerae

Vibrio cholerae is a Gram-negative gastrointestinal pathogen responsible for the diarrheal disease cholera. Expression of key virulence factors, cholera toxin and toxin-coregulated pilus, is regulated directly by ToxT and indirectly by two transmembrane transcription regulators (TTRs), ToxR and TcpP, that promote the expression of toxT. TcpP abundance and activity are controlled by TcpH, a single-pass transmembrane protein, which protects TcpP from a two-step proteolytic process known as regulated intramembrane proteolysis (RIP). The mechanism of TcpH-mediated protection of TcpP represents a major gap in our understanding of V. cholerae pathogenesis. The absence of tcpH leads to unimpeded degradation of TcpP in vitro and a colonization defect in a neonate mouse model of V. cholerae colonization. Here, we show that TcpH protects TcpP from RIP via direct interaction. We also demonstrate that α-linolenic acid, a dietary fatty acid, promotes TcpH-dependent inhibition of RIP via co-association of TcpP and TcpH molecules within detergent-resistant membranes (DRMs) in a mechanism requiring the TcpH transmembrane domain. Taken together, our data support a model where V. cholerae cells use exogenous α-linolenic acid to remodel the phospholipid bilayer in vivo, leading to co-association of TcpP and TcpH within DRMs where RIP of TcpP is inhibited by TcpH, thereby promoting V. cholerae pathogenicity.

IMPORTANCE

Vibrio cholerae continues to pose a significant global burden on health and an alternative therapeutic approach is needed, due to evolving multidrug resistance strains. Transcription of toxT, stimulated by TcpP and ToxR, is essential for V. cholerae pathogenesis. Our results show that TcpP, one of the major regulators of toxT gene expression, is protected from proteolysis by TcpH, via direct interaction. Furthermore, we identified a gut metabolite, α-linolenic acid, that stimulates the co-association of TcpP and TcpH within detergent-resistant membranes (also known as lipid-ordered membrane domains), thereby supporting TcpH-dependent antagonism of TcpP proteolysis. Data presented here extend our knowledge of RIP, virulence gene regulation in V. cholerae, and, to the best of our knowledge, provides the first evidence that lipid-ordered membranes exist within V. cholerae. The model presented here also suggests that TTRs, common among bacteria and archaea, and co-component signal transduction systems present in Enterobacteria, could also be influenced similarly.

Transcriptome Analysis Reveals Cross-Talk between the Flagellar Transcriptional Hierarchy and Secretion System in Plesiomonas shigelloides

Plesiomonas shigelloides, a Gram-negative bacillus, is the only member of the Enterobacteriaceae family able to produce polar and lateral flagella and cause gastrointestinal and extraintestinal illnesses in humans. The flagellar transcriptional hierarchy of P. shigelloides is currently unknown. In this study, we identified FlaK, FlaM, FliA, and FliAL as the four regulators responsible for polar and lateral flagellar regulation in P. shigelloides. To determine the flagellar transcription hierarchy of P. shigelloides, the transcriptomes of the WT and ΔflaK, ΔflaM, ΔfliA, and ΔfliAL were carried out for comparison in this study. Quantitative Real-Time Polymerase Chain Reaction (qRT-PCR) and luminescence screening assays were used to validate the RNA-seq results, and the Electrophoretic Mobility Shift Assay (EMSA) results revealed that FlaK can directly bind to the promoters of fliK, fliE, flhA, and cheY, while the FlaM protein can bind directly to the promoters of flgO, flgT, and flgA. Meanwhile, we also observed type VI secretion system (T6SS) and type II secretion system 2 (T2SS-2) genes downregulated in the transcriptome profiles, and the killing assay revealed lower killing abilities for ΔflaK, ΔflaM, ΔfliA, and ΔfliAL compared to the WT, indicating that there was a cross-talk between the flagellar hierarchy system and bacterial secretion system. Invasion assays also showed that ΔflaK, ΔflaM, ΔfliA, and ΔfliAL were less effective in infecting Caco-2 cells than the WT. Additionally, we also found that the loss of flagellar regulators causes the differential expression of some of the physiological metabolic genes of P. shigelloides. Overall, this study aims to reveal the transcriptional hierarchy that controls flagellar gene expression in P. shigelloides, as well as the cross-talk between motility, virulence, and physiological and metabolic activity, laying the groundwork for future research into P. shigelloides' coordinated survival in the natural environment and the mechanisms that infect the host.

Amino Acid-Induced Chemotaxis Plays a Key Role in the Adaptation of Vibrio harveyi from Seawater to the Muscle of the Host Fish

Vibrio harveyi is a normal flora in natural marine habitats and a significant opportunistic pathogen in marine animals. This bacterium can cause a series of lesions after infecting marine animals, in which muscle necrosis and ulcers are the most common symptoms. This study explored the adaptation mechanisms of V. harveyi from the seawater environment to host fish muscle environment. The comprehensive transcriptome analysis revealed dramatic changes in the transcriptome of V. harveyi during its adaptation to the host fish muscle environment. Based on Gene Ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) analysis, flagellar assembly, oxidative phosphorylation, bacterial chemotaxis, and two-component systems play crucial roles in V. harveyi's adaptation to host fish muscle. A comparison of biological phenotypes revealed that V. harveyi displayed a significant increase in flagellar length, swimming, twitching, chemotaxis, adhesion, and biofilm formation after induction by host fish muscle, and its dominant amino acids, especially bacterial chemotaxis induced by host muscle, Ala and Arg. It could be speculated that the enhancement of bacterial chemotaxis induced by amino acids plays a key role in the adaptation of V. harveyi from seawater to the muscle of the host fish.

Matching the β-oxidation gene repertoire with the wide diversity of fatty acids

Bacteria can use fatty acids (FAs) from their environment as carbon and energy source. This catabolism is performed by the enzymes of the well-known β-oxidation machinery, producing reducing power and releasing acetyl-CoA that can feed the tricarboxylic acid cycle. FAs are extremely diverse: they can be saturated or (poly)unsaturated and are found in different sizes. The need to degrade such a wide variety of compounds may explain why so many seemingly homologous enzymes are found for each step of the β-oxidation cycle. In addition, the degradation of unsaturated fatty acids requires specific auxiliary enzymes for isomerase and reductase reactions. Furthermore, the β-oxidation cycle can be blocked by dead-end products, which are taken care of by acyl-CoA thioesterases. Yet, the functional characterization of the enzymes required for the degradation of the full diversity of FAs remains to be documented in most bacteria.

A novel quorum sensing regulator LuxT contributes to the virulence of Vibrio cholerae

Vibrio cholerae is a waterborne bacterium that primarily infects the human intestine and causes cholera fatality. Quorum sensing (QS) negatively regulates the expression of V. cholerae virulence gene. However, the primary associated mechanisms remain undetermined. This investigation identified a new QS regulator from the TetR family, LuxT, which increases V. cholerae virulence by directly inhibiting hapR expression. HapR is a master QS regulator that suppresses virulence cascade expression. The expression of luxT increased 4.8-fold in the small intestine of infant mice than in Luria-Bertani broth. ΔluxT mutant strain revealed a substantial defect in the colonizing ability of the small intestines. At low cell densities, the expression level of hapR was upregulated by luxT deletion, suggesting that LuxT can suppress hapR transcription. The electrophoretic mobility shift analysis revealed that LuxT directly binds to the hapR promoter region. Furthermore, luxT expression was upregulated by the two-component system ArcB/ArcA, which responses to changes in oxygen levels in response to the host's small intestine's anaerobic signals. In conclusion, this research reveals a novel cell density-mediated virulence regulation pathway and contributes to understanding the complex association between V. cholerae virulence and QS signals. This evidence furnishes new insights for future studies on cholerae's pathogenic mechanisms.

Transcriptome Analysis Reveals the Effect of PdhR in Plesiomonas shigelloides

The pyruvate dehydrogenase complex regulator (PdhR) was originally identified as a repressor of the pdhR-aceEF-lpd operon, which encodes the pyruvate dehydrogenase complex (PDHc) and PdhR itself. According to previous reports, PdhR plays a regulatory role in the physiological and metabolic pathways of bacteria. At present, the function of PdhR in Plesiomonas shigelloides is still poorly understood. In this study, RNA sequencing (RNA-Seq) of the wild-type strain and the ΔpdhR mutant strains was performed for comparison to identify the PdhR-controlled pathways, revealing that PdhR regulates ~7.38% of the P. shigelloides transcriptome. We found that the deletion of pdhR resulted in the downregulation of practically all polar and lateral flagella genes in P. shigelloides; meanwhile, motility assay and transmission electron microscopy (TEM) confirmed that the ΔpdhR mutant was non-motile and lacked flagella. Moreover, the results of RNA-seq and quantitative Real-Time Polymerase Chain Reaction (qRT-PCR) showed that PdhR positively regulated the expression of the T3SS cluster, and the ΔpdhR mutant significantly reduced the ability of P. shigelloides to infect Caco-2 cells compared with the WT. Consistent with previous research, pyruvate-sensing PdhR directly binds to its promoter and inhibits pdhR-aceEF-lpd operon expression. In addition, we identified two additional downstream genes, metR and nuoA, that are directly negatively regulated by PdhR. Furthermore, we also demonstrated that ArcA was identified as being located upstream of pdhR and lpdA and directly negatively regulating their expression. Overall, we revealed the function and regulatory pathway of PdhR, which will allow for a more in-depth investigation into P. shigelloides pathogenicity as well as the complex regulatory network.

The Response Regulator VC1795 of Vibrio Pathogenicity Island-2 Contributes to Intestinal Colonization by Vibrio cholerae

Vibrio cholerae is an intestinal pathogen that can cause severe diarrheal disease. The disease has afflicted millions of people since the 19th century and has aroused global concern. The Vibrio Pathogenicity Island-2 (VPI-2) is a 57.3 kb region, VC1758-VC1809, which is present in choleragenic V. cholerae. At present, little is known about the function of VC1795 in the VPI-2 of V. cholerae. In this study, the intestinal colonization ability of the ΔVC1795 strain was significantly reduced compared to that of the wild-type strain, and the colonization ability was restored to the wild-type strain after VC1795 gene replacement. This result indicated that the VC1795 gene plays a key role in the intestinal colonization and pathogenicity of V. cholerae. Then, we explored the upstream and downstream regulation mechanisms of the VC1795 gene. Cyclic adenylate receptor protein (CRP) was identified as being located upstream of VC1795 by a DNA pull-down assay and electrophoretic mobility shift assays (EMSAs) and negatively regulating the expression of VC1795. In addition, the results of Chromatin immunoprecipitation followed by sequencing (ChIP-seq), EMSAs, and Quantitative Real-Time Polymerase Chain Reaction (qRT-PCR) indicated that VC1795 directly negatively regulates the expression of its downstream gene, VC1794. Furthermore, by using qRT-PCR, we hypothesized that VC1795 indirectly positively regulates the toxin-coregulated pilus (TCP) cluster to influence the colonization ability of V. cholerae in intestinal tracts. In short, our findings support the key regulatory role of VC1795 in bacterial pathogenesis as well as lay the groundwork for the further determination of the complex regulatory network of VC1795 in bacteria.

Advances in cholera research: from molecular biology to public health initiatives

The aquatic bacterium Vibrio cholerae is the etiological agent of the diarrheal disease cholera, which has plagued the world for centuries. This pathogen has been the subject of studies in a vast array of fields, from molecular biology to animal models for virulence activity to epidemiological disease transmission modeling. V. cholerae genetics and the activity of virulence genes determine the pathogenic potential of different strains, as well as provide a model for genomic evolution in the natural environment. While animal models for V. cholerae infection have been used for decades, recent advances in this area provide a well-rounded picture of nearly all aspects of V. cholerae interaction with both mammalian and non-mammalian hosts, encompassing colonization dynamics, pathogenesis, immunological responses, and transmission to naïve populations. Microbiome studies have become increasingly common as access and affordability of sequencing has improved, and these studies have revealed key factors in V. cholerae communication and competition with members of the gut microbiota. Despite a wealth of knowledge surrounding V. cholerae, the pathogen remains endemic in numerous countries and causes sporadic outbreaks elsewhere. Public health initiatives aim to prevent cholera outbreaks and provide prompt, effective relief in cases where prevention is not feasible. In this review, we describe recent advancements in cholera research in these areas to provide a more complete illustration of V. cholerae evolution as a microbe and significant global health threat, as well as how researchers are working to improve understanding and minimize impact of this pathogen on vulnerable populations.

RpoN is required for the motility and contributes to the killing ability of Plesiomonas shigelloides

BACKGROUND

RpoN, also known as σ⁵⁴, first reported in Escherichia coli, is a subunit of RNA polymerase that strictly controls the expression of different genes by identifying specific promoter elements. RpoN has an important regulatory function in carbon and nitrogen metabolism and participates in the regulation of flagellar synthesis, bacterial motility and virulence. However, little is known about the effect of RpoN in Plesiomonas shigelloides.

RESULTS

To identify pathways controlled by RpoN, RNA sequencing (RNA-Seq) of the WT and the rpoN deletion strain was carried out for comparison. The RNA-seq results showed that RpoN regulates ~ 13.2% of the P. shigelloides transcriptome, involves amino acid transport and metabolism, glycerophospholipid metabolism, pantothenate and CoA biosynthesis, ribosome biosynthesis, flagellar assembly and bacterial secretion system. Furthermore, we verified the results of RNA-seq using quantitative real-time reverse transcription PCR, which indicated that the absence of rpoN caused downregulation of more than half of the polar and lateral flagella genes in P. shigelloides, and the ΔrpoN mutant was also non-motile and lacked flagella. In the present study, the ability of the ΔrpoN mutant to kill E. coli MG1655 was reduced by 54.6% compared with that of the WT, which was consistent with results in RNA-seq, which showed that the type II secretion system (T2SS-2) genes and the type VI secretion system (T6SS) genes were repressed. By contrast, the expression of type III secretion system genes was largely unchanged in the ΔrpoN mutant transcriptome and the ability of the ΔrpoN mutant to infect Caco-2 cells was also not significantly different compared with the WT.

CONCLUSIONS

We showed that RpoN is required for the motility and contributes to the killing ability of P. shigelloides and positively regulates the T6SS and T2SS-2 genes.

Animal models for dissecting Vibrio cholerae intestinal pathogenesis and immunity

The human diarrheal disease cholera is caused by the bacterium Vibrio cholerae. Efforts to develop animal models that closely mimic cholera to study the pathogenesis of this disease began >125 years ago. Here, we review currently used non-surgical, oral inoculation-based animal models for investigation of V. cholerae intestinal colonization and disease and highlight recent discoveries that have illuminated mechanisms of cholera pathogenesis and immunity, particularly in the area of how V. cholerae interacts with the gut microbiome to influence infection. The emergence of high-throughput tools for studies of pathogen-host interactions, along with continued advances in host genetic engineering and manipulation in animal models of V. cholerae will deepen understanding of cholera pathogenesis, uncovering knowledge important for control of this globally important bacterial pathogen.

The global regulators ArcA and CytR collaboratively modulate Vibrio cholerae motility

Background

Vibrio cholerae, a Gram-negative bacterium, is highly motile owing to the presence of a single polar flagellum. The global anaerobiosis response regulator, ArcA regulates the expression of virulence factors and enhance biofilm formation in V. cholerae. However, the function of ArcA for the motility of V. cholerae is yet to be elucidated. CytR, which represses nucleoside uptake and catabolism, is known to play a chief role in V. cholerae pathogenesis and flagellar synthesis but the mechanism that CytR influences motility is unclear.

Results

In this study, we found that the ΔarcA mutant strain exhibited higher motility than the WT strain due to ArcA directly repressed flrA expression. We further discovered that CytR directly enhanced fliK expression, which explained why the ΔcytR mutant strain was retarded in motility. On the other hand, cytR was a direct ArcA target and cytR expression was directly repressed by ArcA. As expected, cytR expression was down-regulated.

Conclusions

Overall, ArcA plays a critical role in V. cholerae motility by regulating flrA expression directly and fliK indirectly in the manner of cytR.