ClpP protease modulates bacterial growth, stress response, and bacterial virulence in Brucella abortus

The process of intracellular proteolysis through ATP-dependent proteases is a biologically conserved phenomenon. The stress responses and bacterial virulence of various pathogenic bacteria are associated with the ATP-dependent Clp protease. In this study, a Brucella abortus 2308 strain, ΔclpP, was constructed to characterize the function of ClpP peptidase. The growth of the ΔclpP mutant strain was significantly impaired in the TSB medium. The results showed that the ΔclpP mutant was sensitive to acidic pH stress, oxidative stress, high temperature, detergents, high osmotic environment, and iron deficient environment. Additionally, the deletion of clpP significantly affected Brucella virulence in macrophage and mouse infection models. Integrated transcriptomic and proteomic analyses of the ΔclpP strain showed that 1965 genes were significantly affected at the mRNA and/or protein levels. The RNA-seq analysis indicated that the ΔclpP strain exhibited distinct gene expression patterns related to energy production and conversion, cell wall/membrane/envelope biogenesis, carbohydrate transport, and metabolism. The iTRAQ analysis revealed that the differentially expressed proteins primarily participated in amino acid transport and metabolism, energy production and conversion, and secondary metabolites biosynthesis, transport and catabolism. This study provided insights into the preliminary molecular mechanism between Clp protease to bacterial growth, stress response, and bacterial virulence in Brucella strains.

A comprehensive review on human disease-causing bacterial proteases and their impeding agents

Proteases are enzymes that catalyze the amide bond dissociation in polypeptide and protein peptide units. They are categorized into seven families and are responsible for a wide spectrum of human ailments, such as various types of cancers, skin infections, urinary tract infections etc. Specifically, the bacterial proteases cause a huge impact in the disease progression. Extracellular bacterial proteases break down the host defense proteins, while intracellular proteases are essential for pathogens virulence. Due to its involvement in disease pathogenesis and virulence, bacterial proteases are considered to be potential drug targets. Several studies have reported potential bacterial protease inhibitors in both Gram-positive and Gram-negative disease causing pathogens. In this study, we have comprehensively reviewed about the various human disease-causing cysteine, metallo, and serine bacterial proteases as well as their potential inhibitors.

Cellular functions of the ClpP protease impacting bacterial virulence

Proteostasis mechanisms significantly contribute to the sculpting of the proteomes of all living organisms. ClpXP is a central AAA+ chaperone-protease complex present in both prokaryotes and eukaryotes that facilitates the unfolding and subsequent degradation of target substrates. ClpX is a hexameric unfoldase ATPase, while ClpP is a tetradecameric serine protease. Substrates of ClpXP belong to many cellular pathways such as DNA damage response, metabolism, and transcriptional regulation. Crucially, disruption of this proteolytic complex in microbes has been shown to impact the virulence and infectivity of various human pathogenic bacteria. Loss of ClpXP impacts stress responses, biofilm formation, and virulence effector protein production, leading to decreased pathogenicity in cell and animal infection models. Here, we provide an overview of the multiple critical functions of ClpXP and its substrates that modulate bacterial virulence with examples from several important human pathogens.

Genome-Wide Identification of Ralstonia solanacearum Genes Required for Survival in Tomato Plants

Ralstonia solanacearum is an extremely destructive phytopathogenic bacterium for which there is no effective control method. Though many pathogenic factors have been identified, the survival strategies of R. solanacearum in host plants remain unclear. Transposon insertion sequencing (Tn-seq) is a high-throughput genetic screening technology. This study conducted a Tn-seq analysis using the in planta environment as selective pressure to identify R. solanacearum genes required for survival in tomato plants. One hundred thirty genes were identified as putative genes required for survival in tomato plants. Sixty-three of these genes were classified into four Clusters of Orthologous Groups categories. The absence of genes that encode the outer membrane lipoprotein LolB (RS_RS01965) or the membrane protein RS_RS04475 severely decreased the in planta fitness of R. solanacearum. RS_RS09970 and RS_RS04490 are involved in tryptophan and serine biosynthesis, respectively. Mutants that lack RS_RS09970 or RS_RS04490 did not cause any wilt symptoms in susceptible tomato plants. These results confirmed the importance of genes related to "cell wall/membrane/envelope biogenesis" and "amino acid transport and metabolism" for survival in plants. The gene encoding NADH-quinone oxidoreductase subunit B (RS_RS10340) is one of the 13 identified genes involved in "energy production and conversion," and the Clp protease gene (RS_RS08645) is one of the 11 identified genes assigned to "posttranslational modification, protein turnover, and chaperones." Both genes were confirmed to be required for survival in plants. In conclusion, this study globally identified and validated R. solanacearum genes required for survival in tomato plants and provided essential information for a more complete view of the pathogenic mechanism of R. solanacearum. IMPORTANCE Tomato plant xylem is a nutritionally limiting and dynamically changing habitat. Studies on how R. solanacearum survives in this hostile environment are important for our full understanding of the pathogenic mechanism of this bacterium. Though many omics approaches have been employed to study in planta survival strategies, the direct genome-wide identification of R. solanacearum genes required for survival in plants is still lacking. This study performed a Tn-seq analysis in R. solanacearum and revealed that genes in the categories "cell wall/membrane/envelope biogenesis," "amino acid transport and metabolism," "energy production and conversion," "posttranslational modification, protein turnover, chaperones" and others play important roles in the survival of R. solanacearum in tomato plants.

Revisiting Persistent Salmonella Infection and the Carrier State: What Do We Know?

One characteristic of the few Salmonella enterica serovars that produce typhoid-like infections is that disease-free persistent infection can occur for months or years in a small number of individuals post-convalescence. The bacteria continue to be shed intermittently which is a key component of the epidemiology of these infections. Persistent chronic infection occurs despite high levels of circulating specific IgG. We have reviewed the information on the basis for persistence in S. Typhi, S. Dublin, S. Gallinarum, S. Pullorum, S. Abortusovis and also S. Typhimurium in mice as a model of persistence. Persistence appears to occur in macrophages in the spleen and liver with shedding either from the gall bladder and gut or the reproductive tract. The involvement of host genetic background in defining persistence is clear from studies with the mouse but less so with human and poultry infections. There is increasing evidence that the organisms (i) modulate the host response away from the typical Th1-type response normally associated with immune clearance of an acute infection to Th2-type or an anti-inflammatory response, and that (ii) the bacteria modulate transformation of macrophage from M1 to M2 type. The bacterial factors involved in this are not yet fully understood. There are early indications that it might be possible to remodulate the response back towards a Th1 response by using cytokine therapy.

Extensive Horizontal Gene Transfer within and between Species of Coagulase-Negative Staphylococcus

Members of the gram-positive bacterial genus Staphylococcus have historically been classified into coagulase-positive Staphylococcus (CoPS) and coagulase-negative Staphylococcus (CoNS) based on the diagnostic presentation of the coagulase protein. Previous studies have noted the importance of horizontal gene transfer (HGT) and recombination in the more well-known CoPS species Staphylococcus aureus, yet little is known of the contributions of these processes in CoNS evolution. In this study, we aimed to elucidate the phylogenetic relationships, genomic characteristics, and frequencies of HGT in CoNS, which are now being recognized as major opportunistic pathogens of humans. We compiled a data set of 1,876 publicly available named CoNS genomes. These can be delineated into 55 species based on allele differences in 462 core genes and variation in accessory gene content. CoNS species are a reservoir of transferrable genes associated with resistance to diverse classes of antimicrobials. We also identified nine types of the mobile genetic element SCCmec, which carries the methicillin resistance determinant mecA. Other frequently transferred genes included those associated with resistance to heavy metals, surface-associated proteins related to virulence and biofilm formation, type VII secretion system, iron capture, recombination, and metabolic enzymes. The highest frequencies of receipt and donation of recombined DNA fragments were observed in Staphylococcus capitis, Staphylococcus caprae, Staphylococcus hominis, Staphylococcus haemolyticus, and members of the Saprophyticus species group. The variable rates of recombination and biases in transfer partners imply that certain CoNS species function as hubs of gene flow and major reservoir of genetic diversity for the entire genus.

Bacterial ClpP Protease Is a Potential Target for Methyl Gallate

Methyl gallate (MG) is an effective microbicide with great potential application in the integrated management of plant diseases and an important potential drug for clinical application. However, its target remains unknown. This study conducted a transposon sequencing (Tn-seq) under MG treatment in plant pathogenic bacterium Ralstonia solanacearum. Tn-seq identified that the mutation of caseinolytic protease proteolytic subunit gene clpP significantly increased the resistance of R. solanacearum to MG, which was validated by the in-frame gene deletion. iTRAQ (isobaric tags for relative and absolute quantitation) proteomics analysis revealed that chemotaxis and flagella associated proteins were the major substrates degraded by ClpP under the tested condition. Moreover, sulfur metabolism-associated proteins were potential substrates of ClpP and were upregulated by MG treatment in wild-type R. solanacearum but not in clpP mutant. Furthermore, molecular docking confirmed the possible interaction between MG and ClpP. Collectively, this study revealed that MG might target bacterial ClpP, inhibit the activity of ClpP, and consequently disturb bacterial proteostasis, providing a theoretical basis for the application of MG.

Acyldepsipeptide activated ClpP1P2 macromolecule of Leptospira, an ideal Achilles' heel to hamper the cell survival and deregulate ClpP proteolytic activity

Antibiotic acyldepsipeptide (ADEP) targets the bacterial ClpP serine protease and can inhibit the growth of numerous bacterial species by activating/dysregulating the protease activity within the cell. The spirochete Leptospira interrogans harbors two ClpP isoforms (LepClpP1 and LepClpP2). Supplementation of ADEP in the Leptospira growth medium resulted in the inhibition of bacterial growth. The ADEP mediated activation of the LepClpP mixture was dependent on the time allowed for the self-assembly of LepClpP1 and LepClpP2. The dynamic light scattering of the LepClpP mixture in the presence of the ADEP indicated a conformational transformation of the LepClpP machinery. Serine 98, a catalytic triad residue of the LepClpP1 in the LepClpP1P2 heterocomplex, was critical for the ADEP mediated activation. The computational prototype of the LepClpP1P2 structure suggested that the hydrophobic pockets wherein the ADEPs or the physiological chaperone ClpX predominantly dock are exclusively present in the LepClpP2 heptamer. Using the ADEP as a tool, this investigation provides an insight into the molecular function of the LepClpP1P2 in a coalition with its ATPase chaperone LepClpX. The shreds of the evidence illustrated in this investigation verify that ADEP1 possesses the ability to control the LepClpP system in an unconventional approach than the other organisms.

Immunological and bacteriological shifts associated with a flagellin-hyperproducing Salmonella Enteritidis mutant in chickens

Salmonella Enteritidis causes infections in humans and animals which are often associated with extensive gut colonization and bacterial shedding in faeces. The natural presence of flagella in Salmonella enterica has been shown to be enough to induce pro-inflammatory responses in the gut, resulting in recruitment of polymorphonuclear cells, gut inflammation and, consequently, reducing the severity of systemic infection in chickens. On the other hand, the absence of flagellin in some Salmonella strains favours systemic infection as a result of the poor intestinal inflammatory responses elicited. The hypothesis that higher production of flagellin by certain Salmonella enterica strains could lead to an even more immunogenic and less pathogenic strain for chickens was here investigated. In the present study, a Salmonella Enteritidis mutant strain harbouring deletions in clpP and fliD genes (SE ΔclpPfliD), which lead to overexpression of flagellin, was generated, and its immunogenicity and pathogenicity were comparatively assessed to the wild type in chickens. Our results showed that SE ΔclpPfliD elicited more intense immune responses in the gut during early stages of infection than the wild type did, and that this correlated with earlier intestinal and systemic clearance of the bacterium.

Construction and evaluation of Vibrio alginolyticus ΔclpP mutant, as a safe live attenuated vibriosis vaccine

Vibrio alginolyticus is a common and serious pathogen threatening the progress of coastal aquaculture. ClpP protease has been proved to be closely associated with biofilm formation, stress tolerance, autolysis and virulence in several pathogens. Hence, targeting ClpP may be a potentially viable, attractive option for the preparation of vaccine in preventing vibriosis. In this study, an in-frame deleted mutant strain (ΔclpP) was constructed by allelic exchange mutagenesis to investigate physiological role of clpP in pathogenicity of V. alginolyticus and evaluate its potential as a live attenuated vaccine. The results exhibited that ΔclpP showed no differences in external morphology, growth, swarming motility and ECPase activity. However, ΔclpP represented an increment in biofilm formation, and a decrement in adherence to CIK cells. In addition, virulence of ΔclpP was examined in pearl gentian grouper and was found to be seriously attenuated. ΔclpP induced high antibody titers and provided a valid protection with a relative percent survival value of 83.8% without histopathologic abnormality. Our results indicated ΔclpP showed a great potential to be a live attenuated vaccine.

ClpP participates in stress tolerance, biofilm formation, antimicrobial tolerance, and virulence of Enterococcus faecalis

Background

ClpP is important for bacterial growth and plays an indispensable role in cellular protein quality control systems by refolding or degrading damaged proteins, but the physiological significance of ClpP in Enterococcus faecalis remains obscure. A clpP deletion mutant (△clpP) was constructed using the E. faecalis OG1RF strain to clarify the effect of ClpP on E. faecalis. The global abundance of proteins was determined by a mass spectrometer with tandem mass tag labeling.

Results

The ΔclpP mutant strain showed impaired growth at 20 °C or 45 °C at 5% NaCl or 2 mM H₂O₂. The number of surviving ΔclpP mutants decreased after exposure to the high concentration (50× minimal inhibitory concentration) of linezolid or minocycline for 96 h. The ΔclpP mutant strain also demonstrated decreased biofilm formation but increased virulence in a Galleria mellonella model. The mass spectrometry proteomics data indicated that the abundances of 135 proteins changed (111 increased, 24 decreased) in the ΔclpP mutant strain. Among those, the abundances of stress response or virulence relating proteins: FsrA response regulator, gelatinase GelE, regulatory protein Spx (spxA), heat-inducible transcription repressor HrcA, transcriptional regulator CtsR, ATPase/chaperone ClpC, acetyl esterase/lipase, and chaperonin GroEL increased in the ΔclpP mutant strain; however, the abundances of ribosomal protein L4/L1 family protein (rplD), ribosomal protein L7/L12 (rplL2), 50S ribosomal protein L13 (rplM), L18 (rplR), L20 (rplT), 30S ribosomal protein S14 (rpsN2) and S18 (rpsR) all decreased. The abundances of biofilm formation-related adapter protein MecA increased, while the abundances of dihydroorotase (pyrC), orotate phosphoribosyltransferase (pyrE), and orotidine-5′-phosphate decarboxylase (pyrF) all decreased in the ΔclpP mutant strain.

Conclusion

The present study demonstrates that ClpP participates in stress tolerance, biofilm formation, antimicrobial tolerance, and virulence of E. faecalis.

The Temporal Expression of Global Regulator Protein CsrA Is Dually Regulated by ClpP During the Biphasic Life Cycle of Legionella pneumophila

Legionella pneumophila, an environmental bacterium that parasitizes protozoa, is the causative pathogen of Legionnaires' disease. L. pneumophila adopts a distinct biphasic life cycle that allows it to adapt to environmental conditions for survival, replication, and transmission. This cycle consists of a non-virulent replicative phase (RP) and a virulent transmissive phase (TP). Timely and fine-tuned expression of growth and virulence factors in a life cycle-dependent manner is crucial. Herein, we report evidence that CsrA, a key regulator of the switch between the RP and the TP, is dually regulated in a ClpP-dependent manner during the biphasic life cycle of L. pneumophila. First, we show that the protein level of CsrA is temporal during the life cycle and is degraded by ClpP during the TP. The ectopic expression of CsrA in a ΔclpP mutant, but not in the wild type, inhibits both the initiation of the RP in vitro and the invasiveness to Acanthamoeba castellanii, indicating that the ClpP-mediated proteolytic pathway regulates the CsrA protein level. We further show that the temporally expressed IHFB is the transcriptional inhibitor of csrA and is degraded via a ClpP-dependent manner during the RP. During the RP, the level of CsrA is increased by promoting the degradation of IHFB and reducing the degradation of the accumulated CsrA via a ClpP-dependent manner. During the TP, the level of CsrA is decreased by inhibiting the degradation of IHFB and promoting the degradation of the accumulated CsrA via a ClpP-dependent manner as well. In conclusion, our results show that the growth-stage-specific expression level of CsrA is dually regulated by ClpP-dependent proteolysis at both the transcription and protein levels during the biphasic life cycle of L. pneumophila.

Cross Talk between SigB and PrfA in Listeria monocytogenes Facilitates Transitions between Extra- and Intracellular Environments

The foodborne pathogen Listeria monocytogenes can modulate its transcriptome and proteome to ensure its survival during transmission through vastly differing environmental conditions. While L. monocytogenes utilizes a large array of regulators to achieve survival and growth in different intra- and extrahost environments, the alternative sigma factor σ^B and the transcriptional activator of virulence genes protein PrfA are two key transcriptional regulators essential for responding to environmental stress conditions and for host infection. Importantly, emerging evidence suggests that the shift from extrahost environments to the host gastrointestinal tract and, subsequently, to intracellular environments requires regulatory interplay between σ^B and PrfA at transcriptional, posttranscriptional, and protein activity levels. Here, we review the current evidence for cross talk and interplay between σ^B and PrfA and their respective regulons and highlight the plasticity of σ^B and PrfA cross talk and the role of this cross talk in facilitating successful transition of L. monocytogenes from diverse extrahost to diverse extra- and intracellular host environments.

Putative virulence factors of Plesiomonas shigelloides

Plesiomonas shigelloides is a Gram-negative rod-shaped bacterium which has been isolated from humans, animals and the environment. It has been associated with diarrhoeal disease in humans and various epizootic diseases in animals. In this study P. shigelloides strains were isolated from the faecal material of a captive Yangtze finless porpoise (Neophocaena asiaeorientalis asiaeorientalis; YFP) living in semi-natural conditions in China. Plesiomonas shigelloides strain EE2 was subjected to whole genome sequencing. The draft genome was then compared to the genome sequences of ten other P. shigelloides isolates using the Pathosystems Resource Integration Center pipeline. In addition to several virulence factors which have been previously reported, we are proposing new candidate virulence factors such as a repeats-in-toxin protein, lysophospholipase, a twin-arginine translocation system and the type VI secretion effector Phospholipase A1.

ClpP Protease, a Promising Antimicrobial Target

The caseinolytic protease proteolytic subunit (ClpP) is a serine protease playing an important role in proteostasis of eukaryotic organelles and prokaryotic cells. Alteration of ClpP function has been proved to affect the virulence and infectivity of a number of pathogens. Increased bacterial resistance to antibiotics has become a global problem and new classes of antibiotics with novel mechanisms of action are needed. In this regard, ClpP has emerged as an attractive and potentially viable option to tackle pathogen fitness without suffering cross-resistance to established antibiotic classes and, when not an essential target, without causing an evolutionary selection pressure. This opens a greater window of opportunity for the host immune system to clear the infection by itself or by co-administration with commonly prescribed antibiotics. A comprehensive overview of the function, regulation and structure of ClpP across the different organisms is given. Discussion about mechanism of action of this protease in bacterial pathogenesis and human diseases are outlined, focusing on the compounds developed in order to target the activation or inhibition of ClpP.

The Role of ClpP Protease in Bacterial Pathogenesis and Human Diseases

In prokaryotic cells and eukaryotic organelles, the ClpP protease plays an important role in proteostasis. The disruption of the ClpP function has been shown to influence the infectivity and virulence of a number of bacterial pathogens. More recently, ClpP has been found to be involved in various forms of carcinomas and in Perrault syndrome, which is an inherited condition characterized by hearing loss in males and females and by ovarian abnormalities in females. Hence, targeting ClpP is a potentially viable, attractive option for the treatment of different ailments. Herein, the biochemical and cellular activities of ClpP are discussed along with the mechanisms by which ClpP affects bacterial pathogenesis and various human diseases. In addition, a comprehensive overview is given of the new classes of compounds in development that target ClpP. Many of these compounds are currently primarily aimed at treating bacterial infections. Some of these compounds inhibit ClpP activity, while others activate the protease and lead to its dysregulation. The ClpP activators are remarkable examples of small molecules that inhibit protein-protein interactions but also result in a gain of function.

Characterization of Pectobacterium carotovorum proteins differentially expressed during infection of Zantedeschia elliotiana in vivo and in vitro which are essential for virulence

The identification of phytopathogen proteins that are differentially expressed during the course of the establishment of an infection is important to better understand the infection process. In vitro approaches, using plant extracts added to culture medium, have been used to identify such proteins, but the biological relevance of these findings for in planta infection are often uncertain until confirmed by in vivo studies. Here, we compared the proteins of Pectobacterium carotovorum ssp. carotovorum strain PccS1 differentially expressed in Luria-Bertani medium supplemented with extracts of the ornamental plant Zantedeschia elliotiana cultivar 'Black Magic' (in vitro) and in plant tissues (in vivo) by two-dimensional electrophoresis coupled with mass spectrometry. A total of 53 differentially expressed proteins (>1.5-fold) were identified (up-regulated or down-regulated in vitro, in vivo or both). Proteins that exhibited increased expression in vivo but not in vitro, or in both conditions, were identified, and deletions were made in a number of genes encoding these proteins, four of which (clpP, mreB, flgK and eda) led to a loss of virulence on Z. elliotiana, although clpP and mreB were later also shown to be reduced in growth in rich and minimal media. Although clpP, flgK and mreB have previously been reported as playing a role in virulence in plants, this is the first report of such a role for eda, which encodes 2-keto-3-deoxy-6-phosphogluconate (KDPG) aldolase, a key enzyme in Entner-Doudoroff metabolism. The results highlight the value of undertaking in vivo as well as in vitro approaches for the identification of new bacterial virulence factors.

ClpP-deletion impairs the virulence of Legionella pneumophila and the optimal translocation of effector proteins

Background

The opportunistic bacterial pathogen Legionella pneumophila uses substrate effectors of Dot/Icm type IVB secretion system (T4BSS) to accomplish survival and replication in amoebae cells and mammalian alveolar macrophages. During the conversion between its highly resistant, infectious dormant form and vigorously growing, uninfectious replicative form, L. pneumophila utilizes a complicated regulatory network in which proteolysis may play a significant role. As a highly conserved core protease, ClpP is involved in various cellular processes as well as virulence in bacteria, and has been proved to be required for the expression of transmission traits and cell division of L. pneumophila.

Results

The clpP-deficient L. pneumophila strain failed to replicate and was digested in the first 3 h post-infection in mammalian cells J774A.1. Further investigation demonstrates that the clpP deficient mutant strain was unable to escape the endosome-lysosomal pathway in host cells. We also found that the clpP deficient mutant strain still expresses T4BSS components, induces contact-dependent cytotoxicity and translocate effector proteins RalF and LegK2, indicating that its T4BSS was overall functional. Interestingly, we further found that the translocation of several effector proteins is significantly reduced without ClpP.

Conclusions

The data indicate that ClpP plays an important role in regulating the virulence and effector translocation of Legionella pneumophila.

Electronic supplementary material

The online version of this article (doi:10.1186/s12866-016-0790-8) contains supplementary material, which is available to authorized users.

Non-monotonic Response to Monotonic Stimulus: Regulation of Glyoxylate Shunt Gene-Expression Dynamics in Mycobacterium tuberculosis

Understanding how dynamical responses of biological networks are constrained by underlying network topology is one of the fundamental goals of systems biology. Here we employ monotone systems theory to formulate a theorem stating necessary conditions for non-monotonic time-response of a biochemical network to a monotonic stimulus. We apply this theorem to analyze the non-monotonic dynamics of the σB-regulated glyoxylate shunt gene expression in Mycobacterium tuberculosis cells exposed to hypoxia. We first demonstrate that the known network structure is inconsistent with observed dynamics. To resolve this inconsistency we employ the formulated theorem, modeling simulations and optimization along with follow-up dynamic experimental measurements. We show a requirement for post-translational modulation of σB activity in order to reconcile the network dynamics with its topology. The results of this analysis make testable experimental predictions and demonstrate wider applicability of the developed methodology to a wide class of biological systems.

Thermal control of virulence factors in bacteria: a hot topic

Pathogenic bacteria sense environmental cues, including the local temperature, to control the production of key virulence factors. Thermal regulation can be achieved at the level of DNA, RNA or protein and although many virulence factors are subject to thermal regulation, the exact mechanisms of control are yet to be elucidated in many instances. Understanding how virulence factors are regulated by temperature presents a significant challenge, as gene expression and protein production are often influenced by complex regulatory networks involving multiple transcription factors in bacteria. Here we highlight some recent insights into thermal regulation of virulence in pathogenic bacteria. We focus on bacteria which cause disease in mammalian hosts, which are at a significantly higher temperature than the outside environment. We outline the mechanisms of thermal regulation and how understanding this fundamental aspect of the biology of bacteria has implications for pathogenesis and human health.

Comparative transcriptome analysis between csrA-disruption Clostridium acetobutylicum and its parent strain

This study represented the first attempt to investigate the global regulation of CsrA through transcriptome analysis in Gram-positive bacteria.

CsrA regulates Helicobacter pylori J99 motility and adhesion by controlling flagella formation

BACKGROUND

Motility mediated by the flagella of Helicobacter pylori has been shown to be required for normal colonization and is thought to be important for the bacteria to move toward the gastric mucus in niches adjacent to the epithelium. Barnard et al. showed that CsrA appears to be necessary for full motility and the ability to infect mice, but its mechanism of regulation is still unclear.

METHODS

Motility and cell adhesion ability were determined in wild-type, csrA mutant, and revertant J99 strains. The bacterial shape and flagellar structure were evaluated by transmission electron microscopy. The expression of two major flagellins, flaA/flaB, and the alternative sigma factor rpoN (σ(54)) were determined by real-time quantitative RT-PCR and Western blot.

RESULTS

The csrA mutant showed loss of motility and lower adhesion ability compared with the wild-type and revertant J99 strains. The csrA mutant was not flagellated. Transcription of flaA and flaB mRNA decreased to only 40% and 16%, respectively, in the csrA mutant compared with the wild-type J99 (p = .006 and <.0001, respectively), and Western blot analysis showed dramatically reduced FlaA/FlaB proteins in a csrA mutant. The disruption of csrA also decreased expression of rpoN to 48% in the csrA mutant, but the degradation rate of rpoN mRNA was not changed.

CONCLUSION

These results suggest that CsrA regulates H. pylori J99 flagella formation and thereby affects bacterial motility.

The role of ClpP, RpoS and CsrA in growth and filament formation of Salmonella enterica serovar Typhimurium at low temperature

BACKGROUND

Salmonellae are food-borne pathogens of great health and economic importance. To pose a threat to humans, Salmonellae normally have to cope with a series of stressful conditions in the food chain, including low temperature. In the current study, we evaluated the importance of the Clp proteolytic complex and the carbon starvation protein, CsrA, for the ability of Salmonella Typhimurium to grow at low temperature.

RESULTS

A clpP mutant was severely affected in growth and formed pin point colonies at 10°C. Contrary to this, rpoS and clpP/rpoS mutants were only slightly affected. The clpP mutant formed cold resistant suppressor mutants at a frequency of 2.5 × 10(-3) and these were found not to express RpoS. Together these results indicated that the impaired growth of the clpP mutant was caused by high level of RpoS. Evaluation by microscopy of the clpP mutant revealed that it formed filamentous cells when grown at 10°C, and this phenotype too, disappered when rpoS was mutated in parallel indicating a RpoS-dependency. A csrA (sup) mutant was also growth attenuated a low temperature. An rpoS/csrA (sup) double mutant was also growth attenuated, indicating that the phenotype of the csrA mutant was independent from RpoS.

CONCLUSIONS

The cold sensitivity of clpP mutant was associated with increased levels of RpoS and probably caused by toxic levels of RpoS. Although a csrA mutant also accumulated high level of RpoS, growth impairment caused by lack of csrA was not related to RpoS levels in a similar way.