Regulation of heat-shock response in bacteria

Stress Responses in Pathogenic Vibrios and Their Role in Host and Environmental Survival

Vibrio is a genus of bacteria commonly found in estuarine, marine, and freshwater environments. Vibrio species have evolved to occupy diverse niches in the aquatic ecosystem, with some having complex lifestyles. About a dozen of the described Vibrio species have been reported to cause human disease, while many other species cause disease in other organisms. Vibrio cholerae causes epidemic cholera, a severe dehydrating diarrheal disease associated with the consumption of contaminated food or water. The human pathogenic non-cholera Vibrio species, Vibrio parahaemolyticus and Vibrio vulnificus, cause gastroenteritis, septicemia, and other extra-intestinal infections. Infections caused by V. parahaemolyticus and V. vulnificus are normally acquired through exposure to sea water or through consumption of raw or undercooked contaminated seafood. The human pathogenic Vibrios are exposed to numerous different stress-inducing agents and conditions in the aquatic environment and when colonizing a human host. Therefore, they have evolved a variety of mechanisms to survive in the presence of these stressors. Here we discuss what is known about important stress responses in pathogenic Vibrio species and their role in bacterial survival.

Adaptations of Vibrio parahaemolyticus to Stress During Environmental Survival, Host Colonization, and Infection

Vibrio parahaemolyticus (Vp) is an aquatic Gram-negative bacterium that may infect humans and cause gastroenteritis and wound infections. The first pandemic of Vp associated infection was caused by the serovar O3:K6 and epidemics caused by the other serovars are increasingly reported. The two major virulence factors, thermostable direct hemolysin (TDH) and/or TDH-related hemolysin (TRH), are associated with hemolysis and cytotoxicity. Vp strains lacking tdh and/or trh are avirulent and able to colonize in the human gut and cause infection using other unknown factors. This pathogen is well adapted to survive in the environment and human host using several genetic mechanisms. The presence of prophages in Vp contributes to the emergence of pathogenic strains from the marine environment. Vp has two putative type-III and type-VI secretion systems (T3SS and T6SS, respectively) located on both the chromosomes. T3SS play a crucial role during the infection process by causing cytotoxicity and enterotoxicity. T6SS contribute to adhesion, virulence associated with interbacterial competition in the gut milieu. Due to differential expression, type III secretion system 2 (encoded on chromosome-2, T3SS2) and other genes are activated and transcribed by interaction with bile salts within the host. Chromosome-1 encoded T6SS1 has been predominantly identified in clinical isolates. Acquisition of genomic islands by horizontal gene transfer provides enhanced tolerance of Vp toward several antibiotics and heavy metals. Vp consists of evolutionarily conserved targets of GTPases and kinases. Expression of these genes is responsible for the survival of Vp in the host and biochemical changes during its survival. Advanced genomic analysis has revealed that various genes are encoded in Vp pathogenicity island that control and expression of virulence in the host. In the environment, the biofilm gene expression has been positively correlated to tolerance toward aerobic, anaerobic, and micro-aerobic conditions. The genetic similarity analysis of toxin/antitoxin systems of Escherichia coli with VP genome has shown a function that could induce a viable non-culturable state by preventing cell division. A better interpretation of the Vp virulence and other mechanisms that support its environmental fitness are important for diagnosis, treatment, prevention and spread of infections. This review identifies some of the common regulatory pathways of Vp in response to different stresses that influence its survival, gut colonization and virulence.

Temperature-sensitive protein expression in protocells

We engineered a synthetic temperature regulation toolbox to enable protocells to sense and respond to heat, utilizing RNA thermometers. The thermo-sensitive protocells were generated by encapsulating temperature feedback transcription/translation machinery in droplets. Based on these temperature-sensing devices, the protocells can be operated with logic AND gates, differentially processing temperature stimuli into biological signals.

Chaperonomics in leptospirosis

INTRODUCTION

Knowledge of the function of molecular chaperones is required for a better understanding of cellular proteostasis. Nevertheless, such information is currently dispersed as most of previous studies investigated chaperones on a single-angle basis. Recently, a new subdiscipline of chaperonology, namely 'chaperonomics' (defined as 'systematic analysis of chaperone genes, transcripts, proteins, or their interaction networks using omics technologies'), has been emerging to better understand biological, physiological, and pathological roles of chaperones. Areas covered: This review provides broad overviews of bacterial chaperones, heat shock proteins (HSPs), and leptospirosis, and then focuses on recent progress of chaperonomics applied to define roles of HSPs in various pathogenic and saprophytic leptospiral species and serovars. Expert commentary: Comprehensive analysis of leptospiral chaperones/HSPs using a chaperonomics approach holds great promise for better understanding of functional roles of chaperones/HSPs in bacterial survival and disease pathogenesis. Moreover, this new approach may also lead to further development of chaperones/HSPs-based diagnostics and/or vaccine discovery for leptospirosis.

Coping with High Temperature: A Unique Regulation in A. tumefaciens

Elevation of temperature is a frequent and considerable stress for mesophilic bacteria. Therefore, several molecular mechanisms have evolved to cope with high temperature. We have been studying the response of Agrobacterium tumefaciens to temperature stress, focusing on two aspects: the heat-shock response and the temperature-dependent regulation of methionine biosynthesis. The results indicate that the molecular mechanisms involved in A. tumefaciens control of growth at high temperature are unique and we are still missing important information essential for understanding how these bacteria cope with temperature stress.

Screening of Neem extracts for microbial anti-chaperone activity by employing in vitro enzyme refolding assay

Microbial heat shock proteins (Hsps) play an important role in pathogenesis and development of resistance to existing drugs. New compounds that target microbial molecular chaperones have the potential of combating the challenge of anti-microbial resistance. The present study was aimed at assessing the employment of in vitro enzyme refolding assay to detect anti-chaperone activity of Neem (Azadirachta indica) extracts. Protein extracts of thermotolerant Escherichia coli cells were used as a source of Hsps or chaperones. Thermotolerance was found to be induced by pre-treating E. coli cells at 47 °C before subjecting them to a lethal temperature of 55 °C. This thermotolerance correlated with over-expression of specific proteins and reduced aggregation as evident from the SDS-PAGE profiles. Refolding assays of denatured enzymes exhibited 45% activity regain in presence of cell protein extracts containing chaperones compared to less than 5% regain in BSA negative controls. The chaperone activity was found to be ATP dependent. Addition of Neem extracts to refolding reaction mixtures distinctly reduced the activity regain (20%) in a dose dependent manner (500 and 1000 ppm). The negative influence of plant extract on refolding of the enzyme in the presence of chaperones gives evidence to its anti-chaperone activity. We propose that the employment of in vitro enzyme refolding assays will help not only to analyze the activity of known and putative chaperones but also to screen natural compounds for anti-microbial-Hsp activity.

Role and mechanism of the Hsp70 molecular chaperone machines in bacterial pathogens

Heat shock proteins are highly conserved, stress-inducible, ubiquitous proteins that maintain homeostasis in both eukaryotes and prokaryotes. Hsp70 proteins belong to the heat shock protein family and enhance bacterial survival in hostile environments. Hsp70, known as DnaK in prokaryotes, supports numerous processes such as the assembly and disassembly of protein complexes, the refolding of misfolded and clustered proteins, membrane translocation and the regulation of regulatory proteins. The chaperone-based activity of Hsp70 depends on dynamic interactions between its two domains, known as the ATPase domain and the substrate-binding domain. It also depends on interactions between these domains and other co-chaperone molecules such as the Hsp40 protein family member DnaJ and nucleotide exchange factors. DnaJ is the primary chaperone that interacts with nascent polypeptide chains and functions to prevent their premature release from the ribosome and misfolding before it is targeted by DnaK. Adhesion of bacteria to host cells is mediated by both host and bacterial Hsp70. Following infection of the host, bacterial Hsp70 (DnaK) is in a position to initiate bacterial survival processes and trigger an immune response by the host. Any mutations in the dnaK gene have been shown to decrease the viability of bacteria inside the host. This review will give insights into the structure and mechanism of Hsp70 and its role in regulating the protein activity that contributes to pathogenesis.

Changes in global gene expression of Vibrio parahaemolyticus induced by cold- and heat-stress

BACKGROUND

Vibrio (V.) parahaemolyticus causes seafood-borne gastro-intestinal bacterial infections in humans worldwide. It is widely found in marine environments and is isolated frequently from seawater, estuarine waters, sediments and raw or insufficiently cooked seafood. Throughout the food chain, V. parahaemolyticus encounters different temperature conditions that might alter metabolism and pathogenicity of the bacterium. In this study, we performed gene expression profiling of V. parahaemolyticus RIMD 2210633 after exposure to 4, 15, 20, 37 and 42 °C to describe the cold and heat shock response.

METHODS

Gene expression profiles of V. parahaemolyticus RIMD 2210633 after exposure to 4, 15, 20, 37 and 42 °C were investigated via microarray. Gene expression values and RT-qPCR experiments were compared by plotting the log2 values. Moreover, volcano plots of microarray data were calculated to visualize the distribution of differentially expressed genes at individual temperatures and to assess hybridization qualities and comparability of data. Finally, enriched terms were searched in annotations as well as functional-related gene categories using the Database for Annotation, Visualization and Integrated Discovery.

RESULTS

Analysis of 37 °C normalised transcriptomics data resulted in differential expression of 19 genes at 20 °C, 193 genes at 4 °C, 625 genes at 42 °C and 638 genes at 15 °C. Thus, the largest number of significantly expressed genes was observed at 15 and 42 °C with 13.3 and 13%, respectively. Genes of many functional categories were highly regulated even at lower temperatures. Virulence associated genes (tdh1, tdh2, toxR, toxS, vopC, T6SS-1, T6SS-2) remained mostly unaffected by heat or cold stress.

CONCLUSION

Along with folding and temperature shock depending systems, an overall temperature-dependent regulation of expression could be shown. Particularly the energy metabolism was affected by changed temperatures. Whole-genome gene expression studies of food related pathogens such as V. parahaemolyticus reveal how these pathogens react to stress impacts to predict its behaviour under conditions like storage and transport.

Upregulation of transcripts for metabolism in diverse environments is a shared response associated with survival and adaptation of Klebsiella pneumoniae in response to temperature extremes

Klebsiella pneumoniae being ubiquitous in nature encounters wide differences in environmental condition. The organism's abundance in natural water reservoirs exposed to temperature variation forms the basis of its persistence and spread in the soil and other farm produce. In order to investigate the effect of temperature changes on the survival and adaptation of the bacteria, the transcriptional response of K. pneumoniae subjected to low (20 °C) and high (50 °C) temperature shock were executed using Applied Biosystems SOLiD platform. Approximately, 33 and 34% of protein coding genes expressed in response to 20 and 50 °C, respectively, displayed significant up- or downregulation (p < 0.01). Most of the significantly expressed transcripts mapped to metabolism, membrane transport, and cell motility were downregulated at 50 °C, except for protein folding, sorting, and degradation, suggesting that heat stress causes general downregulation of gene expression together with induction of heat shock proteins. While at 20 °C, the transcripts of carbohydrate, lipid, and amino acid metabolism were highly upregulated. Hypothetical proteins as well as canonical heat and cold shock proteins, viz. grpE, clpX, recA, and deaD were upregulated commonly in response to 20 and 50 °C. Significant upregulation of genes encoding ribosomal proteins at 20 and 50 °C possibly suggest their role in the survival of K. pneumoniae cells under low- and high-temperature stress.

Development of a Stress-Inducible Controlled Expression (SICE) system in Lactococcus lactis for the production and delivery of therapeutic molecules at mucosal surfaces

In recent years, recombinant lactic acid bacteria (LAB) have been successfully used as safe mucosal delivery vectors. Herein, we report on the development of a Stress-Inducible Controlled Expression (SICE) system in L. lactis for the production and delivery of proteins of health interest (both therapeutic and vaccine related) at mucosal surfaces. This system is episomal in nature and is composed of a vector carrying an expression cassette under the transcriptional control of a stress-inducible promoter. The functionality of the SICE system was validated in vivo using two different routes of administration: oral and intranasal, and in two different murine models of human pathologies: (i) a model of therapy against inflammatory bowel diseases (IBD) and (ii) a model of vaccination against human papillomavirus type-16 (HPV-16).

Thermotherapy in dermatology

Heat has been used as a medicinal and healing modality throughout human history. Today, thermotherapy is being studied in the treatment of many diseases. Although the exact anti-infective mechanism of thermotherapy is yet to be solved, this historically important healing method has shown significant results in the treatments of a variety of dermatological infectious diseases ranging from simple acne to bacterial, parasitic and viral infections, in modern medicine. Induction of cellular apoptosis in medium doses and necrosis in high doses has made thermotherapy an important modality in the treatment of malignant tumors. Especially in dermatology, significant results have been achieved in the treatment of Bowen's disease, melanoma and simple warts. Thermotherapy, which today has also shown advancements in cosmetology, can be delivered by liquid nitrogen in the form of hypothermia and a variety of ways ranging from hot water pads to ultrasound and even to lasers, in the form of hyperthermia. In this article, the place of this historically important treatment method in modern medicine, especially in dermatology, has been reviewed by an extensive search of the literature.

Thermotherapy in dermatologic infections

The use of local induced hyperthermia or thermotherapy for dermatologic infections has not been fully explored in the more recent medical literature. Herein, we discuss the rationale behind the use of thermotherapy and review reported clinical experience with its use in the management of cutaneous infections.

Effect of stress pretreatment on survival of probiotic bacteria in gastrointestinal tract simulator

The effect of stress pretreatment on survival of probiotic Lactobacillus acidophilus La-5, Lactobacillus rhamnosus GG, and Lactobacillus fermentum ME-3 cultures was investigated in the single bioreactor gastrointestinal tract simulator (GITS). The cultures were pregrown in pH-auxostat, subjected to temperature, acid, or bile stress treatment, fast frozen in liquid nitrogen (LN(2)), and tested for survival in GITS. After LN(2) freezing the colony forming ability of L. rhamnosus GG and L. fermentum ME-3 nonstressed and stressed cells was well retained (average survival of 75.4 +/- 18.3% and 88.0 +/- 7.2%, respectively). L. acidophilus La-5 strain showed good survival of auxostat nonstressed cells after fast freezing (94.2 +/- 15.0), however the survival of stress pretreated cells was considerably lower (30.8 +/- 8.5%). All LN(2) frozen auxostat cultures survived well in the acid phase of the GIT simulation (survival 81 +/- 21%); however, after the bile phase, the colony formation ability of L. acidophilus La-5, L. rhamnosus GG, and L. fermentum ME-3 decreased by approximately 1.4 +/- 0.2, 3.8 +/- 0.3, and 3.5 +/- 1.2 logarithmic units, respectively. No statistically relevant positive effect of stress pretreatments on survival of LN(2) frozen L. acidophilus La-5, L. rhamnosus GG, and L. fermentum ME-3 in GITS was observed.

Cloning and molecular characterization of GroESL heat-shock operon in methylotrophic bacterium Methylovorus Sp. strain SS1 DSM 11726

The groESL bicistronic operon of a restricted facultative methylotrophic bacterium Methylovorus sp. strain SS1 DSM 11726 was cloned and characterized. It was found to consist of two ORFs encoding proteins with molecular masses of 11,395 and 57,396 daltons, which showed a high degree of homology to other bacterial GroES and GroEL proteins. The genes were clustered in the transcription order groES-groEL. Northern blot analyses suggested that the groESL operon is transcribed as a bicistronic 2.2-kb mRNA, the steady-state level of which was markedly increased by temperature elevation. Primer extension analysis demonstrated one potential transcription start site preceding the groESL operon, which is located 100 bp upstream of the groES start codon. The transcription start site was preceded by a putative promoter region highly homologous to the consensus sequences of Escherichia coli sigma 32-type heat shock promoter, which functioned under both normal and heat shock conditions in E. coli. Heat shock mRNA was maximally produced by Methylovorus sp. strain SS1 approximately 10 min after increasing the temperature from 30 to 42 degrees C. The groESL operon was also induced by hydrogen peroxide or salt shock.

Interplay between the heat shock response and translation in Escherichia coli

It is widely accepted that the heat shock response is critical for quality control of mature proteins. This function is carried out mainly by chaperones and proteases. Recently, a new group of conserved heat shock proteins essential for growth at high temperature has been characterized. These proteins are involved in regulating and maintaining efficient translation under heat shock.

Mycoplasmas regulate the expression of heat-shock protein genes through CIRCE-HrcA interactions

Mycoplasmas in general are rarely exposed to severe environmental changes except during its colonization and infection processes. Genomic analysis indicates that Mycoplasma hyopneumoniae possesses the genes of a single sigma factor and the HrcA repressor of negative regulation of the heat-shock response. A perfect inverted repeat sequence (5'-CTGGCACTT-N(9)-AAGTGCCAA-3') upstream of the DnaK gene has also been identified. In the present study, we demonstrate the functionality of HrcA-CIRCE interactions using the gel electrophoretic mobility shift assay. The presence of the unique sigma factor, HrcA repressor, and the CIRCE-like sequences reveals that mycoplasmal species may all use the negative regulatory mechanism in the heat-shock response. It is conceivable that mycoplasmas may have evolved a single HrcA repressor-based mechanism which might be the most simple and economical way of controlling HSP gene expression.

Extensive functional overlap between sigma factors in Escherichia coli

Bacterial core RNA polymerase (RNAP) must associate with a sigma factor to recognize promoter sequences. Escherichia coli encodes seven sigma factors, each believed to be specific for a largely distinct subset of promoters. Using microarrays representing the entire E. coli genome, we identify 87 in vivo targets of sigma32, the heat-shock sigma factor, and estimate that there are 120-150 sigma32 promoters in total. Unexpectedly, 25% of these sigma32 targets are located within coding regions, suggesting novel regulatory roles for sigma32. The majority of sigma32 promoter targets overlap with those of sigma70, the housekeeping sigma factor. Furthermore, their DNA sequence motifs are often interdigitated, with RNAPsigma70 and RNAPsigma32 initiating transcription in vitro with similar efficiency and from identical positions. SigmaE-regulated promoters also overlap extensively with those for sigma70. These results suggest that extensive functional overlap between sigma factors is an important phenomenon.

Alterations in the virulence potential of enteric pathogens and bacterial-host cell interactions under simulated microgravity conditions

Host immune mechanisms were proposed to decline under microgravity conditions during spaceflights, which might result in severe infections in astronauts. Therefore, it was important to investigate the effects of microgravity on infecting organisms and their interaction with host cells. Data showed that simulated microgravity (SMG) conditions markedly increased production of the enterotoxigenic Escherichia coli (ETEC) heat-labile enterotoxin, which induced fluid secretory responses in a mouse model. SMG also enhanced production of tumor necrosis factor-alpha in murine macrophages infected with enteropathogenic E. coli (EPEC). In a similar fashion, simulated microgravity conditions augmented the invasive potential of Salmonella enterica serovar typhimurium and enhanced production of tumor necrosis-factor alpha in S. typhimurium-infected epithelial cells. Furthermore, coculturing of macrophages and S. typhimurium in a simulated microgravity environment resulted in activation of stress-associated mitogen-activated protein kinase kinase 4. Using the antiorthostatic tail suspension mouse model, which simulates some aspects of microgravity, oral inoculation of S. typhimurium markedly reduced the 50% lethal dose compared to mice infected under normal gravitational conditions. Microarray analysis revealed simulated microgravity-induced alterations in the expression of 22 genes in S. typhimurium, and protein expression profiles were altered in both EPEC and S. typhimurium, based on two-dimensional gel electrophoresis. These studies indicated alterations in the virulence potential of bacteria and in host responses to these pathogens under simulated microgravity conditions, which may represent an important environmental signal. Such studies are essential for better understanding bacterial-host cell interactions, particularly in the context of spaceflights and space habitations of long duration.

Transcriptional heat shock response in the smallest known self-replicating cell, Mycoplasma genitalium

Mycoplasma genitalium is a human bacterial pathogen linked to urethritis and other sexually transmitted diseases as well as respiratory and joint pathologies. Though its complete genome sequence is available, little is understood about the regulation of gene expression in this smallest known, self-replicating cell, as its genome lacks orthologues for most of the conventional bacterial regulators. Still, the transcriptional repressor HrcA (heat regulation at CIRCE [controlling inverted repeat of chaperone expression]) is predicted in the M. genitalium genome as well as three copies of its corresponding regulatory sequence CIRCE. We investigated the transcriptional response of M. genitalium to elevated temperatures and detected the differential induction of four hsp genes. Three of the up-regulated genes, which encode DnaK, ClpB, and Lon, possess CIRCE within their promoter regions, suggesting that the HrcA-CIRCE regulatory mechanism is functional. Additionally, one of three DnaJ-encoding genes was up-regulated, even though no known regulatory sequences were found in the promoter region. Transcript levels returned to control values after 1 h of incubation at 37 degrees C, reinforcing the transient nature of the heat shock transcriptional response. Interestingly, neither of the groESL operon genes, which encode the GroEL chaperone and its cochaperone GroES, responded to heat shock. These data suggest that M. genitalium selectively regulates a limited number of genes in response to heat shock.

Behavior of lipids in biological wastewater treatment processes

Lipids (characterized as oils, greases, fats and long-chain fatty acids) are important organic components of wastewater. Their amount, for example, in municipal wastewater is approximately 30-40% of the total chemical oxygen demand. The concern over the behavior of lipids in biological treatment systems has led to many studies, which have evaluated their removal, but still the exact behavior of lipids in these processes is not well understood. In this review, we discuss the current knowledge of how lipids/fatty acids affect both aerobic and anaerobic processes and specific methods that have been used in an attempt to enhance their removal from wastewater. Overall, the literature shows that lipids/fatty acids are readily removed by biological treatment methods, inhibitory to microbial growth as well as the cause of foaming, growth of filamentous bacteria and floc flotation.

The in vivo and in vitro characterization of DnaK from Agrobacterium tumefaciens RUOR

Molecular chaperones of the heat shock protein 70 family (Hsp70; also called DnaK in prokaryotes) play an important role in the folding and functioning of cellular protein machinery. The dnaK gene from the plant pathogen Agrobacterium tumefaciens RUOR was amplified using the polymerase chain reaction and the DnaK protein (Agt DnaK) was over-produced as a His-tagged protein in Escherichia coli. The Agt DnaK amino acid sequence was 96% identical to the A. tumefaciens C58 DnaK sequence and 65% identical to the E. coli DnaK sequence. Agt DnaK was shown to be able to functionally replace E. coli DnaK in vivo using complementation assays with an E. coli dnaK756 mutant strain and a dnaK52 deletion strain. Over-production and purification of Agt DnaK was successful, and allowed for further characterization of the protein. Kinetic analysis of the basal ATPase activity of purified Agt DnaK revealed a Vmax of 1.3 nmol phosphate released per minute per milligram DnaK, and a Km of 62 microM ATP. Thus, this is the first study to provide both in vivo and in vitro evidence that Agt DnaK has the properties of a molecular chaperone of the Hsp70 family.

Expression of heat-shock genesgroESLinXanthomonas campestrisis upregulated by CLP in an indirect manner

CLP is a homologue of cyclic AMP-receptor protein in Xanthomonas campestris. In this study, proteomic analysis and Western blotting showed that the clp mutant (TC820) of X. campestris synthesizes less GroESL proteins than the parental P20H. The groESL upstream regions, nt -583 to -32 (552 bp) and nt -178 to -29 (150 bp) relative to the groESL initiation codon, were cloned for transcriptional fusion assays. The 150-bp region, bearing putative sigma24- and sigma32-binding sites and the CIRCE element all known to regulate groESL operon, expressed the same levels of beta-galactosidase (300 U/ml) in both strains, indicating that CLP is not involved in the expression from this region. At early exponential phase, the 552-bp region displayed extremely high levels of promoter activity, 11,000 U/ml in P20H versus 5000 U/ml in TC820. The enzyme levels were about 2000 U/ml at stationary phase in both strains, indicating high levels of expression when cells cease growing. These results suggest that the sequence responding to CLP regulation resides between nt -178 and -583. However, since this region has no CLP-binding site and showed no binding to CLP in gel retardation assay, CLP is likely acting indirectly. This communication appears to be the first description of the positive regulation of a bacterial heat-shock operon by a CRP homologue.

Pathways of chaperone-mediated protein folding in the cytosol

Cells are faced with the task of folding thousands of different polypeptides into a wide range of conformations. For many proteins, the folding process requires the action of molecular chaperones. In the cytosol of prokaryotic and eukaryotic cells, molecular chaperones of different structural classes form a network of pathways that can handle substrate polypeptides from the point of initial synthesis on ribosomes to the final stages of folding.

Susceptibility and adaptive response to bile salts in Propionibacterium freudenreichii: physiological and proteomic analysis

Tolerance to digestive stresses is one of the main factors limiting the use of microorganisms as live probiotic agents. Susceptibility to bile salts and tolerance acquisition in the probiotic strain Propionibacterium freudenreichii SI41 were characterized. We showed that pretreatment with a moderate concentration of bile salts (0.2 g/liter) greatly increased its survival during a subsequent lethal challenge (1.0 g/liter, 60 s). Bile salts challenge led to drastic morphological changes, consistent with intracellular material leakage, for nonadapted cells but not for preexposed ones. Moreover, the physiological state of the cells during lethal treatment played an important role in the response to bile salts, as stationary-phase bacteria appeared much less sensitive than exponentially growing cells. Either thermal or detergent pretreatment conferred significantly increased protection toward bile salts challenge. In contrast, some other heterologous pretreatments (hypothermic and hyperosmotic) had no effect on tolerance to bile salts, while acid pretreatment even might have sensitized the cells. Two-dimensional electrophoresis experiments revealed that at least 24 proteins were induced during bile salts adaptation. Identification of these polypeptides suggested that the bile salts stress response involves signal sensing and transduction, a general stress response (also triggered by thermal denaturation, oxidative toxicity, and DNA damage), and an alternative sigma factor. Taken together, our results provide new insights into the tolerance of P. freudenreichii to bile salts, which must be taken into consideration for the use of probiotic strains and the improvement of technological processes.

Biphasic kinetics of growth and bacteriocin production with Lactobacillus amylovorus DCE 471 occur under stress conditions

Micro-organisms used during the production of fermented foods are subjected to several abiotic stresses. Microbial survival during these processes strongly depends on the ability of the cells to adapt and become more tolerant to the environmental conditions. Cultivation of Lactobacillus amylovorus DCE 471, a potential strain for use during type II sourdough fermentations, at low temperatures, unfavourable pH and high salt concentrations resulted in biphasic growth patterns. In addition, two separate bacteriocin peaks, as well as a dramatic change in cellular morphology, were observed. In general, an increase of the specific bacteriocin production occurred during the second growth phase. Finally, the observed sugar consumption profiles were affected by the applied fermentation temperature. Moreover, the highest bacteriocin activity occurred during maltose consumption at a low constant temperature of 28 degrees C and a constant pH of 5.4. Plate counts from both growth phases revealed the existence of two colony types. Irregular colonies were found to outnumber smoother colonies during the first growth phase, while the second growth phase was characterized by a greater number of smooth colonies. Electron microscopy was used to investigate the observed morphological switch at the single-cell level. Single, rod-shaped cells changed into elongated cells that grew in chains. Colony and cell morphology changes coincided with the biphasic growth pattern.

Isolation of acid-inducible genes of Mycobacterium tuberculosis with the use of recombinase-based in vivo expression technology

A better understanding of mycobacterial gene regulation under certain stress conditions (e.g., low pH) may provide insight into mechanisms of adaptation during infection. To identify mycobacterial promoters induced at low pH, we adapted the recombinase-based in vivo expression technology (RIVET) promoter trap system for use with mycobacteria. Our results show that the TnpR recombinase of transposon gammadelta is active in Mycobacterium smegmatis and Mycobacterium tuberculosis. We developed a method to perform sequential double selection with mycobacteria by using RIVET, with a kanamycin preselection and a sucrose postselection. A library of M. tuberculosis DNA inserted upstream of tnpR was created, and using the double selection, we identified two promoters which are upregulated at low pH. The promoter regions drive the expression of a gene encoding a putative lipase, lipF (Rv3487c), as well as a PE-PGRS gene, Rv0834c, in a pH-dependent manner in both M. smegmatis and M. tuberculosis. The acid inducibility of lipF and Rv0834c was independent of the stress response sigma factor, SigF, as acid induction of the two genes in an M. tuberculosis sigF mutant strain was similar to that in the wild-type strain. No induction of lipF or Rv0834c was observed during infection of J774 murine macrophages, an observation which is in agreement with previous reports on the failure of phagosomes containing M. tuberculosis to acidify.

Virulence and the heat shock response

The major adaptive response to elevation in temperature is the heat shock response that involves the induction of many proteins--called heat shock proteins. These include chaperones, proteases, alternative sigma factors and other regulatory and structural proteins. The heat shock response is also turned on by other stress conditions, such as oxidative stress or pH changes. Bacterial entry into the host organism involves a significant environmental change, which is expected to induce the heat shock response. Indeed, some of the heat shock proteins are themselves virulence factors while others affect pathogenesis indirectly, by increasing bacterial resistance to host defenses or regulating virulence genes. The cross talk between heat shock and virulence genes is discussed.

Molecular characterization of GroES and GroEL homologues from Clostridium botulinum

We report novel findings of significant amounts of 60- and 10-kDa proteins on SDS-PAGE in a culture supernatant of the Clostridium botulinum type D strain 4947 (D-4947). The N-terminal amino acid sequences of the purified proteins were closely related to those of other bacterial GroEL and GroES proteins, and both positively cross-reacted with Escherichia coli GroEL and GroES antibodies. Native GroEL homologue as an oligomeric complex is a weak ATPase whose activity is inhibited by the presence of GroES homologue. The 2634-bp groESL operon of D-4947 was isolated by PCR and sequenced. The sequence included two complete open reading frames (282 and 1629 bp), which were homologous to the groES and groEL gene family of bacterial proteins. Southern and Northern blot analyses indicate that the groESL operon is encoded on the genomic DNA of D-4947 as a single copy, and not on that of its specific toxin-converting phage.

Characterization of the dual-specificity phosphatasePYST2 and its transcripts

PYST2 is a member of a structurally homologous subfamily of MAP kinase phosphatases. A computer-based analysis of the PYST2 locus revealed that it harbors two alternative open reading frames promoted by two conserved promoter regions. Using Northern blot analysis and reverse transcription-polymerase chain reaction followed by sequencing and alignment of the products, we confirmed the existence of two mRNAs that were transcribed from this genomic region. Western blot analysis indicated that these transcripts were translated. Functional bioinformatic analysis of both transcripts revealed that exon 2 exists in only one of the PYST2 transcripts, designated PYST2-L, and has the consensus elements of the phosphatase catalytic domain (PCD). We found that the translation from the PYST2-L transcript starts 46 codons upstream from the (already-known) PYST2 5' sequence. Furthermore, the existence of three PYST2-L transcripts was indicated. These transcripts differ only in their 5' untranslated regions (5'UTRs). Unlike PYST2-L, the other mRNA (PYST2-S) is devoid of any known PCD. Analysis of the predicted Pyst2-S protein revealed the presence of the vertebrate metallothionein signature I, the mammalian defensin, and the zinc-containing alcohol dehydrogenase motifs. These motifs might confer on this protein the ability to sense changes in the cellular environment. From these and previous results, we speculate that Pyst2-S may function as a negative regulator of Pyst2-L.

Interactions among strategies associated with bacterial infection: pathogenicity, epidemicity, and antibiotic resistance

Infections have been the major cause of disease throughout the history of human populations. With the introduction of antibiotics, it was thought that this problem should disappear. However, bacteria have been able to evolve to become antibiotic resistant. Nowadays, a proficient pathogen must be virulent, epidemic, and resistant to antibiotics. Analysis of the interplay among these features of bacterial populations is needed to predict the future of infectious diseases. In this regard, we have reviewed the genetic linkage of antibiotic resistance and bacterial virulence in the same genetic determinants as well as the cross talk between antibiotic resistance and virulence regulatory circuits with the aim of understanding the effect of acquisition of resistance on bacterial virulence. We also discuss the possibility that antibiotic resistance and bacterial virulence might prevail as linked phenotypes in the future. The novel situation brought about by the worldwide use of antibiotics is undoubtedly changing bacterial populations. These changes might alter the properties of not only bacterial pathogens, but also the normal host microbiota. The evolutionary consequences of the release of antibiotics into the environment are largely unknown, but most probably restoration of the microbiota from the preantibiotic era is beyond our current abilities.

Proteome analysis in the study of the bacterial heat-shock response

In recent years, it has become clear that, in addition to the regulation of the expression of specific genes, there are global regulatory systems that control the simultaneous expression of a large number of genes in response to a variety of environmental stresses. The first of these global control systems, and of substantial importance, is the heat-shock response. The heat-shock response is characterized by the induction of a large set of proteins (heat-shock proteins-HSPs) upon shifts to higher temperature and upon exposure to conditions in which proteins are denatured (i.e., alcohols, heavy metals). The heat-shock response is universal and many of the heat-shock proteins are highly conserved among species. In bacteria, the heat-shock response has been studied extensively in several Gram-positive bacteria (Bacillus subtilis) and in the Gram-negative bacteria (i.e., Escherichia coli, Agrobacterium tumefaciens). The first recognition of the molecular abundance of the bacterial heat-shock proteins took place with the introduction of high-resolution two-dimensional polyacrylamide gels (2D gels) to analyze complex mixtures of cellular proteins. Two-dimensional gels, followed by mass spectrometry, were used to define the heat-shock stimulons in several bacteria, and to study the regulatory elements that control the heat-shock response. Here, we review the heat-shock response and its regulation in bacteria. The review will emphasize the use of proteome analysis in the study of this response, and will point out those open questions that can be investigated with proteomics, including mass spectrometry techniques.

Heat shock proteome of Agrobacterium tumefaciens: evidence for new control systems

The regulation of Agrobacterium tumefaciens heat shock genes involves a transcriptional activator (RpoH) and repressor elements (HrcA-CIRCE). Using proteome analysis and mutants in these control elements, we show that the heat shock induction of 32 (out of 56) heat shock proteins is independent of RpoH and HrcA. These results indicate the existence of additional regulatory factors in the A. tumefaciens heat shock response.

Initial characterization of the Streptococcus gordonii htpX gene

Examination of the Streptococcus gordonii chromosomal region, which lies immediately upstream of the glucosyltransferase positive regulatory determinant rgg, revealed two open reading frames. Based on nucleotide sequences, these genes were similar to the Listeria monocytogenes lemA gene, which is involved in antigen presentation, and the Escherichia coli htpX heat shock gene, which has an unknown function. Northern hybridization analysis indicated that S. gordonii lemA and htpX genes were associated with a ca. 1.7-kb polycistronic transcript. Although levels of the lemA/htpX transcript did not increase in response to heat to levels seen with dnaK controls, insertional inactivation of htpX resulted in changes in adhesiveness, cellular morphology and detergent-extractable surface antigens in cells grown at 41 degrees C, implying that htpX may be involved in surface protein expression. Insertional inactivation of lemA and htpX indicated that, despite their proximity to rgg and the structural gene, gtfG, these upstream genes do not affect S. gordonii glucosyltransferase activity.

Phased A-tracts bind to the alpha subunit of RNA polymerase with increased affinity at low temperature

Previously we showed that the expression of a Clostridium perfringens phospholipase C gene (plc) is activated by promoter upstream phased A-tracts in a low temperature-dependent manner. In this paper we characterize the interaction between the alpha subunit of C. perfringens RNA polymerase and the phased A-tracts. Hydroxyl radical footprinting and fluorescence polarization assaying revealed that the alpha subunit binds to the minor grooves of the phased A-tracts through its C-terminal domain with increased affinity at low temperature. The result provides a molecular mechanism underlying the activation of the plc promoter by the phased A-tracts.