Temperature regulation of virulence genes in pathogenic bacteria: a general strategy for human pathogens?

Fitness and transcriptomic analysis of pathogenic Vibrio parahaemolyticus in seawater at different shellfish harvesting temperatures

IMPORTANCE

Given the involvement of Vibrio parahaemolyticus (Vp) in a wide range of seafood outbreaks, a systematical characterization of Vp fitness and transcriptomic changes at temperatures of critical importance for seafood production and storage is needed. In this study, one of each virulent Vp strain (tdh+ and trh+) was tested. While no difference in survival behavior of the two virulent strains was observed at 10°C, the tdh+ strain had a faster growth rate than the trh+ strain at 30°C. Transcriptomic analysis showed that a significantly higher number of genes were upregulated at 30°C than at 10°C. The majority of differentially expressed genes of Vp at 30°C were annotated to functional categories supporting cellular growth. At 10°C, the downregulation of the biofilm formation and histidine metabolism indicates that the current practice of storing seafood at low temperatures not only protects seafood quality but also ensures seafood safety.

Comparison of Yersinia enterocolitica DNA Methylation at Ambient and Host Temperatures

Pathogenic bacteria recognize environmental cues to vary gene expression for host adaptation. Moving from ambient to host temperature, Yersinia enterocolitica responds by immediately repressing flagella synthesis and inducing the virulence plasmid (pYV)-encoded type III secretion system. In contrast, shifting from host to ambient temperature requires 2.5 generations to restore motility, suggesting a link to the cell cycle. We hypothesized that differential DNA methylation contributes to temperature-regulated gene expression. We tested this hypothesis by comparing single-molecule real-time (SMRT) sequencing of Y. enterocolitica DNA from cells growing exponentially at 22 °C and 37 °C. The inter-pulse duration ratio rather than the traditional QV scoring was the kinetic metric to compare DNA from cells grown at each temperature. All 565 YenI restriction sites were fully methylated at both temperatures. Among the 27,118 DNA adenine methylase (Dam) sites, 42 had differential methylation patterns, while 17 remained unmethylated regardless of the temperature. A subset of the differentially methylated Dam sites localized to promoter regions of predicted regulatory genes including LysR-type and PadR-like transcriptional regulators and a cyclic-di-GMP phosphodiesterase. The unmethylated Dam sites localized with a bias to the replication terminus, suggesting they were protected from Dam methylase. No cytosine methylation was detected at Dcm sites.

Pathogenic bacteria significantly increased under oxygen depletion in coastal waters: A continuous observation in the central Bohai Sea

The spread of pathogenic bacteria in coastal waters endangers the health of the local people and jeopardizes the safety of the marine environment. However, their dynamics during seasonal hypoxia in the Bohai Sea (BHS) have not been studied. Here, pathogenic bacteria were detected from the 16S rRNA gene sequencing database and were used to explore their dynamics and driving factors with the progressively deoxygenating in the BHS. Our results showed that pathogenic bacteria were detected in all samples, accounting for 0.13 to 24.65% of the total number of prokaryotic sequences in each sample. Pathogenic Proteobacteria was dominated in all samples, followed by Firmicutes, Actinobacteria, Tenericutes, and Bacteroidetes, etc. β-diversity analysis showed that pathogenic bacteria are highly temporally heterogeneous and regulated by environmental factors. According to RDA analysis, these variations may be influenced by salinity, ammonia, DO, phosphate, silicate, and Chl a. Additionally, pathogenic bacteria in surface water and hypoxia zone were found to be significantly separated in August. The vertical distribution of pathogenic bacterial communities is influenced by several variables, including DO and nutrition. It is noteworthy that the hypoxia zones increase the abundance of certain pathogenic genera, especially Vibrio and Arcobacter, and the stability of the pathogenic bacterial community increased from May to August. These phenomena indicate that the central Bohai Sea is threatened by an increasingly serious pathogenic community from May to August. And the developing hypoxia zone in the future may intensify this phenomenon and pose a more serious threat to human health. This study provides new insight into the changes of pathogenic bacteria in aquatic ecosystems and may help to make effective policies to control the spread of pathogenic bacteria.

Analysis of the Localization of NLRs upon Shigella flexneri Infection Exemplified by NOD1

NOD-like receptors (NLRs) are a family of pattern recognition receptors, able to respond to conserved microbial structures and endogenous danger signals. The NLR NOD1 responds to bacterial peptidoglycan, leading to recruitment of RIPK2, following activation of NFκB and MAPK pathways. In this chapter, we describe a fluorescent light microscopic approach to analyze the subcellular distribution of NOD1 upon infection with the invasive, Gram-negative bacterial pathogen Shigella flexneri. This method is based on exogenously expressed EGFP-tagged NOD1 and describes a protocol to obtain inducible cell lines with functional NOD1 signaling. The described protocol is useful to study NOD1 function, also in living cells, using live cell imaging and can be adopted for the study of other NLR proteins.

Assaying RIPK2 Activation by Complex Formation

The receptor-interacting serine/threonine-protein kinase-2 (RIPK2, RIP2) is a key player in downstream signaling of nuclear oligomerization domain (NOD)-like receptor (NLR)-mediated innate immune response against bacterial infections. RIPK2 is recruited following activation of the pattern recognition receptors (PRRs) NOD1 and NOD2 by sensing bacterial peptidoglycans leading to activation of NF-κB and MAPK pathways and the production of pro-inflammatory cytokines. Upon NOD1/2 activation, RIPK2 forms complexes in the cytoplasm of human cells, also called RIPosomes. These can be induced by Shigella flexneri or by the inhibition of RIPK2 by small compounds, such as GSK583 and gefitinib.In this chapter, we describe fluorescent light microscopic and Western blot approaches to analyze the cytoplasmic aggregation of RIPK2 upon infection with the invasive, Gram-negative bacterial pathogen Shigella flexneri, or by the treatment with RIPK2 inhibitors. This method is based on HeLa cells stably expressing eGFP-tagged RIPK2 and describes a protocol to induce and visualize RIPosome formation. The described method is useful to study the deposition of RIPK2 in speck-like structures, also in living cells, using live cell imaging and can be adopted for the study of other inhibitory proteins or to further analyze the process of RIPosome structure assembly.

Redefining fundamental concepts of transcription initiation in bacteria

Despite enormous progress in understanding the fundamentals of bacterial gene regulation, our knowledge remains limited when compared with the number of bacterial genomes and regulatory systems to be discovered. Derived from a small number of initial studies, classic definitions for concepts of gene regulation have evolved as the number of characterized promoters has increased. Together with discoveries made using new technologies, this knowledge has led to revised generalizations and principles. In this Expert Recommendation, we suggest precise, updated definitions that support a logical, consistent conceptual framework of bacterial gene regulation, focusing on transcription initiation. The resulting concepts can be formalized by ontologies for computational modelling, laying the foundation for improved bioinformatics tools, knowledge-based resources and scientific communication. Thus, this work will help researchers construct better predictive models, with different formalisms, that will be useful in engineering, synthetic biology, microbiology and genetics.

Stochastic determination of the spatial variation of potentially pathogenic bacteria communities in a large subtropical river

Understanding the composition and assembly mechanism of waterborne pathogen is essential for preventing the pathogenic infection and protecting the human health. Here, based on 16S rRNA sequencing, we investigated the composition and spatial variation of potentially pathogenic bacteria from different sections of the Pearl River, the most important source of water for human in Southern China. The results showed that the potential pathogen communities consisted of 6 phyla and 64 genera, covering 11 categories of potential pathogens mainly involving animal parasites or symbionts (AniP), human pathogens all (HumPA), and intracellular parasites (IntCelP). Proteobacteria (75.87%) and Chlamydiae (20.56%) were dominant at the phylum level, and Acinetobacter (35.01%) and Roseomonas (8.24%) were dominant at the genus level. Multivariate analysis showed that the potential pathogenic bacterial community was significantly different among the four sections in the Pearl River. Both physicochemical factors (e.g., NO₃-N, and suspended solids) and land use (e.g., urban land and forest) significantly shaped the pathogen community structure. However, spatial effects contributed more to the variation of pathogen community based on variation partitioning and path analysis. Null model based normalized stochasticity ratio analysis further indicated that the stochastic process rather than deterministic process dominated the assembly mechanisms by controlling the spatial patterns of potential pathogens. In conclusion, high-throughput sequencing shows great potential for monitoring the potential pathogens, and provided more comprehensive information on the potentially pathogenic community. Our study highlighted the importance of considering the influences of dispersal-related processes in future risk assessments for the prevention and control of pathogenic bacteria.

A Brief History of Shigella

The history of Shigella, the causative agent of bacillary dysentery, is a long and fascinating one. This brief historical account starts with descriptions of the disease and its impact on human health from ancient time to the present. Our story of the bacterium starts just before the identification of the dysentery bacillus by Kiyoshi Shiga in 1898 and follows the scientific discoveries and principal scientists who contributed to the elucidation of Shigella pathogenesis in the first 100 years. Over the past century, Shigella has proved to be an outstanding model of an invasive bacterial pathogen and has served as a paradigm for the study of other bacterial pathogens. In addition to invasion of epithelial cells, some of those shared virulence traits include toxin production, multiple-antibiotic resistance, virulence genes encoded on plasmids and bacteriophages, global regulation of virulence genes, pathogenicity islands, intracellular motility, remodeling of host cytoskeleton, inflammation/polymorphonuclear leukocyte signaling, apoptosis induction/inhibition, and "black holes" and antivirulence genes. While there is still much to learn from studying Shigella pathogenesis, what we have learned so far has also contributed greatly to our broader understanding of bacterial pathogenesis.

Temperature-Dependent Growth Modeling of Environmental and Clinical Legionella pneumophila Multilocus Variable-Number Tandem-Repeat Analysis (MLVA) Genotypes

Legionella pneumophila causes waterborne infections resulting in severe pneumonia. High-resolution genotyping of L. pneumophila isolates can be achieved by multiple-locus variable-number tandem-repeat analysis (MLVA). Recently, we found that different MLVA genotypes of L. pneumophila dominated different sites in a small drinking-water network, with a genotype-related temperature and abundance regime. The present study focuses on understanding the temperature-dependent growth kinetics of the genotypes that dominated the water network. Our aim was to model mathematically the influence of temperature on the growth kinetics of different environmental and clinical L. pneumophila genotypes and to compare it with the influence of their ecological niches. Environmental strains showed a distinct temperature preference, with significant differences among the growth kinetics of the three studied genotypes (Gt4, Gt6, and Gt15). Gt4 strains exhibited superior growth at lower temperatures (25 and 30°C), while Gt15 strains appeared to be best adapted to relatively higher temperatures (42 and 45°C). The temperature-dependent growth traits of the environmental genotypes were consistent with their distribution and temperature preferences in the water network. Clinical isolates exhibited significantly higher growth rates and reached higher maximal cell densities at 37°C and 42°C than the environmental strains. Further research on the growth preferences of L. pneumophila clinical and environmental genotypes will result in a better understanding of their ecological niches in drinking-water systems as well as in the human body.IMPORTANCELegionella pneumophila is a waterborne pathogen that threatens humans in developed countries. The bacteria inhabit natural and man-made freshwater environments. Here we demonstrate that different environmental L. pneumophila genotypes have different temperature-dependent growth kinetics. Moreover, Legionella strains that belong to the same species but were isolated from environmental and clinical sources possess adaptations for growth at different temperatures. These growth preferences may influence the bacterial colonization at specific ecological niches within the drinking-water network. Adaptations for growth at human body temperatures may facilitate the abilities of some L. pneumophila strains to infect and cause illness in humans. Our findings may be used as a tool to improve Legionella monitoring in drinking-water networks. Risk assessment models for predicting the risk of legionellosis should take into account not only Legionella concentrations but also the temperature-dependent growth kinetics of the isolates.

Investigation of Reference Genes in Vibrio parahaemolyticus for Gene Expression Analysis Using Quantitative RT-PCR

Vibrio parahaemolyticus is a significant human pathogen capable of causing foodborne gastroenteritis associated with the consumption of contaminated raw or undercooked seafood. Quantitative RT-PCR (qRT-PCR) is a useful tool for studying gene expression in V. parahaemolyticus to characterize its virulence factors and understand the effect of environmental conditions on its pathogenicity. However, there is not a stable gene in V. parahaemolyticus that has been identified for use as a reference gene for qRT-PCR. This study evaluated the stability of 6 reference genes (16S rRNA, recA, rpoS, pvsA, pvuA, and gapdh) in 5 V. parahaemolyticus strains (O3:K6-clinical strain-tdh⁺, ATCC33846-tdh⁺, ATCC33847-tdh⁺, ATCC17802-trh⁺, and F13-environmental strain-tdh⁺) cultured at 4 different temperatures (15, 25, 37 and 42°C). Stability values were calculated using GeNorm, NormFinder, BestKeeper, and Delta CT algorithms. The results indicated that recA was the most stably expressed gene in the V. parahaemolyticus strains cultured at different temperatures. This study examined multiple V. parahaemolyticus strains and growth temperatures, hence the finding provided stronger evidence that recA can be used as a reference gene for gene expression studies in V. parahaemolyticus.

The structure and retrotransposition mechanism of LTR-retrotransposons in the asexual yeast Candida albicans

Retrotransposons constitute a major part of the genome in a number of eukaryotes. Long-terminal repeat (LTR) retrotransposons are one type of the retrotransposons. Candida albicans have 34 distinct LTR-retrotransposon families. They respectively belong to the Ty1/copia and Ty3/gypsy groups which have been extensively studied in the model yeast Saccharomyces cerevisiae. LTR-retrotransposons carry two LTRs flanking a long internal protein-coding domain, open reading frames. LTR-retrotransposons use RNA as intermediate to synthesize double-stranded DNA copies. In this article, we describe the structure feature, retrotransposition mechanism and the influence on organism diversity of LTR retrotransposons in C. albicans. We also discuss the relationship between pathogenicity and LTR retrotransposons in C. albicans.

Temperature-regulated expression of outer membrane proteins in Shigella flexneri

BACKGROUND

Bacteria exist widely in a diversity of natural environments. In order to survive adverse conditions such as nutrient depletion, biochemical and biological disturbances, and high temperature, bacteria have developed a wide variety of coping mechanisms. Temperature is one of the most important factors that can enhance the expression of microbial proteins. This study was conducted to investigate how outer membrane proteins (OMPs) of the bacterium Shigella flexneri respond to stress, especially during fever when the host's body temperature is elevated.

METHODS

OMPs of S. flexneri ATCC 12022 and clinical isolate SH057 were extracted from an overnight culture grown at 37, 38.5, and 40°C. Comparisons of the expressed proteins under the different growth conditions were based on equal numbers of bacterial cells loaded in the SDS-PAGE gels. Separated proteins were stained with Coomassie brilliant blue. Selected proteins showing increased expression at 38.5 and 40°C were characterized by performing MALDI-ToF-ToF.

RESULTS

Different degrees of expression were demonstrated for different proteins expressed at 37°C compared to 38.5 and 40°C. The proteins with molecular sizes of 18.4, 25.6, and 57.0 kDa showed increased expression level at increasing temperature and were identified as Dps, WrbA, and PepA, respectively.

CONCLUSION

This study revealed that strains of S. flexneri respond at the proteomic level during stress caused by elevated temperature by decreasing the expression of proteins, maintaining the level of important proteins, or enhancing the levels of proteins presumably involved in survival and virulence.

Natural variation in the temperature range permissive for vernalization in accessions of Arabidopsis thaliana

Vernalization is an acceleration of flowering in response to chilling, and is normally studied in the laboratory at near-freezing (2-4 °C) temperatures. Many vernalization-requiring species, such as Arabidopsis thaliana, are found in a range of habitats with varying winter temperatures. Natural variation in the temperature range that elicits a vernalization response in Arabidopsis has not been fully explored. We characterized the effect of intermediate temperatures (7-19 °C) on 15 accessions and the well-studied reference line Col-FRI. Although progressively warmer temperatures are gradually less effective at activating expression of the vernalization-specific gene VERNALIZATION-INSENSITIVE 3 (VIN3) and in accelerating flowering, there is substantial natural variation in the upper threshold (T(max) ) of the flowering-time response. VIN3 is required for the T(max) (13 °C) response of Col-FRI. Surprisingly, even 16 °C treatment caused induction of VIN3 in six tested lines, despite the ineffectiveness of this temperature in accelerating flowering for two of them. Finally, we present evidence that mild acceleration of flowering by 19 °C exposure may counterbalance the flowering time delay caused by non-inductive photoperiods in at least one accession, creating an appearance of photoperiod insensitivity.

Growth temperature-dependent contributions of response regulators, σB, PrfA, and motility factors to Listeria monocytogenes invasion of Caco-2 cells

Foodborne pathogens encounter rapidly changing environmental conditions during transmission, including exposure to temperatures below 37°C. The goal of this study was to develop a better understanding of the effects of growth temperatures and temperature shifts on regulation of invasion phenotypes and invasion-associated genes in Listeria monocytogenes. We specifically characterized the effects of L. monocytogenes growth at different temperatures (30°C vs. 37°C) on (i) the contributions to Caco-2 invasion of different regulators (including σ(B), PrfA, and 14 response regulators [RRs]) and invasion proteins (i.e., InlA and FlaA), and on (ii) gadA, plcA, inlA, and flaA transcript levels and their regulation. Overall, Caco-2 invasion efficiency was higher for L. monocytogenes grown at 30°C than for bacteria grown at 37°C (p = 0.0051 for the effect of temperature on invasion efficiency; analysis of variance); the increased invasion efficiency of the parent strain 10403S (serotype 1/2a) observed after growth at 30°C persisted for 2.5 h exposure to 37°C. For L. monocytogenes grown at 30°C, the motility RRs DegU and CheY and σ(B), but not PrfA, significantly contributed to Caco-2 invasion efficiency. For L. monocytogenes grown at 37°C, none of the 14 RRs tested significantly contributed to Caco-2 invasion, whereas σ(B) and PrfA contributed synergistically to invasion efficiency. At both growth temperatures there was significant synergism between the contributions to invasion of FlaA and InlA; this synergism was more pronounced after growth at 30°C than at 37°C. Our data show that growth temperature affects invasion efficiency and regulation of virulence-associated genes in L. monocytogenes. These data support increasing evidence that a number of environmental conditions can modulate virulence-associated phenotypes of foodborne bacterial pathogens, including L. monocytogenes.

Differential proteomic analysis of Clostridium perfringens ATCC13124; identification of dominant, surface and structure associated proteins

Background

Clostridium perfringens is a medically important clostridial pathogen causing diseases in man and animals. To invade, multiply and colonize tissues of the host, a pathogen must be able to evade host immune system, and obtain nutrients essential for growth. The factors involved in these complex processes are largely unknown and of crucial importance to understanding microbial pathogenesis. Many of the virulence determinants and putative vaccine candidates for bacterial pathogens are known to be surface localized.

Results

Using 2-DE mass spectrometry strategy, we identified major surface (22) and cell envelope (10) proteins from Clostridium perfringens ATCC13124 and those differentially expressed (11) in cells grown on cooked meat medium (CMM) in comparison with cells grown in reference state (tryptose-yeast extract-glucose medium). Riboflavin biosynthesis protein, ornithine carbamoyltransferase, cystathionine beta-lyase, and threonine dehydratase were the predominant proteins that exhibited 2.19 to 8.5 fold increase in the expression level in cells growing on CMM.

Conclusion

Ornithine carbamoyltransferase and cystathionine beta-lyase were over-expressed in cells grown on cooked meat medium and also identified in the surface protein fraction and the former was immunogenic; making them potential vaccine candidates. Based upon bioinformatic analysis; choloylglycine hydrolase family protein, cell wall-associated serine proteinase, and rhomboid family protein were predicted as surface protein markers for specific detection of C. perfringens from the environment and food. Most of the proteins over-expressed in CMM were shown to have putative function in metabolism, of which seven were involved in amino acid transport and metabolism or lipid metabolism.

Thermosensors in eubacteria: role and evolution

Temperature is an important physical stress factor sensed by bacteria and used to regulate gene expression. Three different macromolecules have been identified being able to sense temperature: DNA, mRNA and proteins. Depending on the induction mechanism, two different pathways have to be distinguished, namely the heat shock response and the high temperature response. While the heat shock response is induced by temperature increments and is transient, the high temperature response needs a specific temperature to become induced and proceeds as long as cells are exposed to that temperature. The heat shock response is induced by denatured proteins and aimed to prevent formation of protein aggregates by refolding or degradation, and the high temperature response is mainly used by pathogenic bacteria to detect entry into a mammalian host followed by induction of their virulence genes. All known high temperature sensors are present in two alternative conformations depending on the temperature. Heat shock sensors are either molecular chaperones or proteases which keep either a positive transcriptional regulator inactive or a negative regulator active or do not attack the regulator, respectively, under physiological conditions. Denatured proteins either titrate the molecular chaperones or activate the protease. The evolution of the different temperature sensors is discussed.

H-NS represses inv transcription in Yersinia enterocolitica through competition with RovA and interaction with YmoA

Yersinia enterocolitica is able to efficiently invade Peyer's patches with the aid of invasin, an outer member protein involved in the attachment and invasion of M cells. Invasin is encoded by inv, which is positively regulated by RovA in both Y. enterocolitica and Yersinia pseudotuberculosis while negatively regulated by YmoA in Y. enterocolitica and H-NS in Y. pseudotuberculosis. In this study we present data indicating H-NS and RovA bind directly and specifically to the inv promoter of Y. enterocolitica. We also show that RovA and H-NS from Y. enterocolitica bind to a similar region of the inv promoter and suggest they compete for binding sites. This is similar to recently published data from Y. pseudotuberculosis, revealing a potentially conserved mechanism of inv regulation between Y. enterocolitica and Y. pseudotuberculosis. Furthermore, we present data suggesting H-NS and YmoA form a repression complex on the inv promoter, with H-NS providing the binding specificity and YmoA interacting with H-NS to form a repression complex. We also demonstrate that deletion of the predicted H-NS binding region relieves the requirement for RovA-dependent transcription of the inv promoter, consistent with RovA acting as a derepressor of H-NS-mediated repression. Levels of H-NS and YmoA are similar between 26 degrees C and 37 degrees C, suggesting that the H-NS/YmoA repression complex is present at both temperatures, while the levels of rovA transcript are low at 37 degrees C and high at 26 degrees C, leading to expression of inv at 26 degrees C. Expression of RovA at 37 degrees C results in transcription of inv and production of invasin. Data presented here support a model of inv regulation where the level of RovA within the cell governs inv expression. As RovA levels increase, RovA can successfully compete for binding to the inv promoter with the H-NS/YmoA complex, resulting in derepression of inv transcription.

Unraveling the secret lives of bacteria: use of in vivo expression technology and differential fluorescence induction promoter traps as tools for exploring niche-specific gene expression

A major challenge for microbiologists is to elucidate the strategies deployed by microorganisms to adapt to and thrive in highly complex and dynamic environments. In vitro studies, including those monitoring genomewide changes, have proven their value, but they can, at best, mimic only a subset of the ensemble of abiotic and biotic stimuli that microorganisms experience in their natural habitats. The widely used gene-to-phenotype approach involves the identification of altered niche-related phenotypes on the basis of gene inactivation. However, many traits contributing to ecological performance that, upon inactivation, result in only subtle or difficult to score phenotypic changes are likely to be overlooked by this otherwise powerful approach. Based on the premise that many, if not most, of the corresponding genes will be induced or upregulated in the environment under study, ecologically significant genes can alternatively be traced using the promoter trap techniques differential fluorescence induction and in vivo expression technology (IVET). The potential and limitations are discussed for the different IVET selection strategies and system-specific variants thereof. Based on a compendium of genes that have emerged from these promoter-trapping studies, several functional groups have been distinguished, and their physiological relevance is illustrated with follow-up studies of selected genes. In addition to confirming results from largely complementary approaches such as signature-tagged mutagenesis, some unexpected parallels as well as distinguishing features of microbial phenotypic acclimation in diverse environmental niches have surfaced. On the other hand, by the identification of a large proportion of genes with unknown function, these promoter-trapping studies underscore how little we know about the secret lives of bacteria and other microorganisms.

High-throughput method for detecting genomic-deletion polymorphisms

DNA microarrays have been successfully used with different microorganisms, including Mycobacterium tuberculosis, to detect genomic deletions relative to a reference strain. However, the cost and complexity of the microarray system are obstacles to its widespread use in large-scale studies. In order to evaluate the extent and role of large sequence polymorphisms (LSPs) or insertion-deletion events in bacterial populations, we developed a technique, termed deligotyping, which hybridizes multiplex-PCR products to membrane-bound, highly specific oligonucleotide probes. The approach has the benefits of being low cost and capable of simultaneously interrogating more than 40 bacterial strains for the presence of 43 genomic regions. The deletions represented on the membrane were selected from previous comparative genomic studies and ongoing microarray experiments. Highly specific probes for these deletions were designed and attached to a membrane for hybridization with strain-derived targets. The targets were generated by multiplex PCR, allowing simultaneous amplifications of 43 different genomic loci in a single reaction. To validate our approach, 100 strains that had been analyzed with a high-density microarray were analyzed. The membrane accurately detected the deletions identified by the microarray approach, with a sensitivity of 99.9% and a specificity of 98.0%. The deligotyping technique allows the rapid and reliable screening of large numbers of M. tuberculosis isolates for LSPs. This technique can be used to provide insights into the epidemiology, genomic evolution, and population structure of M. tuberculosis and can be adapted for the study of other organisms.

Role of the Hha/YmoA family of proteins in the thermoregulation of the expression of virulence factors

Virulent bacteria are able to sense temperature changes and respond by modifying the expression of--among others--genes that code for virulence factors. The chromatin-associated protein H-NS has been shown to play a role in the thermomodulation of virulence factor expression. In addition to H-NS, proteins of the Hha/YmoA family have also been identified in different enterobacteria as participating in the thermoregulation of some virulence factors. For one of these proteins, the Hha protein, it has been shown that it interacts with H-NS, and both proteins form a nucleoid-protein complex responsible for the thermoregulation of, at least, E. coli hemolysin. The presence of genes coding for homologues of both proteins on some conjugative plasmids and their relation to thermoregulation suggests that this complex could also play a role in the regulation of plasmid transfer.

Regulation of the cytotoxic enterotoxin gene in Aeromonas hydrophila: characterization of an iron uptake regulator

The cytotoxic enterotoxin Act from a diarrheal isolate, SSU, of Aeromonas hydrophila is aerolysin related and crucial to the pathogenesis of Aeromonas infections. To elucidate the role of environmental signals which influence the expression of the cytotoxic enterotoxin gene (act), a portion of the act gene, including the putative promoter region, was fused in frame to a truncated alkaline phosphatase gene (phoA) of Escherichia coli. The act::phoA reporter gene was then introduced into the chromosome of A. hydrophila by using the suicide vector pJQ200SK, allowing the fusion protein to be secreted out into the culture medium. Western blot analysis demonstrated the presence of a correctly size 110-kDa fusion protein in the culture supernatant, which reacted with both anti-Act and anti-alkaline phosphatase antibodies. Based on alkaline phosphatase (PhoA) activity in the culture supernatant, we demonstrated that calcium significantly increased the activity of the act promoter but that glucose and iron repressed its activity in a dose-dependent fashion. The act promoter exhibited optimal activity at pH 7.0 and at 37 degrees C, and maximal PhoA activity was noted when the culture was aerated. Using a Vibrio cholerae iron uptake regulator gene (fur) as a probe, a 2.6-kb SalI/HindIII DNA fragment from an A. hydrophila chromosome was cloned and sequenced. The DNA sequence revealed a 429-bp open reading frame that exhibited 69% homology at the DNA level with the fur gene and 79% homology at the amino acid level with the iron uptake regulator (Fur) protein of V. cholerae. Complementation experiments demonstrated that the A. hydrophila fur gene could restore iron regulation in an E. coli fur-minus mutant. Using the suicide vector pDMS197, we generated a fur isogenic mutant of wild-type A. hydrophila SSU. Northern blot analysis data indicated that the repression in the transcription of the act gene by iron was relieved in the fur isogenic mutant. Further, iron regulation in the fur isogenic mutant of A. hydrophila could be restored by complementation. These results are important in understanding the regulation of the act gene under in vivo conditions.

Global differential gene expression in response to growth temperature alteration in group A Streptococcus

Pathogens are exposed to different temperatures during an infection cycle and must regulate gene expression accordingly. However, the extent to which virulent bacteria alter gene expression in response to temperatures encountered in the host is unknown. Group A Streptococcus (GAS) is a human-specific pathogen that is responsible for illnesses ranging from superficial skin infections and pharyngitis to severe invasive infections such as necrotizing fasciitis and streptococcal toxic shock syndrome. GAS survives and multiplies at different temperatures during human infection. DNA microarray analysis was used to investigate the influence of temperature on global gene expression in a serotype M1 strain grown to exponential phase at 29 degrees C and 37 degrees C. Approximately 9% of genes were differentially expressed by at least 1.5-fold at 29 degrees C relative to 37 degrees C, including genes encoding transporter proteins, proteins involved in iron homeostasis, transcriptional regulators, phage-associated proteins, and proteins with no known homologue. Relatively few known virulence genes were differentially expressed at this threshold. However, transcription of 28 genes encoding proteins with predicted secretion signal sequences was altered, indicating that growth temperature substantially influences the extracellular proteome. TaqMan real-time reverse transcription-PCR assays confirmed the microarray data. We also discovered that transcription of genes encoding hemolysins, and proteins with inferred roles in iron regulation, transport, and homeostasis, was influenced by growth at 40 degrees C. Thus, GAS profoundly alters gene expression in response to temperature. The data delineate the spectrum of temperature-regulated gene expression in an important human pathogen and provide many unforeseen lines of pathogenesis investigation.

Multiple environmental factors regulate the expression of the carbohydrate-selective OprB porin of Pseudomonas aeruginosa

In response to low extracellular glucose concentration, Pseudomonas aeruginosa induces the expression of the outer membrane carbohydrate-selective OprB porin. The promoter region of the oprB gene was cloned into a lacZ transcriptional fusion vector, and the construct was mobilized into P. aeruginosa OprB-deficient strain, WW100, to evaluate additional environmental factors that influence OprB porin gene expression. Growth temperature, pH of the growth medium, salicylate concentration, and carbohydrate source were found to differentially influence porin expression. This expression pattern was compared to those of whole-cell [14C]glucose uptake under conditions of high osmolarity, ionicity, variable pH, growth temperatures, and carbohydrate source. These studies revealed that the high-affinity glucose transport genes are down-regulated by salicylic acid, differentially regulated by pH and temperature, and are specifically responsive to exogenous glucose induction.Key words: Pseudomonas aeruginosa, OprB porin, glucose transport, regulation.

In vivo genetic analysis of bacterial virulence

In vitro assays contribute greatly to our understanding of bacterial pathogenesis, but they frequently cannot replicate the complex environment encountered by pathogens during infection. The information gained from such studies is therefore limited. In vivo models, on the other hand, can be difficult to use, and this has to some extent diminished the incentive to perform studies in living animals. However, several recently developed techniques permit in vivo examination of many genes simultaneously. Most of these methods fall into two broad classes: in vivo expression technology and signature-tagged mutagenesis. In vivo expression technology is a promoter-trap strategy designed to identify genes whose expression is induced in a specific environment, typically that encountered in a host. Signature-tagged mutagenesis uses comparative hybridization to isolate mutants unable to survive specified environmental conditions and has been used to identify genes critical for survival in the host. Both approaches have so far been used exclusively for investigating pathogen-host interactions, but they should be easily adaptable to the study of other processes.

The Yersinia enterocolitica pYV virulence plasmid contains multiple intrinsic DNA bends which melt at 37 degrees C

Temperature has a pleiotropic effect on Yersinia enterocolitica gene expression. Temperature-dependent phenotypes include the switching between two type III protein secretion systems, flagellum biosynthesis (</=30 degrees C) and virulence plasmid-encoded Yop secretion (37 degrees C). The mechanism by which temperature exerts this change in genetic programming is unclear; however, altered gene expression by temperature-dependent changes in DNA topology has been implicated. Here, we present evidence that the Y. enterocolitica virulence plasmid, pYV, undergoes a conformational transition between 30 and 37 degrees C. Using a simplified two-dimensional, single-gel assay, we show that pYV contains multiple regions of intrinsic curvature, including virF, the positive activator of virulence genes. These bends are detectable at 30 degrees C but melt at 37 degrees C, the temperature at which the cells undergo phenotypic switching. We also show that pACYC184, a plasmid used as a reporter of temperature-induced changes in DNA supercoiling, has a single region of intrinsic bending detected by our assay. Topoisomers of pACYC184, with and without this bend, isolated from Y. enterocolitica were resolved by using chloroquine gels. The single bend has a dramatic influence on temperature-dependent DNA supercoiling. These data suggest that the Y. enterocolitica pYV plasmid may undergo a conformational change at the host temperature due to melting of DNA bends followed by compensatory adjustments in superhelical density. Hence, changes in DNA topology may be the temperature-sensing mechanism for virulence gene expression in Y. enterocolitica and other enteric pathogens.

Environmental modulation of oral treponeme virulence in a murine model

This investigation examined the effects of environmental alteration on the virulence of the oral treponemes Treponema denticola and Treponema pectinovorum. The environmental effects were assessed by using a model of localized inflammatory abscesses in mice. In vitro growth of T. denticola and T. pectinovorum as a function of modification of the cysteine concentration significantly enhanced abscess formation and size. In contrast, growth of T. denticola or T. pectinovorum under iron-limiting conditions (e.g., dipyridyl chelation) had no effect on abscess induction in comparison to that when the strains were grown under normal iron conditions. In vivo modulation of the microenvironment at the focus of infection with Cytodex beads demonstrated that increasing the local inflammation had no effect on lesion induction or size. In vivo studies involved the determination of the effects of increased systemic iron availability (e.g., iron dextran or phenylhydrazine) on the induction, kinetics, and size of lesions. T. denticola induced significantly larger lesions in mice with iron pretreatment and demonstrated systemic manifestations of the infectious challenge and an accompanying spreading lesion with phenylhydrazine pretreatment (e.g., increases in circulating free hemoglobin). In contrast, T. pectinovorum virulence was minimally affected by this in vivo treatment to increase iron availability. T. denticola virulence, as evaluated by lesion size, was increased additively by in vivo iron availability, and cysteine modified growth of the microorganism. Additionally, galactosamine sensitized mice to a lethal outcome following infection with both T. denticola and T. pectinovorum, suggesting an endotoxin-like activity in these treponemes. These findings demonstrated the ability to modify the virulence capacity of T. denticola and T. pectinovorum by environmental conditions which can be evaluated by using in vivo murine models.

Temperature sensing in bacterial gene regulation--what it all boils down to

Many bacterial gene regulatory circuits are controlled by temperature. Temperature-mediated regulation occurs at the level of transcription and translation. Supercoiling, changes in mRNA conformation and protein conformation are all implicated in thermosensing. Bacterial virulence functions are often temperature regulated and thus many an example of thermoregulation comes from pathogenic organisms. H-NS is at the crossroads of regulation in many such systems. mRNA melting has also been shown to act as a thermosensing mechanism in various contexts. Proteins can also act as temperature sensors as exemplified by the gene regulator TlpA in Salmonella typhimurium.

Inactivated whole-cell bacterial vaccines: current status and novel strategies

Inactivated bacterial whole-cell vaccines have been the most widely studied prophylactic treatment for infectious diseases. They offer an economical, and potentially safe, effective means of preventing disease. The disadvantages of these vaccines have been that parenteral administration, while effective in some instances, may have caused adverse reactions in vaccinees, while oral administration often required high doses and resulted in short-term immunity. More recent studies describing new approaches for improving antigenicity of inactivated whole-cell vaccines and the enhancement of immune responses to oral immunization offer great hope for improving the efficacy of these agents. Promising whole cell vaccines include those against Vibrio cholerae, enterotoxigenic Escherichia coli, and more recently Campylobacter jejuni.

Subgingival temperature and microbiota in initial periodontitis

The association between subgingival temperature, other clinical characteristics, and the subgingival microbiota was examined in adult subjects with initial periodontitis and differing levels of gingival inflammation. 43 subjects were measured at 6 sites per tooth for pocket depth, attachment level, presence of plaque, gingival redness, bleeding on probing and subgingival temperature at 3-month intervals for 1 year. Subgingival plaque was sampled from 15 initial active periodontitis sites (10 subjects), 121 gingivitis, sites (20 subjects) and 202 healthy sites (13 subjects), and included the 5 hottest and 5 coldest sites in each subject. Plaque samples were analyzed for 13 subgingival species using whole-genomic DNA probes. The major influences on the subgingival microbiota were the clinical status of sites, pocket depth, and the presence of supragingival plaque. No significant association between species and site temperature was observed. Initial active sites were associated with Bacteroides forsythus and Campylobacter rectus, and had a higher mean subgingival temperature and deeper mean pocket depth than inactive sites. A weak association between pocket depth and site temperature was noted. The major influence on subgingival temperature of sites was the anterior to posterior anatomical temperature gradient in the mandible and maxilla.

Isolation and characterization of the dnaKJ operon from Actinobacillus actinomycetemcomitans

The dnaKJ operon of Actinobacillus actinomycetemcomitans Y4 was cloned by the DNA-probing method using synthetic oligonucleotides designed on the basis of two conserved regions in DnaK/hsp70 proteins and sequenced by inverse PCR. The sequenced region was shown to contain two open reading frames coding for proteins analogous to DnaK and DnaJ.

A proteinaceous gene regulatory thermometer in Salmonella

Novel utilization of the coiled-coil motif is presented that enables TlpA, an autoregulatory repressor protein in Salmonella, to sense temperature shifts directly and thereby to modulate the extent of transcription repression. Salmonella cells shifted to higher temperatures, such as those encountered at host entry, showed derepressed tlpA activity. tlpA::lacZ fusions indicated that the promoter itself is insensitive to thermal shifts and that transcription control was exerted by the autorepressor TlpA only. In vitro studies with highly purified TlpA showed concentration and temperature dependence for both fully folded conformation and function, indicating that the thermosensing in TlpA is based on monomer-to-coiled-coil equilibrium.

Calcineurin is required for virulence of Cryptococcus neoformans

Cyclosporin A (CsA) and FK506 are antimicrobial, immunosuppressive natural products that inhibit signal transduction. In T cells and Saccharomyces cerevisiae, CsA and FK506 bind to the immunophilins cyclophilin A and FKBP12 and the resulting complexes inhibit the Ca2+-regulated protein phosphatase calcineurin. We find that growth of the opportunistic fungal pathogen Cryptococcus neoformans is sensitive to CsA and FK506 at 37 degrees C but not at 24 degrees C, suggesting that CsA and FK506 inhibit a protein required for C. neoformans growth at elevated temperature. Genetic evidence supports a model in which immunophilin-drug complexes inhibit calcineurin to prevent growth at 37 degrees C. The gene encoding the C. neoformans calcineurin A catalytic subunit was cloned and disrupted by homologous recombination. Calcineurin mutant strains are viable but do not survive in vitro conditions that mimic the host environment (elevated temperature, 5% CO2 or alkaline pH) and are no longer pathogenic in an animal model of cryptococcal meningitis. Introduction of the wild-type calcineurin A gene complemented these growth defects and restored virulence. Our findings demonstrate that calcineurin is required for C. neoformans virulence and may define signal transduction elements required for fungal pathogenesis that could be targets for therapeutic intervention.

The hemagglutinin genes hagB and hagC of Porphyromonas gingivalis are transcribed in vivo as shown by use of a new expression vector

The hemagglutinin genes hagB and hagC of Porphyromonas gingivalis, a putative periodontopathic microorganism, have been cloned, sequenced, and characterized. However, the roles of these putative virulence genes have not yet been determined. In this study, an in vivo expression technology vector termed pPGIVET was constructed and used to determine if hagB and hagC were expressed during an infectious process. We constructed pPGIVET as a conjugative suicide plasmid containing a multiple-cloning site (MCS) upstream of two tandem promoterless reporter genes that encode tetracycline resistance [tetA(Q)2] and galactokinase (galK). The promoter and a portion of the open reading frame (ORF) of hagB were inserted into the MCS in both a positive and a negative orientation relative to the reporter genes. These constructs were conjugated into P. gingivalis 381. Southern blot analysis of different transconjugants indicated that Campbell insertions had occurred at the chromosomal hagB locus and also at the hagC locus, which has high (99%) homology to the ORF of hagB. pPGIVET-labeled clones in which the hag promoters were positively oriented relative to the reporter genes expressed tetracycline resistance and galactokinase activity in vitro and in vivo at significantly higher levels than did the wild-type strain or clones in which the hag promoters were negatively oriented. Expression of tetracycline resistance allowed substantial enrichment of heterodiploids over wild-type cells during a mixed infection in the mouse abscess model. These results indicate that hagB and hagC are transcriptionally active in vivo and suggested that pPGIVET may be used to isolate P. gingivalis genes expressed only during an infectious process.

Transcription of the mutL repair, miaA tRNA modification, hfq pleiotropic regulator, and hflA region protease genes of Escherichia coli K-12 from clustered Esigma32-specific promoters during heat shock

The amiB-mutL-miaA-hfq-hflX-hflK-hflC superoperon of Escherichia coli contains genes that are important for diverse cellular functions, including DNA mismatch repair (mutL), tRNA modification (miaA), pleiotropic regulation (hfq), and proteolysis (hflX-hflK-hflC). We show that this superoperon contains three E simga(32)-dependent heat shock promoters, P(mutL)HS,P(miaA)HS, and P1(hfq)HS, in addition to four E sigma(70)-dependent promoters, P(mutL), P(miaA), P2(hfq), and P3(hfq). Transcripts from P(mutL)HS and P(miaA)HS were most prominent in vivo during extreme heat shock (50 degrees C), whereas P1(hfq)HS transcripts were detectable under nonshock conditions and increased significantly after heat shock at 50 degrees C. The P(mutL)HS, P(miaA)HS, and P1(hfq)HS transcripts were not detected in an rpoH null mutant. All three promoters were transcribed by E sigma (32) in vitro at 37 degrees C and contain -35 and -10 regions that resemble the E sigma(32) consensus. In experiments to assess the possible physiological relevance of the P(mutL)HS and P(miaA)HS promoters, we found that E. coli prototrophic strain MG 1655 increased in cell mass and remained nearly 100% viable for several hours at 50 degrees C in enriched media. In these cells, a significant fraction of mutL and hfq-hflA region transcripts were from P(mutL)HS and P1(hfq)HS, respectively, and the amounts of the miaA, hfq, hflX, hflK, and hflC transcripts increased in comparison with those in nonstressed cells. The cellular amounts of MutL and the hfq gene product (HF-I protein) were maintained during heat shock at 44 or 50 degrees C. Consistent with their expression patterns, miaA and hfq were essential for growth and viability, respectively, at temperatures of 45 degrees C and above. Together, these results suggest that there is a class of E sigma(32) promoters that functions mainly at high temperatures to ensure E. coli function and survival.

Regulation of virulence by environmental signals in group A streptococci: influence of osmolarity, temperature, gas exchange, and iron limitation on emm transcription

Transcription of the gene encoding the antiphagocytic M protein (emm) of the group A streptococci has been shown to be regulated by CO2 (M. G. Caparon, R. T. Geist, J. Perez-Casal, and J. R. Scott, J. Bacteriol. 174:5693-5701, 1992). We tested the influence of additional environmental growth conditions on emm expression. Increased osmolarity, low temperature, growth with free exchange of gasses, or the restricted availability of iron resulted in decreased transcription from the emm promoter.

The Lly protein protects Legionella pneumophila from light but does not directly influence its intracellular survival in Hartmannella vermiformis

The lly locus (legiolysin) mediates the browning of the culture medium of Legionella pneumophila in the late stationary growth phase, presumably as a result of synthesis of homogentisic acid. Mutagenesis of the lly gene of the L. pneumophila Philadelphia I derivative JR32 did not affect intracellular replication in the natural host Hartmannella vermiformis. The Lly-negative mutant, however, showed a markedly decreased resistance to ordinary light. The cloned lly gene conferred an increased resistance to light in recombinant L. pneumophila and Escherichia coli K-12, indicating a contribution of the Lly protein to ecological adaptation of Legionella species.

Biological and genetic characterization of TnphoA mutants of Salmonella typhimurium TML in the context of gastroenteritis

TnphoA transposon insertion mutants of phoN-negative derivatives of Salmonella typhimurium TML (of human gastroenteritic origin) were selected by growing mutagenized recipient bacteria under a variety of growth conditions. Ninety-seven individual mutants, which expressed alkaline phosphatase, were collected and tested for their ability to invade HEp-2 cells. Seven smooth mutants had a reduced ability to invade HEp-2 cells, and three smooth mutants were consistently more invasive than their corresponding parental strains. One rough mutant was of similar invasiveness and two were of reduced invasiveness when compared with that of parental strains. The seven smooth hypoinvasive mutants, the three smooth hyperinvasive mutants, and the three rough mutant strains were tested for their abilities to invade ileal enterocytes by the rabbit ileal invasion assay described previously (3). All smooth mutants exhibited parental levels of invasiveness. The rough mutants were hypoinvasive in the rabbit ileal invasion assay. The HEp-2 system is therefore not a good predictor of behavior in gut tissue in this model. DNA sequences flanking the transposon were determined for five mutants which were hypoinvasive in the HEp-2 cell assay. The mutations were found to be insertions in two previously identified invasion genes, invG and invH, and in a gene not normally associated with invasion, pagC. These observations lead one to be cautious in the interpretation of the biological significance of data obtained from invasion of tissue culture monolayers when extrapolated to gut tissue.

Cloning, sequencing and expression of the dnaJ gene of Coxiella burnetii

A 6-kb EcoRI genomic DNA fragment of Coxiella burnetii, isolated from a recombinant bacteriophage lambda ZapII library, allowed heterologous genetic complementation of Escherichia coli deleted for its dnaJ gene. The C. burnetii dnaJ gene was expressed in E. coli and identified by Western blot analysis using polyclonal antibodies raised against purified E. coli DnaJ protein. Deletion mapping and genetic complementation demonstrated that C. burnetii dnaJ is present on a 2-kb EcoRI-HindIII genomic DNA fragment, from which the nt sequence of the C. burnetii dnaJ gene was determined.

Host-microbe interaction in the gastrointestinal tract

In order for an infection to occur, the target organ must come in contact with sufficient microbes, the microbe must possess specific virulence factors, these virulence factors must be expressed, and the defenses of the organ system must be overcome. This dynamic process, which is ongoing in all living entities, can be described by the following relationship: [formula: see text] The establishment of infection first occurs in a particular organ. This phenomenon is known as tissue trophism and the association of microbes with organ systems governs the practice of clinical microbiology and infectious disease. With some microbes (e.g., Giardia, Cryptosporidium) the interaction with the particular organ is so specific that infections are almost always confined to one site; with others (e.g., Salmonella, enterovirus) the microbe has the potential to become systemic. When attempting to establish health risk assessment from microbes by contact with food and drinking water, one must therefore consider that the gastrointestinal tract is a complex organ system with a variety of specific host defense mechanisms. It is only when the microbe has particular virulence factors for sites in gastrointestinal tract, and the specific host defense mechanisms in the gastrointestinal tract are breached, that infection of this organ system occurs. Therefore, the general terms "immunosuppression" or "immunocompromise" are meaningless unless the specific immune defect is known. A description of the microbial virulence factors active against the gastrointestinal tract and the defense mechanisms of this organ system are reviewed to provide a biological basis health risk assessment and future food and drinking water regulations.

Heat stress alters the virulence of a rifampin-resistant mutant of Francisella tularensis LVS

We have studied the stress response of a rifampin-resistant mutant of Francisella tularensis LVS. This mutant, Rif 7, was avirulent with an intraperitoneally administered 50% lethal dose greater than 10(7) CFU in a murine model of infection. Exposure of Rif 7 to heat stress for 5 h in vitro resulted in a 2-log decrease in its 50% lethal dose (P < 0.02). The increase in virulence was dependent on the time of exposure to high temperature and was maximal at 5 h. Envelope preparations from heat-stressed cells showed increased levels of several proteins. Notable among these were polypeptides with approximate molecular masses of 16, 60, and 75 kDa. Increases in both virulence and envelope protein levels were reversed when heat-treated cells were subsequently grown at 37 degrees C. Inhibition of protein synthesis by actinomycin D during heat stress blocked the increase in virulence of Rif 7. Cell-free media from the heat-stressed Rif 7 reacted with the whole spectrum of bacterial proteins were not toxic to mice. Hyperimmune serum against Rif 7 reacted with the whole spectrum of bacterial proteins in Western blots (immunoblots), although its reaction with 34- and 45-kDa proteins and two 60- and 75-kDa proteins upregulated during heat stress was weak. Other stress conditions, low iron and low pH, caused similar increases in the virulence of Rif 7. However, examination of the protein profile did not reveal any major common polypeptides induced by different stresses. Heat-treated Rif 7 bacteria were fully able to replicate in macrophages in vitro and in the host tissues, even though heat treatment only partially restored virulence.

The three Bacillus anthracis toxin genes are coordinately regulated by bicarbonate and temperature

The two Bacillus anthracis toxins are composed of three proteins, protective antigen, lethal factor, and edema factor. The structural genes for these three components are located on the virulence plasmid pXO1. We constructed transcriptional fusions between the regulatory region of each of these genes and lacZ. Each construct was then inserted as a single copy at the corresponding toxin gene locus on pXO1, resulting in three isogenic strains. Two environmental factors, bicarbonate and temperature, were found to induce beta-galactosidase synthesis in each recombinant strain. Furthermore, the transcription of the three toxin genes appears to be coordinately regulated.

Growth temperature reversibly modulates the virulence of Legionella pneumophila

In chemostat culture, the virulence of two strains of Legionella pneumophila was shown to be significantly (P < 0.05) reduced when the culture temperature was lowered from 37 to 24 degrees C. This modulation was reversed by returning the temperature to 37 degrees C, which resulted in a statistically significant (P < 0.05) increase in virulence.