Virulence and the heat shock response

Topoisomerase 1 Activity Is Reduced in Response to Thermal Stress in Fruit Flies and in Human HeLa Cells

In the modern world with climate changes and increasing pollution, different types of stress are becoming an increasing challenge. Hence, the identification of reliable biomarkers of stress and accessible sensors to measure such biomarkers are attracting increasing attention. In the current study, we demonstrate that the activity, but not the expression, of the ubiquitous enzyme topoisomerase 1 (TOP1), as measured in crude cell extracts by the REEAD sensor system, is markedly reduced in response to thermal stress in both fruit flies (Drosophila melanogaster) and cultivated human cells. This effect was observed in response to both mild-to-moderate long-term heat stress and more severe short-term heat stress in D. melanogaster. In cultivated HeLa cells a reduced TOP1 activity was observed in response to both cold and heat stress. The reduced TOP1 activity appeared dependent on one or more cellular pathways since the activity of purified TOP1 was unaffected by the utilized stress temperatures. We demonstrate successful quantitative measurement of TOP1 activity using an easily accessible chemiluminescence readout for REEAD pointing towards a sensor system suitable for point-of-care assessment of stress responses based on TOP1 as a biomarker.

Biofilm Homeostasis Interference Therapy via 1 O2 -Sensitized Hyperthermia and Immune Microenvironment Re-Rousing for Biofilm-Associated Infections Elimination

The recurrence of biofilm-associated infections (BAIs) remains high after implant-associated surgery. Biofilms on the implant surface reportedly shelter bacteria from antibiotics and evade innate immune defenses. Moreover, little is currently known about eliminating residual bacteria that can induce biofilm reinfection. Herein, novel "interference-regulation strategy" based on bovine serum albumin-iridium oxide nanoparticles (BIONPs) as biofilm homeostasis interrupter and immunomodulator via singlet oxygen (¹ O₂ )-sensitized mild hyperthermia for combating BAIs is reported. The catalase-like BIONPs convert abundant H₂ O₂ inside the biofilm-microenvironment (BME) to sufficient oxygen gas (O₂ ), which can efficiently enhance the generation of ¹ O₂ under near-infrared irradiation. The ¹ O₂ -induced biofilm homeostasis disturbance (e.g., sigB, groEL, agr-A, icaD, eDNA) can disrupt the sophisticated defense system of biofilm, further enhancing the sensitivity of biofilms to mild hyperthermia. Moreover, the mild hyperthermia-induced bacterial membrane disintegration results in protein leakage and ¹ O₂ penetration to kill bacteria inside the biofilm. Subsequently, BIONPs-induced immunosuppressive microenvironment re-rousing successfully re-polarizes macrophages to pro-inflammatory M1 phenotype in vivo to devour residual biofilm and prevent biofilm reconstruction. Collectively, this ¹ O₂ -sensitized mild hyperthermia can yield great refractory BAIs treatment via biofilm homeostasis interference, mild-hyperthermia, and immunotherapy, providing a novel and effective anti-biofilm strategy.

Pathogenicity and virulence of bacterial strains associated with summer mortality in marine mussels (Perna canaliculus)

The occurrence of pathogenic bacteria has emerged as a plausible key component of summer mortalities in mussels. In the current research, four bacterial isolates retrieved from moribund Greenshell࣪ mussels, Perna canaliculus, from a previous summer mortality event, were tentatively identified as Vibrio and Photobacterium species using morpho-biochemical characterization and MALDI-TOF MS and confirmed as V. celticus, P. swingsii, P. rosenbergii, and P. proteolyticum using whole genome sequencing. These isolates were utilized in a laboratory challenge where mussels were injected with cell concentrations ranging from 105 to 109 CFU/mussel. Of the investigated isolates, P. swingsii induced the highest mortality. Additionally, results from quantitative polymerase chain reaction analysis, focusing on known virulence genes were detected in all isolates grown under laboratory conditions. Photobacterium rosenbergii and P. swingsii showed the highest expression levels of these virulence determinants. These results indicate that Photobacterium spp. could be a significant pathogen of P. canaliculus, with possible importance during summer mortality events. By implementing screening methods to detect and monitor Photobacterium concentrations in farmed mussel populations, a better understanding of the host-pathogen relationship can be obtained, aiding the development of a resilient industry in a changing environment.

HtrA of Actinobacillus pleuropneumoniae is a virulence factor that confers resistance to heat shock and oxidative stress

Actinobacillus pleuropneumoniae is the causative agent of porcine pleuropneumonia, which is a severe and often fatal disease that results in significant economic loss. The means by which A. pleuropneumoniae survives within the host are not clear. High temperature requirement A (HtrA) proteases have been shown to affect cell viability during stressful conditions and are virulence factors in many bacterial species. In this study, we examined the biological role of HtrA during A. pleuropneumoniae infection by analyzing the impact of htrA mutation on virulence-associated phenotypes. We found that htrA mutation had a dramatic impact on stress tolerance. The htrA mutant (ΔhtrA) displayed a lethal phenotype at elevated temperature (42°C). Further, ΔhtrA exhibited increased susceptibility to H₂O₂-induced oxidative stress when compared to the parental strain (SLW01) and a complementation strain (ΔhtrA-Compl). Animal infection assays demonstrated that absence of HtrA led to decreased in vivo colonization ability, and ΔhtrA is less virulent in pigs relative to SLW01. Furthermore, pig competitive infection assays demonstrated fewer blood associated CFUs with ΔhtrA infection than with SLW01. These results demonstrate HtrA plays a significant role in the survival and growth of A. pleuropneumoniae during stressful conditions, and that immune escape and invasiveness are important to the process of A. pleuropneumoniae infection.

Transcriptome response of a new serotype of avian type Klebsiella varicella strain to chicken sera

Klebsiella variicola is a newly discovered pathogen of zoonotic importance, commonly causing serious systemic infection via the bloodstream route. However, the mechanism by which K. variicola survives and grows in the bloodstream is poorly understood. In a previous study, a strain of Klebsiella causing chicken bloodstream infection was obtained, and whole genome sequencing showed that it was a new ST174 type K. variicola. Therefore, the present study aimed to determine the molecular mechanism underlying the survival and development of K. variicola in host serum. First, we compared the transcriptomes of K. variicola grown in Luria-Bertani broth and chicken serum. We sequenced six RNA libraries from the two groups, each library had three repeats. A total of 1046 differentially expressed genes were identified. Functional annotation analysis showed that the differentially expressed genes are mainly involved in adaptive metabolism, biosynthesis pathways (including biosynthesis of siderophore group nonribosomal peptides and lipopolysaccharide (LPS) biosynthesis), stress resistance, and several known virulence regulatory systems (including the ABC transporter system, the two-component signal transduction system and the quorum sensing system). These genes are expected to contribute to the adaptation and growth of K. variicola in host birds. This analysis provides a new insight into the pathogenesis of K. variicola.

McsB forms a gated kinase chamber to mark aberrant bacterial proteins for degradation

In Gram-positive bacteria, the McsB protein arginine kinase is central to protein quality control, labeling aberrant molecules for degradation by the ClpCP protease. Despite its importance for stress response and pathogenicity, it is still elusive how the bacterial degradation labeling is regulated. Here, we delineate the mechanism how McsB targets aberrant proteins during stress conditions. Structural data reveal a self-compartmentalized kinase, in which the active sites are sequestered in a molecular cage. The ‘closed’ octamer interconverts with other oligomers in a phosphorylation-dependent manner and, unlike these ‘open’ forms, preferentially labels unfolded proteins. In vivo data show that heat-shock triggers accumulation of higher order oligomers, of which the octameric McsB is essential for surviving stress situations. The interconversion of open and closed oligomers represents a distinct regulatory mechanism of a degradation labeler, allowing the McsB kinase to adapt its potentially dangerous enzyme function to the needs of the bacterial cell.

Understanding GroEL and DnaK Stress Response Proteins as Antigens for Bacterial Diseases

Bacteria do not simply express a constitutive panel of proteins but they instead undergo dynamic changes in their protein repertoire in response to changes in nutritional status and when exposed to different environments. These differentially expressed proteins may be suitable to use for vaccine antigens if they are virulence factors. Immediately upon entry into the host organism, bacteria are exposed to a different environment, which includes changes in temperature, osmotic pressure, pH, etc. Even when an organism has already penetrated the blood or lymphatics and it then enters another organ or a cell, it can respond to these new conditions by increasing the expression of virulence factors to aid in bacterial adherence, invasion, or immune evasion. Stress response proteins such as heat shock proteins and chaperones are some of the proteins that undergo changes in levels of expression and/or changes in cellular localization from the cytosol to the cell surface or the secretome, making them potential immunogens for vaccine development. Herein we highlight literature showing that intracellular chaperone proteins GroEL and DnaK, which were originally identified as playing a role in protein folding, are relocated to the cell surface or are secreted during invasion and therefore may be recognized by the host immune system as antigens. In addition, we highlight literature showcasing the immunomodulation effects these proteins can have on the immune system, also making them potential adjuvants or immunotherapeutics.

Adaptation to pH stress by Vibrio fischeri can affect its symbiosis with the Hawaiian bobtail squid (Euprymna scolopes)

Many microorganisms engaged in host-microbe interactions pendulate between a free-living phase and a host-affiliated stage. How adaptation to stress during the free-living phase affects host-microbe associations is unclear and understudied. To explore this topic, the symbiosis between Hawaiian bobtail squid (Euprymna scolopes) and the luminous bacterium Vibrio fischeri was leveraged for a microbial experimental evolution study. V. fischeri experienced adaptation to extreme pH while apart from the squid host. V. fischeri was serially passaged for 2000 generations to the lower and upper pH growth limits for this microorganism, which were pH 6.0 and 10.0, respectively. V. fischeri was also serially passaged for 2000 generations to vacillating pH 6.0 and 10.0. Evolution to pH stress both facilitated and impaired symbiosis. Microbial evolution to acid stress promoted squid colonization and increased bioluminescence for V. fischeri, while symbiont adaptation to alkaline stress diminished these two traits. Oscillatory selection to acid and alkaline stress also improved symbiosis for V. fischeri, but the facilitating effects were less than that provided by microbial adaptation to acid stress. In summary, microbial adaptation to harsh environments amid the free-living phase may impact the evolution of host-microbe interactions in ways that were not formerly considered.

Upregulation of the clpB gene in response to heat shock and beta-lactam antibiotics in Acinetobacter baumannii

The role of the clpB gene encoding HSP/chaperone ClpB was evaluated in the multiresistant antibiotic cells of Acinetobacter baumannii (RS4 strain) under stress-induced heat shock and different beta-lactams. The expression of the clpB gene was assessed by qPCR during heat shock at 45 °C and subinhibitory concentrations of ampicillin (30 μg mL^-1), amoxicillin + sulbactam (8/12 μg mL^-1), cefepime (30 μg mL^-1), sulfamethoxazole + trimethoprim (120/8 μg mL^-1) and meropenem (18 μg mL^-1). The results indicated a transient increase in clpB transcription in all treatments except cefepime. Both in the presence of ampicillin and amoxicillin/sulbactam for 20 min, the mRNA-clpB synthesis was 1.4 times higher than that of the control at time zero. Surprisingly, the mRNA-clpB levels were more than 30-fold higher after 10 min of incubation with meropenem and more than eightfold higher in the presence of trimethoprim/sulfamethoxazole. In addition, western blot assays showed that the RS4 strain treated with meropenem showed a marked increase in ClpB protein expression. Our data indicate that during exposure to beta-lactams, A. baumannii adjusts the transcription levels of the clpB mRNA and protein to respond to stress, suggesting that the chaperone may act as a key cellular component in the presence of antibiotics in this bacterium.

Lack of AcrB Efflux Function Confers Loss of Virulence on Salmonella enterica Serovar Typhimurium

AcrAB-TolC is the paradigm resistance-nodulation-division (RND) multidrug resistance efflux system in Gram-negative bacteria, with AcrB being the pump protein in this complex. We constructed a nonfunctional AcrB mutant by replacing D408, a highly conserved residue essential for proton translocation. Western blotting confirmed that the AcrB D408A mutant had the same native level of expression of AcrB as the parental strain. The mutant had no growth deficiencies in rich or minimal medium. However, compared with wild-type SL1344, the mutant had increased accumulation of Hoechst 33342 dye and decreased efflux of ethidium bromide and was multidrug hypersusceptible. The D408A mutant was attenuated in vivo in mouse and Galleria mellonella models and showed significantly reduced invasion into intestinal epithelial cells and macrophages in vitro A dose-dependent inhibition of invasion was also observed when two different efflux pump inhibitors were added to the wild-type strain during infection of epithelial cells. RNA sequencing (RNA-seq) revealed downregulation of bacterial factors necessary for infection, including those in the Salmonella pathogenicity islands 1, 2, and 4; quorum sensing genes; and phoPQ Several general stress response genes were upregulated, probably due to retention of noxious molecules inside the bacterium. Unlike loss of AcrB protein, loss of efflux function did not induce overexpression of other RND efflux pumps. Our data suggest that gene deletion mutants are unsuitable for studying membrane transporters and, importantly, that inhibitors of AcrB efflux function will not induce expression of other RND pumps.IMPORTANCE Antibiotic resistance is a major public health concern. In Gram-negative bacteria, overexpression of the AcrAB-TolC multidrug efflux system confers resistance to clinically useful drugs. Here, we show that loss of AcrB efflux function causes loss of virulence in Salmonella enterica serovar Typhimurium. This is due to the reduction of bacterial factors necessary for infection, which is likely to be caused by the retention of noxious molecules inside the bacterium. We also show that, in contrast to loss of AcrB protein, loss of efflux does not induce overexpression of other efflux pumps from the same family. This indicates that there are differences between loss of efflux protein and loss of efflux that make gene deletion mutants unsuitable for studying the biological function of membrane transporters. Understanding the biological role of AcrB will help to assess the risks of targeting efflux pumps as a strategy to combat antibiotic resistance.

Expression of the stress-response regulators CtsR and HrcA in the uropathogen Staphylococcus saprophyticus during heat shock

The uropathogen Staphylococcus saprophyticus is an ubiquitous bacterium but little is known about mechanisms that allow its persistence in diverse environments. Here we evaluated S. saprophyticus growth and survival during heat shock, the expression of stress response regulators ctsR and hrcA through qRT-PCR and heat shock protein synthesis through ³⁵S-Met metabolic labeling. S. saprophyticus does not tolerate temperatures much higher than the optimal 37 °C, as its growth is greatly affected at 42 °C, though viability is maintained up to 48 °C. At 42 °C, the expression of ctsR and hrcA repressor genes approximately triple when compared to 37 °C and continue to increase together with temperature till 48 °C. Expression of hrcA peaks after 20 min of heat shock and decreases significantly after 30 min, indicating that heat stress response regulated by this gene may last 20-30 min. An increase in temperature is accompanied by the synthesis of at least eight proteins, three of which are likely the chaperones DnaK, GroEL and ClpB. In silico analysis indicate that the groEL gene may be regulated by HrcA, clpB by CtsR and dnaK by both repressors. This is the first work to discuss heat stress response in S. saprophyticus and a step forward in the understanding of mechanisms that make this a widespread and emergent pathogen.

The Capricious Nature of Bacterial Pathogens: Phasevarions and Vaccine Development

Infectious diseases are a leading cause of morbidity and mortality worldwide, and vaccines are one of the most successful and cost-effective tools for disease prevention. One of the key considerations for rational vaccine development is the selection of appropriate antigens. Antigens must induce a protective immune response, and this response should be directed to stably expressed antigens so the target microbe can always be recognized by the immune system. Antigens with variable expression, due to environmental signals or phase variation (i.e., high frequency, random switching of expression), are not ideal vaccine candidates because variable expression could lead to immune evasion. Phase variation is often mediated by the presence of highly mutagenic simple tandem DNA repeats, and genes containing such sequences can be easily identified, and their use as vaccine antigens reconsidered. Recent research has identified phase variably expressed DNA methyltransferases that act as global epigenetic regulators. These phase-variable regulons, known as phasevarions, are associated with altered virulence phenotypes and/or expression of vaccine candidates. As such, genes encoding candidate vaccine antigens that have no obvious mechanism of phase variation may be subject to indirect, epigenetic control as part of a phasevarion. Bioinformatic and experimental studies are required to elucidate the distribution and mechanism of action of these DNA methyltransferases, and most importantly, whether they mediate epigenetic regulation of potential and current vaccine candidates. This process is essential to define the stably expressed antigen target profile of bacterial pathogens and thereby facilitate efficient, rational selection of vaccine antigens.

Impact of Moderate Temperature Changes on Neisseria meningitidis Adhesion Phenotypes and Proteome

Neisseria meningitidis, the meningococcus, bears the potential to cause life-threatening invasive diseases, but it usually colonizes the nasopharynx without causing any symptoms. Within the nasopharynx, Neisseria meningitidis must face temperature changes depending on the ambient air temperature. Indeed, the nasopharyngeal temperature can be substantially lower than 37°C, the temperature commonly used in experimental settings. Here, we compared the levels of meningococcal biofilm formation, autoaggregation, and cellular adherence at 32°C and 37°C and found a clear increase in all these phenotypes at 32°C suggestive of a stronger in vivo colonization capability at this temperature. A comparative proteome analysis approach revealed differential protein expression levels between 32°C and 37°C, predominantly affecting the bacterial envelope. A total of 375 proteins were detected. Use of database annotation or the PSORTb algorithm predicted 49 of those proteins to be localized in the outer membrane, 21 in either the inner or outer membrane, 35 in the periplasm, 56 in the inner membrane, and 208 in the cytosol; for 6 proteins, no annotation or prediction was available. Temperature-dependent regulation of protein expression was seen particularly in the periplasm as well as in the outer and inner membranes. Neisserial heparin binding antigen (NHBA), NMB1030, and adhesin complex protein (ACP) showed the strongest upregulation at 32°C and were partially responsible for the observed temperature-dependent phenotypes. Screening of different global regulators of Neisseria meningitidis suggested that the extracytoplasmic sigma factor σ^E might be involved in temperature-dependent biofilm formation. In conclusion, subtle temperature changes trigger adaptation events promoting mucosal colonization by meningococci.

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.

Molecular characterization of heat-shock protein 90 gene and its expression in Gobiocypris rarus juveniles exposed to pentachlorophenol

Heat-shock protein 90 (HSP90) is an abundant and highly conserved molecular chaperone, and it fulfills a housekeeping function in contributing to the folding, maintenance of structural integrity, and proper regulation of a subset of cytosolic proteins. In this study, the full-length 2693-bp cDNA of HSP90 was cloned by rapid amplification of cDNA ends (RACE) technique from the liver of rare minnow (Gobiocypris rarus) for the first time, designated as GrHSP90. The complete coding sequence of GrHSP90 is 2181 bp in length, which encodes a polypeptide of 726 amino acids with a predicted molecular mass of 83.4 kDa and a theoretical isoelectric point of 4.90. Phylogenetic tree analysis indicated that deduced protein GrHSP90 had extensive sequence similarities to other fish HSP90s. Tissue distribution showed that GrHSP90 was constitutively expressed in a wide range of tissues including gill, blood, brain, fin, gonad, heart, intestine, kidney, liver, muscle, spleen, skin, and swim bladder. The highest expression was found in the gonad. Furthermore, significant increase in GrHSP90 mRNA in the liver was observed after exposure to pentachlorophenol ≥8 µg/L (p < 0.05). Our results suggest that GrHSP90 is indeed an ortholog of the HSP90 family and may be act as a biomarker to assess the effect of environmental contaminant.

Thermal control of virulence factors in bacteria: a hot topic

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

Mast cell chymase degrades the alarmins heat shock protein 70, biglycan, HMGB1, and interleukin-33 (IL-33) and limits danger-induced inflammation

During infection and tissue damage, virulence factors and alarmins are pro-inflammatory and induce activation of various immune cells including macrophages and mast cells (MCs). Activated MCs instantly release preformed inflammatory mediators, including several proteases. The chymase mouse mast cell protease (MCPT)-4 is thought to be pro-inflammatory, whereas human chymase also degrades pro-inflammatory cytokines, suggesting that chymase instead limits inflammation. Here we explored the contribution of MCPT4 and human chymase to the control of danger-induced inflammation. We found that protein extracts from wild type (WT), carboxypeptidase A3-, and MCPT6-deficient mice and MCs and recombinant human chymase efficiently degrade the Trichinella spiralis virulence factor heat shock protein 70 (Hsp70) as well as endogenous Hsp70. MC-(W(sash))-, serglycin-, NDST2-, and MCPT4-deficient extracts lacked this capacity, indicating that chymase is responsible for the degradation. Chymase, but not MC tryptase, also degraded other alarmins, i.e. biglycan, HMGB1, and IL-33, a degradation that was efficiently blocked by the chymase inhibitor chymostatin. IL-7, IL-22, GM-CSF, and CCL2 were resistant to chymase degradation. MCPT4-deficient conditions ex vivo and in vivo showed no reduction in added Hsp70 and only minor reduction of IL-33. Peritoneal challenge with Hsp70 resulted in increased neutrophil recruitment and TNF-α levels in the MCPT4-deficient mice, whereas IL-6 and CCL2 levels were similar to the levels found in WT mice. The rapid and MC chymase-specific degradation of virulence factors and alarmins may depend on the presence of accessible extended recognition cleavage sites in target substrates and suggests a protective and regulatory role of MC chymase during danger-induced inflammation.

Transcriptional profiling of Haemophilus parasuis SH0165 response to tilmicosin

The Haemophilus parasuis respiratory tract pathogen poses a severe threat to the swine industry despite available antimicrobial therapies. To gain a more detailed understanding of the molecular mechanisms underlying H. parasuis response to tilmicosin treatment, microarray technology was applied to analyze the variation in gene expression of isolated H. parasuis SH0165 treated in vitro with subinhibitory (0.25 μg/ml) and inhibitory (8 μg/ml) concentrations. Tilmicosin treatment induced differential expression of 405 genes, the encoded products of which are mainly involved in the heat shock response, protein synthesis, and intracellular transportation. The subinhibitory and inhibitory concentrations of tilmicosin induced distinctive gene expression profiles of shared and unique changes, respectively. These changes included 302 genes mainly involved in protein export and the phosphotransferase system to sustain cell growth, and 198 genes mainly related to RNA polymerase, recombination, and repair to inhibit cell growth. In silico analysis of functions related to the differentially expressed genes suggested that adaptation of H. parasuis SH0165 to tilmicosin involves modulation of protein synthesis and membrane transport. Collectively, the genes comprising each transcriptional profile of H. parasuis response to tilmicosin provide novel insights into the physiological functions of this economically significant bacterium and may represent targets of future molecular therapeutic strategies.

Cloning and characterization of the HSP90 beta gene from Tanichthys albonubes Lin (Cyprinidae): effect of copper and cadmium exposure

Heat shock protein 90 (HSP90) is a highly conserved molecular chaperone important in the maturation of a broad spectrum of proteins. In order to evaluate the effect of copper (Cu(2+)) and cadmium (Cd(2+)) on the expression of HSP90 from Tanichthys albonubes (designated TaHSP90), the full-length complementary DNA (cDNA) of TaHSP90 was cloned using reverse transcription PCR and rapid amplification of cDNA ends (RACE) techniques. A 2,687-bp sequence was sequenced and consisted of an open reading frame (ORF) of 2,181 bp encoding a polypeptide of 727 amino acids with five HSP90 family signatures. Homologous analysis revealed that TaHSP90 gene shared high similarity with other known HSP90 genes and belonged to HSP90β subtype. Fluorescent real-time quantitative PCR was used to examine the expression pattern of TaHSP90β mRNA in different tissues (liver, muscle, gill, fin, eye, ovary, intestine and brain), and the result indicated that TaHSP90β was widely expressed in all examined tissues at different levels. Sensitivity of TaHSP90β to copper and cadmium was examined by exposing fish to different concentrations of Cu(2+) (0, 13.50 and 27.00 μg/L) and Cd(2+) (0, 1.15, 2.31 mg/L) for 24, 48, 72 and 96 h, respectively. The copper treatment induced TaHSP90β expression slight increase only at 24 and 48 h, while cadmium treatment caused slight down-regulation of TaHSP90β only 72 and 96 h. Our data suggest that the cloning and expression analysis of T. albonubes HSP90β gene provided useful molecular information of T. albonubes responses in stress conditions and potential ways to monitor the chronic stressors in T. albonubes culture environments.

Turning up the heat: immune brinksmanship in the acute-phase response

The acutephase response (APR) is a systemic response to severe trauma, infection, and cancer, although many of the numerous cytokine-mediated components of the APR are incompletely understood. Some of these components, such as fever, reduced availability of iron and zinc, and nutritional restriction due to anorexia, appear to be stressors capable of causing harm to both the pathogen and the host. We review how the host benefits from differences in susceptibility to stress between pathogens and the host. Pathogens, infected host cells, and neoplastic cells are generally more stressed or vulnerable to additional stress than the host because: (a) targeted local inflammation works in synergy with APR stressors; (b) proliferation/growth increases vulnerability to stress; (c) altered pathogen physiology results in pathogen stress or vulnerability; and (d) protective heat shock responses are partially abrogated in pathogens since their responses are utilized by the host to enhance immune responses. Therefore, the host utilizes a coordinated system of endogenous stressors to provide additional levels of defense against pathogens. This model of immune brinksmanship can explain the evolutionary basis for the mutually stressful components of the APR.

Effect of the diclazuril on Hsp90 in the second-generation merozoites of Eimeria tenella

Eimeria tenella (E. tenella) is one of the most virulent pathogens of coccidiosis. In apicomplexan parasites, Hsp90 (Heat shock protein 90) is essential for the invasion and survival in host cells. In this study, the effect of diclazuril, an effective benzeneacetonitrile anticoccidial agent, on the expression of Hsp90 in the second-generation merozoites of E. tenella was investigated. We inoculated 8 × 10(4) oocysts/chicken suspended in 1 ml of distilled water, and chickens were challenged with E. tenella oocysts and provided with normal feed as Control group; chickens challenged with E. tenella oocysts and provided with 1mg/kg diclazuril in feed from 96 h to 120 h after inoculation as treatment group. Then the second-generation merozoites were obtained after 120 h from the infected caeca. Our results showed that the transcription level of mzHsp90 was reduced by 29.7% in the diclazuril treatment group, accompanied by reduced level of mzHsp90 protein in second-generation merozoites prepared from infected chickens. We also found that the subcellular localization of mzHsp90 was more dispersed in these merozoites. Moreover, we demonstrated that the effects of diclazuril on mzHsp90 expression were direct by in vitro experiments. Taken together, our data provide insights into the molecular mechanisms of diclazuril in the chemotherapy of E. tenella, and suggest that mzHsp90 represents a promising target for the intervention with E. tenella infection.

Transcriptome analysis of avian pathogenic Escherichia coli O1 in chicken serum reveals adaptive responses to systemic infection

Infections of avian pathogenic Escherichia coli (APEC) result in annual multimillion-dollar losses to the poultry industry. Despite this, little is known about the mechanisms by which APEC survives and grows in the bloodstream. Thus, the aim of this study was to identify molecular mechanisms enabling APEC to survive and grow in this critical host environment. To do so, we compared the transcriptome of APEC O1 during growth in Luria-Bertani broth and chicken serum. Several categories of genes, predicted to contribute to adaptation and growth in the avian host, were identified. These included several known virulence genes and genes involved in adaptive metabolism, protein transport, biosynthesis pathways, stress resistance, and virulence regulation. Several genes with unknown function, which were localized to pathogenicity islands or APEC O1's large virulence plasmid, pAPEC-O1-ColBM, were also identified, suggesting that they too contribute to survival in serum. The significantly upregulated genes dnaK, dnaJ, phoP, and ybtA were subsequently subjected to mutational analysis to confirm their role in conferring a competitive advantage during infection. This genome-wide analysis provides novel insight into processes that are important to the pathogenesis of APEC O1.

Histoplasma capsulatum heat-shock 60 orchestrates the adaptation of the fungus to temperature stress

Heat shock proteins (Hsps) are among the most widely distributed and evolutionary conserved proteins. Hsps are essential regulators of diverse constitutive metabolic processes and are markedly upregulated during stress. A 62 kDa Hsp (Hsp60) of Histoplasma capsulatum (Hc) is an immunodominant antigen and the major surface ligand to CR3 receptors on macrophages. However little is known about the function of this protein within the fungus. We characterized Hc Hsp60-protein interactions under different temperature to gain insights of its additional functions oncell wall dynamism, heat stress and pathogenesis. We conducted co-immunoprecipitations with antibodies to Hc Hsp60 using cytoplasmic and cell wall extracts. Interacting proteins were identified by shotgun proteomics. For the cell wall, 84 common interactions were identified among the 3 growth conditions, including proteins involved in heat-shock response, sugar and amino acid/protein metabolism and cell signaling. Unique interactions were found at each temperature [30°C (81 proteins), 37°C (14) and 37/40°C (47)]. There were fewer unique interactions in cytoplasm [30°C (6), 37°C (25) and 37/40°C (39)] and four common interactions, including additional Hsps and other known virulence factors. These results show the complexity of Hsp60 function and provide insights into Hc biology, which may lead to new avenues for the management of histoplasmosis.

Investigations of transcript expression in fathead minnow (Pimephales promelas) brain tissue reveal toxicological impacts of RDX exposure

Production, usage and disposal of the munitions constituent (MC) cyclotrimethylenetrinitramine (RDX) has led to environmental releases on military facilities. The chemical attributes of RDX are conducive for leaching to surface water which may put aquatic organisms at risk of exposure. Because RDX has been observed to cause aberrant neuromuscular effects across a wide range of animal phyla, we assessed the effects of RDX on central nervous system (CNS) functions in the representative aquatic ecotoxicological model species, fathead minnow (Pimephales promelas). We developed a fathead minnow brain-tissue cDNA library enriched for transcripts differentially expressed in response to RDX and trinitrotoluene (TNT) exposure. All 4,128 cDNAs were sequenced, quality filtered and assembled yielding 2230 unique sequences and 945 significant blastx matches (E ≤10(-5)). The cDNA library was leveraged to create custom-spotted microarrays for use in transcript expression assays. The impact of RDX on transcript expression in brain tissue was examined in fathead minnows exposed to RDX at 0.625, 2.5, 5, 10mg/L or an acetone-spike control for 10 days. Overt toxicity of RDX in fathead minnow occurred only at the highest exposure concentration resulting in 50% mortality and weight loss. Conversely, Bayesian analysis of microarray data indicated significant changes in transcript expression at concentrations as low as 0.625 mg/L. In total, 154 cDNAs representing 44 unique transcripts were differentially expressed in RDX exposures, the majority of which were validated by reverse transcriptase-quantitative PCR (RT-qPCR). Investigation of molecular pathways, gene ontology (GO) and individual gene functions affected by RDX exposures indicated changes in metabolic processes involved in: oxygen transport, neurological function, calcium binding/signaling, energy metabolism, cell growth/division, oxidative stress and ubiquitination. In total, our study indicated that RDX exposure affected molecular processes critical to CNS function in fathead minnow.

DnaK and GroEL are induced in response to antibiotic and heat shock in Acinetobacter baumannii

We studied the expression of DnaK and GroEL in Acinetobacter baumannii cells (strains ATCC 19606 and RS4) under stress caused by heat shock or antibiotics. A Western blot assay showed that DnaK and GroEL levels increased transiently more than 2-fold after exposure of bacterial cells to heat shock for 20 min at 50 °C. Heat induction of DnaK and GroEL was blocked completely when an inhibitor of transcription, rifampicin, was added 1 min before a temperature upshift to 50 °C, suggesting that the induction of these chaperones depends on transcription. A. baumannii cells pretreated at 45 °C for 30 min were better able to survive at 50 °C for 60 min than cells pretreated at 37 °C, indicating that A. baumannii is able to acquire thermotolerance. DnaK and GroEL were successfully induced in cells pre-incubated with a subinhibitory concentration of streptomycin. Moreover, bacterial cells pretreated for 30 min at 45 °C were better able to survive streptomycin exposure than cells pretreated at physiological temperatures. DnaK expression was upregulated in a multidrug-resistant strain of A. baumannii (RS4) in the presence of different antimicrobials (ampicillin+sulbactam, cefepime, meropenem and sulphamethoxazole+trimethoprim). This study is to the best of our knowledge the first to show that A. baumannii DnaK and GroEL could play an important role in the stress response induced by antibiotics.

Putative cis-regulatory elements associated with heat shock genes activated during excystation of Cryptosporidium parvum

Background

Cryptosporidiosis is a ubiquitous infectious disease, caused by the protozoan parasites Cryptosporidium hominis and C. parvum, leading to acute, persistent and chronic diarrhea worldwide. Although the complications of this disease can be serious, even fatal, in immunocompromised patients of any age, they have also been found to lead to long term effects, including growth inhibition and impaired cognitive development, in infected immunocompetent children. The Cryptosporidium life cycle alternates between a dormant stage, the oocyst, and a highly replicative phase that includes both asexual vegetative stages as well as sexual stages, implying fine genetic regulatory mechanisms. The parasite is extremely difficult to study because it cannot be cultured in vitro and animal models are equally challenging. The recent publication of the genome sequence of C. hominis and C. parvum has, however, significantly advanced our understanding of the biology and pathogenesis of this parasite.

Methodology/Principal Findings

Herein, our goal was to identify cis-regulatory elements associated with heat shock response in Cryptosporidium using a combination of in silico and real time RT-PCR strategies. Analysis with Gibbs-Sampling algorithms of upstream non-translated regions of twelve genes annotated as heat shock proteins in the Cryptosporidium genome identified a highly conserved over-represented sequence motif in eleven of them. RT-PCR analyses, described herein and also by others, show that these eleven genes bearing the putative element are induced concurrent with excystation of parasite oocysts via heat shock.

Conclusions/Significance

Our analyses suggest that occurrences of a motif identified in the upstream regions of the Cryptosporidium heat shock genes represent parts of the transcriptional apparatus and function as stress response elements that activate expression of these genes during excystation, and possibly at other stages in the life cycle of the parasite. Since heat shock and excystation represent a critical step in the development of the infectious sporozoite form of Cryptosporidium, these results provide important insight into the pathogenicity of the parasite.

Molecular chaperones in pathogen virulence: emerging new targets for therapy

Infectious organisms have to cope with demanding and rapidly changing environments during establishment in the host. This is particularly relevant for pathogens that utilize different hosts to complete their life cycle. In addition to homeotic environmental challenges, other stressful factors, such as oxidative bursts, are often triggered in response to infection. It is not surprising that many successful pathogens have developed robust chaperone systems to conquer the stressful environments in the host. In addition to discussing ingenious ways by which pathogens have utilized chaperones, the potential of exploiting pathogen chaperones as drug targets is also discussed.

Exploration of the late stages of the tomato-Phytophthora parasitica interactions through histological analysis and generation of expressed sequence tags

The oomycete Phytophthora parasitica is a soilborne pathogen infecting numerous plants. The infection process includes an initial biotrophic stage, followed by a necrotrophic stage. The aim here was to identify genes that are involved in the late stages of infection. Using the host tomato and a transformed strain of P. parasitica expressing the green fluorescent protein (GFP), the various infection steps from recognition of the host to the colonization of plant tissues were studied. This late stage was selected to generate 4000 ESTs (expressed sequence tags), among which approx. 80% were from the pathogen. Comparison with an EST data set created previously from in vitro growth of P. parasitica allowed the identification of several genes, the expression of which might be regulated during late stages of infection. Changes in gene expression of several candidate genes predicted from in silico analysis were validated by quantitative RT-PCR experiments. These results give insights into the molecular bases of the necrotrophic stage of an oomycete pathogen.

Seasonality of infectious diseases

Seasonality, a periodic surge in disease incidence corresponding to seasons or other calendar periods, characterizes many infectious diseases of public health importance. The recognition of seasonal patterns in infectious disease occurrence dates back at least as far as the Hippocratic era, but mechanisms underlying seasonality of person-to-person transmitted diseases are not well understood. Improved understanding will enhance understanding of host-pathogen interactions and will improve the accuracy of public health surveillance and forecasting systems. Insight into seasonal disease patterns may be gained through the use of autocorrelation methods or construction of periodograms, while seasonal oscillation of infectious diseases can be easily simulated using simple transmission models. Models demonstrate that small seasonal changes in host or pathogen factors may be sufficient to create large seasonal surges in disease incidence, which may be important particularly in the context of global climate change. Seasonality represents a rich area for future research.

FourU: a novel type of RNA thermometer in Salmonella

The translation of many heat shock and virulence genes is controlled by RNA thermometers. Usually, they are located in the 5'-untranslated region (5'-UTR) and block the Shine-Dalgarno (SD) sequence by base pairing. Destabilization of the structure at elevated temperature permits ribosome binding and translation initiation. We have identified a new type of RNA thermometer in the 5'-UTR of the Salmonella agsA gene, which codes for a small heat shock protein. Transcription of the agsA gene is controlled by the alternative sigma factor sigma(32). Additional translational control depends on a stretch of four uridines that pair with the SD sequence. Mutations in this region affect translation in vivo. Structure probing experiments demonstrate a temperature-controlled opening of the SD region in vitro. Toeprinting (primer extension inhibition) shows that ribosome binding is dependent on high temperatures. Together with a postulated RNA thermometer upstream of the Yersinia pestis virulence gene lcrF (virF), the 5'-UTR of Salmonella agsA might be the founding member of a new class of RNA thermometers that we propose to name 'fourU' thermometers.

Genome-wide transcriptional analysis of temperature shift in L. interrogans serovar lai strain 56601

Background

Leptospira interrogans is an important mammalian pathogen. Transmission from an environmental source requires adaptation to a range of new environmental conditions in the organs and tissues of the infected host. Several studies have shown that a shift in culture temperature from 28°C to 37°C, similar to that encountered during infection of a host from an environmental source, is associated with differential synthesis of several proteins of the outer membrane, periplasm and cytoplasm. The whole genome of the Leptospira interrogans serogroup Icterohaemorrhagiae serovar lai type strain #56601 was sequenced in 2003 and microarrays were constructed to compare differential transcription of the whole genome at 37°C and 28°C.

Results

DNA microarray analyses were used to investigate the influence of temperature on global gene expression in L. interrogans grown to mid-exponential phase at 28°C and 37°C. Expression of 106 genes differed significantly at the two temperatures. The differentially expressed genes belonged to nine functional categories: Cell wall/membrane biogenesis genes, hemolysin genes, heat shock proteins genes, intracellular trafficking and secretion genes, two-component system and transcriptional regulator genes, information storage and processing genes, chemotaxis and flagellar genes, metabolism genes and genes with no known homologue. Real-time reverse transcription-PCR assays confirmed the microarray data.

Conclusion

Microarray analyses demonstrated that L. interrogans responds globally to temperature alteration. The data delineate the spectrum of temperature-regulated gene expression in an important human pathogen and provide many new insights into its pathogenesis.

Virulence factors of septicemic Escherichia coli strains

Extraintestinal pathogenic Escherichia coli strains (ExPEC) are the cause of a diverse spectrum of invasive human and animal infections, often leading to septicemia. This review deals with the virulence genes of septicemic ExPEC strains. We discuss the meaning of a virulence gene and survey the genomic, genetic and physiological studies on these strains. Apparently, there are a few virulence factors, which are conserved in the septicemic strains, implying that they are essential for the infection. For the other virulence-related genes a high level of diversity is observed, demonstrating that all stages of the infection can be mediated by a number of alternative virulence factors. The variable profile of virulence genes in septicemic E. coli strains, as well as a prevalence of mobility-related sequences point out the existence of a "mix and match" combinatorial system.

Characterization of the binding of diarrheagenic strains of E. coli to plant surfaces and the role of curli in the interaction of the bacteria with alfalfa sprouts

Diarrheagenic Escherichia coli were able to bind to plant surfaces, including alfalfa sprouts and open seed coats, and tomato and Arabidopsis thaliana seedlings incubated in water. The characteristics of the binding differed with the bacterial strain examined. Laboratory K12 strains of E. coli failed to show significant binding to any of the plant surfaces examined, suggesting that some of the genes present and expressed in pathogenic strains and absent or unexpressed in K12 strains may be required for binding to plants. When a plasmid carrying the mlrA gene (a positive regulator of curli biosynthesis) or a plasmid carrying the operons that encode the synthesis of curli (csgA-G) was introduced into K12 strains, the bacteria acquired the ability to bind to sprouts. CsgA mutants of an avian pathogenic E. coli and an O157:H7 strain showed no reduction in their ability to bind to sprouts. Thus, the production of curli appears to be sufficient to allow K12 strains to bind, but curli are not necessary for the binding of pathogenic strains, suggesting that pathogenic strains may have more than one mechanism for binding to plant surfaces.

Thermotolerance and virulence of Aspergillus fumigatus: role of the fungal nucleolus

The ability to thrive at 37 degrees C is characteristic of all human pathogens and has long been suspected to play a role in the pathogenesis of aspergillosis. As a thermotolerant fungus, Aspergillus fumigatus is capable of growth at temperatures that approach the upper limit for all eukaryotes, suggesting that the organism has evolved unique mechanisms of stress resistance that may be relevant to its ability to adapt to the stress of growth in the host. High temperature is a strain on many biological systems, particularly those involved in complex macromolecular assemblies such as ribosomes. This review will discuss the relationship between thermotolerance and virulence in pathogenic fungi, emphasizing the link to ribosome biogenesis in A. fumigatus. Future work in this area will help determine how rapid growth is accomplished at elevated temperature and may offer new avenues for the development of novel antifungals that disrupt thermotolerant ribosome assembly.

Transcriptome analysis of the Mg2+-responsive PhoP regulator inYersinia pestis

PhoP was previously shown to be important for Yersinia pestis survival in macrophage and under macrophage-induced stresses. In this work, a phoP disruptant of Y. pestis 201 was generated using the Red cloning procedure. The transcription profile of the wild-type Y. pestis was then compared with that of the phoP mutant under Mg2+-limiting conditions. It was revealed that PhoP/PhoQ governed a wide set of cellular pathways in Y. pestis, especially including the positive regulation of many metabolic processes, Mg2+ transport, peptidoglycan remodeling, lipopolysaccharide (LPS) modification and various stress-protective functions. The Mg2+ transport system regulated by PhoP may make Y. pestis to maintain the magnesium homeostasis under low Mg2+ environments. The PhoP-controlled stress-protective functions likely constitute the molecular basis for the observation that mutation of the phoP gene rendered the bacteria more sensitive to various macrophage-induced stresses. Modification of LPS mediated by PhoP is hypothesized to not only neutralize negative charges as normally done by Mg2+ ions, but also mediate the resistance of Y. pestis to antimicrobial peptides. The microarray results provide a population of candidate genes or pathways, and further biochemical experiments are needed to elucidate the PhoP-dependent mechanisms by which Y. pestis survives the antibacterial strategies employed by host macrophages.

The role of sigmaB in the stress response of Gram-positive bacteria -- targets for food preservation and safety

The alternative sigma factor sigmaB modulates the stress response of several Gram-positive bacteria, including Bacillus subtilis and the food-borne human pathogens Bacillus cereus, Listeria monocytogenes and Staphylococcus aureus. In all these bacteria, sigmaB is responsible for the transcription of genes that can confer stress resistance to the vegetative cell. Recent findings indicate that sigmaB also plays an important role in antibiotic resistance, pathogenesis and cellular differentiation processes such as biofilm formation and sporulation. Although there are important differences in the regulation of sigmaB and in the set of genes regulated by sigmaB in B. subtilis, B. cereus, L. monocytogenes and S. aureus, there are also some conserved themes. A mechanistic understanding of the sigmaB activation processes and assessment of its regulon could provide tools for pathogen control and inactivation both in the food industry and clinical settings.

Beyond transcription--new mechanisms for the regulation of molecular chaperones

Molecular chaperones are an essential part of the universal heat shock response that allows organisms to survive stress conditions that cause intracellular protein unfolding. During the past few years, two new mechanisms have been found to control the activity of several chaperones under stress conditions-the regulation of chaperone activity by the redox state and by the temperature of the environment. Hsp33, for example, is redox-regulated. Hsp33 is specifically activated by disulfide bond formation during oxidative stress, where it becomes a highly efficient chaperone holdase that binds tightly to unfolding proteins. Certain small heat shock proteins, such as Hsp26 and Hsp16.9, on the other hand, are temperature regulated. Exposure to heat shock temperatures causes these oligomeric proteins to disassemble, thereby changing them into highly efficient chaperones. The ATP-dependent chaperone folding system DnaK/DnaJ/GrpE also appears to be temperature regulated, switching from a folding to a holding mode during heat stress. Both of these novel post-translational regulatory strategies appear to have one ultimate goal: to significantly increase the substrate binding affinity of the affected chaperones under exactly those stress conditions that require their highest chaperone activity. This ensures that protein folding intermediates remain bound to the chaperones under stress conditions and are released only after the cells return to non-stress conditions.

Gene expression in Porphyromonas gingivalis after contact with human epithelial cells

Porphyromonas gingivalis, a gram-negative oral anaerobe, is strongly associated with adult periodontitis. The adherence of the organism to host epithelium signals changes in both cell types as bacteria initiate infection and colonization and epithelial cells rally their defenses. We hypothesized that the expression of a defined set of P. gingivalis genes would be consistently up-regulated during infection of HEp-2 human epithelial cells. P. gingivalis genome microarrays were used to compare the gene expression profiles of bacteria that adhered to HEp-2 cells and bacteria that were incubated alone. Genes whose expression was temporally up-regulated included those involved in the oxidative stress response and those encoding heat shock proteins that are essential to maintaining cell viability under adverse conditions. The results suggest that contact with epithelial cells induces in P. gingivalis stress-responsive pathways that promote the survival of the bacterium.

Comparative transcriptome analysis of Yersinia pestis in response to hyperosmotic and high-salinity stress

DNA microarray was used as a tool to investigate genome-wide transcriptional responses of Yersinia pestis to hyperosmotic and high-salinity stress. Hyperosmotic stress specifically upregulated genes responsible for ABC-type transport and the cytoplasmic accumulation of certain polysaccharides, while high-salinity stress induced the transcription of genes encoding partition proteins and several global transcriptional regulators. Genes whose transcription was enhanced by both kinds of stress comprised those encoding osmoprotectant transport systems and a set of virulence determinants. The number of genes downregulated by the two kinds of stress was much lower than that of upregulated genes, suggesting that neither kind of stress severely depresses cellular processes in general. Many differentially regulated genes still exist whose functions remain unknown. Y. pestis recognized high-salinity and hyperosmotic stress as different kinds of environmental stimuli, and different mechanisms enabled acclimation to these two kinds of stress, although Y. pestis still executed common mechanisms to accommodate both types of stress.

DNA microarray analysis of the heat- and cold-shock stimulons in Yersinia pestis

DNA microarray was used as a tool to define the heat- and cold-shock stimulons in Yersinia pestis. Heat shock dramatically enhanced the transcription of genes encoding major heat-shock proteins (MHSPs) that are important for cell survival against the heat. Many other genes were also greatly up-regulated, but their roles in heat-shock response need to be elucidated. Meanwhile, heat shock retarded most of the metabolic processes, i.e. RNA transcription, protein translation, aerobic respiration, energy metabolism, small molecule metabolism, peptidoglycan biosynthesis, sulfate uptake and cysteine biosynthesis. In response to cold shock, Y. pestis has evolved complex adaptive mechanisms by elevating the transcription of a specific set of genes whose protein products are designed to prevent or eliminate cold-induced DNA or RNA structuring, to remodel cell membrane components for maintenance of normal functions, to elevate the energy generation for ensuring ATP-dependent responses during cold adaptation and to synthesize or transport compatible solutes such as cryoprotectants, and at the same time, by repressing the mRNA level of certain genes whose protein products are not needed for bacterial growth at low temperatures, such as the MHSPs. These results provide a set of new candidate genes for hypothesis-based investigations of their roles in stress response, host adaptation and pathogenicity of this deadly pathogen.

Global gene expression profile of Yersinia pestis induced by streptomycin

Plague, caused by Y ersinia pestis, is one of the most dangerous diseases that impressed a horror onto human consciousness that persists to this day. Cases of plague can be normally controlled by timely antibiotic administration. Streptomycin is the first-line antibiotic for plague treatment. In this study, a DNA microarray was used to investigate the changes in the gene expression profile of Y. pestis upon exposure to streptomycin. A total of 345 genes were identified to be differentially regulated, 144 of which were up-regulated, and 201 down-regulated. Streptomycin-induced transcriptional changes occurred in genes responsible for heat shock response, drug/analogue sensitivity, biosynthesis of the branched-chain amino acids, chemotaxis and mobility and broad regulatory functions. A wide set of genes involved in energy metabolism, biosynthesis of small macromolecules, synthesis and modification of macromoclecules and degradation of small and macro molecules were among those down-regulated. The results reveal general changes in gene expression that are consistent with known mechanisms of action of streptomycin and many new genes that are likely to play important roles in the response to streptomycin treatment, providing useful candidates for investigating the specific mechanisms of streptomycin action.

Replicon-specific regulation of small heat shock genes in Agrobacterium tumefaciens

Four genes coding for small heat shock proteins (sHsps) were identified in the genome sequence of Agrobacterium tumefaciens, one on the circular chromosome (hspC), one on the linear chromosome (hspL), and two on the pAT plasmid (hspAT1 and hspAT2). Induction of sHsps at elevated temperatures was revealed by immunoblot analyses. Primer extension experiments and translational lacZ fusions demonstrated that expression of the pAT-derived genes and hspL is controlled by temperature in a regulon-specific manner. While the sHsp gene on the linear chromosome turned out to be regulated by RpoH (sigma32), both copies on pAT were under the control of highly conserved ROSE (named for repression of heat shock gene expression) sequences in their 5' untranslated region. Secondary structure predictions of the corresponding mRNA strongly suggest that it represses translation at low temperatures by masking the Shine-Dalgarno sequence. The hspC gene was barely expressed (if at all) and not temperature responsive.

Disruption of the Aspergillus fumigatus gene encoding nucleolar protein CgrA impairs thermotolerant growth and reduces virulence

Aspergillus fumigatus CgrA is the ortholog of a yeast nucleolar protein that functions in ribosome synthesis. To determine how CgrA contributes to the virulence of A. fumigatus, a Delta cgrA mutant was constructed by targeted gene disruption, and the mutant was reconstituted to wild type by homologous introduction of a functional cgrA gene. The Delta cgrA mutant had the same growth rate as the wild type at room temperature. However, when the cultures were incubated at 37 degrees C, a condition that increased the growth rate of the wild-type and reconstituted strains approximately threefold, the Delta cgrA mutant was unable to increase its growth rate. The absence of cgrA function caused a delay in both the onset and rate of germination at 37 degrees C but had little effect on germination at room temperature. The Delta cgrA mutant was significantly less virulent than the wild-type or reconstituted strain in immunosuppressed mice and was associated with smaller fungal colonies in lung tissue. However, this difference was less pronounced in a Drosophila infection model at 25 degrees C, which correlated with the comparable growth rates of the two strains at this temperature. To determine the intracellular localization of CgrA, the protein was tagged at the C terminus with green fluorescent protein, and costaining with propidium iodide revealed a predominantly nucleolar localization of the fusion protein in living hyphae. Together, these findings establish the intracellular localization of CgrA in A. fumigatus and demonstrate that cgrA is required for thermotolerant growth and wild-type virulence of the organism.