Effects of environmental stresses on the activities of the uspA, grpE and rpoS promoters of Escherichia coli O157:H7

The potential of white-rot fungi for algal control: Mechanisms, Strategies, and Challenges

As human society and industrialization have progressed, harmful algal blooms have contributed to global ecological pollution which makes the development of a novel and effective algal control strategy imminent. This is because existing physical and chemical methods for dealing with the problem have issues like cost and secondary pollution. Benefiting from their environmentally friendly and biocompatible properties, white-rot fungi (WRF) have been studied to control algal growth. WRF control algae by using algae for carbon or nitrogen, antagonism, and enhancing allelopathies. It can be better applied to practice by immobilization. This paper reviews the mechanism for WRF control of algae growth and its practical application. It demonstrates the limitations of WRF controlling algae growth and aids the further study of biological methods to regulate eutrophic water in algae growth research. In addition, it provides theoretical support for the fungi controlling algae growth.

Algicidal Molecular Mechanism and Toxicological Degradation of Microcystis aeruginosa by White-Rot Fungi

Current research on the inhibition of Microcystis aeruginosa growth is primarily focused on algae-lysing bacteria, and few studies have investigated the inhibitory mechanisms by which fungi affect it at the molecular level. A comparative analysis of the effects of Phanerochaete chrysosporium on the expression of the algal cell antioxidant protease synthesis gene prx, the biological macromolecule damage and repair genes recA, grpE, and fabZ, and the photosynthesis system-related genes psaB, psbD1 and rbcL, as well as genes for algal toxin synthesis mcyB, were performed to elucidate the molecular mechanism of Phanerochaete chrysosporium against Microcystis aeruginosa cells. RT-qPCR technology was used to study the molecular mechanism of algal cell inhibition by Phanerochaete chrysosporium liquid containing metabolites of Phanerochaete chrysosporium, Phanerochaete chrysosporium supernatant and Phanerochaete chrysosporium inactivated via high temperature sterilization at the gene expression level. Compared with the control, the chlorophyll-a contents dropped, and the recA, grpE, fabZ, and prx increased, but the psaB, psbD1, rbcL and mcyB showed that they were significantly reduced, which indicated that Phanerochaete chrysosporium can not only effectively destroy algal cells, but they may also reduce the expression of the Microcystis aeruginosa toxin gene and significantly block the metabolic system underlying the growth of algal cells and the synthesis of microcystins.

Effect of Hyperosmotic Salt Concentration and Temperature on Viability of Escherichia coli during Cold Storage

Escherichia coli cells were suspended in phosphate-buffered saline solutions (pH 7.4) at physiological (0.9 %) and hyperosmotic (3.5, 5.0, and 10.0 %) concentrations of sodium chloride (NaCl) and stored at 5, 10, 15, 20, and 25 °C up to 48 d. During storage at 5 and 10 °C, viable cell counts decreased approximately from 9 log CFU/ml to 6-7 log CFU/ml, and NaCl showed slight protective effect on the decrease. When stored at 15, 20, and 25 °C, the counts decreased with increases in NaCl concentration and/or storage temperature. The cells in 10.0 % NaCl suspension became nondetectable after storage at 25 °C for 28 d. Under some storage conditions (NaCl ≤ 5 %, 20 and 25 °C), the counts approached constant values, indicating possible adaptation to NaCl. Injured cells were observed at 5.0 and 10.0 % NaCl. However, recovery was observed only at 5.0 % NaCl during storage at 20 °C. In addition, more cells were detected on nonselective medium when incubated at 37 °C than at 25 °C. Higher hyperosmotic NaCl solutions at higher storage temperatures reduced more viable cells of E. coli.

Universal stress proteins contribute Edwardsiella piscicida adversity resistance and pathogenicity and promote blocking host immune response

Universal stress proteins (Usps) exist ubiquitously in bacteria and other organisms. Usps play an important role in adaptation of bacteria to a variety of environmental stresses. There is increasing evidence that Usps facilitate pathogens to adapt host environment and are involved in pathogenicity. Edwardsiella piscicida (formerly included in E. tarda) is a severe fish pathogen and infects various important economic fish including tilapia (Oreochromis niloticus). In E. piscicida, a number of systems and factors that are involved in stress resistance and pathogenesis were identified. However, the function of Usps in E. piscicida is totally unknown. In this study, we examined the expressions of 13 usp genes in E. piscicida and found that most of these usp genes were up-regulated expression under high temperature, oxidative stress, acid stress, and host serum stress. Particularly, among these usp genes, usp13, exhibited dramatically high expression level upon several stress conditions. To investigate the biological role of usp13, a markerless usp13 in-frame mutant strain, TX01Δusp13, was constructed. Compared to the wild type TX01, TX01Δusp13 exhibited markedly compromised tolerance to high temperature, hydrogen peroxide, and low pH. Deletion of usp13 significantly retarded bacterial biofilm growth and decreased resistance against serum killing. Pathogenicity analysis showed that the inactivation of usp13 significantly impaired the ability of E. piscicida to invade into host cell and infect host tissue. Introduction of a trans-expressed usp13 gene restored the lost virulence of TX01Δusp13. In support of these results, host immune response induced by TX01 and TX01Δusp13 was examined, and the results showed reactive oxygen species (ROS) levels in TX01Δusp13-infected macrophages were significantly higher than those in TX01-infected cells. The expression level of several cytokines (IL-6, IL-8, IL-10, TNF-α, and CC2) in TX01Δusp13-infected fish was significantly higher than that in TX01-infected fish. These results suggested that the deletion of usp13 attenuated the ability of bacteria to overcome the host immune response to pathogen infection. Taken together, our study indicated Usp13 of E. piscicida was not only important participant in adversity resistance, but also was essential for E. piscicida pathogenicity and contributed to block host immune response to pathogen infection.

Assembly and Characterization of a Pathogen Strain Collection for Produce Safety Applications: Pre-growth Conditions Have a Larger Effect on Peroxyacetic Acid Tolerance Than Strain Diversity

Effective control of foodborne pathogens on produce requires science-based validation of interventions and control strategies, which typically involves challenge studies with a set of bacterial strains representing the target pathogens or appropriate surrogates. In order to facilitate these types of studies, a produce-relevant strain collection was assembled to represent strains from produce outbreaks or pre-harvest environments, including Listeria monocytogenes (n = 11), Salmonella enterica (n = 23), shiga-toxin producing Escherichia coli (STEC) (n = 13), and possible surrogate organisms (n = 8); all strains were characterized by whole genome sequencing (WGS). Strain diversity was assured by including the 10 most common S. enterica serotypes, L. monocytogenes lineages I-IV, and E. coli O157 as well as selected "non-O157" STEC serotypes. As it has previously been shown that strains and genetic lineages of a pathogen may differ in their ability to survive different stress conditions, a subset of representative strains for each "pathogen group" (e.g., Salmonella, STEC) was selected and assessed for survival of exposure to peroxyacetic acid (PAA) using strains pre-grown under different conditions including (i) low pH, (ii) high salt, (iii) reduced water activity, (iv) different growth phases, (v) minimal medium, and (vi) different temperatures (21°C, 37°C). The results showed that across the three pathogen groups pre-growth conditions had a larger effect on bacterial reduction after PAA exposure as compared to strain diversity. Interestingly, bacteria exposed to salt stress (4.5% NaCl) consistently showed the least reduction after exposure to PAA; however, for STEC, strains pre-grown at 21°C were as tolerant to PAA exposure as strains pre-grown under salt stress. Overall, our data suggests that challenge studies conducted with multi-strain cocktails (pre-grown under a single specific condition) may not necessarily reflect the relevant phenotypic range needed to appropriately assess different intervention strategies.

Vibrio vulnificus RtxA1 Toxin Expression Upon Contact With Host Cells Is RpoS-Dependent

The expression of virulence genes in bacteria is known to be regulated by various environmental and host factors. Vibrio vulnificus, an estuarine bacterium, experiences a dramatic environmental change during its infection process. We reported that V. vulnificus RtxA1 toxin caused acute cell death only when close contact to host cells was allowed. A sigma factor RpoS is a very important regulator for the maximal survival of pathogens under stress conditions. Here, we studied the role of RpoS in V. vulnificus cytotoxicity and mouse lethality. The growth of rpoS mutant strain was comparable to that of wild-type in heart infusion (HI) media and DMEM with HeLa cell lysate. An rpoS mutation resulted in decreased cytotoxicity, which was restored by in trans complementation. Interestingly, host contact increased the expression and secretion of V. vulnificus RtxA1 toxin, which was decreased and delayed by the rpoS mutation. Transcription of the cytotoxic gene rtxA1 and its transporter rtxB1 was significantly increased after host factor contact, whereas the activity was decreased by the rpoS mutation. In contrast, the rpoS mutation showed no effect on the transcriptional activity of a cytolytic heamolysin gene (vvhA). Additionally, the LD₅₀ of the rpoS mutant was 15-fold higher than that of the wild-type in specific pathogen-free CD-1 female mice. Taken together, these results show that RpoS regulates the expression of V. vulnificus RtxA1 toxin and its transporter upon host contact.

Twenty-Five Years of Investigating the Universal Stress Protein: Function, Structure, and Applications

Since the initial discovery of universal stress protein A (UspA) 25 years ago, remarkable advances in molecular and biochemical technologies have revolutionized our understanding of biology. Many studies using these technologies have focused on characterization of the uspA gene and Usp-type proteins. These studies have identified the conservation of Usp-like proteins across bacteria, archaea, plants, and even some invertebrate animals. Regulation of these proteins under diverse stresses has been associated with different stress-response genes including spoT and relA in the stringent response and the dosR two-component signaling pathways. These and other foundational studies suggest Usps serve regulatory and protective roles to enable adaptation and survival under external stresses. Despite these foundational studies, many bacterial species have multiple paralogs of genes encoding these proteins and ablation of the genes does not provide a distinct phenotype. This outcome has limited our understanding of the biochemical functions of these proteins. Here, we summarize the current knowledge of Usps in general and UspA in particular across different genera as well as conclusions about their functions from seminal studies in diverse organisms. Our objective has been to organize the foundational studies in this field to identify the significant impediments to further understanding of Usp functions at the molecular level. We propose ideas and experimental approaches that may overcome these impediments and drive future development of molecular approaches to understand and target Usps as central regulators of stress adaptation and survival. Despite the fact that the full functions of Usps are still not known, creative many applications have already been proposed, tested, and used. The complementary approaches of basic research and applications, along with new technology and analytic tools, may yield the elusive yet critical functions of universal stress proteins in diverse systems.

Iron-dependent reconfiguration of the proteome underlies the intracellular lifestyle of Brucella abortus

Brucella ssp. is a facultative intracellular pathogen that causes brucellosis, a worldwide zoonosis that affects a wide range of mammals including humans. A critical step for the establishment of a successful Brucella infection is its ability to survive within macrophages. To further understand the mechanisms that Brucella utilizes to adapt to an intracellular lifestyle, a differential proteomic study was performed for the identification of intracellular modulated proteins. Our results demonstrated that at 48 hours post-infection Brucella adjusts its metabolism in order to survive intracellularly by modulating central carbon metabolism. Remarkably, low iron concentration is likely the dominant trigger for reprogramming the protein expression profile. Up-regulation of proteins dedicated to reduce the concentration of reactive oxygen species, protein chaperones that prevent misfolding of proteins, and proteases that degrade toxic protein aggregates, suggest that Brucella protects itself from damage likely due to oxidative burst. This proteomic analysis of B. abortus provides novel insights into the mechanisms utilized by Brucella to establish an intracellular persistent infection and will aid in the development of new control strategies and novel targets for antimicrobial therapy.

Microbial spoilage, quality and safety within the context of meat sustainability

Meat is a nutrient-dense food that provides ideal conditions for microbes to grow and defines its perishable nature. Some organisms simply spoil it while others are a threat to our health. In either case, meat must be discarded from the food chain and, being wasted and consequently an environmental burden. Worldwide, more than 20% of the meat produced is either lost or wasted. Hence, coordinated efforts from farm to table are required to improve microbial control as part of our effort towards global sustainability. Also, new antimicrobial systems and technologies arise to better fulfill consumer trends and demands, new lifestyles and markets, but for them to be used to their full extent, it is imperative to understand how they work at the molecular level. Undetected survivors, either as injured, dormant, persister or viable but non-culturable (VBNC) cells, undermine proper risk evaluation and management.

The response of foodborne pathogens to osmotic and desiccation stresses in the food chain

In combination with other strategies, hyperosmolarity and desiccation are frequently used by the food processing industry as a means to prevent bacterial proliferation, and particularly that of foodborne pathogens, in food products. However, it is increasingly observed that bacteria, including human pathogens, encode mechanisms to survive and withstand these stresses. This review provides an overview of the mechanisms employed by Salmonella spp., Shiga toxin producing E. coli, Cronobacter spp., Listeria monocytogenes and Campylobacter spp. to tolerate osmotic and desiccation stresses and identifies gaps in knowledge which need to be addressed to ensure the safety of low water activity and desiccated food products.

Legionella pneumophila transcriptional response to chlorine treatment

Legionella pneumophila is a ubiquitous environmental microorganism found in freshwater that can cause an acute form of pneumonia known as Legionnaires' disease. Despite widespread use of chlorine to ensure drinking water quality and awareness that L. pneumophila may escape these treatments, little is known about its effects on L. pneumophila. The aim of this study was to investigate the L. pneumophila transcriptional response induced by chlorine treatment. Transcriptome analysis, using DNA arrays, showed that a sublethal dose of chlorine induces a differential expression of 391 genes involved in stress response, virulence, general metabolism, information pathways and transport. Many of the stress response genes were significantly upregulated, whereas a significant number of virulence genes were repressed. In particular, exposure of L. pneumophila to chlorine induced the expression of cellular antioxidant proteins, stress proteins and transcriptional regulators. In addition, glutathione S-transferase specific activity was enhanced following chlorine treatment. Our results clearly indicate that chlorine induces expression of proteins involved in cellular defence mechanisms against oxidative stress that might be involved in adaptation or resistance to chlorine treatment.

Green fluorescent protein-based biosensor to detect and quantify stress responses induced by DNA-degrading colicins

Here we report the development of a whole-cell biosensor to detect and quantify the induction of the SOS response activated by DNA-degrading colicins. This biosensor utilizes the SOS-responsive cda promoter to regulate the expression of green fluorescent protein. The biosensor assay revealed induction of stress for all DNA-degrading reference colicins (E2, E7, and E8).

Regulation of nleA in Shiga toxin-producing Escherichia coli O84:H4 strain 4795/97

Many Shiga toxin-producing Escherichia coli (STEC) strains express a type III secretion system (TTSS) encoded by the locus of enterocyte effacement (LEE). Using the TTSS, STEC is able to inject effector proteins directly into eukaryotic host cells, where they cause characteristic attaching and effacing (A/E) lesions. In addition to the LEE-encoded effectors, a number of non-LEE-encoded effectors, located on phage-associated elements, have been described. One of them, the non-LEE-encoded effector A (NleA), is widely distributed among pathogenic E. coli. In this study, we investigated the influence of environmental conditions on the expression of the phage-encoded effector nleA gene (designated nleA(4795)) present in STEC O84:H4 strain 4795/97. We demonstrated that a particular NaCl concentration and starvation stress increase the activity of the nleA(4795) promoter. Moreover, several regulators that control nleA(4795) expression were identified. The involvement of the LEE regulators Ler, GrlA, and GrlR show that nleA(4795) is integrated in the LEE regulation circuit. Furthermore, the binding of Ler to sequences upstream of nleA(4795) underlined these findings.

Adaptation of Vibrio vulnificus and an rpoS mutant to bile salts

Vibrio vulnificus is an opportunistic pathogen commonly found in oyster and marine environments, which frequently encounters different stresses in its natural habitat, food processing environment and during infection. In this paper, the adaptation of V. vulnificus to bile and the role of RpoS in this process were examined using a wild-type strain and an rpoS isogenic mutant. Adaptation to bile was readily induced in the exponential phase cells in phosphate-buffered saline with 2% bile salts, and the adapted cells exhibited enhanced tolerance against 10% bile. Addition of 1% Brain Heart Infusion medium to the adaptation medium significantly increased the survival of V. vulnificus against bile. The bile-adapted cells were cross-protected against alkaline treatment but sensitized against acid, heat, high salinity and detergents (sodium dodecyl sulfate, Triton X-100, 3-[(3-cholamidopropyl) dimethylammonio]- 1- propanesulfonate, and cetylpyridinium bromide). Addition of efflux pump inhibitor (carbonyl cyanide m-chlorophenylhydrazone) or protein synthesis inhibitor (chloramphenicol) completely eliminated or down-graded the enhanced bile tolerance of the adapted cells, respectively. Production of GroEL was not markedly influenced but DnaK was inhibited in the bile-adapted cells. The bile-adapted parent strain exhibited significantly higher survival than the rpoS mutant against the challenge of high pH, heat, high salinity and detergents. The induction of bile-adaptation in the rpoS mutant occurred at a significantly slower rate than for the parent strain. Results indicate that RpoS plays a significant role in the response of V. vulnificus to bile.

Role of RpoS in the susceptibility of low salinity-adapted Vibrio vulnificus to environmental stresses

Vibrio vulnificus is an opportunistic pathogen commonly found in oyster and marine environments, which frequently encounters low salinity stress in its natural and food processing environment. In this study, the responses of a V. vulnificus wild-type strain C78140o and its rpoS isogenic mutant AH1 to sublethal low salinity were examined to investigate the role of rpoS in this response. Both strains, adapted in low salinity (0.4% NaCl), were protected against the lethal low salinity (0.1% NaCl), but were not protected against heat (45 degrees C) or acid stress (pH 3.5), and were sensitized against 5% bile. Protection of the adapted cells against the lethal low salinity was not inhibited by the addition of chloramphenicol. Hemolysis was detected only in the adapted C78140o cells and its spent medium, and was inhibited by chloramphenicol. Transcription of the mechanosensitive channels (VVl_1542 and VVl_2579) and an aquaporin gene (VVl_2010) was markedly increased in the wild-type cells adapted in low salinity medium, while transcription of these genes was slightly enhanced or inhibited in AH1 cells. Results of this study support the active role of rpoS in the low salinity adaptation of V. vulnificus by regulating the expression of virulence and low salinity-associated factors, although rpoS is not related to the immediate protection of the adapted cells against lethal low salinity.

Allelopathic mechanism of pyrogallol to Microcystis aeruginosa PCC7806 (Cyanobacteria): from views of gene expression and antioxidant system

Pyrogallol is a potent allelochemical on Microcystis aeruginosa, but its allelopathic mechanism is not fully known. In order to explore this mechanism, gene expressions for prx, mcyB, psbA, recA, grpE, fabZ under pyrogallol stress were studied, and activities of the main antioxidant enzymes were also measured. The results showed that expression of grpE and recA showed no significant change under pyrogallol stress, while psbA and mcyB were up-regulated at 4 mg L(-1). Both prx and fabZ were up-regulated even under exposure to 1 mg L(-1) pyrogallol concentration. The activities of superoxide dismutase (SOD) and catalase (CAT) were enhanced under pyrogallol stress. Levels of malodialdehyde (MDA) at 2 and 4 mg L(-1) pyrogallol were significantly higher than those of the controls. It was concluded that oxidant damage is an important mechanism for the allelopathic effect of pyrogallol on M. aeruginosa.

Examination of stress and virulence gene expression in Escherichia coli O157:H7 using targeted microarray analysis

Escherichia coli O157:H7 poses a threat to humans through food- and water-borne transmission. To investigate how environmental stresses affect the Escherichia coli O157:H7 transcriptome, we designed a targeted microarray consisting of stress response and virulence genes (n = 125) to analyze the impact of acidified (pH 3.5), cold (7.5 degrees C), and fresh tryptic soy broth (TSB) (37 degrees C) on E. coli O157:H7 stress response and virulence gene expression. Nutrient replenishment with fresh TSB resulted in 72 differentially expressed genes (> or = 1.5-fold change; p < 0.05), with 65 induced. All queried global and specific stress regulators were affected, as were 12 virulence genes. Cold-shocked cells displayed 17 differentially expressed genes, with 10 being induced. Induction of rpoS, members of the sigma(H) regulon (clpB, dnaK, ftsH), and acid resistance (AR) genes (gadA, gadX) was observed. Porin transcript (ompC, ompF) and gapA and tufA ancillary genes were repressed. Acid shock resulted in 24 differentially expressed genes, with 21 induced. No induction of any stationary phase AR system was observed, though acid-coping mechanisms were recruited, including mar and phoB induction, and repression of ompC and ompF. Stress regulators were induced, including relA, soxS, rpoE, and rpoH. The microarray data were validated by quantitative real-time polymerase chain reaction. Exposure to sublethal stress events led to the induction of diverse stress response networks. In the food chain, sublethal events may render cells increasingly resistant to future stresses, potentially leading to increased survival.

Behavior of Escherichia coli O157:H7 in leafy vegetables

Leafy vegetables, including lettuce and spinach, have been implicated in several outbreaks of foodborne disease caused by Escherichia coli O157:H7, a pathogen of increasing public health significance because of the severity of the gastrointestinal illness and long-term, chronic sequelae that can result from infection. A definitive association between the consumption of leafy vegetables and human disease provides implicit evidence of transfer from animal sources to field crops and retail commodities, including minimally processed or fresh-cut products. Understanding the behavior of E. coli O157:H7 in leafy vegetables during production, after harvest, in storage, during processing, and in packaged fresh-cut products is essential for the development of effective control measures. To this end, previous research on the fate of the species at each step in the production of market-ready leafy vegetables is reviewed in this study. Several critical gaps in knowledge are identified, notably uncertainty about the location of contaminating cells on or in plant tissues, behavior in packaged products stored at low temperatures, and the influence of environmental stresses on growth and infectivity.

Alternative sigma factors and their roles in bacterial virulence

Sigma factors provide promoter recognition specificity to RNA polymerase holoenzyme, contribute to DNA strand separation, and then dissociate from the core enzyme following transcription initiation. As the regulon of a single sigma factor can be composed of hundreds of genes, sigma factors can provide effective mechanisms for simultaneously regulating expression of large numbers of prokaryotic genes. One newly emerging field is identification of the specific roles of alternative sigma factors in regulating expression of virulence genes and virulence-associated genes in bacterial pathogens. Virulence genes encode proteins whose functions are essential for the bacterium to effectively establish an infection in a host organism. In contrast, virulence-associated genes can contribute to bacterial survival in the environment and therefore may enhance the capacity of the bacterium to spread to new individuals or to survive passage through a host organism. As alternative sigma factors have been shown to regulate expression of both virulence and virulence-associated genes, these proteins can contribute both directly and indirectly to bacterial virulence. Sigma factors are classified into two structurally unrelated families, the sigma70 and the sigma54 families. The sigma70 family includes primary sigma factors (e.g., Bacillus subtilis sigma(A)) as well as related alternative sigma factors; sigma54 forms a distinct subfamily of sigma factors referred to as sigma(N) in almost all species for which these proteins have been characterized to date. We present several examples of alternative sigma factors that have been shown to contribute to virulence in at least one organism. For each sigma factor, when applicable, examples are drawn from multiple species.

Growth history influences starvation-induced expression of uspA, grpE, and rpoS and subsequent cryotolerance in Escherichia coli O157:H7

In this study, we investigated the effect of starvation on cryotolerance of Escherichia coli O157:H7 grown in tryptic soy broth (TSB) and Luria-Bertani broth (LB). Starved cells (cells suspended in water at 37 degrees C for 6 h) and control cells (cells in TSB or LB) were frozen at -18 degrees C for up to 240 h in their respective growth media. The E. coli grown in TSB showed a greater starvation effect (the difference in percent survival of starved and control cells) and cryotolerance. The starved E. coli grown in TSB showed a 30% increase in their ability to survive frozen storage for 24 h at -18 degrees C. The corresponding increase in survival for LB-grown E. coli was only 3.8%. Cryotolerance induced by starvation of TSB- and LB-grown E. coli was correlated with the expression of genes involved in general stress response pathways, such as uspA, grpE, and rpoS. The expression of uspA, grpE, and rpoS was quantified by measuring the green fluorescence generated from autofluorescent E. coli harboring puspA::gfp, pgrpE::gfp, and prpoS::gfp gene fusions. The results obtained in this study indicate that uspA, grpE, and rpoS were induced on starvation when E. coli was grown in TSB, and their expression correlated well with subsequent induction of cryotolerance developed at -18 degrees C. In contrast, cells grown in LB and subsequently exposed to starvation conditions showed no increase in expression of uspA, grpE, or rpoS, and, as expected, these cells did not exhibit increased cryotolerance at -18 degrees C. Knowledge of molecular mechanisms involved in cross-protection might make it possible to devise strategies to limit their effects and lead to ways to predict the survival of foodborne pathogens in stressful environments.