scholarly journals Roles of Alkyl Hydroperoxide Reductase Subunit C (AhpC) in Viable but Nonculturable Vibrio parahaemolyticus

2013 ◽  
Vol 79 (12) ◽  
pp. 3734-3743 ◽  
Author(s):  
Hen-Wei Wang ◽  
Chun-Hui Chung ◽  
Tsung-Yong Ma ◽  
Hin-chung Wong

ABSTRACTAlkyl hydroperoxide reductase subunit C (AhpC) is the catalytic subunit responsible for the detoxification of reactive oxygen species that form in bacterial cells or are derived from the host; thus, AhpC facilitates the survival of pathogenic bacteria under environmental stresses or during infection. This study investigates the role of AhpC in the induction and maintenance of a viable but nonculturable (VBNC) state inVibrio parahaemolyticus. In this investigation,ahpC1(VPA1683) andahpC2(VP0580) were identified in chromosomes II and I of this pathogen, respectively. Mutants with deletions of these twoahpCgenes and their complementary strains were constructed from the parent strain KX-V231. The growth of these strains was monitored on tryptic soy agar–3% NaCl in the presence of the extrinsic peroxides H2O2andtert-butyl hydroperoxide (t-BOOH) at different incubation temperatures. The results revealed that bothahpCgenes were protective againstt-BOOH, whileahpC1was protective against H2O2. The protective function ofahpC2at 4°C was higher than that ofahpC1. The times required to induce the VBNC state (4.7 weeks) at 4°C in a modified Morita mineral salt solution with 0.5% NaCl and then to maintain the VBNC state (4.7 weeks) in anahpC2mutant and anahpC1 ahpC2double mutant were significantly shorter than those for the parent strain (for induction, 6.2 weeks; for maintenance, 7.8 weeks) and theahpC1mutant (for induction, 6.0 weeks; for maintenance, 8.0 weeks) (P< 0.03). Complementation with anahpC2gene reversed the effects of theahpC2mutation in shortening the times for induction and maintenance of the VBNC state. This investigation identified the different functions of the twoahpCgenes and confirmed the particular role ofahpC2in the VBNC state ofV. parahaemolyticus.

1999 ◽  
Vol 181 (18) ◽  
pp. 5701-5710 ◽  
Author(s):  
Edson R. Rocha ◽  
C. Jeffrey Smith

ABSTRACT In this study we report the identification and role of the alkyl hydroperoxide reductase (ahp) gene in Bacteroides fragilis. The two components of ahp,ahpC, and ahpF, are organized in an operon, and the deduced amino acid sequences revealed that B. fragilisAhpCF shares approximately 60% identity to orthologues in other gram-positive and gram-negative bacteria. Northern blot hybridization analysis of total RNA showed that the ahpCF genes were transcribed as a polycistronic 2.4-kb mRNA and that ahpCalso was present as a 0.6-kb monocistronic mRNA. ahpC andahpCF mRNAs were induced approximately 60-fold following H2O2 treatment or oxygen exposure of the parent strain but were constitutive in a peroxide-resistant strain. Further investigation using an ahpCF′::β-xylosidase gene transcriptional fusion confirmed that ahpCF had lost normal regulation in the peroxide-resistant strain compared to the parent. The ahpCF mutant was more sensitive to growth inhibition and mutagenesis by organic peroxides than the parent strain, as determined by disk inhibition assays and the frequency of mutation to fusidic acid resistance. This finding suggests that theahp genes play an important role in peroxide resistance inB. fragilis. Under anaerobic conditions, we observed increases in the number of spontaneous fusidic acid-resistant mutants of five- and sevenfold in ahpCF and ahpF strain backgrounds, respectively, and eightfold in the ahpCF katBdouble mutant strain compared to the parent and katBstrains. In addition, ahpCF, ahpF, andahpCF katB mutants were slightly more sensitive to oxygen exposure than the parent strain. Moreover, the isolation of a strain with enhanced aerotolerance and high-level resistance to alkyl hydroperoxides from an ahpCF katB parent suggests that the physiological responses to peroxide toxicity and to the toxic effects of molecular oxygen are overlapping and complex in this obligate anaerobe.


2014 ◽  
Vol 80 (23) ◽  
pp. 7398-7404 ◽  
Author(s):  
Chun-Hui Chung ◽  
Tsung-yong Ma ◽  
Shin-yuan Fen ◽  
Hin-chung Wong

ABSTRACTAlkyl hydroperoxide reductase subunit C gene (ahpC) functions were characterized inVibrio parahaemolyticus, a commonly occurring marine food-borne enteropathogenic bacterium. TwoahpCgenes,ahpC1(VPA1683) andahpC2(VP0580), encoded putative two-cysteine peroxiredoxins, which are highly similar to the homologous proteins ofVibrio vulnificus. The responses of deletion mutants ofahpCgenes to various peroxides were compared with and without gene complementation and at different incubation temperatures. The growth of theahpC1mutant andahpC1 ahpC2double mutant in liquid medium was significantly inhibited by organic peroxides, cumene hydroperoxide andtert-butyl hydroperoxide. However, inhibition was higher at 12°C and 22°C than at 37°C. Inhibiting effects were prevented by the complementaryahpC1gene. Inconsistent detoxification of H2O2byahpCgenes was demonstrated in an agar medium but not in a liquid medium. Complementation with anahpC2gene partially restored the peroxidase effect in the doubleahpC1 ahpC2mutant at 22°C. This investigation reveals thatahpC1is the chief peroxidase gene that acts against organic peroxides inV. parahaemolyticusand that the function of theahpCgenes is influenced by incubation temperature.


2013 ◽  
Vol 79 (23) ◽  
pp. 7305-7312 ◽  
Author(s):  
Wei-cheng Hung ◽  
Wann-Neng Jane ◽  
Hin-chung Wong

ABSTRACTVibrio parahaemolyticusis a halophilic Gram-negative bacterium that causes human gastroenteritis. When the viable but nonculturable (VBNC) state of this bacterium was induced by incubation at 4°C in Morita minimal salt solution containing 0.5% NaCl, the rod-shaped cells became coccoid, and various aberrantly shaped intermediates were formed in the initial stage. This study examined the factors that influence the formation of these aberrantly shaped cells. The proportion of aberrantly shaped cells was not affected in a medium containingd-cycloserine (50 μg/ml) but was lower in a medium containing cephalosporin C (10 μg/ml) than in the control medium without antibiotics. The proportion of aberrantly shaped cells was higher in a culture medium that contained 0.5% NaCl than in culture media containing 1.0 or 1.5% NaCl. The expression of 15 of 17 selected genes associated with cell wall synthesis was enhanced, and the expression of VP2468 (dacB), which encodesd-alanyl-d-alanine carboxypeptidase, was enhanced the most. The proportion of aberrantly shaped cells was significantly lower in thedacBmutant strain than in the parent strain, but the proportion was restored in the presence of the complementarydacBgene. This study suggests that disturbance of the dynamics of cell wall synthesis by enhanced expression of the VP2468 gene is associated with the formation of aberrantly shaped cells in the initial stage of induction of VBNCV. parahaemolyticuscells under specific conditions.


2021 ◽  
Vol ahead-of-print (ahead-of-print) ◽  
Author(s):  
Deepika Swain ◽  
Lalatendu Kesari Jena ◽  
Sanket Sunand Dash ◽  
Rama Shankar Yadav

Purpose The purpose of this paper is to empirically exhibit the moderating effect of learner interaction (LI) on motivation to learn (MTL), mobile learning (ML) and online learning climate (OLC), so as to bring in enhanced rigour to the virtual knowledge dissemination during the times of crisis. Design/methodology/approach A total of 784 valid responses were considered for the confirmatory factor analysis to test the proposed hypotheses. Findings The study found that MTL and ML contributed to improved OLC and high LI moderated the positive relationship between MTL, ML and OLC. LI also directly contributed to an improved OLC. Practical implications Measures need to be designed to crowbar motivation to ensure heightened interaction of learners, to gear up the ML reach soaring heights achieving a dynamic OLC. Acclimatization of the OLC will be the visionary solution to tackle learning disruption during today’s pandemic times and also many other challenges to come in near-far future. Originality/value The current study established the moderating role of LI in influencing OLC, and also motivating facilitator’s for designing upgraded content, and thereby fuelling the intention to learn.


2011 ◽  
Vol 77 (23) ◽  
pp. 8295-8302 ◽  
Author(s):  
Laura-Dorina Dinu ◽  
Susan Bach

ABSTRACTEscherichia coliO157:H7 continues to be an important human pathogen and has been increasingly linked to food-borne illness associated with fresh produce, particularly leafy greens. The aim of this work was to investigate the fate ofE. coliO157:H7 on the phyllosphere of lettuce under low temperature and to evaluate the potential hazard of viable but nonculturable (VBNC) cells induced under such stressful conditions. First, we studied the survival of six bacterial strains following prolonged storage in water at low temperature (4°C) and selected two strains with different nonculturable responses for the construction ofE. coliO157:H7 Tn7gfptransformants in order to quantitatively assess the occurrence of human pathogens on the plant surface. Under a suboptimal growth temperature (16°C), bothE. coliO157:H7 strains maintained culturability on lettuce leaves, but under more stressful conditions (8°C), the bacterial populations evolved toward the VBNC state. The strain-dependent nonculturable response was more evident in the experiments with different inoculum doses (109and 106E. coliO157:H7 bacteria per g of leaf) when strain BRMSID 188 lost culturability after 15 days and strain ATCC 43895 lost culturability within 7 days, regardless of the inoculum dose. However, the number of cells entering the VBNC state in high-cell-density inoculum (approximately 55%) was lower than in low-cell-density inoculum (approximately 70%). We recorded the presence of verotoxin for 3 days in samples that contained a VBNC population of 4 to 5 log10cells but did not detect culturable cells. These findings indicate thatE. coliO157:H7 VBNC cells are induced on lettuce plants, and this may have implications regarding food safety.


mBio ◽  
2018 ◽  
Vol 9 (2) ◽  
pp. e00540-18 ◽  
Author(s):  
Callum J. Highmore ◽  
Jennifer C. Warner ◽  
Steve D. Rothwell ◽  
Sandra A. Wilks ◽  
C. William Keevil

ABSTRACTThe microbiological safety of fresh produce is monitored almost exclusively by culture-based detection methods. However, bacterial food-borne pathogens are known to enter a viable-but-nonculturable (VBNC) state in response to environmental stresses such as chlorine, which is commonly used for fresh produce decontamination. Here, complete VBNC induction of green fluorescent protein-taggedListeria monocytogenesandSalmonella entericaserovar Thompson was achieved by exposure to 12 and 3 ppm chlorine, respectively. The pathogens were subjected to chlorine washing following incubation on spinach leaves. Culture data revealed that total viableL. monocytogenesandSalmonellaThompson populations became VBNC by 50 and 100 ppm chlorine, respectively, while enumeration by direct viable counting found that chlorine caused a <1-log reduction in viability. The pathogenicity of chlorine-induced VBNCL. monocytogenesandSalmonellaThompson was assessed by usingCaenorhabditis elegans. Ingestion of VBNC pathogens byC. elegansresulted in a significant life span reduction (P= 0.0064 andP< 0.0001), and no significant difference between the life span reductions caused by the VBNC and culturableL. monocytogenestreatments was observed.L. monocytogeneswas visualized beyond the nematode intestinal lumen, indicating resuscitation and cell invasion. These data emphasize the risk that VBNC food-borne pathogens could pose to public health should they continue to go undetected.IMPORTANCEMany bacteria are known to enter a viable-but-nonculturable (VBNC) state in response to environmental stresses. VBNC cells cannot be detected by standard laboratory culture techniques, presenting a problem for the food industry, which uses these techniques to detect pathogen contaminants. This study found that chlorine, a sanitizer commonly used for fresh produce, induces a VBNC state in the food-borne pathogensListeria monocytogenesandSalmonella enterica. It was also found that chlorine is ineffective at killing total populations of the pathogens. A life span reduction was observed inCaenorhabditis elegansthat ingested these VBNC pathogens, with VBNCL. monocytogenesas infectious as its culturable counterpart. These data show that VBNC food-borne pathogens can both be generated and avoid detection by industrial practices while potentially retaining the ability to cause disease.


2017 ◽  
Vol 199 (14) ◽  
Author(s):  
Sujina Mali ◽  
Morgan Mitchell ◽  
Spencer Havis ◽  
Abiodun Bodunrin ◽  
Jonathan Rangel ◽  
...  

ABSTRACT Dormancy is a protective state in which diverse bacteria, including Mycobacterium tuberculosis, Staphylococcus aureus, Treponema pallidum (syphilis), and Borrelia burgdorferi (Lyme disease), curtail metabolic activity to survive external stresses, including antibiotics. Evidence suggests dormancy consists of a continuum of interrelated states, including viable but nonculturable (VBNC) and persistence states. VBNC and persistence contribute to antibiotic tolerance, reemergence from latent infections, and even quorum sensing and biofilm formation. Previous studies indicate that the protein mechanisms regulating persistence and VBNC states are not well understood. We have queried the VBNC state of Micrococcus luteus NCTC 2665 (MI-2665) by quantitative proteomics combining gel electrophoresis, high-performance liquid chromatography, and tandem mass spectrometry to elucidate some of these mechanisms. MI-2665 is a nonpathogenic actinobacterium containing a small (2.5-Mb), high-GC-content genome which exhibits a well-defined VBNC state induced by nutrient deprivation. The MI-2665 VBNC state demonstrated a loss of protein diversity accompanied by increased levels of 18 proteins that are conserved across actinobacteria, 14 of which have not been previously identified in VNBC. These proteins implicate an anaplerotic strategy in the transition to VBNC, including changes in the glyoxylate shunt, redox and amino acid metabolism, and ribosomal regulatory processes. Our data suggest that MI-2665 is a viable model for dissecting the protein mechanisms underlying the VBNC stress response and provide the first protein-level signature of this state. We expect that this protein signature will enable future studies deciphering the protein mechanisms of dormancy and identify novel therapeutic strategies effective against antibiotic-tolerant bacterial infections. IMPORTANCE Dormancy is a protective state enabling bacteria to survive antibiotics, starvation, and the immune system. Dormancy is comprised of different states, including persistent and viable but nonculturable (VBNC) states that contribute to the spread of bacterial infections. Therefore, it is imperative to identify how bacteria utilize these different dormancy states to survive antibiotic treatment. The objective of our research is to eliminate dormancy as a route to antibiotic tolerance by understanding the proteins that control dormancy in Micrococcus luteus NCTC 2665. This bacterium has unique advantages for studying dormancy, including a small genome and a well-defined and reproducible VBNC state. Our experiments implicate four previously identified and 14 novel proteins upregulated in VBNC that may regulate this critical survival mechanism.


FEBS Open Bio ◽  
2015 ◽  
Vol 5 (1) ◽  
pp. 124-131 ◽  
Author(s):  
Toshiaki Arai ◽  
Shinya Kimata ◽  
Daichi Mochizuki ◽  
Keita Hara ◽  
Tamotsu Zako ◽  
...  

2019 ◽  
Vol 201 (20) ◽  
Author(s):  
Takako Hirano ◽  
Manabu Okubo ◽  
Hironobu Tsuda ◽  
Masahiro Yokoyama ◽  
Wataru Hakamata ◽  
...  

ABSTRACT Vibrio parahaemolyticus RIMD2210633 secretes both chitinase and chitin oligosaccharide deacetylase and produces β-N-acetyl-d-glucosaminyl-(1,4)-d-glucosamine (GlcNAc-GlcN) from chitin. Previously, we reported that GlcNAc-GlcN induces chitinase production by several strains of Vibrio harboring chitin oligosaccharide deacetylase genes (T. Hirano, K. Kadokura, T. Ikegami, Y. Shigeta, et al., Glycobiology 19:1046–1053, 2009). The metabolism of chitin by Vibrio was speculated on the basis of the findings of previous studies, and the role of chitin oligosaccharide produced from chitin has been well studied. However, the role of GlcNAc-GlcN in the Vibrio chitin degradation system, with the exception of the above-mentioned function as an inducer of chitinase production, remains unclear. N,N′-Diacetylchitobiose, a homodisaccharide produced from chitin, is known to induce the expression of genes encoding several proteins involved in chitin metabolism in Vibrio strains (K. L. Meibom, X. B. Li, A. Nielsen, C. Wu, et al., Proc Natl Acad Sci U S A 101:2524–2529, 2004). We therefore hypothesized that GlcNAc-GlcN also affects the expression of enzymes involved in chitin metabolism in the same manner. In this study, we examined the induction of protein expression by several sugars released from chitin using peptide mass fingerprinting and confirmed the expression of genes encoding enzymes involved in chitin metabolism using real-time quantitative PCR analysis. We then confirmed that GlcNAc-GlcN induces the expression of genes encoding many soluble enzymes involved in chitin degradation in Vibrio parahaemolyticus. Here, we demonstrate that GlcNAc-GlcN enhances the chitin-metabolizing ability of V. parahaemolyticus. IMPORTANCE We demonstrate that β-N-acetyl-d-glucosaminyl-(1,4)-d-glucosamine (GlcNAc-GlcN) enhances the chitin-metabolizing ability of V. parahaemolyticus. Members of the genus Vibrio are chitin-degrading bacteria, and some species of this genus are associated with diseases affecting fish and animals, including humans (F. L. Thompson, T. Iida, and J. Swings, Microbiol Mol Biol Rev 68:403–431, 2004; M. Y. Ina-Salwany, N. Al-Saari, A. Mohamad, F.-A. Mursidi, et al., J Aquat Anim Health 31:3–22, 2019). Studies on Vibrio are considered important, as they may facilitate the development of solutions related to health, food, and aquaculture problems attributed to this genus. This report enhances the current understanding of chitin degradation by Vibrio bacteria.


2019 ◽  
Vol 86 (5) ◽  
Author(s):  
Xinyu Liao ◽  
Donghong Liu ◽  
Tian Ding

ABSTRACT As a novel nonthermal technology, nonthermal plasma (NTP) has attracted a lot of attention. However, it could induce microorganisms into a viable but nonculturable (VBNC) state, posing a potential risk to food safety and public health. In this study, the molecular mechanisms of VBNC Staphylococcus aureus induced by NTP were investigated. With the use of a propidium monoazide quantitative PCR (PMA-qPCR) technique combined with a plate count method, we confirmed that 8.1 to 24.3 kJ NTP induced S. aureus into a VBNC state at a level of 7.4 to 7.6 log10 CFU/ml. The transcriptomic analysis was conducted and revealed that most energy-dependent physiological activities (e.g., metabolism) were arrested in VBNC S. aureus, while the oxidative stress response-related genes (katA, dps, msrB, msrA, and trxA) were significantly upregulated. In addition, this study showed that the ATP depletion by carbonyl cyanide m-chlorophenyl hydrazone (CCCP) pretreatment could accelerate the formation of VBNC S. aureus. The NTP-generated oxidative stress triggers the staphylococcal oxidative stress response, which consumes part of cellular energy (e.g., ATP). The energy allocation is therefore changed, and the energy assigned for other energy-dependent physiological activities (cell growth and division, etc.) is reduced, subsequently forcing S. aureus into a VBNC state. Therefore, the alterations of energy allocation should be some of the major contributors to the induction of VBNC S. aureus with NTP exposure. This study provides valuable knowledge for controlling the formation of VBNC S. aureus during NTP treatment. IMPORTANCE In recent years, nonthermal plasma (NTP) technology has received a lot of attention as a promising alternative to thermal pasteurization in the food industry. However, little is known about the microbial stress response toward NTP, which could be a potential risk to food safety and impede the development of NTP. A viable but nonculturable (VBNC) state is one of the most common survival strategies employed by microorganisms against external stress. This study investigated the mechanisms of the formation of VBNC Staphylococcus aureus by NTP in a more comprehensive and systematic aspect than had been done before. Our work confirmed that the NTP-generated oxidative stress induced changes in energy allocation as a driving force for the formation of VBNC S. aureus. This study could provide better knowledge for controlling the occurrence of VBNC S. aureus induced by NTP, which could lead to more rational design and ensure the development of safe foods.


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