Gene expression profile of Vibrio cholerae in the cold stress‐induced viable but non‐culturable state

bVibrio parahaemolyticus is 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 containing D-cycloserine (50 g/ml) but was lower in a medium containing cephalosporin C (10 g/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 encodes D-alanyl-D-alanine carboxypeptidase, was enhanced the most. The proportion of aberrantly shaped cells was significantly lower in the dacB mutant strain than in the parent strain, but the proportion was restored in the presence of the complementary dacB gene. 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 VBNC V. parahaemolyticus cells under specific conditions.

Section: Resultsmentioning

confidence: 87%

Association of a d -Alanyl- d -Alanine Carboxypeptidase Gene with the Formation of Aberrantly Shaped Cells during the Induction of Viable but Nonculturable Vibrio parahaemolyticus

Hung

Jane

Wong

2013

“…Thus, the VBNC state of pathogenic vibrios remains a consistent threat to public health. A microarray was utilized to analyze a total of 3,707 genes of V. cholerae; 100 genes were found to be expressed in the VBNC state, and the distribution of genes among the various functional groups in the VBNC state was similar to that obtained for stationary-phase cells, suggesting that VBNC bacteria may retain the functions that are essential for viability (33). The metabolic activities of VBNC bacteria generate endogenous ROS, which damage the cell (34) and may cause a loss of culturability and viability, especially in cells with weakened antioxidative activity, whereas the sodC gene (VC1583) was the only antioxidative gene expressed among the superoxide dismutase (SOD), catalase, and AhpC genes (33).…”

Section: Discussionmentioning

confidence: 99%

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

Wang

Chung

et al. 2013

Alkyl 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 in Vibrio parahaemolyticus. In this investigation, ahpC1 (VPA1683) and ahpC2 (VP0580) were identified in chromosomes II and I of this pathogen, respectively. Mutants with deletions of these two ahpC genes 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 H 2 O 2 and tert-butyl hydroperoxide (t-BOOH) at different incubation temperatures. The results revealed that both ahpC genes were protective against t-BOOH, while ahpC1 was protective against H 2 O 2 . The protective function of ahpC2 at 4°C was higher than that of ahpC1. 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 an ahpC2 mutant and an ahpC1 ahpC2 double mutant were significantly shorter than those for the parent strain (for induction, 6.2 weeks; for maintenance, 7.8 weeks) and the ahpC1 mutant (for induction, 6.0 weeks; for maintenance, 8.0 weeks) (P < 0.03). Complementation with an ahpC2 gene reversed the effects of the ahpC2 mutation in shortening the times for induction and maintenance of the VBNC state. This investigation identified the different functions of the two ahpC genes and confirmed the particular role of ahpC2 in the VBNC state of V. parahaemolyticus.

“…These laboratory studies have typically examined copiotrophic bacteria isolated and grown using high concentrations of organic substrates (1)(2)(3). Although possible during phytoplankton blooms and in particles (4,5), such high concentrations are not common, so copiotrophic bacteria are much less abundant than oligotrophic bacteria (6).…”

mentioning

confidence: 99%

Transcriptional Control in Marine Copiotrophic and Oligotrophic Bacteria with Streamlined Genomes

Cottrell

Kirchman

2016

Bacteria often respond to environmental stimuli using transcriptional control, but this may not be the case for marine bacteria such as "Candidatus Pelagibacter ubique," a cultivated representative of the SAR11 clade, the most abundant organism in the ocean. This bacterium has a small, streamlined genome and an unusually low number of transcriptional regulators, suggesting that transcriptional control is low in Pelagibacter and limits its response to environmental conditions. Transcriptome sequencing during batch culture growth revealed that only 0.1% of protein-encoding genes appear to be under transcriptional control in Pelagibacter and in another oligotroph (SAR92) whereas >10% of genes were under transcriptional control in the copiotrophs Polaribacter sp. strain MED152 and Ruegeria pomeroyi. When growth levels changed, transcript levels remained steady in Pelagibacter and SAR92 but shifted in MED152 and R. pomeroyi. Transcript abundances per cell, determined using an internal RNA sequencing standard, were low (<1 transcript per cell) for all but a few of the most highly transcribed genes in all four taxa, and there was no correlation between transcript abundances per cell and shifts in the levels of transcription. These results suggest that low transcriptional control contributes to the success of Pelagibacter and possibly other oligotrophic microbes that dominate microbial communities in the oceans. IMPORTANCEDiverse heterotrophic bacteria drive biogeochemical cycling in the ocean. The most abundant types of marine bacteria are oligotrophs with small, streamlined genomes. The metabolic controls that regulate the response of oligotrophic bacteria to environmental conditions remain unclear. Our results reveal that transcriptional control is lower in marine oligotrophic bacteria than in marine copiotrophic bacteria. Although responses of bacteria to environmental conditions are commonly regulated at the level of transcription, metabolism in the most abundant bacteria in the ocean appears to be regulated by other mechanisms.