Formation of nonculturable Vibrio vulnificus cells and its relationship to the starvation state

Tools to Enumerate and Predict Distribution Patterns of Environmental Vibrio vulnificus and Vibrio parahaemolyticus

Vibrio vulnificus (Vv) and Vibrio parahaemolyticus (Vp) are water- and foodborne bacteria that can cause several distinct human diseases, collectively called vibriosis. The success of oyster aquaculture is negatively impacted by high Vibrio abundances. Myriad environmental factors affect the distribution of pathogenic Vibrio, including temperature, salinity, eutrophication, extreme weather events, and plankton loads, including harmful algal blooms. In this paper, we synthesize the current understanding of ecological drivers of Vv and Vp and provide a summary of various tools used to enumerate Vv and Vp in a variety of environments and environmental samples. We also highlight the limitations and benefits of each of the measurement tools and propose example alternative tools for more specific enumeration of pathogenic Vv and Vp. Improvement of molecular methods can tighten better predictive models that are potentially important for mitigation in more controlled environments such as aquaculture.

Coral Disease and Ingestion: Investigating the Role of Heterotrophy in the Transmission of Pathogenic Vibrio spp. using a Sea Anemone (Exaiptasia pallida) Model System

Understanding disease transmission in corals can be complicated given the intricacy of the holobiont and difficulties associated with ex situ coral cultivation. As a result, most of the established transmission pathways for coral disease are associated with perturbance (i.e., damage) rather than evasion of immune defenses. Here, we investigate ingestion as a potential pathway for the transmission of coral pathogens that evades the mucus membrane. Using sea anemones (Exaiptasia pallida) and brine shrimp (Artemia sp.) to model coral feeding, we tracked the acquisition of the putative pathogens, Vibrio alginolyticus, V. harveyi, and V. mediterranei using GFP-tagged strains. Vibrio sp. were provided to anemones using 3 experimental exposures (i) direct water exposure alone, (ii) water exposure in the presence of a food source (non-spiked Artemia), and (iii) through a "spiked" food source (Vibrio-colonized Artemia) created by exposing Artemia cultures to GFP-Vibrio via the ambient water overnight. Following a 3 h feeding/exposure duration, the level of acquired GFP-Vibrio was quantified from anemone tissue homogenate. Ingestion of spiked Artemia resulted in a significantly greater burden of GFP-Vibrio equating to an 830-fold, 3,108-fold, and 435-fold increase in CFU mL-1 when compared to water exposed trials and a 207-fold, 62-fold, and 27-fold increase in CFU mL-1 compared to water exposed with food trials for V. alginolyticus, V. harveyi, and V. mediterranei, respectively. These data suggest that ingestion can facilitate delivery of an elevated dose of pathogenic bacteria in cnidarians and may describe an important portal of entry for pathogens in the absence of perturbing conditions. IMPORTANCE The front line of pathogen defense in corals is the mucus membrane. This membrane coats the surface body wall creating a semi-impermeable layer that inhibits pathogen entry from the ambient water both physically and biologically through mutualistic antagonism from resident mucus microbes. To date, much of the coral disease transmission research has been focused on mechanisms associated with perturbance of this membrane such as direct contact, vector lesions (predation/biting), and waterborne exposure through preexisting lesions. The present research describes a potential transmission pathway that evades the defenses provided by this membrane allowing unencumbered entry of bacteria as in association with food. This pathway may explain an important portal of entry for emergence of idiopathic infections in otherwise healthy corals and can be used to improve management practices for coral conservation.

Molecular Detection and Distribution of Six Medically Important Vibrio spp. in Selected Freshwater and Brackish Water Resources in Eastern Cape Province, South Africa

Water resources contaminated with pathogenic Vibrio species are usually a source of devastating infection outbreaks that have been a public health concern in both developed and developing countries over the decades. The present study assessed the prevalence of six medically significant Vibrio species in some water resources in Eastern Cape Province, South Africa for 12 months. We detected vibrios in all the 194 water samples analyzed using polymerase chain reaction (PCR). The prevalence of Vibrio cholerae, Vibrio mimicus, Vibrio fluvialis, Vibrio vulnificus, Vibrio alginolyticus, and Vibrio parahaemolyticus in freshwater samples was 34, 19, 9, 2, 3, and 2%, and that in brackish water samples was 44, 28, 10, 7, 46, and 51%, respectively. The population of the presumptive Vibrio spp. isolated from freshwater (628) and brackish water (342) samples that were confirmed by PCR was 79% (497/628) and 85% (291/342), respectively. Twenty-two percent of the PCR-confirmed Vibrio isolates from freshwater (n = 497) samples and 41% of the PCR-confirmed Vibrio isolates from brackish water samples (n = 291) fall among the Vibrio species of interest. The incidences of V. cholerae, V. mimicus, V. fluvialis, V. vulnificus, V. alginolyticus, and V. parahaemolyticus amidst these Vibrio spp. of interest that were recovered from freshwater samples were 75, 14, 4, 6, 1, and 1%, whereas those from brackish water samples were 24, 7, 3, 3, 47, and 18%, respectively. Our observation during the study suggests pollution as the reason for the unusual isolation of medically important vibrios in winter. Correlation analysis revealed that temperature drives the frequency of isolation, whereas salinity drives the composition of the targeted Vibrio species at our sampling sites. The finding of the study is of public health importance going by the usefulness of the water resources investigated. Although controlling and preventing most of the factors that contribute to the prevalence of medically important bacteria, such as Vibrio species, at the sampling points might be difficult, regular monitoring for creating health risk awareness will go a long way to prevent possible Vibrio-related infection outbreaks at the sampling sites and their immediate environment.

Protein Aggregation as a Bacterial Strategy to Survive Antibiotic Treatment

While protein aggregation is predominantly associated with loss of function and toxicity, it is also known to increase survival of bacteria under stressful conditions. Indeed, protein aggregation not only helps bacteria to cope with proteotoxic stresses like heat shocks or oxidative stress, but a growing number of studies suggest that it also improves survival during antibiotic treatment by inducing dormancy. A well-known example of dormant cells are persisters, which are transiently refractory to the action of antibiotics. These persister cells can switch back to the susceptible state and resume growth in the absence of antibiotics, and are therefore considered an important cause of recurrence of infections. Mounting evidence now suggests that this antibiotic-tolerant persister state is tightly linked to-or perhaps even driven by-protein aggregation. Moreover, another dormant bacterial phenotype, the viable but non-culturable (VBNC) state, was also shown to be associated with aggregation. These results indicate that persisters and VBNC cells may constitute different stages of the same dormancy program induced by progressive protein aggregation. In this mini review, we discuss the relation between aggregation and bacterial dormancy, focusing on both persisters and VBNC cells. Understanding the link between protein aggregation and dormancy will not only provide insight into the fundamentals of bacterial survival, but could prove highly valuable in our future battle to fight them.

Synergistic role of abiotic factors driving viable but non-culturable Vibrio cholerae

Vibrio cholerae O1, a natural inhabitant of estuarine environments, is found in a dormant, viable but non-culturable (VBNC) state during interepidemic periods. Although the individual roles of abiotic factors affecting VBNC formation have been extensively studied, their interplay in driving this phenomenon remains largely unaddressed. Here, we identified that major abiotic factors synergize with low nutrient conditions governing entry of cells into the VBNC state. Specifically, V. cholerae cells exposed to a combination of alkaline pH and high salinity under aeration at low temperatures (VBNC-inducing conditions) synergize to facilitate rapid entry into VBNC, whereas the opposite conditions prevented entry into the state. The major virulence regulator ToxR, and the stringent response protein RelA played opposing roles, repressing and facilitating VBNC entry respectively. Further, VBNC-inducing conditions negated the effects of ToxR and RelA, facilitating rapid formation of VBNC cells. In summary, this study highlights the synergy between critical abiotic factors and identified ToxR and RelA as two associated regulators, allowing for the persistence of V. cholerae in aquatic environments. Insights obtained in this study will help better understand environmental survival non-sporulating bacteria and transmission of facultative bacterial pathogens.

Induction of a viable but non-culturable state in Salmonella Typhimurium by thermosonication and factors affecting resuscitation

The objective of this work was to analyze the effects of thermosonication (TS) on induction of a viable but non-culturable (VBNC) state in Salmonella Typhimurium and to examine incubation factors affecting subsequent resuscitation of cells. A TS treatment of 380 W at 53°C for 30 min induced the VBNC state in S. Typhimurium cells in beef peptone yeast (BPY) broth, apple/carrot juice, physiological saline and phosphate buffer solution. The logarithmic and decline phases of growth were more sensitive to the TS treatment compared to stationary phase cells. Meanwhile, VBNC S. Typhimurium could be resuscitated back to culturable cells by using suitable incubation temperatures and media. Addition of Tween 20 hindered resuscitation compared to the use of BPY medium alone. The optimal growth temperature (i.e. 37°C) was the most suitable temperature to resuscitate cells from the VBNC state. The VBNC incidence index decreased with the addition of sodium pyruvate during TS treatment, as it accelerated resuscitation. The results demonstrated that free radicals produced during TS processing and the growth phase of cells affected induction of the VBNC state in S. Typhimurium. Hence, the kinds and amounts of free radicals generated during TS treatment should be analyzed in the future.

Discrimination of viable and dead Vibrio parahaemolyticus subjected to low temperatures using Propidium Monoazide - Quantitative loop mediated isothermal amplification (PMA-qLAMP) and PMA-qPCR

The aim of this study was to determine the effect of cold (4 °C) and subzero (-18 °C, -45 °C) temperatures on the occurrence time of membrane damage to provide Propidium Monoazide (PMA) penetration of Vibrio parahaemolyticus inoculated to the sea bass. Direct plate counting (DPC) and PMA-based quantitative loop-mediated isothermal amplification (qLAMP) and qPCR was utilized for discrimination of dead and live bacteria on the designated storage days (1, 3, 7, and 14). The optimum amount of PMA was 50 μM for inhibition of amplification derived from dead cells in spiked samples. The number of live V. parahaemolyticus was detectable at the end of the 14. day using PMA-qLAMP and PMA-qPCR at all the temperatures. On the 7th day, culturability has lost at any of the storage temperatures and DPCs at -18 °C and -45 °C revealed a difference of about 1 log₁₀ CFU/ml between 1st and 3rd days. The same difference was also observed in PMA-qLAMP and PMA-qPCR on the same days (0.59-0.95 log₁₀ CFU/ml). Subzero temperatures have the highest rate of viability while causing the fastest decrease in culturability in sample groups as a result of the higher level of transition to VBNC state. qLAMP and qPCR methods in the PMA-treated and nontreated groups on the storage days at all temperatures gave similar results (p > 0.05).

Extreme slow growth as alternative strategy to survive deep starvation in bacteria

Bacteria can become dormant or form spores when they are starved for nutrients. Here, we find that non-sporulating Bacillus subtilis cells can survive deep starvation conditions for many months. During this period, cells adopt an almost coccoid shape and become tolerant to antibiotics. Unexpectedly, these cells appear to be metabolically active and show a transcriptome profile very different from that of stationary phase cells. We show that these starved cells are not dormant but are growing and dividing, albeit with a doubling time close to 4 days. Very low nutrient levels, comparable to 10,000-fold diluted lysogeny broth (LB), are sufficient to sustain this growth. This extreme slow growth, which we propose to call ‘oligotrophic growth state’, provides an alternative strategy for B. subtilis to endure nutrient depletion and environmental stresses. Further work is warranted to test whether this state can be found in other bacterial species to survive deep starvation conditions.

Bacteria can become dormant or form spores when starved for nutrients. Here, Gray et al. describe an alternative strategy, or ‘oligotrophic growth state’, showing that non-sporulating Bacillus subtilis cells can survive deep starvation conditions by adopting an almost coccoid shape and extremely low growth rates.

Detection and Verification of the Viable but Nonculturable (VBNC) State of Escherichia coli O157:H7 and Listeria monocytogenes Using Flow Cytometry and Standard Plating

The use of electrolyzed oxidizing (EO) water to inactivate microorganisms on foods has been extensively studied and shown to be effective. However, the prospect of the formation of "viable but nonculturable" (VBNC) cells in pathogens after low free chlorine concentration (FCC) treatments under high organic loads presents safety concerns. This study investigated the effect of EO water FCC on inducing Escherichia coli O157:H7 and Listeria monocytogenes into the VBNC state and studied possible resuscitation triggering procedures of the VBNC cells. A 5-strain cocktail of each pathogen (10⁶ colony forming units [CFU]/mL) was exposed to EO water (FCC of 20, 10, 5, 2.5, 1.25, 0.625 mg/L) and allowed to stand for 1 and 5 min, followed by the addition of neutralizing broth. Treated samples were plated on nonselective agar and analyzed using flow cytometry. For resuscitation, samples treated with identified VBNC induction conditions were exposed to elevated temperatures (37 °C) as well as addition of sodium pyruvate (SP) and Tween® 20 (T20) solutions. The initial culturing procedures suggested complete inactivation of both pathogens at 2.5 and 1.25 mg/L FCC in the growth medium. However, flow cytometry profiles showed VBNC cells were present. Subjecting samples to the recovery procedures further proved that VBNC E. coli O157:H7 can be resuscitated after exposure to SP and T20 at 37 °C, while L. monocytogenes did not resuscitate. These findings show that treating pathogens at low FCC can induce the VBNC state, and culturability of E. coli O157:H7 can be restored under appropriate conditions.

PRACTICAL APPLICATION

VBNC induction conditions for foodborne pathogens during chlorine washing treatment were determined in a broth system and the information can serve as a basis for future studies that address the prevention of VBNC formation during produce wash treatments.

Development of a rapid PCR protocol to detect Vibrio parahaemolyticus in clams

Vibrio parahaemolyticus is part of the natural microflora of estuarine and coastal marine waters and can be also present in seafood, especially shellfish and bivalve molluscs. In this study we compared the reference cultural method ISO 6887-3 with two molecular methods, multiplex PCR and real-time PCR, for the detection of two distinct genetic markers (tlh species-specific gene and tdh virulence gene) of V. parahaemolyticus in bivalve mollusc. The analyses were performed on clams inoculated with V. parahaemolyticus ATCC 43996 at T0 and after a 3 and 6 h of pre-enrichment in alkaline saline peptone water. Counts on agar plates were largely inaccurate, probably due to other Vibrio species grown on the TCBS selective agar. Multiplex PCR assays, performed using primers pairs for tdh and tlh genes, showed a detection limit of 10⁴ CFU/g of shell stock within 6 h of pre-enrichment, respecting however the action level indicated by the National Seafood Sanitation Program guideline. Detection by tdh gene in real-time PCR reached the definitely highest sensitivity in shorter times, 10¹ CFU/g after 3 h of pre-enrichment, while the sensitivity for the tlh gene was not promising, detecting between 10⁵ and 10⁶ CFU/g after 6 h of pre-enrichment. Our findings provide a rapid routine method of detection of V. parahaemolyticus based on tdh gene by real-time PCR for commercial seafood analysis to identify the risk of gastrointestinal diseases.

Inactivation Kinetics ofVibrio parahaemolyticuson Sand Shrimp(Metapenaeus ensis)by Cinnamaldehyde at 4°C

Sand shrimp(Metapenaeus ensis), shrimp shell, and shrimp meat were inoculated with a three-strain cocktail ofVibrio parahaemolyticuswith or without the natural antimicrobial cinnamaldehyde (2.5 mg/ml) and were, then, stored at 4°C for up to 25 days and 18 inactivation curves were obtained.V. parahaemolyticuswere inactivated down to the minimum level of detection (2.48 log CFU/g) on thiosulfate citrate bile salts sucrose agar (TCBS) plates within 7 and 10 days with low and high densities ofV. parahaemolyticusinoculation, 4.5 log CFU/g and 8.2 log CFU/g, respectively. With adding cinnamaldehyde, the inactivation process ofV. parahaemolyticuswith low populations, 4.5 log CFU/g, lasted for only 4 days. Therefore, cinnamaldehyde inactivated cells faster as expected. However, unexpectedly, in shrimp meat cases, cells have much more persistence of over even 25 days before entering the minimum level of detection both with and without cinnamaldehyde treatment. Therefore, a hypothesis was formed that when cells kept in cold environments (4°C) after several days recovered to up to 103–104CFU/g towards the end of the experiments and with starvation (shell and shrimp studies), cells might render a viable but nonculturable (VBNC) state.

Survival behaviour and virulence of the fish pathogen Vibrio ordalii in seawater microcosms

Vibrio ordalii, the causative agent of atypical vibriosis, is a Gram-negative, motile, rod-shaped bacterium that severely affects the salmonid aquaculture industry. V. ordalii has been biochemically, antigenically and genetically characterized. However, studies on the survival behaviour of this bacterium in aquatic environments are scarce, and there is no information regarding its disease transmission and infectious abilities outside of the fish host or regarding water as a possible reservoir. The present study investigated the survival behaviour of V. ordalii Vo-LM-06 and Vo-LM-18 in sterile and non-sterile seawater microcosms. After a year in sterile seawater without nutrients, 1% of both V. ordalii strains survived (~10(3) colony-forming units ml(-1)), and long-term maintenance did not affect bacterial biochemical or genetic properties. Additionally, V. ordalii maintained for 60 d in sterile seawater remained infective in rainbow trout Oncorhynchus mykiss. However, after 2 d of natural seawater exposure, this bacterium became non-culturable, indicating that autochthonous microbiota may play an important role in survival. Recuperation assays that added fresh medium to non-sterile microcosms did not favour V. ordalii recovery on solid media. Our results contribute towards a better understanding of V. ordalii survival behaviour in seawater ecosystems.

Growth Phase, Oxygen, Temperature, and Starvation Affect the Development of Viable but Non-culturable State of Vibrio cholerae

Vibrio cholerae can enter into a viable but non-culturable (VBNC) state in order to survive in unfavorable environments. In this study, we studied the roles of five physicochemical and microbiological factors or states, namely, different strains, growth phases, oxygen, temperature, and starvation, on the development of VBNC of V. cholerae in artificial sea water (ASW). Different strains of the organism, the growth phase, and oxygen levels affected the progress of VBNC development. It was found that the VBNC state was induced faster in V. cholerae serogroup O1 classical biotype strain O395 than in O1 El Tor biotype strains C6706 and N16961. When cells in different growth phases were used for VBNC induction, stationary-phase cells lost their culturability more quickly than exponential-phase cells, while induction of a totally non-culturable state took longer to achieve for stationary-phase cells in all three strains, suggesting that heterogeneity of cells should be considered. Aeration strongly accelerated the loss of culturability. During the development of the VBNC state, the culturable cell count under aeration conditions was almost 10(6)-fold lower than under oxygen-limited conditions for all three strains. The other two factors, temperature and nutrients-rich environment, may prevent the induction of VBNC cells. At 22 or 37°C in ASW, most of the cells rapidly died and the culturable cell count reduced from about 10(8) to 10(6)-10(5) CFU/mL. The total cell counts showed that cells that lost viability were decomposed, and the viable cell counts were the same as culturable cell counts, indicating that the cells did not reach the VBNC state. VBNC state development was blocked when ASW was supplied with Luria-Bertani broth (LB), but it was not affected in ASW with M9, suggesting that specific nutrients in LB may prevent the development of VBNC state. These results revealed that the five factors evaluated in this study had different roles during the progress of VBNC induction. Changing a single factor could influence and even block the development of the VBNC state. These findings provide new insight to help design further studies to better understand the mechanisms which trigger the development and regulation of the VBNC state.

The Road to Metagenomics: From Microbiology to DNA Sequencing Technologies and Bioinformatics

The study of microorganisms that pervade each and every part of this planet has encountered many challenges through time such as the discovery of unknown organisms and the understanding of how they interact with their environment. The aim of this review is to take the reader along the timeline and major milestones that led us to modern metagenomics. This new and thriving area is likely to be an important contributor to solve different problems. The transition from classical microbiology to modern metagenomics studies has required the development of new branches of knowledge and specialization. Here, we will review how the availability of high-throughput sequencing technologies has transformed microbiology and bioinformatics and how to tackle the inherent computational challenges that arise from the DNA sequencing revolution. New computational methods are constantly developed to collect, process, and extract useful biological information from a variety of samples and complex datasets, but metagenomics needs the integration of several of these computational methods. Despite the level of specialization needed in bioinformatics, it is important that life-scientists have a good understanding of it for a correct experimental design, which allows them to reveal the information in a metagenome.

Unveiling the Metabolic Pathways Associated with the Adaptive Reduction of Cell Size During Vibrio harveyi Persistence in Seawater Microcosms

Owing to their ubiquitous presence and ability to act as primary or opportunistic pathogens, Vibrio species greatly contribute to the diversity and evolution of marine ecosystems. This study was aimed at unveiling the cellular strategies enabling the marine gammaproteobacterium Vibrio harveyi to adapt and persist in natural aquatic systems. We found that, although V. harveyi incubation in seawater microcosm at 20 °C for 2 weeks did not change cell viability and culturability, it led to a progressive reduction in the average cell size. Microarray analysis revealed that this morphological change was accompanied by a profound decrease in gene expression affecting the central carbon metabolism, major biosynthetic pathways, and energy production. In contrast, V. harveyi elevated expression of genes closely linked to the composition and function of cell envelope. In addition to triggering lipid degradation via the β-oxidation pathway and apparently promoting the use of endogenous fatty acids as a major energy and carbon source, V. harveyi upregulated genes involved in ancillary mechanisms important for sustaining iron homeostasis, cell resistance to the toxic effect of reactive oxygen species, and recycling of amino acids. The above adaptation mechanisms and morphological changes appear to represent the major hallmarks of the initial V. harveyi response to starvation.

Life under extreme energy limitation: a synthesis of laboratory- and field-based investigations

The ability of microorganisms to withstand long periods with extremely low energy input has gained increasing scientific attention in recent years. Starvation experiments in the laboratory have shown that a phylogenetically wide range of microorganisms evolve fitness-enhancing genetic traits within weeks of incubation under low-energy stress. Studies on natural environments that are cut off from new energy supplies over geologic time scales, such as deeply buried sediments, suggest that similar adaptations might mediate survival under energy limitation in the environment. Yet, the extent to which laboratory-based evidence of starvation survival in pure or mixed cultures can be extrapolated to sustained microbial ecosystems in nature remains unclear. In this review, we discuss past investigations on microbial energy requirements and adaptations to energy limitation, identify gaps in our current knowledge, and outline possible future foci of research on life under extreme energy limitation.

Application of chitosan microparticles for reduction of vibrio species in seawater and live oysters (Crassostrea virginica)

Human Vibrio infections associated with consumption of raw shellfish greatly impact the seafood industry. Vibrio cholerae-related disease is occasionally attributed to seafood, but V. vulnificus and V. parahaemolyticus are the primary targets of postharvest processing (PHP) efforts in the United States, as they pose the greatest threat to the industry. Most successful PHP treatments for Vibrio reduction also kill the molluscs and are not suitable for the lucrative half-shell market, while nonlethal practices are generally less effective. Therefore, novel intervention strategies for Vibrio reduction are needed for live oyster products. Chitosan is a bioactive derivative of chitin that is generally recognized as safe as a food additive by the FDA, and chitosan microparticles (CMs) were investigated in the present study as a potential PHP treatment for live oyster applications. Treatment of broth cultures with 0.5% (wt/vol) CMs resulted in growth cessation of V. cholerae, V. vulnificus, and V. parahaemolyticus, reducing culturable levels to nondetectable amounts after 3 h in three independent experiments. Furthermore, a similar treatment in artificial seawater at 4, 25, and 37°C reduced V. vulnificus levels by ca. 7 log CFU/ml after 24 h of exposure, but 48 h of exposure and elevated temperature were required to achieve similar results for V. parahaemolyticus and V. cholerae. Live oysters that either were artificially inoculated or contained natural populations of V. vulnificus and V. parahaemolyticus showed significant and consistent reductions following CM treatment (5%) compared to the amounts in the untreated controls. Thus, the results strongly support the promising potential for the application of CMs as a PHP treatment to reduce Vibrio spp. in intact live oysters.

Induction of the viable but nonculturable state of Ralstonia solanacearum by low temperature in the soil microcosm and its resuscitation by catalase

Ralstonia solanacearum is the causal agent of bacterial wilt on a wide variety of plants, and enters a viable but nonculturable (VBNC) state under stress conditions in soil and water. Here, we adopted an artificial soil microcosm (ASM) to investigate the VBNC state of R. solanacearum induced by low temperature. The culturability of R. solanacearum strains SL341 and GMI1000 rapidly decreased at 4°C in modified ASM (mASM), while it was stably maintained at 25°C in mASM. We hypothesized that bacterial cells at 4°C in mASM are viable but nonculturable. Total protein profiles of SL341 cells at 4°C in mASM did not differ from those of SL341 culturable cells at 25°C in mASM. Moreover, the VBNC cells maintained in the mASM retained respiration activity. Catalase treatment effectively restored the culturability of nonculturable cells in mASM, while temperature increase or other treatments used for resuscitation of other bacteria were not effective. The resuscitated R. solanacearum from VBNC state displayed normal level of bacterial virulence on tomato plants compared with its original culturable bacteria. Expression of omp, oxyR, rpoS, dps, and the 16S rRNA gene quantified by RT-qPCR did not differ significantly between the culturable and VBNC states of R. solanacearum. Our results suggested that the VBNC bacterial cells in mASM induced by low temperature exist in a physiologically unique state.

Multipurpose assessment for the quantification of Vibrio spp. and total bacteria in fish and seawater using multiplex real-time polymerase chain reaction

BACKGROUND

This study describes the first multiplex real-time polymerase chain reaction assay developed, as a multipurpose assessment, for the simultaneous quantification of total bacteria and three Vibrio spp. (V. parahaemolyticus, V. vulnificus and V. anguillarum) in fish and seawater. The consumption of raw finfish as sushi or sashimi has been increasing the chance of Vibrio outbreaks in consumers. Freshness and quality of fishery products also depend on the total bacterial populations present.

RESULTS

The detection sensitivity of the specific targets for the multiplex assay was 1 CFU mL⁻¹ in pure culture and seawater, and 10 CFU g⁻¹ in fish. While total bacterial counts by the multiplex assay were similar to those obtained by cultural methods, the levels of Vibrio detected by the multiplex assay were generally higher than by cultural methods of the same populations. Among the natural samples without Vibrio spp. inoculation, eight out of 10 seawater and three out of 20 fish samples were determined to contain Vibrio spp.

CONCLUSION

Our data demonstrate that this multiplex assay could be useful for the rapid detection and quantification of Vibrio spp. and total bacteria as a multipurpose tool for surveillance of fish and water quality as well as diagnostic method.

A multi-approach study of influence of growth temperature and nutrient deprivation in a strain of Aeromonas hydrophila

In the present study we investigated the behavior of an Aeromonas hydrophila strain in prolonged nutrient deprivation condition analyzing the possible link among survival, cell morphology and adhesive characteristics and correlating them with the expression of the 43kDa outer membrane protein (OMP). The strain was inoculated in mineral and drinking chlorinated water, and in Nutrient Broth as a control with incubation at 4 and 24°C for 176days. Specimens were analyzed at different times during starvation stress. Viability was assessed by flow cytometry and growth by plate count technique; morphology and adhesivity were detected by optical and electron microscopy. The 43kDa OMP expression at different times was determined after immunoblotting assay using a polyclonal antibody produced in rabbit. The results showed a long-term viability as evidenced by cytofluorimetric analysis; however, the prolonged starvation led to the shift from the normal rod shaped cells to spherical forms in the last phases of incubation especially at 24°C. Concomitantly with the appearance of spherical cells we noted a reduction of the 43kDa OMP content and adhesive ability. Therefore, our results suggest a role of the 43kDa OMP as adhesin in A. hydrophila. In conclusion, we demonstrated that the bacterium can long survive under stress conditions, however adopting strategies which can lead to a loss of some cell surface components involved in the interactions with eukaryotic cells, therefore modifying its virulence properties.

Cellular, physiological, and molecular adaptive responses of Erwinia amylovora to starvation

Erwinia amylovora causes fire blight, a destructive disease of rosaceous plants distributed worldwide. This bacterium is a nonobligate pathogen able to survive outside the host under starvation conditions, allowing its spread by various means such as rainwater. We studied E. amylovora responses to starvation using water microcosms to mimic natural oligotrophy. Initially, survivability under optimal (28 °C) and suboptimal (20 °C) growth temperatures was compared. Starvation induced a loss of culturability much more pronounced at 28 °C than at 20 °C. Natural water microcosms at 20 °C were then used to characterize cellular, physiological, and molecular starvation responses of E. amylovora. Challenged cells developed starvation-survival and viable but nonculturable responses, reduced their size, acquired rounded shapes and developed surface vesicles. Starved cells lost motility in a few days, but a fraction retained flagella. The expression of genes related to starvation, oxidative stress, motility, pathogenicity, and virulence was detected during the entire experimental period with different regulation patterns observed during the first 24 h. Further, starved cells remained as virulent as nonstressed cells. Overall, these results provide new knowledge on the biology of E. amylovora under conditions prevailing in nature, which could contribute to a better understanding of the life cycle of this pathogen.

Distribution of vibrio species isolated from aquatic environments with TCBS agar

Environmental bacteria grown on TCBS agar plates (TCBS strains) were investigated for the presence ofVibrio cholerae in aquatic environments. TCBS strain counts were 0.01 - 0.001 times the total viable counts in pairs of the same samples. The TCBS strains were of two types which required N(a)Cl (salt strain) and did not require N(a)Cl (non-salt strain) to grow in peptone water. Non-salt strains made up 85.3 - 92.1% of TCBS strains isolated from river water. TCBS strains isolated from an estuary contained 40.9% of non-salt strains and 57.4% of salt strains. Salt strains made up 69.2 - 86.8% of TCBS strains isolated from seawater. The percentages ofVibrio species in TCBS strains were 11.9 - 47.9%. V.alginolyticus andV. parahaemolyticus were isolated from seawater.V. vulnificus was only isolated from estuary water.V. cholerae non-Ol was isolated from both river water and estuary water which had low salinity.V. fluvialis was isolated from all three aquatic environments. This investigation suggests thatVibrio species were present in each sample station and thatV. cholerae existed in river water.

Putative mechanisms and biological role of coccoid form formation in Campylobacter jejuni

In certain conditions Campylobacter jejuni cells are capable of changing their cell shape from a typically spiral to a coccoid form (CF). By similarity to other bacteria, the latter was initially considered to be a viable but non-culturable form capable of survival in unfavourable conditions. However, subsequent studies with C. jejuni and closely related bacteria Helicobacter pylori suggested that CF represents a non-viable, degenerative form. Until now, the issue on whether the CF of C. jejuni is viable and infective is highly controversial. Despite some preliminary experiments on characterization of CF cells, neither biochemical mechanisms nor genetic determinants involved in C. jejuni cell shape changes have been characterized. In this review, we highlight known molecular mechanisms and genes involved in CF formation in other bacteria. Since orthologous genes are also present in C. jejuni, we suggest that CF formation in these bacteria is also a regulated and genetically determined process. A possible significance of CF in the lifestyle of this important bacterial pathogen is discussed.

Year round patchiness of Vibrio vulnificus within a temperate Texas bay

AIMS

To investigate with high geographical resolution the small-scale spatial and temporal distribution of the pathogen Vibrio vulnificus throughout the water column in a temperate Texas bay where numerous V. vulnificus infections had been reported by the regional media the previous summer.

METHODS AND RESULTS

Surface and bottom water samples were collected from 19 sites between April 2005 and October 2006 from Matagorda Bay, TX. Physicochemical parameters were measured and V. vulnificus were analysed using quantitative polymerase chain reaction (Q-PCR) as a means of overcoming constraints of traditional culturing techniques. V. vulnificus was detected through out the year, although its temporal and spatial distribution was patchy. V. vulnificus abundances at individual sites ranged from <10 to >1·1×10(3)cellsml(-1) . No statistically reliable predictive model related to the physicochemical parameters could be developed for this pathogen.

CONCLUSIONS

This study demonstrates that year round detection of V. vulnificus while likely in the viable but nonculturable (VBNC) state during the winter months and emphasizes why physicochemical factors are insufficient metrics for robust regression modelling of this pathogen.

SIGNIFICANCE AND IMPACT OF THE STUDY

This study provides an effective new tool, Q-PCR, to study environmental distribution of V. vulnificus and that in the light of the patchy distribution observed, new reliable approaches and a mechanistic understanding of pathogen ecology need to be considered to effectively model the aquatic distribution of V. vulnificus.

Induction and resuscitation of the viable but nonculturable state in a cyanobacteria-lysing bacterium isolated from cyanobacterial bloom

The viable but nonculturable (VBNC) state has been found to be a growth strategy used by many aquatic pathogens; however, few studies have focused on VBNC state on other aquatic bacterial groups. The purpose of this study was to explore the VBNC state of cyanobacteria-lysing bacteria and the conditions that regulate their VBNC state transformation. Three cyanobacteria-lysing heterotrophic bacterial strains (F1, F2 and F3) were isolated with liquid infection method from a lake that has experienced a cyanobacterial bloom. According to their morphological, physiological and biochemical characteristics and results of 16SrDNA sequence analysis, F1, F2 and F3 were identified as strains of Staphylococcus sp., Stappia sp. and Microbacterium sp., respectively. After being co-cultured with the axenic cyanobacterium, Microcystis aeruginosa 905, for 7 days, strains F1, F2 and F3 exhibited an inhibition effect on cyanobacterial growth, which was expressed as a reduction in chlorophyll concentration of 96.0%, 94.9% and 84.8%, respectively. Both autoclaved and filtered bacterial cultures still showed lytic effects on cyanobacterial cells while centrifuged pellets were less efficient than other fractions. This indicated that lytic factors were extracelluar and heat-resistant. The environmental conditions that could induce the VBNC state of strain F1 were also studied. Under low temperature (4°C), distilled deionized water (DDW) induced almost 100% of F1 cells to the VBNC state after 6 days while different salinities (1%, 3% and 5% of NaCl solution) and lake water required 18 days. A solution of the cyanobacterial toxin microcystin-LR (MC-LR) crude extract also induced F1 to the VBNC state, and the effect was stronger than DDW. Even the lowest MC-LR concentration (10 μg L(-1)) could induce 69.7% of F1 cells into VBNC state after 24 h. On the other hand, addition of Microcystis aeruginosa cells caused resuscitation of VBNC state F1 cells within 1 day, expressed as an increase of viable cell number and a decrease of VBNC ratio. Both VBNC state and culturable state F1 cells showed lytic effects on cyanobacteria, with their VBNC ratio varying during co-culturing with cyanobacteria. The findings indicated that VBNC state transformation of cyanobacteria-lysing bacteria could be regulated by cyanobacterial cells or their toxin, and the transformation may play an important role in cyanobacterial termination.

Temporal and spatial variability in the distribution of Vibrio vulnificus in the Chesapeake Bay: a hindcast study

Vibrio vulnificus, an estuarine bacterium, is the causative agent of seafood-related gastroenteritis, primary septicemia, and wound infections worldwide. It occurs as part of the normal microflora of coastal marine environments and can be isolated from water, sediment, and oysters. Hindcast prediction was undertaken to determine spatial and temporal variability in the likelihood of occurrence of V. vulnificus in surface waters of the Chesapeake Bay. Hindcast predictions were achieved by forcing a multivariate habitat suitability model with simulated sea surface temperature and salinity in the Bay for the period between 1991 and 2005 and the potential hotspots of occurrence of V. vulnificus in the Chesapeake Bay were identified. The likelihood of occurrence of V. vulnificus during high and low rainfall years was analyzed. From results of the study, it is concluded that hindcast prediction yields an improved understanding of environmental conditions associated with occurrence of V. vulnificus in the Chesapeake Bay.

Nutrient-dependent, rapid transition of Vibrio cholerae to coccoid morphology and expression of the toxin co-regulated pilus in this form

The acute diarrhoeal disease cholera is caused by the aquatic pathogen Vibrio cholerae upon ingestion of contaminated food or water by the human host. The mechanisms by which V. cholerae is able to persist and survive in the host and aquatic environments have been studied for years; however, little is known about the factors involved in the adaptation or response of V. cholerae transitioning between these two environments. The transition from bacillary to coccoid morphology is thought to be one mechanism of survival that V. cholerae uses in response to environmental stress. Coccoid morphology has been observed for V. cholerae while in a viable but non-culturable (VBNC) state, during times of nutrient limitation, and in the water-diluted stool of cholera-infected patients. In this study we sought conditions to study the coccoid morphology of V. cholerae, and found that coccoid-shaped cells can express and produce the virulence factor toxin co-regulated pilus (TCP) and are able to colonize the infant mouse to the same extent as bacillus-shaped cells. This study suggests that TCP may be one factor that V. cholerae utilizes for adaptation and survival during the transition between the host and the aquatic environment.

Comparison of the effects of environmental parameters on growth rates of Vibrio vulnificus biotypes I, II, and III by culture and quantitative PCR analysis

Vibrio vulnificus is a natural inhabitant of estuarine waters. The three known biotypes include (i) most human pathogens, (ii) primarily eel pathogens, and (iii) pathogens associated with fish and with human wound infections in Israel. Despite the frequently lethal consequences of V. vulnificus infections, the growth rates of the various biotypes and their response to environmental changes are not well characterized. We compared the specific growth rates (μ) of a representative of each biotype by culture and quantitative PCR (qPCR) analysis in a defined medium under varied pH, temperature, and salinity. Growth rates based on culturable concentrations were always higher than those based on qPCR estimates; however, both enumeration methods yielded comparable results on the influence of environmental factors on growth rates. Temperature (25°C, 30°C, 37°C), pH (7.0, 8.0), and salinity (5 to 40‰) all had significant effects on the μ of each biotype. Temperature had the greatest effect on the μ of biotype 1 (CMCP6), whereas salinity had the greatest effect on the μ of biotypes 2 (ATCC 33147) and 3 (302/99). The biotypes' growth rates varied significantly; biotype 1 grew most rapidly, while biotype 3 grew most slowly. The highest growth rates were achieved at 37°C, pH 7.0, and salinities of 15 to 30‰ (μ = 4.0, 2.9, and 2.4 generations h(-1) for biotypes 1, 2, and 3, respectively). Other strains of the biotypes yielded comparable results, suggesting that the physiological responses of the biotypes are differentially affected by parameters that are highly variable both in estuarine environments and between the free-living and pathogen states of V. vulnificus.

Effect of gamma radiation and oregano essential oil on murein and ATP concentration of Staphylococcus aureus

The study was carried out to evaluate the effects of gamma-irradiation alone or in combination with oregano essential oil on murein composition of Staphylococcus aureus and on the intracellular and extracellular concentration of ATP. The bacterial strain was treated with 3 irradiation doses: 1.2 kGy to induce cell damage, 2.9 kGy to obtain a viable but nonculturable state, and 3.5 kGy to cause cell death. Oregano essential oil was used at 0.010% and 0.013% (w/v), which is the minimum inhibitory concentration (MIC). All treatments had a significant effect (P < or = 0.05) on the murein composition, although some muropeptides did not seem to be affected by the treatment. Each treatment influenced differently the relative percentage and number of muropeptides. There was a significant (P < or = 0.05) correlation between the reduction of intracellular ATP and increase in extracellular ATP following treatment of the cells with oregano oil. The reduction of intracellular ATP was even more important when essential oil was combined with irradiation. Also, irradiation alone of S. aureus induced a significant decrease (P < or = 0.05) of the internal ATP and a significant increase (P < or = 0.05) of the external ATP. However, no significant difference (P > 0.05) was observed in ATP concentrations between different radiation doses. Transmission electron microscopic observation revealed that oregano oil and irradiation have an effect on cell wall structure.

Viability and isolation of marine bacteria by dilution culture: theory, procedures, and initial results

Dilution culture, a method for growing the typical small bacteria from natural aquatic assemblages, has been developed. Each of 11 experimental trials of the technique was successful. Populations are measured, diluted to a small and known number of cells, inoculated into unamended sterilized seawater, and examined three times for the presence of 10 or more cells per ml over a 9-week interval. Mean viability for assemblage members is obtained from the frequency of growth, and many of the cultures produced are pure. Statistical formulations for determining viability and the frequency of pure culture production are derived. Formulations for associated errors are derived as well. Computer simulations of experiments agreed with computed values within the expected error, which verified the formulations. These led to strategies for optimizing viability determinations and pure culture production. Viabilities were usually between 2 and 60% and decreased with >5 mg of amino acids per liter as carbon. In view of difficulties in growing marine oligobacteria, these high values are noteworthy. Significant differences in population characteristics during growth, observed by high-resolution flow cytometry, suggested substantial population diversity. Growth of total populations as well as of cytometry-resolved subpopulations sometimes were truncated at levels of near 10 cells per ml, showing that viable cells could escape detection. Viability is therefore defined as the ability to grow to that population; true viabilities could be even higher. Doubling times, based on whole populations as well as individual subpopulations, were in the 1-day to 1-week range. Data were examined for changes in viability with dilution suggesting cell-cell interactions, but none could be confirmed. The frequency of pure culture production can be adjusted by inoculum size if the viability is known. These apparently pure cultures produced retained the size and apparent DNA-content characteristic of the bulk of the organisms in the parent seawater. Three cultures are now available, two of which have been carried for 3 years. The method is thus seen as a useful step for improving our understanding of typical aquatic organisms.

Application of a tetrazolium salt with a water-soluble formazan as an indicator of viability in respiring bacteria

The tetrazolium salt sodium 3'-{1-[(phenylamino)-carbonyl]-3,4-tetrazolium}-bis (4-methoxy-6-nitro)benzene-sulfonic acid hydrate (XTT) was examined for use as a colorimetric indicator of viability in respiring bacteria. XTT was reduced to an orange, water-soluble formazan product by Methylosinus trichosporium OB3b, Pseudomonas putida, Escherichia coli, and Bacillus subtilis. Formazan production was proportional to live cell biomass, and XTT was reduced by all cultures in the absence of added electron-coupling agents. XTT reduction by M. trichosporium OB3b was linear over several hours and was stimulated by the presence of an exogenous substrate (methanol). Addition of cyanide to cultures incubated under oxic conditions gave an initial 10-fold increase in XTT reduction. Viability of bacteria incubated in the absence of exogenous carbon substrates was measured as XTT reduction and compared with viability estimates from plate counts. Results obtained with the two methods were generally comparable, but the XTT assay was superior when cell recovery on plates was low. Incubation of E. coli for 7 days in the absence of exogenous carbon substrates decreased viability by 90%, whereas the corresponding decreases for cultures of M. trichosporium OB3b, P. putida, and B. subtilis were less than 40%.

Isolation of Typical Marine Bacteria by Dilution Culture: Growth, Maintenance, and Characteristics of Isolates under Laboratory Conditions

Marine bacteria in Resurrection Bay near Seward, Alaska, and in the central North Sea off the Dutch coast were cultured in filtered autoclaved seawater following dilution to extinction. The populations present before dilution varied from 0.11 x 10 to 1.07 x 10 cells per liter. The mean cell volume varied between 0.042 and 0.074 mum, and the mean apparent DNA content of the cells ranged from 2.5 to 4.7 fg of DNA per cell. All three parameters were determined by high-resolution flow cytometry. All 37 strains that were obtained from very high dilutions of Resurrection Bay and North Sea samples represented facultatively oligotrophic bacteria. However, 15 of these isolates were eventually obtained from dilution cultures that could initially be cultured only on very low-nutrient media and that could initially not form visible colonies on any of the agar media tested, indicating that these cultures contained obligately oligotrophic bacteria. It was concluded that the cells in these 15 dilution cultures had adapted to growth under laboratory conditions after several months of nutrient deprivation prior to isolation. From the North Sea experiment, it was concluded that the contribution of facultative oligotrophs and eutrophs to the total population was less than 1% and that while more than half of the population behaved as obligately oligotrophic bacteria upon first cultivation in the dilution culture media, around 50% could not be cultured at all. During one of the Resurrection Bay experiments, 53% of the dilution cultures obtained from samples diluted more than 2.5 x 10 times consisted of such obligate oligotrophs. These cultures invariably harbored a small rod-shaped bacterium with a mean cell volume of 0.05 to 0.06 mum and an apparent DNA content of 1 to 1.5 fg per cell. This cell type had the dimensions of ultramicrobacteria. Isolates of these ultramicrobacterial cultures that were eventually obtained on relatively high-nutrient agar plates were, with respect to cell volume and apparent DNA content, identical to the cells in the initially obligately oligotrophic bacterial dilution culture. Determination of kinetic parameters from one of these small rod-shaped strains revealed a high specific affinity for the uptake of mixed amino acids (a degrees (A), 1,860 liters/g of cells per h), but not for glucose or alanine as the sole source of carbon and energy (a degrees (A), +/- 200 liters/g of cells per h). The ultramicrobial strains obtained are potentially a very important part of picoplankton biomass in the areas investigated.

Healthy corals maintain Vibrio in the VBNC state

Vibrio species play an important role in the health and disease of corals. To gain a better understanding of the interactions between Vibrio and coral holobionts we examined the growth of Vibrio in the mucus of the coral Oculina patagonica while the mucus was attached and detached from the coral. Fresh mucus contained ca. 10(2) Vibrio cfu ml(-1) , representing c. 1% of the total viable count. Incubation of detached mucus resulted in a 50 000-fold increase in Vibrio cfu from 1 to 4 h, corresponding to 60% of the total viable counts. This large increase in Vibrio would require an unreasonable doubling time of 11 min. Furthermore, the total microscopic bacterial count increased only 17-fold during the 1-4 h incubation period. These data led to the conclusion that Vibrio species in the mucus were largely in the VBNC state when attached to the coral and 'resuscitated' when the mucus was detached from the coral. We suggest that the coral signal for maintaining Vibrio in the VBNC state is diffusible and unstable. Maintenance of Vibrio in the VBNC state did not require photosynthetic products of the coral holobiont. Vibrio species in the VBNC state may contribute to the health of corals by preventing infections by pathogens.

Ecology of Vibrio vulnificus and Vibrio parahaemolyticus in brackish environments of the Sada River in Shimane Prefecture, Japan

While there are several studies on the ecology of Vibrio vulnificus and Vibrio parahaemolyticus in estuarine water environments around the world, there is little information on the distribution of both organisms during the cold-weather months. Thus, we conducted a multi-year study on the ecology of both organisms in brackish environments of the Sada River, a drainage canal flowing slowly into the Japan Sea from Lake Shinji in Shimane Prefecture, Japan. Water samples were collected twice a month at five sites from August 2000 to May 2002. Both organisms were enumerated in 10 l water, 100 g sediment and 10 g shellfish by the most probable number (MPN) procedure. Isolates were confirmed as V. vulnificus using hemolysin gene PCR. During the last 7 months (including winter) of the study, water and sediment samples were also analyzed for the presence of both organisms. V. parahaemolyticus was isolated from river mouths and coastal environments of average salinity > or = 4.4+/-2.0 ppt throughout the year at cell concentrations of 10(-3) to 10(1) MPN ml(-1). Similar concentrations of V. vulnificus were isolated from coastal environments of average salinity 24.0+/-5.4 ppt, except for two times when water moved to the upper reaches due to high tide and V. vulnificus was rifted to the upper reaches. These findings suggest that both organisms are continuously distributed in the Sada estuary throughout the year regardless of water temperature.

Survival of Vibrio alginolyticus in seawater and retention of virulence of its starved cells

The aim of this study was to evaluate the survival responses of four strains of Vibrio alginolyticus in seawater under starvation conditions. We used microcosms containing sterilised seawater and incubated at ambient temperature (22-25 degrees C). V. alginolyticus maintained its culturability for at least nine months. Long-term-starved cells showed an absence or a decrease in their enzymatic activities. Resuscitation assays of viable but non-culturable (VBNC) cells were conducted and the recovery of these cells was achieved after the addition of nutrients. Amplified 16S ribosomal DNA (rDNA) restriction analysis (ARDRA) was used to confirm that the same strain of V. alginolyticus persisted in all microcosms during a long period of time. Starved cells maintained their infectivity for gilt head sea bream (Sparus aurata) and sea bass (Dicentrachus labrax) as determined by intraperitoneal challenges.

Recovery in culture of viable but nonculturable Vibrio parahaemolyticus: regrowth or resuscitation?

The objective of this study was to explore the recovery of culturability of viable but nonculturable (VBNC) Vibrio parahaemolyticus after temperature upshift and to determine whether regrowth or resuscitation occurred. A clinical strain of V. parahaemolyticus Vp5 was rendered VBNC by exposure to artificial seawater (ASW) at 4 degrees C. Aliquots of the ASW suspension of cells (0.1, 1 and 10 ml) were subjected to increased temperatures of 20 degrees C and 37 degrees C. Culturability of the cells in the aliquots was monitored for colony formation on a rich medium and changes in morphology were measured by scanning (SEM) and transmission (TEM) electron microscopy. Samples of VBNC cells were fixed and examined by SEM, revealing a heterogeneous population comprising small cells and larger, flattened cells. Forty-eight hours after temperature upshift to 20 degrees C or 37 degrees C, both elongation and division by binary fission of the cells were observed, employing SEM and TEM, but only in the 10-ml aliquots. The results suggest that a portion of VBNC cells is able to undergo cell division. It is concluded that a portion of VBNC cells of V. parahaemolyticus subjected to cold temperatures remain viable. After temperature upshift, regrowth of those cells, rather than resuscitation of all bacteria of the initial inoculum, appears to be responsible for recovery of culturability of VBNC cells of V. parahaemolyticus. Nutrient in filtrates of VBNC cells is hypothesized to allow growth of the temperature-responsive cells, with cell division occurring via binary fission, but also including an atypical, asymmetric cell division.

Isolation and characterization of a cold-induced nonculturable suppression mutant of Vibrio vulnificus

The viable but nonculturable (VBNC) suppression mutant formed platable cells at low temperature stress after inoculation in artificial seawater (ASW). Suppression subtractive hybridization was used to identify differentially expressed genes among cDNAs of the VBNC suppression mutant and the wild-type Vibrio vulnificus strain. Glutathione S-transferase was identified as a responsive gene of the VBNC suppression mutant in our assay, and was highly expressed from the VBNC suppression mutant at low temperature stress. Culturability tests revealed that the wild-type cells were sensitive to oxidative stress in the hydrogen peroxide (H(2)O(2)) and to 1-chloro-2,4-dinitrobenzene (CDNB) compared with the VBNC suppression mutant cells. Adding glutathione showed that many wild-type V. vulnificus cells maintained culturability in cold ASW. These results suggest that non-nutritional growth inhibitors, such as peroxide that accumulates at low temperatures, influence VBNC in V. vulnificus cells.

Characterization of marine bacteria and the activity of their enzyme systems involved in degradation of the algal storage glucan laminarin

The algal storage glucan laminarin is one of the most abundant carbon sources for marine prokaryotes. Its degradation was investigated in bacteria isolated during and after a spring phytoplankton bloom in the coastal North Sea. On average, 13% of prokaryotes detected by epifluorescence counts were able to grow in Most Probable Number dilution series on laminarin as sole carbon source. Several bacterial strains were isolated from different dilutions, and phylogenetic characterization revealed that they belonged to different phylogenetic groups. The activity of the laminarin-degrading enzyme systems was further characterized in three strains of Vibrio sp. that were able to grow on laminarin as sole carbon source. At least two types of activity were detected upon degradation of laminarin: release of glucose, and release of glucans larger than glucose. The expression of laminarinase activity was dependent on the presence of the substrate, and was repressed by the presence of glucose. In addition, low levels of activity were expressed under starvation conditions. Laminarinase enzymes showed minimal activity on substrates with similar glucosidic bonds to those of laminarin, but different sizes and secondary and/or tertiary structures. The characteristics found in these enzyme systems may help to elucidate factors hampering rapid carbohydrate degradation by prokaryotes.

Ultrastructure of coccoid viable but non-culturable Vibrio cholerae

Morphology of viable but non-culturable Vibrio cholerae was monitored for 2 years by scanning and transmission electron microscopy. Morphological changes included very small coccoid forms, after extended incubation at 4 degrees C and room temperature, and sequential transformation from curved rods to irregular (approximately 1 microm) rods to approximately 0.8 microm coccoid cells and, ultimately, to tiny coccoid forms (0.07-0.4 microm). Irregular rod-shaped and coccoid cells were equally distributed in microcosms during the first 30-60 days of incubation at both temperatures, but only coccoid cells were observed after incubation for 60 days at 4 degrees C. When V. cholerae O1 and O139, maintained for 30-60 days at both temperatures, were heated to 45 degrees C for 60 s, after serial passage through 0.45 microm and 0.1 microm filters, and plating on Luria-Bertania (LB) agar, only cells larger than 1 microm yielded colonies on LB agar. Approximately 0.1% of heat-treated cultures were culturable. Cell division in the smallest coccoid cells was observed, yielding daughter cells of equal size, whereas other coccoid cells revealed bleb-like, cell wall evagination, followed by transfer of nuclear material. Coccoid cells of V. cholerae O1 and O139 incubated at 4 degrees C for more than 1 year remained substrate responsive and antigenic.