Survival strategies of bacteria in the natural environment

Application of molecular techniques to the elucidation of the microbial community structure of antique paintings

This paper uses molecular techniques to describe the microstructure and microbiological communities of sixteenth century artwork and their relationships. The microbiological populations, analysed by denaturing gradient gel electrophoresis (DGGE), were highly influenced by the chemical composition of the pictorial layers detected by energy-dispersive X-ray analysis. DGGE revealed that the diversity of microbial communities was lower in pictorial layers composed of pigments with metals, such as Pb, Cu and Hg, than in those found in pictorial layers without such compounds. The number of cultivable microorganisms, mainly fungi and bacteria, was very low in comparison to those found by DGGE, revealing the presence of both cultivable and as-yet-uncultivated (or not viable) species in the samples analysed. Both fungi and bacteria were present in a non-random spatial distribution. Environmental scanning electron microscopy and fluorescent in situ hybridisation analyses revealed that bacterial populations were usually found in close contact with the surface of the pictorial layers, and fungal populations were located on the bacterial biofilm. This work shows, for the first time, the correlation between the diversity of the microbial populations and the chemical composition of the pictorial layers of an artwork.

Exploring the physiological state of continental Antarctic endolithic microorganisms by microscopy

In this microscopy study, we show that microorganisms comprising many endolithic communities of the McMurdo Dry Valleys of Antarctica appear in different physiological states. Live/dead microbial fluorescence stains were used to identify the state of microorganisms in the biofilms. The ultrastructures of these microorganisms were then characterized by transmission electron microscopy. Cyanobacteria were associated with heterotrophic bacterial cells, while fungal cells were free-living or formed partners with green alga as lichens. The extracellular polymeric substances, in which the endolithic microorganisms were embedded, formed an integral part of the biofilms observed. Extracellular polymeric substances probably play a significant role in nutrient interactions and protection of microorganisms from the environmental conditions outside the film. Living, moribund, dormant and dead microorganisms shared this microhabitat. The ecological impacts of the observed physiological dynamics are discussed.

Detection of viable Escherichia coli O157:H7 by ethidium monoazide real-time PCR

AIMS

The aim of this study was to develop and optimize a novel method that combines ethidium bromide monoazide (EMA) staining with real-time PCR for the detection of viable Escherichia coli O157:H7 in ground beef. EMA can penetrate dead cells and bind to intracellular DNA, preventing its amplification via PCR.

METHODS AND RESULTS

Samples were stained with EMA for 5 min, iced for 1 min and exposed to bright visible light for 10 min prior to DNA extraction, to allow EMA binding of the DNA from dead cells. DNA was then extracted and amplified by TaqMan real-time PCR to detect only viable E. coli O157:H7 cells. The primers and TaqMan probe used in this study target the uidA gene in E. coli O157:H7. An internal amplification control (IAC), consisting of 0.25 pg of plasmid pUC19, was added in each reaction to prevent the occurrence of false-negative results. Results showed a reproducible application of this technique to detect viable cells in both broth culture and ground beef. EMA, at a final concentration of 10 microg ml(-1), was demonstrated to effectively bind DNA from 10(8) CFU ml(-1) dead cells, and the optimized method could detect as low as 10(4) CFU g(-1) of viable E. coli O157:H7 cells in ground beef without interference from 10(8) CFU g(-1) of dead cells.

CONCLUSIONS

EMA real-time PCR with IAC can effectively separate dead cells from viable E. coli O157:H7 and prevent amplification of DNA in the dead cells.

SIGNIFICANCE AND IMPACT OF THE STUDY

The EMA real-time PCR has the potential to be a highly sensitive quantitative detection technique to assess the contamination of viable E. coli O157:H7 in ground beef and other meat or food products.

Iron-binding characterization and polysaccharide production by Klebsiella oxytoca strain isolated from mine acid drainage

AIMS

To investigate Klebsiella oxytoca strain BAS-10 growth on ferric citrate under anaerobic conditions for exopolysaccharide (EPS) production and localization on cell followed by the purification and the EPS determination of the iron-binding stability constant to EPS or biotechnological applications.

METHODS AND RESULTS

Klebsiella oxytoca ferments ferric citrate under anaerobic conditions and produces a ferric hydrogel, whereas ferrous ions were formed in solution. During growth, cells precipitate and a hydrogel formation was observed: the organic material was constituted of an EPS bound to Fe(III) ions, this was found by chemical analyses of the iron species and transmission electron microscopy of the cell cultures. Iron binding to EPS was studied by cyclic voltammetric measurements, either directly on the hydrogel or in an aqueous solutions containing Fe(III)-citrate and purified Fe(III)-EPS. From the voltammetric data, the stability constant for the Fe(III)-EPS complex can be assumed to have values of approx. 10(12)-10(13). It was estimated that this is higher than for the Fe(III)-citrate complex.

CONCLUSIONS

The production of Fe(III)-EPS under anaerobic conditions is a strategy for the strain to survive in mine drainages and other acidic conditions. This physiological feature can be used to produce large amounts of valuable Fe(III)-EPS, starting from a low cost substrate such as Fe(III)-citrate.

SIGNIFICANT AND IMPACT OF THE STUDY

The data herein demonstrates that an interesting metal-binding molecule can be produced as a novel catalyst for a variety of potential applications and the EPS itself is a valuable source for rhamnose purification.

Is gas-discharge plasma a new solution to the old problem of biofilm inactivation?

Conventional disinfection and sterilization methods are often ineffective with biofilms, which are ubiquitous, hard-to-destroy microbial communities embedded in a matrix mostly composed of exopolysaccharides. The use of gas-discharge plasmas represents an alternative method, since plasmas contain a mixture of charged particles, chemically reactive species and UV radiation, whose decontamination potential for free-living, planktonic micro-organisms is well established. In this study, biofilms were produced using Chromobacterium violaceum, a Gram-negative bacterium present in soil and water and used in this study as a model organism. Biofilms were subjected to an atmospheric pressure plasma jet for different exposure times. Our results show that 99.6 % of culturable cells are inactivated after a 5 min treatment. The survivor curve shows double-slope kinetics with a rapid initial decline in c.f.u. ml(-1) followed by a much slower decline with D values that are longer than those for the inactivation of planktonic organisms, suggesting a more complex inactivation mechanism for biofilms. DNA and ATP determinations together with atomic force microscopy and fluorescence microscopy show that non-culturable cells are still alive after short plasma exposure times. These results indicate the potential of plasma for biofilm inactivation and suggest that cells go through a sequential set of physiological and morphological changes before inactivation.

Resuscitation and quantification of stressed Escherichia coli K12 NCTC8797 in water samples

The aim of this study was to investigate the impact on numbers of using different media for the enumeration of Escherichia coli subjected to stress, and to evaluate the use of different resuscitation methods on bacterial numbers. E. coli was subjected to heat stress by exposure to 55 degrees C for 1h or to light-induced oxidative stress by exposure to artificial light for up to 8h in the presence of methylene blue. In both cases, the bacterial counts on selective media were below the limits of detection whereas on non-selective media colonies were still produced. After resuscitation in non-selective media, using a multi-well MPN resuscitation method or resuscitation on membrane filters, the bacterial counts on selective media matched those on non-selective media. Heat and light stress can affect the ability of E. coli to grow on selective media essential for the enumeration as indicator bacteria. A resuscitation method is essential for the recovery of these stressed bacteria in order to avoid underestimation of indicator bacteria numbers in water. There was no difference in resuscitation efficiency using the membrane filter and multi-well MPN methods. This study emphasises the need to use a resuscitation method if the numbers of indicator bacteria in water samples are not to be underestimated. False-negative results in the analysis of drinking water or natural bathing waters could have profound health effects.

Survival strategies and pathogenicity of Ralstonia solanacearum phylotype II subjected to prolonged starvation in environmental water microcosms

Survival strategies exhibited over 4 years by Ralstonia solanacearum phylotype (ph) II biovar (bv) 2 in environmental water microcosms were examined. The bacterium is a devastating phytopathogen whose ph II bv 2 causes bacterial wilt in solanaceous crops and ornamental plants. Outbreaks of the disease may originate from dissemination of the pathogen in watercourses, where it has to cope with prolonged nutrient limitation. To ascertain the effect of long-term starvation on survival and pathogenicity of R. solanacearum in natural water microcosms, survival experiments were conducted. Microcosms were prepared from different sterile river water samples, inoculated separately with two European strains of ph II at 10(6) c.f.u. ml(-1) and maintained at 24 degrees C for 4 years. In all assayed waters, starved R. solanacearum remained in a non-growing but culturable state during the first year, maintaining approximately the initial numbers. Thereafter, part of the population of R. solanacearum progressively lost the ability to form colonies, and non-culturable but metabolically active cells appeared. During the whole period, the bacterium remained pathogenic on host plants and underwent a transition from typical bacilli to small cocci which tended to aggregate. Some starved R. solanacearum cells filamented and formed buds. Starvation response, viable but non-culturable state, morphological changes and aggregation have not previously been reported for this pathogen as survival mechanisms induced in oligotrophic conditions. The potential existence of long-starved pathogenic cells in environmental waters may raise new concerns about the epidemiology of bacterial wilt disease.

Estimation of microbial viability using flow cytometry

For microorganisms in particular, viability is a term that is difficult to define and a state consequently difficult to measure. The traditional (and gold-standard) usage equates viability and culturability (i.e., the ability to multiply), but the process of determining culturability is often too slow. Flow cytometry provides the opportunity to make rapid and quantitative measurements of dye uptake in large numbers of cells, and we can therefore exploit the flow cytometric approach to evaluate so-called viability stains and to develop protocols for more routine assessments of microbial viability. This unit is primarily commentary, but several basic protocols have been included to ensure that users have a firm basis for attempting these reasonably difficult assays on traditional flow cytometer instruments. What is clear is that each assay must be carefully validated with the particular microorganism of interest before being applied in any research, clinical, or service form.

Epibiotic Vibrio luminous bacteria isolated from some hydrozoa and bryozoa species

Luminous bacteria are isolated from both Hydrozoa and Bryozoa with chitinous structures on their surfaces. All the specimens of the examined hydroid species (Aglaophenia kirchenpaueri, Aglaophenia octodonta, Aglaophenia tubiformis, Halopteris diaphana, Plumularia setacea, Ventromma halecioides), observed under blue light excitation, showed a clear fluorescence on the external side of the perisarc (chitinous exoskeleton) around hydrocladia. In the bryozoan Myriapora truncata, luminous bacteria are present on the chitinous opercula. All the isolated luminous bacteria were identified on the basis of both phenotypic and genotypic analysis. The isolates from A. tubiformis and H. diaphana were unambiguously assigned to the species Vibrio fischeri. In contrast, the isolates from the other hydroids, phenotypically assigned to the species Vibrio harveyi, were then split into two distinct species by phylogenetic analysis of 16S rRNA gene sequences and DNA-DNA hybridization experiments. Scanning electron microscopy analysis and results of culture-based and culture-independent approaches enabled us to establish that luminous vibrios represent major constituents of the bacterial community inhabiting the A. octodonta surface suggesting that the interactions between luminous bacteria and the examined hydrozoan and bryozoan species are highly specific. These interactions might have epidemiological as well as ecological implications because of the opportunistic pathogenicity of luminous Vibrio species for marine organisms and the wide-distribution of the hydrozoan and bryozoan functioning as carriers.

Stress and How Bacteria Cope with Death and Survival

Bacterial populations that are exposed to rapidly changing and sometimes hostile environments constantly switch between growth, survival, and death. Understanding bacterial survival and death are therefore cornerstones in a full comprehension of microbial life. During the last few years, new insights have emerged regarding the mechanisms of bacterial inactivation under stressful conditions. Particularly under mildly lethal stress, the ultimate cause of inactivation often seems mediated by the cell itself and is subject to additional regulation that integrates information about the global state of the cell and its environmental and social surrounding. This article explores the thin line between bacterial growth and inactivation and focuses on some emerging bacterial survival strategies, both from an individual cell and from a population perspective.

Detection, isolation, and identification of Vibrio cholerae from the environment

Microbiological techniques for sampling the aquatic realm have become increasingly sophisticated, especially with advances in molecular biology. These techniques have been used to detect microorganisms that cannot be cultured by conventional bacteriological methods. This has resulted in a deeper and a clearer understanding of the ecology and epidemiology of microorganisms. Important advances have been made in isolation, detection, and identification of Vibrio cholerae over the past decade. The understanding that V. cholerae, like several other pathogenic bacteria, can enter into a state known as "viable but nonculturable" (VBNC) provided important clues on the epidemiology of the pathogen and its ability to cause sudden explosive epidemics at multiple places almost simultaneously. The advances in techniques have also allowed investigators to discern the intricate aspects of the ecology of this pathogen in the aquatic world. In this unit, we present the most accepted methods for the isolation and detection of V. cholerae.

A dormancy state in nonspore-forming bacteria

While cultivation is a convenient way of proliferating and understanding bacteria, studies have shown the formation of nonculturable cells in nonspore-forming bacteria in response to environmental stress and thus in turn have generated immense interest. Whether these cells are in a state of dormancy or in a stage preceding cell death has been considered of paramount importance for the past couple of decades. In this study, osmotic-stress-induced dormant bacterial cells were separated by cell sorting and revived by osmotic down-shift in the absence of nutrients, source(s) that potentially could supply nutrients, and/or the external addition of resuscitation factor(s). Reversal of dormancy followed a definite pattern akin to population asynchrony of dormant cells, and the phenomenon was observed across three species, namely, Enterobacter sp. strain mcp11b, Klebsiella pneumonia strain mcp11d and Escherichia coli. In addition, our study precisely forecasted the presence of multiple subpopulations in dormant cells, which is explained by an emerging theory of survival mechanisms in stressful environments. These observations reveal that the state of dormancy induced by environmental stress in these nonspore-forming bacteria is "reversible" and also implies that it is an orderly and spontaneous adaptation to circumvent adverse conditions.

Development of a risk-based index for source water protection planning, which supports the reduction of pathogens from agricultural activity entering water resources

Source water protection planning (SWPP) is an approach to prevent contamination of ground and surface water in watersheds where these resources may be abstracted for drinking or used for recreation. For SWPP the hazards within a watershed that could contribute to water contamination are identified together with the pathways that link them to the water resource. In rural areas, farms are significant potential sources of pathogens. A risk-based index can be used to support the assessment of the potential for contamination following guidelines on safety and operational efficacy of processes and practices developed as beneficial approaches to agricultural land management. Evaluation of the health risk for a target population requires knowledge of the strength of the hazard with respect to the pathogen load (massxconcentration). Manure handling and on-site wastewater treatment systems form the most important hazards, and both can comprise confined and unconfined source elements. There is also a need to understand the modification of pathogen numbers (attenuation) together with characteristics of the established pathways (surface or subsurface), which allow the movement of the contaminant species from a source to a receptor (water source). Many practices for manure management have not been fully evaluated for their impact on pathogen survival and transport in the environment. A key component is the identification of potential pathways of contaminant transport. This requires the development of a suitable digital elevation model of the watershed for surface movement and information on local groundwater aquifer systems for subsurface flows. Both require detailed soils and geological information. The pathways to surface and groundwater resources can then be identified. Details of land management, farm management practices (including animal and manure management) and agronomic practices have to be obtained, possibly from questionnaires completed by each producer within the watershed. To confirm that potential pathways are active requires some microbial source tracking. One possibility is to identify the molecular types of Escherichia coli present in each hazard on a farm. An essential part of any such index is the identification of mitigation strategies and practices that can reduce the magnitude of the hazard or block open pathways.

Towards more accurate detection of pathogenic Gram-positive bacteria in waters

Medically important bacteria can persist in surface waters longer than was previously thought, by activating specific survival strategies and, thus, may represent a further threat to human health, in that they are non-detectable by the traditional culture methods currently used for the evaluation of microbiological quality. Combining microbial physiology, microbial biochemistry, microbial genetics, microbial ecology and molecular biology techniques allow us to achieve more accurate detection of human pathogens located in natural environments external to the human body.

Microcolony and biofilm formation as a survival strategy for bacteria

Bacterial communities such as biofilms are widely recognized as being important for survival and persistence of bacteria in harsh environments. Mechanistic models of biofilm growth indicate that the way in which the surface is seeded can effect the morphology of simulated biofilms. Experimental studies indicate that genes which are important for chemotaxis also influence biofilm formation, perhaps by influencing aggregation on a surface. Understanding aggregation and microcolony formation could therefore help clarify factors influencing biofilm formation and illuminate how groups influence the fitness of bacteria. In this paper I develop an individual based model to examine how different behaviors involved in microcolony formation on a surface determine patterns of group sizes and link patterns to bacterial fitness.

Inhibition of the resuscitation from the viable but non-culturable state in Enterococcus faecalis

The viable but non-culturable (VBNC) state is a survival strategy adopted by bacteria when exposed to environmental stresses capable of inducing cell growth inhibition and cell death. This state can be summarized as a quiescent form of life waiting for suitable conditions. This strategy has been shown to be activated by medically important bacteria either when present in natural environments or in the human body during the infection process. In this study we have evaluated the effects of antibiotics acting on peptidoglycan or protein synthesis of Enterococcus faecalis in the VBNC state. The activity of the antibiotics was determined by their ability both to inhibit resuscitation (i.e. recovery of cell division) and to bind the molecular target of action. Benzylpenicillin, piperacillin and gentamicin block cell resuscitation at the minimal inhibitory concentrations (MICs) of growing cells, while vancomycin acts only at doses 500 times higher than the MIC. This different behaviour is discussed taking into consideration the mode of action of the antibiotics.

Inability of Escherichia coli to resuscitate from the viable but nonculturable state

After induction of the viable but nonculturable (VBNC) state in Escherichia coli populations, we analysed abiotic and biotic factors suggested to promote the resuscitation process. The response to the stressing conditions implied the formation of three subpopulations, culturable, VBNC and nonviable. In most adverse situations studied, the VBNC subpopulation did not represent the dominant fraction, decreasing with time. This suggests that, in most cases, the VBNC is not a successful phenotype. Combining methods of dilution and inhibition of remaining culturable cells, we designed a working protocol in order to distinguish unequivocally between regrowth and resuscitation. Reversion of abiotic factors inducing nonculturability as well as prevention of additional oxidative stress did not provoke resuscitation. Participation of biotic factors was studied by addition of supernatants from different origin without positive results. These results indicate that the E. coli strain used is not able to resuscitate from the VBNC state. VBNC cells release into the surrounding medium, and could thus aid in the survival of persisting culturable cells. The formation of a VBNC subpopulation could thus be considered as an adaptive process, designed for the benefit of the population as a whole.

Seaweeds as a reservoir for diverse Vibrio parahaemolyticus populations in Japan

Gastroenteritis caused by Vibrio parahaemolyticus has recently been associated with foods prepared with seaweeds, but little is known about the bacterium's abundance and diversity among seaweeds in coastal environment. Therefore, we determined its phenotypic and genotypic diversity in relation to its seasonal abundance in seawater and seaweed samples from three areas of Kii Channel, Japan during June 2003 to May 2004. Isolates were obtained by selective enrichment of samples and detection of V. parahaemolyticus by colony hybridization with a species-specific probe. A total of 128 isolates comprising 16 from each source in each season were characterized by serotyping and ribotyping. V. parahaemolyticus was more abundant in seaweeds (3,762 isolates) than in water samples (2,238 isolates). Twenty and 17 serotypes were found among the selected seaweed and seawater isolates, respectively. Cluster analysis revealed 19, 11, 7 and 9 ribotypes during summer, autumn, winter and spring, respectively. Seaweeds supported a diverse V. parahaemolyticus population throughout the year and thus seaweeds are a reservoir for the organism. However, V. parahaemolyticus occurrence had positive correlation with water temperature and its abundance in seaweeds was at least 50 times higher during summer than in winter.

Susceptibility of Fusobacterium nucleatum to killing by peroxidase-iodide-hydrogen peroxide combination in buffer solution and in human whole saliva

Some Gram-negative anaerobic bacteria have been associated with the infection of tooth supporting tissues, i.e. periodontitis. Of these bacteria, Fusobacterium nucleatum is sensitive to lactoperoxidase/myeloperoxidase-iodide-hydrogen peroxide system in vitro, but salivary concentrations of thiocyanate abolishes the bactericidality. These bacteria are located in periodontal pockets, on oral mucosa and in saliva. Although F. nucleatum most probably does not belong to the group of main periodontal pathogens, it sustains its proportion in the periodontal flora when gingivitis progresses to periodontitis. In this study, the sensitivity of F. nucleatum to different horseradish peroxidase-iodide-hydrogen peroxide combinations was tested both in buffer and in sterilized human whole saliva. Horseradish peroxidase was chosen because it does not bind thiocyanate at pH > or = 6. After 1h incubation at 37 degrees C, the cell viability was estimated by plate count and with flow cytometer using LIVE/DEAD BacLight kit (Molecular Probes, USA). In saliva, the horseradish peroxidase (50 microg/mL)-iodide (2.5 mM)-hydrogen peroxide (2.5 mM) combination decreased the amount of viable bacteria to 37% compared to 85% in the control without any of the components when measured with flow cytometer. Replacement of buffer by saliva decreased the bactericidality of the peroxidase system. However, in buffer less iodide and hydrogen peroxide was needed to produce significant decrease in the number of viable bacteria when measured by plate count than with flow cytometer. Our study shows that horseradish peroxidase-iodide-hydrogen peroxide combination is able to kill F. nucleatum cells in saliva. Horseradish peroxidase-iodide-hydrogen peroxide combination may be useful to diminish the degree of re-colonization of periodontitis-associated bacteria after periodontal therapy and to inhibit the transmission of these bacteria via saliva.

Development of a rapid quantitative PCR assay for direct detection and quantification of culturable and non-culturable Escherichia coli from agriculture watersheds

A real-time quantitative polymerase chain reaction (Q-PCR) assay was developed for detecting and quantifying Escherichia coli in water samples from agricultural watersheds. The assay included optimization of DNA extraction and purification from water samples, and Q-PCR amplification conditions using newly designed species-specific oligonucleotide primers derived from conserved flanking regions of the 16S rRNA gene, the internal transcribed spacer region (ITS) and the 23S rRNA gene. The assay was optimized using a pure culture of E. coli with known quantities spiked into autoclaved agricultural water samples. The optimized assay was capable of a minimum quantification limit of 10 cells/ml of E. coli in the spiked agricultural water samples. A total of 121 surface water samples from three agricultural watersheds across Canada were analyzed, and results were compared with conventional culture-based enumerations of E. coli. The Q-PCR assay revealed significantly higher numbers of E. coli in water samples than the culture-based assay in each agricultural watershed. The new Q-PCR assay can facilitate the quantification of E. coli in a single water sample in < 3 h, including melt curve analysis, across a range of agricultural water quality conditions.

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

Vibrio cholerae is an aetiological agent of cholera that inhabits marine and estuarine environments. It can survive harsh environments by entering the viable but non-culturable (VBNC) state, but the related changes in gene expression have not been described. Here, we experimentally induced the VBNC state in V. cholerae O1, by incubation in artificial seawater at 4 degrees C. Bacterial cells that were incubated for 70 days retained their membrane integrity and were pathogenic, colonizing the gut of iron-dextran-treated mice, even though they formed no colonies on tryptic soy agar (TSA) or TSA amended with pyruvate. We therefore used this stage of cells as the VBNC bacteria. We compared the global transcription pattern of the VBNC cells with that of stationary-phase cells grown in rich medium. A total of 100 genes were induced by more than fivefold in the VBNC state, and the modulated genes were mostly those responsible for cellular processes. Furthermore, real-time RT-PCR analysis verified the changes in the expression levels, showing that the VC0230 [iron(III) ABC transporter], VC1212 (polB), VC2132 (fliG) and VC2187 (flaC) mRNAs were increased in the non-culturable state. Thus, these genes may be suitable markers for the detection of VBNC V. cholerae. To our knowledge, this is the first report of a comprehensive transcriptome analysis of V. cholerae in the VBNC state. The significance of this gene expression profile compared with those of in vivo isolates and non-stressed bacteria (culturable in vitro) is its potential to provide information about the public health risk from dormant bacteria.

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.

Development of an enrichment medium to detect Dekkera/Brettanomyces bruxellensis, a spoilage wine yeast, on the surface of grape berries

Brettanomyces bruxellensis spoilage is a serious problem for the wine industry. Mainly, by producing 4-ethylphenol and 4-ethylguaiacol, it confers off-odors to the wine and changes its aromatic quality. The presence of B. bruxellensis cells on the berry was speculated but it had never been clearly demonstrated. On grape berries, the microbial ecosystem is highly diverse and the population of B. bruxellensis can be very small. The aim of our study was to reveal and confirm the presence of B. bruxellensis on the surface of grape berries. We developed an enrichment medium for B. bruxellensis in order to overcome the detection limit of the molecular methods (species-specific PCR, ITS-RFLP PCR, PCR-DGGE). This medium, named EBB medium, made it possible to detect B. bruxellensis after 10 days of culture. For the first time, the presence of B. bruxellensis has been clearly established in several vineyards and at different stages of the grape development after the veraison. This work led to the conclusion that the grape berry is the primary source of B. bruxellensis. Grape growers and winemakers should take these results into account when deciding on the treatment to apply in the vineyards and the must. With the information provided here, B. bruxellensis prevention could start in the vineyard.

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.

Quantification of viable endospores from a Greenland ice core

Endospores (i.e., bacterial spores) embedded in polar ices present an opportunity to investigate the most durable form of life in an ideal medium for maintaining long-term viability. However, little is known about the endospore distribution and viability in polar ices. We have determined germinable endospore concentrations of bacterial spores capable of germination in a Greenland ice core (GISP2 94 m, ID# G2-271) using two complementary endospore viability assays (EVA), recently developed in our laboratory. These assays are based on bulk spectroscopic analysis (i.e., spectroEVA), and direct microscopic enumeration (i.e., microEVA) of ice core concentrates. Both assays detect dipicolinic acid (DPA) release during l-alanine induced germination via terbium ion (Tb3+)-DPA luminescence. Using spectroEVA, the germinable and total bacterial spore concentrations were found to be 295+/-19 spores mL(-1) and 369+/-36 spores mL(-1), respectively, (i.e., 80% of the endospores were capable of germination). Using microEVA, the germinating endospore concentration was found to be 27+/-2 spores mL(-1). The total cell concentration, as determined by DAPI stain fluorescence microscopy, was 7.0 x 10(3)+/-6.7 x 10(2) cells mL(-1). Culturing attempts yielded 2 CFU mL(-1) (4 degrees C). We conclude that endospores capable of germination in the GISP2 ice cores are readily determined using novel endospore viability assays.

Asynchrony in the growth and motility responses to environmental changes by individual bacterial cells

Knowing how individual cells respond to environmental changes helps one understand phenotypic diversity in a bacterial cell population, so we simultaneously monitored the growth and motility of isolated motile Escherichia coli cells over several generations by using a method called on-chip single-cell cultivation. Starved cells quickly stopped growing but remained motile for several hours before gradually becoming immotile. When nutrients were restored the cells soon resumed their growth and proliferation but remained immotile for up to six generations. A flagella visualization assay suggested that deflagellation underlies the observed loss of motility. This set of results demonstrates that single-cell transgenerational study under well-characterized environmental conditions can provide information that will help us understand distinct functions within individual cells.