Using a green fluorescent protein gene-labeled p-nitrophenol-degrading Moraxella strain to examine the protective effect of alginate encapsulation against protozoan grazing

Detection and isolation of p-nitrophenol-lowering bacteria from intestine of marine fishes caught in Japanese waters

To determine the existence of p-nitrophenol (PNP)-lowering bacteria in intestine of Japanese coastal fish, the gastro-intestinal contents were incubated in Brain Heart Infusion (BHI) broth and minimal medium (MM) broths containing 1 mmol/L PNP at 30 °C for 7 days. Among 26 samples of 19 fish species, 17 samples showed a decrease in PNP of 0.5-0.8 mmol/L in BHI broth, but no decrease was shown in MM broth. Eighteen PNP-lowering bacterial strains were isolated from four fishes. All of the strains were identified as Lactococcus lactis subsp. lactis. Three L. lactis strains JS1-3 isolated from Japanese seabass Lateolabrax japonicus showed the highest PNP-lowering activity (0.44 mmol/L). Optimum temperature and pH for the growth and PNP decreasing corresponded with the marine environment. These results suggested that marine fishes have PNP decreasing bacteria in their intestine. These bacteria might protect host fish from toxicities of PNP and PNP related compounds.

Development of amplified fragment length polymorphism-derived functional strain-specific markers to assess the persistence of 10 bacterial strains in soil microcosms

To augment the information on commercial microbial products, we investigated the persistence patterns of high-priority bacterial strains from the Canadian Domestic Substance List (DSL). Specific DNA markers for each of the 10 DSL bacterial strains were developed using the amplified fragment length polymorphism (AFLP) technique, and the fates of DSL strains introduced in soil were assessed by real-time quantitative PCR (qPCR). The results indicated that all DNA markers had high specificity at the functional strain level and that detection of the target microorganisms was sensitive at a detection limitation range from 1.3 × 10² to 3.25 × 10⁵ CFU/g of dry soil. The results indicated that all introduced strains showed a trend toward a declining persistence in soil and could be categorized into three pattern types. The first type was long-term persistence exemplified by Pseudomonas stutzeri (ATCC 17587) and Pseudomonas denitrificans (ATCC 13867) strains. In the second pattern, represented by Bacillus subtilis (ATCC 6051) and Escherichia hermannii (ATCC 700368), the inoculated strain populations dropped dramatically below the detection threshold after 10 to 21 days, while in the third pattern there was a gradual decrease, with the population falling below the detectable level within the 180-day incubation period. These patterns indicate a selection effect of a microbial community related to the ecological function of microbial strains introduced in soil. As a key finding, the DSL strains can be quantitatively tracked in soil with high sensitivity and specificity at the functional strain level. This provides the basic evidence for further risk assessment of the priority DSL strains.

Bioaugmentation of microbial communities in laboratory and pilot scale sequencing batch biofilm reactors using the TOL plasmid

The aim of this study was to investigate the effectiveness of bioaugmentation and transfer of plasmid pWWO (TOL plasmid) to mixed microbial populations in pilot and laboratory scale sequencing batch biofilm reactors (SBBRs) treating synthetic wastewater containing benzyl alcohol (BA) as a model xenobiotic. The plasmid donor was a Pseudomonas putida strain chromosomally tagged with the gene for the red fluorescent protein carrying a green fluorescent protein labeled TOL plasmid, which confers degradation capacity for several compounds including toluene and BA. In the pilot scale SBBR donor cells were disappeared 84 h after inoculation while transconjugants were not detected at all. In contrast, both donor and transconjugant cells were detected in the laboratory scale reactor where the ratio of transconjugants to donors fluctuated between 1.9 x 10(-1) and 8.9 x 10(-1) during an experimental period of 32 days. BA degradation rate was enhanced after donor inoculation from 0.98 mg BA/min prior to inoculation to 1.9 mg BA/min on the seventeenth day of operation. Survival of a bioaugmented strain, conjugative plasmid transfer and enhanced BA degradation was demonstrated in the laboratory scale SBBR but not in the pilot scale SBBR.

Impact of substrates and cell immobilization on siderophore activity by Pseudomonads in a Fe and/or Cr, Hg, Pb containing-medium

To increase the amount of bioavailable metals in phytoextraction purposes, soil bioaugmentation with Pseudomonads, as siderophore producers with high metal complexation levels, could be relevant. Unfortunately, siderophore synthesis may be inhibited by soluble iron in soil and bacteria can suffer at the same time from the toxicity of some other metals, predation and oligotrophy. To overcome these drawbacks, we attempted to co-locate a carbon substrate and Pseudomonas aeruginosa or P. fluorescens in Ca-alginate beads. First, free-cell cultures showed that glycerol, fructose, mannitol and skim milk enhanced the siderophore activity which was the highest in the medium with neither Fe or TM (toxic metal) (Cr, Hg and Pb) and the lowest in the Fe-containing medium without TM. The negative effect of iron was partly offset when TM was added to the medium. In a second part, co-location of microorganisms and substrates was only feasible with skim milk. By comparison with free cells, siderophore activity by immobilized cells was higher in culture media containing Fe with or without TM (up to a ratio of 9), and varied in a narrow margin, according to the medium composition.

Siderophore production by using free and immobilized cells of two pseudomonads cultivated in a medium enriched with Fe and/or toxic metals (Cr, Hg, Pb)

Pseudomonads are serious candidates for siderophore production applied to toxic metal (TM) solubilization. The bioaugmentation of contaminated soils by these TM-solubilizing bacteria combined with phytoextraction is an emerging clean-up technology. Unfortunately, siderophore synthesis may be drastically reduced by soluble iron in soils and bacteria can suffer from TM toxicity. In this study, we compared siderophore production by Pseudomonas aeruginosa and Pseudomonas fluorescens by using free and immobilized cells in Ca-alginate beads incubated in a medium containing Fe and/or TM (mixture of Cr, Hg, and Pb in concentrations which represented the soluble fraction of a contaminated agricultural soil). Free cell growth was stimulated by Fe, whatever the microorganism, the inoculum size and the presence or not of TM might have been. P. aeruginosa was less sensitive to TM than P. fluorescens. By comparison with free cells, immobilization with the high inoculum size showed less sensitivity to TM most probably because of lower metal diffusion in beads. Indeed, a maximum of 99.1% of Cr, 57.4% of Hg, and 99.6% of Pb were adsorbed onto beads. The addition of iron in the culture medium reduced significantly siderophore production of free cells while it led only to a low decrease with their immobilized counterparts, in particular with P. aeruginosa. In culture medium enriched with Fe and/or TM, siderophore-specific production of immobilized cells was higher than for free cells.

Effect of carbon starvation on p-nitrophenol degradation by a Moraxella strain in buffer and river water

This study examines the effect of carbon starvation on the ability of a Moraxella sp. strain to degrade p-nitrophenol (PNP). Carbon starvation for 24 h decreased the induction time for p-nitrophenol degradation by the bacterium in a minimal salt medium from 6 to 1 h but it did not completely eliminate the induction time. Moraxella cells with 2-day carbon starvation had an induction time of 3 h and the induction time of the 3-day starved cells was 6 h. A 100% increase in density of the non-starved cells did not affect the induction time for p-nitrophenol degradation by the bacterium, indicating that the initial increase in cell density of the carbon-starved culture did not cause the faster onset of p-nitrophenol degradation. However, the initial uptake of p-nitrophenol of the 1-day carbon-starved Moraxella cells was 3-fold higher than the non-starved cells. A green fluorescent protein gene (gfp)-labelled Moraxella (M6 strain) was constructed to examine the survival of and p-nitrophenol degradation by the bacterium in non-sterile river water samples. Similar p-nitrophenol degradation behaviour was observed in the river water samples inoculated with the M6 cells. The time needed for complete degradation of p-nitrophenol by the non-starved M6 was 19-27 and 33 h in samples spiked with 80, 200 and 360 microM p-nitrophenol, respectively. However, the 1-day carbon-starved inocula required about 16 h to degrade the p-nitrophenol completely regardless of its concentration in the water samples. Survival of the carbon-starved and non-starved M6 was not significantly different from each other in the river water regardless of the p-nitrophenol concentration. In the absence of p-nitrophenol, the inoculum density decreased continuously. At 200 and 360 microM p-nitrophenol, the cell densities of M6 increased in the first two days of incubation and declined steadily afterward.

Single-cell microbiology: tools, technologies, and applications

The field of microbiology has traditionally been concerned with and focused on studies at the population level. Information on how cells respond to their environment, interact with each other, or undergo complex processes such as cellular differentiation or gene expression has been obtained mostly by inference from population-level data. Individual microorganisms, even those in supposedly "clonal" populations, may differ widely from each other in terms of their genetic composition, physiology, biochemistry, or behavior. This genetic and phenotypic heterogeneity has important practical consequences for a number of human interests, including antibiotic or biocide resistance, the productivity and stability of industrial fermentations, the efficacy of food preservatives, and the potential of pathogens to cause disease. New appreciation of the importance of cellular heterogeneity, coupled with recent advances in technology, has driven the development of new tools and techniques for the study of individual microbial cells. Because observations made at the single-cell level are not subject to the "averaging" effects characteristic of bulk-phase, population-level methods, they offer the unique capacity to observe discrete microbiological phenomena unavailable using traditional approaches. As a result, scientists have been able to characterize microorganisms, their activities, and their interactions at unprecedented levels of detail.

Protistan grazing analysis by flow cytometry using prey labeled by in vivo expression of fluorescent proteins

Selective grazing by protists can profoundly influence bacterial community structure, and yet direct, quantitative observation of grazing selectivity has been difficult to achieve. In this investigation, flow cytometry was used to study grazing by the marine heterotrophic flagellate Paraphysomonas imperforata on live bacterial cells genetically modified to express the fluorescent protein markers green fluorescent protein (GFP) and red fluorescent protein (RFP). Broad-host-range plasmids were constructed that express fluorescent proteins in three bacterial prey species, Escherichia coli, Enterobacter aerogenes, and Pseudomonas putida. Micromonas pusilla, an alga with red autofluorescence, was also used as prey. Predator-prey interactions were quantified by using a FACScan flow cytometer and analyzed by using a Perl program described here. Grazing preference of P. imperforata was influenced by prey type, size, and condition. In competitive feeding trials, P. imperforata consumed algal prey at significantly lower rates than FP (fluorescent protein)-labeled bacteria of similar or different size. Within-species size selection was also observed, but only for P. putida, the largest prey species examined; smaller cells of P. putida were grazed preferentially. No significant difference in clearance rate was observed between GFP- and RFP-labeled strains of the same prey species or between wild-type and GFP-labeled strains. In contrast, the common chemical staining method, 5-(4,6-dichloro-triazin-2-yl)-amino fluorescein hydrochloride, depressed clearance rates for bacterial prey compared to unlabeled or RFP-labeled cells.

Use of bioluminescent Escherichia coli O157:H7 to study intra-protozoan survival of bacteria within Tetrahymena pyriformis

A method was developed that enabled real-time monitoring of the uptake and survival of bioluminescent Escherichia coli O157 within the freshwater ciliate Tetrahymena pyriformis. Constitutively bioluminescent E. coli O157 pLITE27 was cocultured with T. pyriformis in nutrient-deficient (Chalkley's) and in nutrient-rich (proteose peptone, yeast extract) media. Non-internalised bacteria were inactivated by addition of colistin, indicated by a decline in bioluminescence. Protozoa were subsequently lysed with Triton X-100 which lead to a further drop in bioluminescence, consistent with release of live internal bacteria from T. pyriformis into the colistin-containing environment. Bioluminescence measurements for non-lysed cultures indicated that internalised E. coli O157 pLITE27 cells were only slowly digested by T. pyriformis, in both media, over the time period studied. The results suggest that bioluminescent bacteria are useful tools in the study of bacterial intra-protozoan survival.