Biomedical subjects

M Troussellier

Publications and source records attributed to M Troussellier.

13 recordsLinked to original sources

PubMed2007

Microbial community dynamics during assays of harbour oil spill bioremediation: a microscale simulation study.

AIMS: Microcosm experiments simulating an oil spill event were performed to evaluate the response of the natural microbial community structure of Messina harbour seawater following the accidental load of petroleum. METHODS AND RESULTS: An experimental harbour seawater microcosm, supplemented with nutrients and crude oil, was monitored above 15 days in comparison with unpolluted ones (control microcosms). Bacterial cells were counted with a Live/Dead BacLight viability kit; leucine aminopeptidase, beta-glucosidase, alkaline phosphatase, lipase and esterase enzymes were measured using fluorogenic substrates. The microbial community dynamic was monitored by isolation of total RNA, RT-PCR amplification of 16S rRNA, cloning and sequencing. Oil addition stimulated an increase of the total bacterial abundance, leucine aminopeptidase and phosphatase activity rates, as well as a change in the community structure. This suggested a prompt response of micro-organisms to the load of petroleum hydrocarbons. CONCLUSIONS: The present study on the viability, specific composition and metabolic characteristics of the microbial community allows a more precise assessment of oil pollution. Both structural and functional parameters offer interesting perspectives as indicators to monitor changes caused by petroleum hydrocarbons. SIGNIFICANCE AND IMPACT OF THE STUDY: A better knowledge of microbial structural successions at oil-polluted sites is essential for environmental bioremediation. Data obtained in microcosm studies improve our understanding of natural processes occurring during oil spills.

Alcanivoraceae↗

PubMed2005

Assessing terminal restriction fragment length polymorphism suitability for the description of bacterial community structure and dynamics in hydrocarbon-polluted marine environments.

The distribution of bacterial communities terminal restriction fragment length polymorphism (T-RFLP) fingerprint patterns was evaluated at three proximal hydrocarbon-contaminated sites located within the harbour of Messina. In order to analyse the short-term variability of the individual terminal restriction fragment (T-RF) patterns, water samples were collected at the three sites on three occasions within 3 months (T(0), T(90) and T(91)). Four sample sizes, from 50 to 1000 ml for each collected sample, were analysed separately (36 total analysed samples) to evaluate the relationship between the sample size and the bacterial diversity estimates. The dominant T-RF groups mostly belonged to signatures of putative hydrocarbon-degrading bacteria, as revealed by the virtual analysis of the obtained bands. In order to test whether significant differences were occurring between the analysed samples, the Kruskal-Wallis non-parametric test was applied to the T-RF data set. Neither significant influence of the sample size nor short spatial variability within the three sampled sites was detected for each sampling time. On the contrary, significant temporal changes in the diversity of the bacterial communities were observed. These results were confirmed by the non-metric multidimensional scales (nMDS) analysis of the whole set of samples, which indicated three main groups corresponding to the three different sampling times. In summary, the T-RFLP technique, although a polymerase chain reaction-based method, proved to be a suitable technique for monitoring polluted marine environments, typically characterized by low diversity and high relative abundances of a few dominant groups.

Bacteria↗

PubMed2004

Water quality and health status of the Senegal River estuary.

The Senegal River estuary was sampled in May 2002 to get the first data on both the trophic and sanitary status of the water of the main river of the northwest African coast. Several physical, chemical and microbiological variables were measured twice along a transect. Inorganic nutrient concentrations were low while phytoplanktonic abundances (0.58-1.8 x 10(5) cells ml(-1)), bacterial abundances (0.27-8.1 x 10(7) cells ml(-1)), activity (22-474 pmol l(-1) h(-1)), were among the highest recorded in such ecosystems. Microbiological variables revealed a eutrophicated status for this estuary. Largest abundances of fecal contamination bacterial indicators were only detected in localized areas (Saint-Louis city and surrounding areas). The apparent good survival of fecal indicator bacteria in the estuarine waters despite a long residence time (4-5 days) has been evaluated by complementary survival experiments. Exposed to a salinity gradient, a local Escherichia coli strain showed a significantly better survival than those of an E. coli reference strain.

Environmental Monitoring↗

PubMed2003

Bacterial contamination of Mediterranean coastal seawater as affected by riverine inputs: simulation approach applied to a shellfish breeding area (Thau lagoon, France).

Consequences of short-term changes in thermotolerant coliform loads on their spatio-temporal distribution in a Mediterranean lagoon with large-scale mollusk farming (Thau lagoon, France) were explored using a simulation approach. Simulations were based on bacterial transport and survival coupled models forced by the input of bacterial loads from the two main rivers (Vène and Pallas) that flow into the lagoon. Different flow types (reference, sudden and constant), bringing the same bacterial load, were considered and subsequent spatial and temporal bacterial contamination of lagoon surface water and shellfish was estimated. Simulation results showed that as long as loads were high, hydrodynamical processes governed the distribution of bacterial abundance in receiving areas. As soon as loads decreased or when time supply increased, biological die-off processes became dominant. Bacterial contamination of shellfish induced by the different flow types appeared to depend on the receiving area. In the case of Pallas River area, a sudden input of bacteria led to a high bacterial contamination of shellfish but only during a short period ( approximately 1 day). A constant input of the same amount of bacteria induced a lower but significant contamination during all the simulation period (10 days). On the contrary, bacterial inputs from the Vène River led to shellfish contamination only when bacteria were delivered through a flood event. Exposure time of bacteria to adverse environmental conditions appeared to be the main explanation to the above-mentioned differences. Consequences of our results in terms of environmental management strategy were discussed.

Animals↗

PubMed2001

Flow cytometry in oceanography 1989--1999: environmental challenges and research trends.

BACKGROUND: The present review is based on the identification of four major environmental crises that have been approached from a biological oceanographic viewpoint. These crises are the release of contaminants in near shore marine waters, the collapse of marine resources that were renewable until recently, the loss of biodiversity, and global climate change METHODS: The review examines the contribution of cytometry-based biological oceanography to the resolution of the four environmental crises. Using a database of 302 papers, flow cytometric (FCM) studies in biological oceanography over the 1989--1999 decade are examined. Future biological oceanographic applications of FCM are discussed. RESULTS: Most of the published FCM oceanographic studies focus on phytoplankton and bacterioplankton. Analysis of our 1989-1999 database shows the predominance of studies dedicated to phytoplankton (77%), followed by heterotrophic bacteria (21%). The latter progressively increased over the last decade, together with the improved understanding of the biogeochemical and trophic roles of marine bacteria. Most studies on these two microorganisms were conducted in vitro until 1996, after which the trend reversed in favor of in situ research. The most investigated areas were those with major international sampling efforts, related to the changing climate. Concerning environmental topics, 62% of papers on phytoplankton and bacterioplankton focused on the structure of microbial communities and fluxes (e.g., production, grazing); this provides the basis for biological oceanographic studies on resources and climate change. CONCLUSIONS: Future progress in the biological oceanographic use of FCM will likely fall into two categories, i.e., applications where FCM will be combined with the development of other methods and those where FCM will be the main analytical tool. It is expected that FCM and other cytometric approaches will improve the ability of biological oceanography to address the major environmental challenges that are confronting human societies.

Animals↗

PubMed2001

Using light scatter signal to estimate bacterial biovolume by flow cytometry.

BACKGROUND: In the past decade, flow cytometry has become a useful and precise alternative to microscopic bacterial cell counts in aquatic samples. However, little evidence of its usefulness for the evaluation of bacterial biovolumes has emerged in from the literature. METHODS: The light scattering and cell volume of starved bacterial strains and natural bacterial communities from the Black Sea were measured by flow cytometry and epifluorescence microscopy, respectively, in order to establish a relationship between light scattering and cell volume. RESULTS: With the arc-lamp flow cytometer, forward angle light scatter (FALS) was related to cell size in both the starved strains and natural communities, although regression parameters differed. We tested the predictive capacity of the FALS verous cell size relationship in a bacterial community from the North Sea. That analysis showed that a reliable bacterial biovolume prediction of a natural bacterial community can be obtained from FALS using a model generated from natural bacterial community data. CONCLUSIONS: Bacterial biovolume is likely to be related to FALS measurements. It is possible to establish a generally applicable model derived from natural bacterial assemblages for flow cytometric estimation of bacterial biovolumes by light scatter.

Aeromonas hydrophila↗

PubMed2001

Microbial community dynamics in Mediterranean nutrient-enriched seawater mesocosms: changes in the genetic diversity of bacterial populations.

A mesocosm experiment was performed to study the influence of nutrients on activity and diversity of bacterial assemblages from the Mediterranean Sea. Changes in the diversity of the predominant bacterial populations were monitored by DGGE fingerprinting of PCR products derived from 16S rRNA encoding genes. Fluctuations in the diversity of the most active populations was inferred by performing the DGGE fingerprinting on the basis of the cellular rRNA after reverse transcription and PCR amplification. DNA-derived DGGE patterns obtained from duplicate control and nutrient-enriched mesocosms showed differences in the development of the bacterial communities between control and nutrient-enriched experimental mesocosms. Multidimensional scaling analysis of the DNA-derived DGGE fingerprints indicated that duplicate treatments were reproducible. DNA- and RNA-derived DGGE fingerprints of bacterial assemblages changed over time, showing that the composition of the bacterial assemblages, as well as the most active bacterial populations changed during different phases of the incubation. Sequences of predominant DGGE bands in RNA-derived patterns were similar to 16S rRNA gene sequences of members of the alpha-, gamma- and delta-Proteobacteria and of the Cytophaga-Flavobacterium-Bacteroides phylum (CFB). Bands corresponding to Ruegeria-like bacteria and members of the CFB became especially dominant during the course of incubation, suggesting that these populations were important contributors to bacterial production and activity in the post-grazing phase of the experiment.

Journal Article↗

PubMed2001

Microbial community dynamics in Mediterranean nutrient-enriched seawater mesocosms: changes in abundances, activity and composition.

Quantitative and qualitative changes in bacterial communities from the Mediterranean Sea were compared in duplicate batch mesocosms with or without addition of inorganic nutrients. Methods including traditional microbial ecology techniques, molecular biology and flow cytometry were combined to determine abundances, production, cell size, activity, culturability and taxonomic diversity of bacterial cells. Addition of nutrients and confinement resulted in an increase of bacterial densities which were rapidly controlled by protozoan grazing. Changes in bacterial activity and morphology were observed during the growth phase of bacteria and under grazing pressure. The proportion of medium-size and culturable cells increased during the growth phase. These cells were preferentially consumed by grazers resulting in a strong limitation of bacterial production. As a consequence of the grazing pressure, large cells were produced and contributed to the remaining bacterial productivity after grazing. Grazing had an effect on the taxonomic composition of bacterial communities by preferentially eliminating gamma-Proteobacteria, alpha-Proteobacteria were preserved. It seems that some species from the genera Ruegeria and Cytophaga may have developed defence strategies to escape predation.

Journal Article↗

PubMed2000

Relationships among Bacterial Cell Size, Productivity, and Genetic Diversity in Aquatic Environments using Cell Sorting and Flow Cytometry.

The study of relationships between cell size and productivity is of key importance in microbial ecology to understand which members of natural aquatic communities are responsible for the overall activity and/or productivity. Flow sorting of microorganisms from different environmental samples was used to analyze the activity of bacterial cells depending on their biovolume. Bacterial cells from five different natural samples taken along the Mediterranean coast including fresh- and seawaters were incubated with tritiated leucine, then stained with SYTO 13 and sorted by flow cytometry according to their average side-angle-scattered (SSC) light. In all samples, a bell-shaped relationship was found between cell biovolume and activity, whereas activity of a given cell-size class varied between samples. In contrast, an inverse relationship was found between biovolumes and abundances. These results suggest that medium-sized cells with highest growth rates are probably submitted to intense grazing. For one sample, bacteria within five different size classes were sorted and the genetic diversity of cells within each sorted size class and that of the whole community were analyzed by the denaturing gradient gel electrophoresis (DGGE) method. The genetic diversity, as determined at the community level was highly represented into the pool of small cells, whereas only few species were present into larger cell subpopulations. The results suggest that only a few genotypes may be dominant within the largest and most productive cells. Furthermore, cell size polymorphism as well as heterogeneous cellular activities were found within some species.

Journal Article↗

PubMed1999

Coupling Bacterial Activity Measurements with Cell Sorting by Flow Cytometry.

> Abstract A new procedure to investigate the relationship between bacterial cell size and activity at the cellular level has been developed; it is based on the coupling of radioactive labeling of bacterial cells and cell sorting by flow cytometry after SYTO 13 staining. Before sorting, bacterial cells were incubated in the presence of tritiated leucine using a procedure similar to that used for measuring bacterial production by leucine incorporation and then stained with SYTO 13. Subpopulations of bacterial cells were sorted according to their average right-angle light scatter (RALS) and fluorescence. Average RALS was shown to be significantly related to the average biovolume. Experiments were performed on samples collected at different times in a Mediterranean seawater mesocosm enriched with nitrogen and phosphorus. At four sampling times, bacteria were sorted in two subpopulations (cells smaller and larger than 0.25 µm(3)). The results indicate that, at each sampling time, the growth rate of larger cells was higher than that of smaller cells. In order to confirm this tendency, cell sorting was performed on six subpopulations differing in average biovolume during the mesocosm follow-up. A clear increase of the bacterial growth rates was observed with increasing cell size for the conditions met in this enriched mesocosm.http://link.springer-ny.com/link/service/journals/00248/bibs/38n2p180.html

Journal Article↗

PubMed1997

Changes in Cellular States of the Marine Bacterium Deleya aquamarina under Starvation Conditions.

In this study, we have used different fluorescent dyes and techniques to characterize the heterogeneity and changes of the physiological states encountered by the marine bacterium Deleya aquamarina during a 92-day starvation survival experiment at 20 and 5(deg)C. Changes of physiological states were investigated on a single-cell basis by flow cytometry and epifluorescence microscopy in conjunction with fluorescent dyes specific for various cellular functions and constituents. Heterogeneities within populations with regard to functions (respiration, substrate responsiveness, enzymatic activity, and cytoplasmic membrane permeability), constituent (DNA), and cell volume (light scatter) were compared to the evolution of viable plate counts (CFU). At 20(deg)C, CFU changes were divided into three stages corresponding to stability up to day 13 followed by a rapid drop between days 13 and 42 and then by stabilization at a level of 10 to 20% during the remaining survival period. Most of the cellular fractions showing a metabolic activity were close to the evolution of the culturable cells, suggesting the absence of viable but nonculturable cells. On the other hand, cells with selective cytoplasmic membrane permeability but without any metabolic activity were observed, and this stage was followed by DNA alteration occurring at different rates after the loss of membrane cytoplasmic permeability. We observed a greater maintenance of culturability, physiological functions, DNA, and cellular volume at the lower temperature. These results have different ecological implications from both methodological and conceptual viewpoints.

Journal Article↗

PubMed1993

Recent applications of flow cytometry in aquatic microbial ecology.

Microorganisms (unicellular algae, bacteria) constitute fundamental compartments of aquatic ecosystems because of their high concentrations and activities. The evaluation and understanding of their behavior and role raise different problems for which traditional methodologies are often inadequate, whether they refer to global or classical microscopic analyses. Flow cytometry (FCM) has been recently used to study microorganisms in aquatic environments. Although this technology is still applied on a limited scale in our field, a large number of works has been done showing that FCM seems to be a promising tool for aquatic microbial ecology. This paper summarizes, from the literature produced during the last decade and with original data obtained in our laboratory, the main questions related to the cell identification, the evaluation of cell viability, biomasses and productions and the measurements of bacterial and phytoplanktonic activities. The representatives of sampling and observation scales is also discussed within the framework of the FCM measurements.

Bacteria↗

PubMed1984

Dynamics of pollution-indicator and heterotrophic bacteria in sewage treatment lagoons.

The spatio-temporal dynamics of pollution-indicator bacteria and aerobic heterotrophic bacteria were studied in the sewage treatment lagoons of an urban wastewater center after 26 months of biweekly sampling at eight stations in these lagoons. Robust statistical methods of time-series analysis were used to study successional steps (through chronological clustering) and rhythmic behavior through time (through contingency periodogram). The aerobic heterotrophic bacterial community showed two types of temporal evolution: in the first four stations, it seems mainly controlled by the nutrient support capacity of the sewage input, whereas in the remaining part of the lagoon, it seems likely that the pollution-indicator bacteria are gradually replaced by other bacterial types that are better adapted to this environment. On the other hand, the pollution-indicator bacteria showed an annual cycle which increased in amplitude at distances further from the wastewater source. The main events in this cycle were produced simultaneously at all stations, indicating control of these bacterial populations by climatic factors, which act through physical and chemical factors, and also through other biological components of this ecosystem (phytoplankton and zooplankton). Finally, we use results from this study to suggest a modified design for a future study program.

Bacteria↗