Tirso García de Oteyza

Oil-contamination effects on a hypersaline microbial mat community (Camargue, France) as studied with microsensors and geochemical analysis

Abstract Pristine microbial mat samples from a hypersaline pond of a solar saltern (Camargue, France) were transferred into microcosms, contaminated in the laboratory with a viscous sulphur-rich crude oil, and characterized over time with microsensors for O2, pH and H2S, respectively. The goal was to gain information on how oil pollution affects the major autotrophic and heterotrophic processes involved in carbon cycling in coastal mats. Further, GC-MS analysis of mat samples taken directly after microsensor measurements was performed to investigate how the composition and the amount of oil changed over time in the oil contaminated mats. Pronounced biogeochemical changes in the microbial mat samples were observed during the experiment. The obtained results indicate that oil contamination stimulated organotrophic aerobic respiration and that C21-C28 alkanes of the crude oil were degraded/oxidized over time within the contaminated mats.

Microcosm experiments of oil degradation by microbial mats. II. The changes in microbial species

The influence of microbial mats on the degradation of two crude oils (Casablanca and Maya) and the effect of oil pollution on the mat structure were assessed using model ecosystems, prepared under laboratory conditions subject to tidal movements, from pristine Ebro Delta microbial-mat ecosystems. Both selected oils are examples of those currently used for commercial purposes. Casablanca crude oil is aliphatic with a low viscosity; Maya represents a sulphur-rich heavy crude oil that is predominantly aromatic. In the unpolluted microcosms, Microcoleus chthonoplastes-, Phormidium- and Oscillatoria-like were the dominant filamentous cyanobacterial morphotypes, whilst Synechoccocus-, Synechocystis- and Gloeocapsa-like were the most abundant unicellular cyanobacteria. After oil contamination, no significant changes of chlorophyll a and protein concentrations were observed, though cyanobacterial diversity shifts were monitored. Among filamentous cyanobacteria, M. chthonoplastes-like morphotype was the most resistant for both oils, unlike the other cyanobacteria, which tolerated Casablanca but not Maya. Unicellular cyanobacteria seemed to be resistant to pollution with both essayed oils, with the exception of the morphotype resembling Gloeocapsa, which was sensitive to both oils. The crude-oil addition also had a significant effect on certain components of the heterotrophic microbial community. Casablanca oil induced an increase in anaerobic heterotrophic bacteria, whereas the opposite effect was observed in those heterotrophs when polluted with Maya oil. The overall results, microbiological and crude-oil transformation analysis, indicate that the indigenous community has a considerable potential to degrade oil components by means of the metabolic cooperation of phototrophic and heterotrophic populations.

Molecular composition of the gas chromatography amenable fractions of maya crude oil. a reference oil for microbial degradation experiments

Abstract Maya oil constitutes a representative example of heavy sulphur-rich oils of increasing use in refineries which has been used as reference oil in the microbial degradation experiments performed within the MATBIOPOL project. A detailed study of the composition of n-alkanes, isoprenoid hydrocarbons, hopanes, steranes, polycyclic aromatic hydrocarbons, sulphur-compounds, carbazoles, phenols and alkyl carboxylic acids is reported in the present study. The distributions of these compounds indicate that the oil is geochemically mature and non biodegraded. However, the degree of thermal maturation does not reach the maximum geochemical conditions of hydrocarbon generation. The composition of these biomarkers also indicates that the oil originated from organic matter deposited in evaporitic environments. The content in phenols, carbazoles and other polar and acidic molecules may induce toxic effects in the microorganisms that may eventually increase the crude oil degradation rate upon spillage in coastal areas.

Fatty acids, hydrocarbons, sterols and alkenones of microbial mats from coastal ecosystems of the ebro delta

Abstract Fatty acids, hydrocarbons, ketones, alcohols and sterols have been analyzed in microbial mats collected in a coastal environment of the Ebro delta. In general, cyanobacteria, diatoms and haptophyceae contribute significantly to the organic matter of these mats. Dinoflagellates are also important. Evaluation of the long-term redox status of the mats based on the sterol composition, e.g. Δ5-stenol, 5α(H)- and 5β(H)- stanol ratios, shows a good correspondence with the degree of stationary growth of purple phototrophic bacteria (as indicated by the ratio between cyclopropylnonadecanoic and n-octadec-11(Z)-enoic acids) and the relative proportion of sulphate reducing bacteria remains (iso- and anteiso-pentadecanoic acids). Comparison of the composition of these mats to that of mats developed in hypersaline environments, namely carbonate and gypsum deposition, from the same area shows that diatoms, dinoflagellate and haptophyceae inputs are also very relevant in the former. In the gypsum mats these inputs are negligible except for the C37-C38 alkenones from haptophyceae. Cyclopropylnonadecanoic, n-octadec-11(Z)-enoic and iso- and anteiso-pentadecanoic acids are major constituents of the fatty acid distributions of the carbonate and gypsum mats, suggesting a higher efficiency of the phototrophic bacteria from hypersaline than coastal mats for the uptake of the hydrogen sulphide generated by the sulphate reducers. In addition, the cyclopropylnonadecanoic/n-octadec-11(Z)-enoic acid ratio in the carbonate and gypsum mats is higher than in the coastal mat, indicating a lower degree of stationary growth in the latter.

Diversity shifts and crude oil transformation in polluted microbial mat microcosms

Abstract Diversity shifts linked to crude oil transformation were studied in microbial mats developed under laboratory conditions using a molecular approach and basic biomass determination (protein and predominant pigment content). For this purpose two different microcosms were established, one simulating a four-day black tide and the other trying to reflect the colonisation of contaminated black sediment by the indigenous populations of Ebro Delta microbial mats inoculated over the polluted substrate. The crude oil used as a contaminant was Casablanca, a light oil with low viscosity and low sulphur content similar to Arabian light. In the first microcosm, Microcosm I, neither crude oil degradation nor changes of total and phototrophic biomass were detected. Nevertheless, DGGE profiles showed noticeable changes that suggested a slight increase in the diversity of the bacterial populations, assuming that the number of bands was directly correlated to the diversity of species. Furthermore, when attention is focused on the Chromatiaceae family, the same behaviour was observed in the pigmented zone, while in the black sediment diversity diminished over time. Cyanobacteria exhibited a decrease in the diversity in both depths analysed. In the second microcosm, Microcosm II, small changes to the aliphatic hydrocarbon fraction were observed in the initial millimetres of the contaminated black sediment. An increase in the total and phototrophic biomass was observed over time and when DGGE patterns were analysed, shifts were observed and the final consequence was a decrease in the diversity of total bacterial populations. The same trend was observed for Cyanobacteria and for the Chromatiaceae family. Despite the pressure on indigenous bacterial populations from Ebro delta microbial mats, they can grow after a short black tide and are able to successfully colonise contaminated sediment to ultimately form a well-established microbial mat.