Marine bacterial community shift during experimental diesel oil pollution

LANFRANCONI, M.P.; BOSCH, R.; NOGALES, B

Uppsala (SUECIA)

Conferencia; BAGECO 10 Bacterial Genetics and Ecology-Coexisting on a Changing Planet; 2009

Refined petroleum products are present around recreational coastal areas due to human-derived activities. Recently, gradual changes in bacterial communities were observed near a marina in the coast of Mallorca. However, relationships between these changes and hydrocarbon pollution were difficult to demonstrate. Based on those results, we focused our study in analyzing changes in diversity of marine bacterial communities in microcosms prepared with 45 l of pristine coastal waters which were exposed to low concentrations of diesel oil. With this approach we expected to reduce the influence of uncontrollable environmental variables. Two different sets of microcosms were prepared at two time points (summer and winter) to assess for seasonal changes in the response of bacterial communities. In diesel-treated microcosms we observed an increase in the number of bacterial cells, higher bacterial activity, and an apparent negative effect of diesel in the abundance of autofluorescent picocyanobacteria. T-RFLP analysis of 16SrRNA after RT-PCR amplification showed that bacterial community shifted rapidly in response to diesel addition. Besides, 16S rRNA cDNA libraries were generated to analyze the phylogenetic diversity of gene transcripts. Clones belonging to major phylogenetic lineages commonly found in marine environments were obtained in both, control and diesel-treated microcosms, including Alpha-, Gamma-Proteobacteria, and Bacteroidetes. However, there were differences in the phylogenetic affiliation of the corresponding cloned sequences. Characteristically, diesel treatment had an effect on important bacterial groups such as SAR11 and picocyanobacteria, which were not observed in libraries from treated microcosms. Certain groups increased in abundance after the treatment, but there was a different response of the community in winter as compared to summer. Thus, there was an increase in the number of sequences belonging to the Roseobacter clade in winter (particularly a group related to Roseobacter denitrificans), and an increase in the number of sequences from the Oceanospirillaceae in summer (particularly, the appearance of clones highly related to a carbazole-degrading strain). Interestingly, we have not detected typical marine hydrocarbon degraders, such as Alcanivorax and Cycloclasticus, commonly found in other related works. This could be due to one important feature of our study in which the treatment was done with low concentrations of hydrocarbon instead of simulating an oil spill. Our results suggest that there are both general and particular patterns in the response of bacterial communities to diesel pollution, and therefore show the complexity of bacterial responses to pollution events with low concentrations of refined hydrocarbons.