Short-term changes in the composition of active marine bacterial assemblages in response to diesel oil pollution.
Bottom Line: A reduction in diversity (Shannon index, calculated on the basis of T-RFLP data) was observed only in summer microcosms.After diesel treatment there was a reduction in the number of phylotypes related to SAR11, SAR86 and picocyanobacteria, while phylotypes of the Roseobacter clade, and the OMG group seemed to be favoured.Our results show that diesel pollution alone caused profound effects on the bacterioplankton of oligotrophic seawater, and explained many of the differences in diversity reported previously in pristine and polluted sites in this coastal area.
Affiliation: Microbiologia, Department de Biologia, Universitat de les Illes Balears, 07122 Palma de Mallorca, Spain.Show MeSH
Mentions: In contrast with the results for Alphaproteobacteria, there were important differences in the proportion and composition of gammaproteobacterial sequences in winter and summer diesel‐treated microcosms (Figs 4 and 7). Gammaproteobacterial sequences were the second most abundant group in the winter microcosm libraries as reported previously in the area sampled (Aguiló‐Ferretjans et al., 2008). The sequences belonged mainly to the groups SAR86 and OMG (Cho and Giovannoni, 2004): OM60, KI89A and SAR92. Control libraries from summer microcosms had similar proportion and composition of Gammaproteobacteria than the libraries from winter microcosms. However, in the library from the diesel treatment in summer microcosms, clones affiliated to the Gammaproteobacteria outnumbered by far those of the Alphaproteobacteria (Fig. 4B). The increase in Gammaproteobacteria was confirmed by FISH using Gam42a probe (Manz et al., 1992). Percentages of cells hybridizing with this probe in control and diesel‐treated summer microcosms after 65 h were 3% and 18% respectively. A group of clone sequences (7 clones) from the summer diesel microcosm affiliated with the OM60 group clustered together with MAW74 and MAS35, clones previously obtained in the nearby marina (Aguiló‐Ferretjans et al., 2008). Most of the rest of gammaproteobacterial sequences in this microcosm (23) were affiliated to the family Oceanospirillaceae, which includes some of the oligotrophic marine hydrocarbon degrading bacteria described so far (Garrity et al., 2005). The clones were related to Oceanospirillum, Neptuniibacter, and to strain CAR‐SF, a carbazole‐degrading bacterium related to Neptunomonas naphthovorans (Fuse et al., 2003). Sequences related to isolate CAR‐SF were also detected in microcosms with contaminated sediments of Milazzo Harbor supplemented with nutrients (Yakimov et al., 2005). Proliferation of hydrocarbon degraders of the genus Alcanivorax, Cycloclasticus or Thalassolituus was not observed in this study as was in others (Kasai et al., 2002; Cappello et al., 2007; Coulon et al., 2007; McKew et al., 2007; Teira et al., 2007), probably due to the conditions of our experiment done with low concentrations of diesel and without nutrient addition.
Affiliation: Microbiologia, Department de Biologia, Universitat de les Illes Balears, 07122 Palma de Mallorca, Spain.