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Diversity of indigenous microbial consortia and natural occurrence of obligate hydrocarbon-degrading bacteria ( OHCB) are of central importance for efficient bioremediation techniques. To investigate the microbial population dynamics and composition of oil-degrading consortia, we have established a series of identical oil-degrading mesocosms at three different locations, Bangor ( Menai Straits, Irish Sea), Helgoland ( North Sea) and Messina ( Messina Straits, Mediterranean Sea). Changes in microbial community composition in response to oil spiking, nutrient amendment and filtration were assessed by ARISA and DGGE fingerprinting and 16 Sr RNA gene library analysis. Bacterial and protozoan cell numbers were quantified by fluorescence microscopy. Very similar microbial population sizes and dynamics, together with key oil-degrading microorganisms, for example, Alcanivorax borkumensis, were observed at all three sites; however, the composition of microbial communities was largely site specific and included variability in relative abundance of OHCB. Reduction in protozoan grazing had little effect on prokaryotic cell numbers but did lead to a decrease in the percentage of A. borkumensis 16 S r RNA genes detected in clone libraries. These results underline the complexity of marine oil-degrading microbial communities and cast further doubt on the feasibility of bioaugmentation practices for use in a broad range of geographical locations. [ABSTRACT FROM AUTHOR]

For preliminary screening of human impact on Antarctic coasts, the compositions of microbial communities were analyzed in seawater at two sites located in the Terra Nova Bay of Antarctica (Ross Sea) by a combination of 16S rRNA gene sequencing and culture techniques. The bacterial community in the sample from the Rod Bay site, located at the proximity to the Italian Station, was characterized by a high abundance of 16S rRNA gene sequences belonging to the microflora typically found in soil and freshwater environments. In contrast, the seawater sample from the Adelie Cove station, a pristine reference site, contained 16S rRNA gene sequences typically found in marine areas affected by algal blooms and sea ice decay. The addition of crude oil to the Rod Bay seawater sample rapidly induced a shift in the composition of the bacterial community with appearance of novel taxonomic groups and a dramatic increase in the relative abundance of γ-Proteobacteria sequences, whereas no significant changes were detected in the bacterial community of the Adelie Cove sample under the same conditions. Bacteria-exhibiting features with potential interest for industrial and environmental applications were isolated from the Rod Bay oil-enriched sample. In particular, hydrocarbon-degrading, cold-adapted bacteria were selectively enriched, isolated and screened for their ability to synthesize polyunsaturated fatty acids. Twenty two bacterial strains were isolated from the oil enrichment culture and identified. Eighteen isolates were found to be members of γ-Proteobacteria, while the remainder were representatives of α-Proteobacteria, CFB and high G + C divisions. [Copyright &y& Elsevier]