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Uric acid is a promising hydrophobic nitrogen source for biostimulation of microbial activities in oil-impacted marine environments. This study investigated metabolic processes and microbial community changes in a series of microcosms using sediment from the Mediterranean and the Red Sea amended with ammonium and uric acid. Respiration, emulsification, ammonium and protein concentration measurements suggested a rapid production of ammonium from uric acid accompanied by the development of microbial communities containing hydrocarbonoclastic bacteria after 3 weeks of incubation. About 80 % of uric acid was converted to ammonium within the first few days of the experiment. Microbial population dynamics were investigated by Ribosomal Intergenic Spacer Analysis and Illumina sequencing as well as by culture-based techniques. Resulting data indicated that strains related to Halomonas spp. converted uric acid into ammonium, which stimulated growth of microbial consortia dominated by Alcanivorax spp. and Pseudomonas spp. Several strains of Halomonas spp. were isolated on uric acid as the sole carbon source showed location specificity. These results point towards a possible role of halomonads in the conversion of uric acid to ammonium utilized by hydrocarbonoclastic bacteria. [ABSTRACT FROM AUTHOR]

Protozoan grazers play an important role in controlling the density of crude-oil degrading marine communities as has been evidenced in a number of microcosm experiments. However, small bioreactors contain a low initial titre of protozoa and the growth of hydrocarbon-depleting bacteria is accompanied by the fast depletion of mineral nutrients and oxygen, which makes microcosms rather unsuitable for simulating the sequence of events after the oil spill in natural seawater environment. In the present study, the population dynamics of marine protozoan community have been analysed in a 500 l mesocosm experiment involving bioaugmented oil booms that contained oil sorbents and slow-release fertilisers. A significant increase in numbers of marine flagellates and ciliates on biofilms of oil-degrading microbes was microscopically observed as early as 8 days after the start of the experiment, when protozoa exhibited a population density peak making up to 3,000 cells ml−1. Further, the protozoan density varied throughout the experiment, but never dropped below 80 cells ml−1. An 18S rRNA gene-based fingerprinting analysis revealed several changes within the eukaryotic community over the whole course of the experiment. Initial growth of flagellates and small ciliates was followed by a predominance of larger protozoa. According to microscopic observations and SSU rRNA molecular analyses, most predominant were the ciliates belonging to Euplotidae and Scuticociliatia. This is the first study to characterise the eukaryotic communities specifically in a large-scale oil bioremediation trial using both microscopy-based and several molecular techniques. [ABSTRACT FROM AUTHOR]

A correction to the article "Conversion of Uric Acid into Ammonium in Oil-Degrading Marine Microbial Communities: a Possible Role of Halomonads" that was published in June 12, 2015 issue is presented.

Alcanivorax borkumensis is a cosmopolitan marine bacterium that uses oil hydrocarbons as its exclusive source of carbon and energy. Although barely detectable in unpolluted environments, A. borkumensis becomes the dominant microbe in oil-polluted waters. A. borkumensis SK2 has a streamlined genome with a paucity of mobile genetic elements and energy generation-related genes, but with a plethora of genes accounting for its wide hydrocarbon substrate range and efficient oil-degradation capabilities. The genome further specifies systems for scavenging of nutrients, particularly organic and inorganic nitrogen and oligo-elements, biofilm formation at the oil-water interface, biosurfactant production and niche-specific stress responses. The unique combination of these features provides A. borkumensis SK2 with a competitive edge in oil-polluted environments. This genome sequence provides the basis for the future design of strategies to mitigate the ecological damage caused by oil spills. [ABSTRACT FROM AUTHOR]

Two of the largest crude oil-polluted areas in the world are the semi-enclosed Mediterranean and Red Seas, but the effect of chronic pollution remains incompletely understood on a large scale. We compared the influence of environmental and geographical constraints and anthropogenic forces (hydrocarbon input) on bacterial communities in eight geographically separated oil-polluted sites along the coastlines of the Mediterranean and Red Seas. The differences in community compositions and their biodegradation potential were primarily associated (P < 0.05) with both temperature and chemical diversity. Furthermore, we observed a link between temperature and chemical and biological diversity that was stronger in chronically polluted sites than in pristine ones where accidental oil spills occurred. We propose that low temperature increases bacterial richness while decreasing catabolic diversity and that chronic pollution promotes catabolic diversification. Our results further suggest that the bacterial populations in chronically polluted sites may respond more promptly in degrading petroleum after accidental oil spills. [ABSTRACT FROM AUTHOR]