Marinobacter

Abstract: On the basis of phenotypical characteristics and analysis of 16S rRNA sequence, a new species belonging to a new genus is described, and the name Marinobacter hydrocarbonoclasticus is proposed. This organism, isolated from Mediterranean seawater near a petroleum refinery, is a gram-negative, aerobic, rod-shaped bacterium. It grows at NaCl concentrations of 0.08 to 3.5 M and uses various hydrocarbons as the sole source of carbon and energy. Its DNA has a guanine-plus-cytosine content of 52.7 mol%. The 16S rRNA analysis shows a clear affiliation between M. hydrocarbonoclasticus and the gamma group of the phylum Proteobacteria. A close phylogenetic relationship appears among the species Marinomonas vaga, Oceanospirillum linum, Halomonas elongata, and Pseudomonas aeruginosa. Because of the impossibility of finding a single most closely related species, we suggest that this bacterium be assigned to a new genus, at least temporarily. The possibility of a revision of this status when new data appear is, however, not excluded. The type strain is M. hydrocarbonoclasticus SP.17 (= ATCC 49840).

Abstract: The bacterial populations associated with sea ice sampled from Antarctic coastal areas were investigated by use of a phenotypic approach and a phylogenetic approach based on genes encoding 16S rRNA (16S rDNA). The diversity of bacteria associated with sea ice was also compared with the bacterial diversity of seawater underlying sea ice. Psychrophilic (optimal growth temperature, 20 degrees C; growth can occur at approximately 4 degrees C) isolated from sea ice cores and under-ice seawater were quite similar. Overall, bacterial isolates from Antarctic sea ice were found to belong to four phylogenetic groups, the alpha and gamma subdivisions of the Proteobacteria, the gram-positive branch, and the Flexibacter-Bacteroides-Cytophaga phylum. Most of the sea ice strains examined appeared to be novel taxa based on phylogenetic comparisons, with 45% of the strains being psychrophilic. 16S rDNA sequence analysis revealed that psychrophilic strains belonged to the genera Colwellia, Shewanella, Marinobacter, Planococcus, and novel phylogenetic lineages adjacent to Colwellia and Alteromonas and within the Flexibacter-Bacteroides-Cytophaga phylum. Psychrotrophic strains were found to be members of the genera Pseudoalteromonas, Psychrobacter, Halomonas, Pseudomonas, Hyphomonas, Sphingomonas, Arthrobacter, Planococcus, and Halobacillus. From this survey, it is proposed that ice diatom assemblages provide niches conducive to the proliferation of a diverse array of psychrophilic bacterial species.

Abstract: Most aerobic bacteria secrete siderophores to facilitate iron acquisition. Two families of siderophores were isolated from strains belonging to two different genera of marine bacteria. The aquachelins, from Halomonas aquamarina strain DS40M3, and the marinobactins, from Marinobacter sp. strains DS40M6 and DS40M8, each contain a unique peptidic head group that coordinates iron(III) and an appendage of one of a series of fatty acid moieties. These siderophores have low critical micelle concentrations (CMCs). In the absence of iron, the marinobactins are present as micelles at concentrations exceeding their CMC; upon addition of iron(III), the micelles undergo a spontaneous phase change to form vesicles. These observations suggest that unique iron acquisition mechanisms may have evolved in marine bacteria.

Abstract: Many hypersaline environments are often contaminated with petroleum compounds. Among these, oil and natural gas production sites all over the world and hundreds of kilometers of coastlines in the more arid regions of Gulf countries are of major concern due to the extent and magnitude of contamination. Because conventional microbiological processes do not function well at elevated salinities, bioremediation of hypersaline environments can only be accomplished using high salt-tolerant microorganisms capable of degrading petroleum compounds. In the last two decades, there have been many reports on the biodegradation of hydrocarbons in moderate to high salinity environments. Numerous microorganisms belonging to the domain Bacteria and Archaea have been isolated and their phylogeny and metabolic capacity to degrade a variety of aliphatic and aromatic hydrocarbons in varying salinities have been demonstrated. This article focuses on our growing understanding of bacteria and archaea responsible for the degradation of hydrocarbons under aerobic conditions in moderate to high salinity conditions. Even though organisms belonging to various genera have been shown to degrade hydrocarbons, members of the genera Halomonas Alcanivorax, Marinobacter, Haloferax, Haloarcula, and Halobacterium dominate the published literature. Despite rapid advances in understanding microbial taxa that degrade hydrocarbons under aerobic conditions, not much is known about organisms that carry out similar processes in anaerobic conditions. Also, information on molecular mechanisms and pathways of hydrocarbon degradation in high salinity is scarce and only recently there have been a few reports describing genes, enzymes and breakdown steps for some hydrocarbons. These limited studies have clearly revealed that degradation of oxygenated and non-oxygenated hydrocarbons by halophilic and halotolerant microorganisms occur by pathways similar to those found in non-halophiles.