Marinobacterium profundum sp. nov., a marine bacterium from deep-sea sediment.

A Gram-stain-negative, rod-shaped and motile strain, designated PAMC 27536T, was isolated from deep-sea sediment in the East Sea, Korea. Analysis of the 16S rRNA gene sequence of the strain showed an affiliation with the genus Marinobacterium. Phylogenetic analyses revealed that strain PAMC 27536T was related most closely to Marinobacterium rhizophilum CL-YJ9T with a 16S rRNA gene sequence similarity of 98.5 % and to other members of the genus Marinobacterium (94.0-91.7 %). Genomic relatedness analyses between strain PAMC 27536T and M. rhizophilum KCCM 42386T gave an average nucleotide identity of 85.6 % and an estimated DNA-DNA hybridization of 24.6 % using the genome-to-genome distance calculator, indicating that they represent genomically distinct species. Cells of strain PAMC 27536T grew optimally at 25-30 °C and pH 7.0-7.5 in the presence of 3 % (w/v) sea salts. The major cellular fatty acids were C16 : 1ω6c and/or C16 : 1ω7c, C18 : 1ω6c and/or C18 : 1ω7c, and C16 : 0. The major isoprenoid quinone was Q-8. The genomic DNA G+C content was 56.1-57.2 mol%. Based on the phylogenetic, chemotaxonomic, genomic and phenotypic data presented, a novel species with the name Marinobacterium profundum sp. nov. is proposed, with PAMC 27536T ( = KCCM 43095T = JCM 30410T) as the type strain.

Microbial Fe(III) reduction as a potential iron source from Holocene sediments beneath Larsen Ice Shelf.

Recent recession of the Larsen Ice Shelf C has revealed microbial alterations of illite in marine sediments, a process typically thought to occur during low-grade metamorphism. In situ breakdown of illite provides a previously-unobserved pathway for the release of dissolved Fe2+ to porewaters, thus enhancing clay-rich Antarctic sub-ice shelf sediments as an important source of Fe to Fe-limited surface Southern Ocean waters during ice shelf retreat after the Last Glacial Maximum. When sediments are underneath the ice shelf, Fe2+ from microbial reductive dissolution of illite/Fe-oxides may be exported to the water column. However, the initiation of an oxygenated, bioturbated sediment under receding ice shelves may oxidize Fe within surface porewaters, decreasing dissolved Fe2+ export to the ocean. Thus, we identify another ice-sheet feedback intimately tied to iron biogeochemistry during climate transitions. Further constraints on the geographical extent of this process will impact our understanding of iron-carbon feedbacks during major deglaciations.