2:30 PM - 2:45 PM
[BCG28-05] Dense microbial community at the surface of manganese nodule formed in ultra-oligotrophic seafloor
SYBR Green I staining was applied for cryo-sections prepared from this nodule sample, and revealed that the microbial cell density at the surface part (about 0.5 mm) was almost three orders of magnitude higher than that of surrounding sediment. Sequencing of 16S rDNA (~1400 bp) indicated that the composition of microbial community (both bacteria and archea) inhabiting in this nodule was different from that of surrounding sediment, showing that manganese nodule provided specific habitat for these microorganisms. Most of recognized bacteria were heterotrophs, and known manganese-oxidizing bacteria were not detected. On the other hand, most of archea were the member of Marine Group I, and the percentage of Nitrosopumilus sp. was especially high at the nodule surface. This organism is ammonia-oxidizing autotrophic archea, and its metabolism requires malticopper oxidase that utilizes Cu as a cofactor.
Although the availability of electron donor is very limited in the seafloor of ultra-oligotrophic South Pacific Gyre, Nitrosopumilus sp. can grow autotrophically even under very low ammonia concentration, and its growth is considered to be stimulated on the Cu-accumulated substances such as manganese nodule. Known manganese-oxidizing microorganisms all possess malticopper oxidase and it has critical roles in manganese oxidation. This fact implies the possibility that Nitrosopumilus sp. may contribute to the formation of manganese nodule.