Immobilisation of manganese, cobalt and nickel by deep-sea-sediment microbial communities

Abstract

Box core samples BC26 and BC36 from geologically different settings were examined to test the hypothesis that autochthonous microbial communities from polymetallic-nodule-rich Central Indian Basin sediments actively participate in immobilising metal ions. The bottom water dissolved oxygen concentration was reported to be 4.2-4.3 mL·L −1 in the northern siliceous ooze (BC26) and 4.1-4.2 mL·L −1 in the southern pelagic red clay (BC36); the sedimentation rates for these regions were 0.834 and 0.041 cm·kyr −1 , respectively. An onboard experiment, conducted under oxic and sub-oxic conditions with 100 μmol of Mn, Co and Ni, showed that microbial immobilisation under sub-oxic conditions was higher than in azide-treated controls in BC26 for Mn, Co and Ni at 30, 2 and 4 cm below sea floor (bsf), respectively, after 45 days. The trend in immobilisation was BC26 > BC36, Co > Mn > Ni under oxic conditions and Mn > Co > Ni under sub-oxic conditions. The depth of maximum immobilisation for Co in BC26 under sub-oxic conditions coincided with the yield of cultured Co-tolerant bacteria and Ni only with organic carbon at 4 cm bsf. This study demonstrates that the organic carbon content and bioavailable metal concentrations in sediments regulate microbial participation in metal immobilisation.