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 BC 26>BC 36, 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.

Keywords:

• metals
• microbes
• immobilisation
• sediment
• Central Indian Basin

Acknowledgements

We are grateful to the Director, National Institute of Oceanography, Goa, for his encouragement. Dr. V.K. Banakar, Project Leader of the programme “Preliminary exploration of cobalt-rich seamount crusts in the northern Indian Ocean” funded by the Ministry of Earth Sciences, Government of India, kindly permitted SPP to participate and execute this work on board. The Project Leader, Dr R. Sharma and team members of the Polymetallic Nodules Environmental Impact Assessment Programme of the Ministry of Earth Sciences, Government of India are also thanked for the support of this work. The Chief Scientist, Dr N.H. Khadge, Captain, and Crew onboard Akademic Boris Petrov cruise no. 26 were extremely cooperative. Dr N.T. Manoj and M.P. Pawaskar helped in generating the map and Dr B.N. Nath and M.B.L. Mascarenhas-Pereira gave valuable suggestions. SPP and AD are indebted to all labmates for their positive support. The authors thank Ministry of Earth Sciences (Government of India), for funding. AD and SPP acknowledge the Council of Scientific and Industrial Research, New Delhi, India, for the award of Senior Research Fellowships. Comments from anonymous reviewers greatly improved the contents. This manuscript has NIO contribution number 4920.