Bacterial activity in hydrogenetic ferromanganese crust from the Indian Ocean: a combined geochemical, experimental and pyrosequencing study

The Afanasiy-Nikitin Seamount (ANS) in the Equatorial Indian Ocean harbors hydrogenetic ferromanganese (Fe–Mn) crusts. It was hypothesized that the bacteria associated with the crust catalyze the precipitation of metal hydroxides in seawater more than abiotic dissolution, contributing to hydrogenetic accretion on the seamount. To test this hypothesis, Fe–Mn crust samples were collected from the flanks of the ANS. Geochemical properties of water samples collected were analyzed, and simulatory laboratory experiments were conducted to quantify bacterial accretion rates. Pyrosequencing was used to delineate the community associated with the crust. The environmental parameters of the water column indicated significant differences ( p Ni (0.003) > Co (0.002 mg g −1 ) with added glucose (0.01%) and Fe (9.09) > Mn (0.87) > Ni (0.0043) > Co (0.0008 mg g −1 ) without added glucose. Unlike the hydrothermal vent sites of the Pacific where ε- and ζ- Proteobacteria were reported to be dominant, the hydrogenetic Fe–Mn crusts of the ANS revealed sequences related to known Fe-, Mn- and S-oxidizing bacteria of the γ- and α- Proteobacterial groups. Thus, the different selective pressures in the two environments could be one of the factors that have brought about a difference in their bacterial diversity. Besides, the ambient nutrient levels could have triggered the participation of the Proteobacterial community of the ANS in the precipitation of Fe–Mn rich minerals.