MANGANESE REDUCTION BY MICROBES FROM OXIC REGIONS OF THE LAKE VANDA (ANTARCTICA) WATER COLUMN

Depth profiles of metals in Lake Vanda, a permanently ice-covered, str atified Antarctic lake, suggest the importance of particulate manganes e oxides in the scavenging, transport, and release of metals. Since ma nganese oxides can be solubilized by manganese-reducing bacteria, micr obially mediated manganese reduction was investigated in Lake Vanda. M icrobes concentrated from oxic regions of the water column, encompassi ng a peak of soluble manganese [Mn(II)], reduced synthetic manganese o xides (MnO2) when incubated aerobically. Pure cultures of manganese-re ducing bacteria were readily isolated from waters collected near the o xic Mn(II) peak Based on phylogenetic analysis of the 16S rRNA gene se quence, most of the isolated manganese reducers belong to the genus Ca rnobacterium. Cultures of a phylogenetically representative strain of Carnobacterium reduced synthetic MnO2 in the presence of sodium azide, as was seen in field assays. Unlike anaerobes that utilize manganese oxides as terminal electron accepters in respiration, isolates of the genus Carnobacterium reduced Mn(IV) via a diffusible compound under ox ic conditions. The release of adsorbed trace metals accompanying the s olubilization of manganese oxides may provide populations of Carnobact erium with a source of nutrients in this extremely oligotrophic enviro nment.