FE(III) OXIDE REDUCTION BY A NOVEL SUBSURFACE FERMENTATIVE BACTERIUM

Here we report the isolation of a gram-negative Firmicute that mediates iron oxide reduction during anaerobic fermentative growth. Enrichment cultures were established using a clay-rich saprolite inoculum from a six meter deep sediment core collected at Oak Ridge Tennessee. Defined media was prepared by mimicking the principal chemical components of the groundwater determined by an on-site monitoring well adjacent to the core sampling location. The anaerobic enrichment cultures were maintained in liquid media, and then diluted to extinction in agar shake tubes. After multiple transfers of single colonies, we isolated a spore-forming obligate anaerobe designated as strain RU4. This bacterium grows by fermentation of fumarate and is able to catalyze the reductive dissolution of ferrihydrite during fermentative growth. Transmission electron microscopy of strain RU4 shows a thin cell wall and an outer-membrane. The cells stain gram-negative. Based on the 16s rRNA gene sequence (1509 bp), strain RU4 is most closely related genera in the Veillonellaceae family, all at a relatively low similarity (91% identity). Phylogenetic analyses showed RU4 is basal to the Sporomusa clade and represents a distinct lineage within this family. The phylogenetic position of this bacterium and its low similarity in 16s rRNA gene sequence with other known bacterial isolates suggest that strain RU4 may belong to a novel genus.