Microbial reduction of Fe(III) in acidic sediments: Isolation of Acidiphilium cryptum JF-5 capable of coupling the reduction of Fe(III) to the oxidation of glucose

To evaluate the microbial populations involved in the reduction of Fe(III) in an acidic, iron-rich sediment, the anaerobic flow of supplemental carbon and reductant was evaluated in sediment microcosms at the in situ temperat ure of 12 degrees C, Supplemental glucose and cellobiose stimulated the for mation of Fe(II); 42 and 21% of the reducing equivalents that were theoreti cally obtained from glucose and cellobiose, respectively, were recovered in Fe(II). Likewise, supplemental H-2 was consumed by acidic sediments and yi elded additional amounts of Fe(II) in a ratio of approximately 1:2, In cont rast, supplemental lactate did not stimulate the formation of Fe(LI), Suppl emental acetate was not consumed and inhibited the formation of Fe(LI), Mos t-probable-number estimates demonstrated that glucose utilizing acidophilic Fe(III)-reducing bacteria approximated to 1% of the total direct counts of 4',6-diamidino-2-phenylindole-stained bacteria. From the highest growth-po sitive dilution of the most-probable-number series at pH 2.3 supplemented w ith glucose, an isolate, JF-5, that could dissimilate Fe(III) was obtained. JF-5 was an acidophilic, gram-negative, facultative anaerobe that complete ly oxidized the following substrates via the dissimilation of Fe(III): gluc ose, fructose, xylose, ethanol, glycerol, malate, glutamate, fumarate, citr ate, succinate, and H-2. Growth and the reduction of Fe(III) did not occur in the presence of acetate, Cells of JF-5 grown under Fe(III)-reducing cond itions formed blebs, i.e., protrusions that were still in contact with the cytoplasmic membrane. Analysis of the 16S rRNA gene sequence of JF-5 demons trated that it was closely related to an Australian isolate of Acidiphilium cryptum (99.6% sequence similarity), an organism not previously shown to c ouple the complete oxidation of sugars to the reduction of Fe(III), These c ollective results indicate that the in situ reduction of Pe(III) in acidic sediments can be mediated by heterotrophic Acidiphilium species that are ca pable of coupling the reduction of Fe(III) to the complete oxidation of a l arge variety of substrates including glucose and H-2.