Alkaliphilus metalliredigens QYMF

SEM (19,000X) grown with Fe(III)-EDTA at pH
9.6. Scale bar =1.0 µm. Courtesy of Dr. B. Blair.

Alkaliphilus metalliredigens can reduce Fe(III)-citrate, Fe(III)-EDTA, Co(III)-EDTA, or Cr(VI) as electron acceptors with yeast extract or lactate as electron donors (Ye et al., 2004). Growth during iron reduction occurs over the pH range of 7.5 to 11.0, a sodium chloride range of 0 to 80 g/l and a temperature range of 4°C to 45°C (Ye et al., 2004). Optimal growth conditions during iron reduction in the presence of borate (2 g/l) were observed at a pH of 9.6, a sodium chloride concentration of 20 g/l and a temperature of approximately 35°C. A. metalliredigens is a strict anaerobe that can tolerate up to 1.5% (w/v) borax (Na2B4O7), and the cells are straight rods that produce endospores. The microorganism appears to be a novel metal-reducing bacterium that is distantly related to other commonly studied iron-reducing microorganisms. At the present time, the most closely related microorganisms are Alkaliphilus transvaalensis and Alkaliphilus crotonatoxidans. A. transvaalensis was isolated from deep gold mines in South Africa, and could grow in the pH range of 8.5 to 12.5 (Takai et al., 2001). A. crotonatoxidans was isolated from an anaerobic digester for the treatment of bean curd waste water, and has a pH range of 5.5 to 9.0 (Cao et al., 2003).

Motivation for Genome Sequence Determination.
Dissimilatory metal reduction has widened the realm of life-supporting biological reactions (Nealson and Cox, 2002), and has been implicated as an important biochemical process on early Earth (Liu et al., 1997; Weigel and Hanel, 2002). The ability to reduce metals can be exploited for the bioreduction or immobilization of many toxic metals, including cobalt, chromium, uranium, and technetium. Sites contaminated with toxic metals can have drastically different environmental conditions, and the biological reduction of most metals has commonly been studied at circum neutral pH values and mesophilic temperatures (Straub et al., 2001). Little is known about metal reduction under different extreme conditions, and only recently has bacterial Fe(III) reduction been demonstrated under thermophilic, psychrophilic, or acidic conditions. The whole-genome sequence determination for this low G+C, Gram-positive bacterium will provide insight into the genetic and biochemical diversity of metal-reducing microorganisms with the ability to tolerate and thrive in different environmental conditions.