Dissimilatory reduction of Fe(III) and other electron acceptors by a Thermus isolate

A thermophilic. bacterium that can use O-2, NO3-, Fe(III), and S-0 as termi nal electron accepters for growth was isolated from groundwater sampled at a 3.2-km depth in a South African gold mine. This organism, designated SA-O I, clustered most closely with members of the genus Thermus, as determined by 16S rRNA gene (rDNA) sequence analysis. The 16S rDNA sequence of SA-OI w as >98% similar to that of Thermus strain NMX2 A.1, which was previously is olated by other investigators from a thermal spring in New Mexico, Strain N MX2 Al was also able to seduce Fe(III) and other electron accepters. Neithe r SA-01 nor NMX2 A.1 grew fermentatively, i.e., addition of an external ele ctron acceptor was required for anaerobic growth. Thermus strain SA-01 redu ced soluble Fe(III) complexed with citrate or nitrilotriacetic acid (NTA); however, it could reduce only relatively small quantities (0.5 mM) of hydro us ferric oxide except when the humic acid analog 2,6-anthraquinone disulfo nate was added as an electron shuttle, in which ease 10 mM Fe(III) was redu ced. Fe(III)-NTA was reduced quantitatively to Fe(II); reduction of Fe(III) -NTA was coupled to the oxidation of lactate and supported growth through t hree consecutive transfers, Suspensions of Thermus strain SA-01 cells also reduced Mn(IV), Co(III)-EDTA, Cr(VI), and U(VI). Mn(IV)-oxide was reduced i n the presence of either lactate or H-2. Both strains were also able to min eralize NTA to CO, and to couple its oxidation to Fe(III) reduction and gro wth. The optimum temperature for growth and Fe(III) reduction by Thermus st rains SA-01 and NMX2 A.1 is approximately 65 degrees C their optimum pH is 6.5 to 7.0. This is the first report of a Thermus sp. being able to couple the oxidation of organic compounds to the reduction of Fe, Mn, or S.