Affiliation:
1. Department of Biology, New Mexico Institute of Mining and Technology, Socorro, New Mexico 878011;
2. Pacific Northwest National Laboratory, Richland, Washington 993522; and
3. Department of Geosciences, Princeton University, Princeton, New Jersey 085443
Abstract
ABSTRACT
A thermophilic bacterium that can use O
2
, NO
3
−
, Fe(III), and S
0
as terminal electron acceptors for growth was isolated from groundwater sampled at a 3.2-km depth in a South African gold mine. This organism, designated SA-01, clustered most closely with members of the genus
Thermus
, as determined by 16S rRNA gene (rDNA) sequence analysis. The 16S rDNA sequence of SA-01 was >98% similar to that of
Thermus
strain NMX2 A.1, which was previously isolated by other investigators from a thermal spring in New Mexico. Strain NMX2 A.1 was also able to reduce Fe(III) and other electron acceptors. Neither SA-01 nor NMX2 A.1 grew fermentatively, i.e., addition of an external electron acceptor was required for anaerobic growth.
Thermus
strain SA-01 reduced soluble Fe(III) complexed with citrate or nitrilotriacetic acid (NTA); however, it could reduce only relatively small quantities (0.5 mM) of hydrous ferric oxide except when the humic acid analog 2,6-anthraquinone disulfonate was added as an electron shuttle, in which case 10 mM Fe(III) was reduced. 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 three 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 in the presence of either lactate or H
2
. Both strains were also able to mineralize NTA to CO
2
and to couple its oxidation to Fe(III) reduction and growth. The optimum temperature for growth and Fe(III) reduction by
Thermus
strains SA-01 and NMX2 A.1 is approximately 65°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.
Publisher
American Society for Microbiology
Subject
Ecology,Applied Microbiology and Biotechnology,Food Science,Biotechnology
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