A sulfate-reducing bacterium using trinitrotoluene (TNT) as the sole nitrogen source was isolated with pyruvate and sulfate as the energy sources. The organism was able to reduce TNT to triaminotoluene (TAT) in growing cultures and cell suspensions and to further transform TAT to still unknown products. Pyruvate, H2, or carbon monoxide served as the electron donors for the reduction of TNT. The limiting step in TNT conversion to TAT was the reduction of 2,4-diamino-6-nitrotoluene (2,4-DANT) to triaminotoluene. The reduction proceeded via 2,4-diamino-6-hydroxylaminotoluene (DAHAT) as an intermediate. The intermediary formation of DAHAT was only observed in the presence of carbon monoxide or hydroxylamine, respectively. The reduction of DAHAT to triaminotoluene was inhibited by both CO and NH2OH. The inhibitors as well as DANT and DAHAT significantly inhibited sulfide formation from sulfite. The data were taken as evidence for the involvement of dissimilatory sulfite reductase in the reduction of DANT and/or DAHAT to triaminotoluene. Hydrogenase purified from Clostridium pasteurianum and carbon monoxide dehydrogenase partially purified from Clostridium thermoaceticum also catalyzed the reduction of DANT in the presence of methyl viologen or ferredoxin, however, as the main reduction product DAHAT rather than triaminotoluene was formed. The findings could explain the function of CO as an electron donor for the DANT reduction (to DAHAT) and the concomitant inhibitory effect of CO on triaminotoluene formation (from DAHAT) by the inhibition of sulfite reductase.(ABSTRACT TRUNCATED AT 250 WORDS)

D edicated to Professor A chim Trebst on the occasion o f his 60th birthdayCarbon Isotope Fractionation. Autotrophy. A cetyl-C oA Pathway, Reductive Citric Acid Cycle, Calvin Cycle Carbon isotope fractionation during autotrophic growth o f different bacteria which possess different autotrophic C 0 2 fixation pathways has been studied. 13C /l2C -R atios in the cell carbon of the follow ing bacteria were determined ( C 0 2 fixation pathway suggested or proven in paren theses): A lkaligenes eutrophus (reductive pentose phosphate cycle), D esulfobacterium autotrophicum and A cetobacterium w oodii (reductive acetyl-C oA pathway), D esulfobacter hydrogenophilus and T herm oproteus neutrophilus (reductive citric acid cycle). The A ö l3C values, which indicate the p e r m ille deviation o f the 13C content o f cell carbon from that o f the C O : used as the sole carbon source, range from -10%c (reductive citric acid cycle) over -26%c (reductive pentose phosphate cycle) to -36%c (reductive acetyl-C oA pathway). A cetate formed via the acetyl-C oA pathway by the acetogenic Acetobacterium w oodii showed a A 6 I3C = -40%c. These data are discussed in view of the different C 0 2 fixation reactions used by the bacteria and especially with regard to the isotopic com position of sedim entary carbon through time.

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