Anaerobic oxidations of cysteate: degradation via L-cysteate : 2-oxoglutarate aminotransferase in Paracoccus pantotrophus

Anoxic, fresh-water enrichment cultures to oxidize different organosulfonat es were set up with nitrate, ferric iron or sulfate as electron accepters. Pure cultures were easily obtained with two naturally occurring sulfonates, cysteate (2-amino-3-sulfopropionate) and taurine (2-aminoethanesulfonate), under nitrate-reducing conditions. These two sulfonates were also oxidized during reduction of iron(III), though isolation of pure cultures was not s uccessful. One nitrate-reducing cysteate-oxidizing bacterium, strain NKNCYS A, was studied in detail. It was identified as Paracoccus pantotrophus. Eig hteen sulfonates were tested, and the organism degraded cysteate, taurine, isethionate (2-hydroxyethanesulfonate). sulfoacetate or 3-amino-propanesulf onate with concomitant reduction of nitrate, presumably to molecular nitrog en. The carbon skeleton of these substrates was converted to cell material and, presumably, CO2. The amino group was released as ammonia and the sulfo no moiety was recovered as sulfate. Cell-free extracts of P. pantotrophus N KNCYSA contained constitutive L-cysteate:2-oxoglutarate aminotransferase (E C 2.6.1.-) and glutamate dehydrogenase (EC 1.4.1.4). Taurine:pyruvate amino transferase, in contrast, was inducible.