Kinetics of perchlorate- and chlorate-respiring bacteria

Ten chlorate-respiring bacteria were isolated from wastewater and a perchlo rate-degrading bioreactor, Eight of the isolates were able to degrade perch lorate, and all isolates used oxygen and chlorate as terminal electron acce pters. The growth kinetics of two perchlorate-degrading isolates, designate d "Dechlorosoma" sp, strains KJ and PI)X, were examined with acetate as the electron donor in batch tests. The maximum observed aerobic growth rates o f KJ and PDX (0.27 and 0.28 h(-1), respectively) were only slightly higher than the anoxic growth rates obtained by these isolates during growth with chlorate (0.26 and 0.21 h(-1), respectively). The maximum observed growth r ates of the two non-perchlorate-utilizing isolates (PDA and PDB) were much higher under aerobic conditions (0.64 and 0.41 h(-1), respectively) than un der anoxic (chlorate-reducing) conditions (0.18 and 0.21 h(-1), respectivel y), The maximum growth rates of PDX on perchlorate and chlorate were identi cal (0.21 h(-1)) and exceeded that of strain KJ on perchlorate (0.14 h(-1)) . Growth of one isolate (PDX) was more rapid on acetate than on lactate. Th ere were substantial differences in the half-saturation constants measured for anoxic growth of isolates on acetate with excess perchlorate (470 mg/li ter for KJ and 45 mg/liter for PDX). Biomass yields (grams of cells per gra m of acetate) for strain KJ were not statistically different in the presenc e of the electron accepters oxygen (0.46 +/- 0.07 [n = 7]), chlorate (0.44 +/- 0.05 [n = 7]), and perchlorate (0.50 +/- 0.08 [n = 7]). These studies p rovide evidence that facultative microorganisms with the capability for per chlorate and chlorate respiration exist, that not all chlorate-respiring mi croorganisms are capable of anoxic growth on perchlorate, and that isolates have dissimilar growth kinetics using different electron donors and accept ers.