Kinetics of Perchlorate- and Chlorate-Respiring Bacteria

Abstract

Ten chlorate-respiring bacteria were isolated from wastewater and a perchlorate-degrading bioreactor. Eight of the isolates were able to degrade perchlorate, and all isolates used oxygen and chlorate as terminal electron acceptors. The growth kinetics of two perchlorate-degrading isolates, designated “ Dechlorosoma ” sp. strains KJ and PDX, were examined with acetate as the electron donor in batch tests. The maximum observed aerobic growth rates of 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 rates 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 under anoxic (chlorate-reducing) conditions (0.18 and 0.21 h ⁻¹ , respectively). The maximum growth rates of PDX on perchlorate and chlorate were identical (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. There were substantial differences in the half-saturation constants measured for anoxic growth of isolates on acetate with excess perchlorate (470 mg/liter for KJ and 45 mg/liter for PDX). Biomass yields (grams of cells per gram of acetate) for strain KJ were not statistically different in the presence of the electron acceptors oxygen (0.46 ± 0.07 [ n = 7]), chlorate (0.44 ± 0.05 [ n = 7]), and perchlorate (0.50 ± 0.08 [ n = 7]). These studies provide evidence that facultative microorganisms with the capability for perchlorate and chlorate respiration exist, that not all chlorate-respiring microorganisms are capable of anoxic growth on perchlorate, and that isolates have dissimilar growth kinetics using different electron donors and acceptors.