Measurement of chlorite dismutase activities in perchlorate respiring bacteria

Chlorite dismutase (CD) catalyzes the disproportionation of chlorite to chloride (ClO₂^-→Cl^-+O₂) and is present in bacteria capable of cell respiration using perchlorate or chlorate. The activity of this enzyme has previously been measured by monitoring oxygen evolution using a Clark-type dissolved oxygen (DO) probe. We demonstrate here, using two other methods to measure CD activity (a chloride-specific electrode and ion chromatography (IC)) via chloride production, that the DO probe method underestimates dismutation rates. Of the three methods, the chloride probe was the easiest to use and did not require extensive sample handling or post-experimental analysis. Using the chloride electrode method, we determined whole cell rate constants (V_max=64 U/mg DW, K_m=0.17 mM) for the chlorate-grown suspensions of Dechlorosoma sp. strain KJ. We compared the CD activities of strain KJ at a fixed chlorite concentration (0.6 mM) to four other perchlorate respiring bacteria (PRB), and to one non-PRB (Pseudomonas aeruginosa). Chlorate-grown cultures of the five PRB strains had CD activities ranging from 25 to 50 U/mg of cell dry weight (DW), while aerobically grown cultures of the PRB had much lower CD activities (0.5-4 U/mg DW). To our knowledge, this is the first systematic comparison of the different methods to measure CD activities, and the first comparison of CD activities of different PRBs.