Kinetics of manganese oxidation by cell-free extracts of bacteria isolated from manganese concretions from soil.

A study of the kinetics of Mn oxidation catalyzed by cell extracts of two bacterial isolates (E(1), Pseudomonas III [new isolate] and E(4), Citrobacter freundii) isolated from the core of manganese concretions from Greek soils is presented. The reaction velocity of Mn oxidation was determined from the rate of consumption of Mn. The oxidation of Mn was followed by measuring changes in Mn concentration by activation analysis and by atomic absorption spectrophotometry. The reaction velocity was directly proportional to cell extract concentration when the reaction time was 1 h. At longer reaction times, the relationship deviated from linearity because substrate concentration became limiting. The rate of Mn oxidation increased with the Mn concentration. Analysis of the results by application of the integrated Michaelis equation for determining Michaelis constants and maximal velocities either in the presence (K(m) = 3.33 mumol/ml and V(max) = 1.25 mumol/ml.h) or in the absence of maleate buffer (K(m) = 2.52 mumol/ml and V(max) = 2.04 mumol/ml.h) indicated a strong affinity between the oxidizing system and manganese. All results in this study are consistent with an enzymatic manganese-oxidizing system and give an indication of the mechanism of biological Mn oxidation in soil which differs from that in the marine environment.