Effects of seawater cations and temperature on manganese dioxide-reductase activity in a marine Bacillus

Abstract

The seawater cations, Na(+), K(+), Mg(2+), and Ca(2+), each stimulated MnO(2)-reductase activity of whole cells and cell extracts of Bacillus 29. Concentrations of Na(+) and K(+) which stimulated whole cells and cell extracts maximally were equivalent to those in two- to fivefold diluted seawater. Cell-extract activity was strongly stimulated by Ca(2+) and Mg(2+) up to a concentration of 0.01 M Mg(2+) and 0.002 M Ca(2+), with little additional stimulation above these concentrations. Whole-cell activity was stimulated biphasically with increasing concentrations of Ca(2+) and Mg(2+). Comparison of the effects of individual cations or mixtures of them at concentrations equivalent to their concentration in fivefold diluted seawater showed that more activity was obtained with 0.01 M Mg(2+) or 0.002 M Ca(2+) than with 0.1 M Na(+), and more with 0.1 M Na(+) than with 0.0022 M K(+). Fivefold diluted seawater permitted as much or more activity as solutions of individual or synthetic mixtures of the cations. Pre-exposure experiments showed that the ionic history of whole cells was important to their ultimate activity. The MnO(2)-reductase activity of induced whole cells exhibited a temperature optimum near 40 C. Cell extracts had different temperature optima (T(opt)), depending on whether induced glucose-linked activity (T(opt) = 25 C), uninduced glucose-linked, ferricyanide-dependent activity (T(opt) = 30 C), or uninduced ferrocyanide-linked activity (T(opt) = 40 C) were being measured. Some of these optima are higher than previously reported.