Effects of Seawater Cations and Temperature on Manganese Dioxide-Reductase Activity in a Marine Bacillus

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Abstract
The seawater cations, Na+, K+, Mg2+, and Ca2+, each stimulated MnO2-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 Ca2+ and Mg2+ up to a concentration of 0.01 M Mg2+ and 0.002 M Ca2+, with little additional stimulation above these concentrations. Whole-cell activity was stimulated biphasically with increasing concentrations of Ca2+ and Mg2+. 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 Mg2+ or 0.002 M Ca2+ 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 MnO2-reductase activity of induced whole cells exhibited a temperature optimum near 40 C. Cell extracts had different temperature optima (Topt), depending on whether induced glucose-linked activity (Topt = 25 C), uninduced glucose-linked, ferricyanide-dependent activity (Topt = 30 C), or uninduced ferrocyanide-linked activity (Topt = 40 C) were being measured. Some of these optima are higher than previously reported.

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