Influence of Manganese on Growth of a Sheathless Strain of Leptothrix discophora

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Mn2+ exerted various effects on the growth of Leptothrix discophora strain SS-1 in batch cultures depending on the concentration added to the medium. Concentrations of 0.55 to 5.5 μM Mn2+, comparable to those in the environment from which strain SS-1 was isolated, decreased cell yield and prolonged stationary-phase survival, but did not affect growth rate. Elevated concentrations of 55 to 910 μM Mn2+ also decreased cell yield and prolonged survival, but growth rate was decreased as well. The addition of 1,820 μM Mn2+ caused a decline in cell numbers followed by an exponential rise after 80 h of incubation, indicating the development of a population of cells resistant to Mn2+ toxicity. When 360 μM Mn2+ or less was added to growth flasks, Mn2+ was oxidized to manganese oxide (MnOx, where x is ∼2), which appeared as brown particles in the medium. Quantification of Mn oxidation during growth of cultures to which 55 μM Mn2+ was added showed that nearly all of the Mn2+ was oxidized by the beginning of the stationary phase of growth (15 to 25 h). This result suggested that the decrease in cell yield observed at low and moderate concentrations of Mn2+ was related to the formation of MnOx, which may have bound cationic nutrients essential to the growth of SS-1. The addition of excess Fe3+ to cultures containing 55 μM Mn2+ increased cell yield to levels near those found in cultures with no added Mn2+, indicating that iron deprivation by MnOx was at least partly responsible for the decreased cell yield.

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