Cation Transport in Serratia marcescens and Serratia marinorubra

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RESUMO

The sodium, potassium, and magnesium ion contents of Serratia marcescens and those of its salt-tolerant relative, S. marinoruba, were determined by atomic-absorption spectrometry. The intracellular K+ and Mg2+ contents of both microorganisms were found to be dependent on the ionic strength of the growth or suspending medium. The Mg2+ content of S. marinoruba was generally greater than that of S. marcescens. The Na+ content of the cells was normally low and did not increase as the cells aged or when the cells were grown in media of high ionic strength. The transport of K+ by resting cells suspended in hypertonic solution was studied by chemical and light-scattering techniques and was found to be more rapid in S. marcescens than in S. marinorubra. The slower rate of K+ transport in S. marinorubra is probably related to the lower glycogen reserves found in resting cells of this microorganism. K+ transport was found to have a pH optimum of 5.5 to 6.1 for S. marcescens, and the Km for K+ was approximately 1.6 mm. Na+ and Mg2+ were not taken up by the cells, although the presence of Mg2+ tended to decrease rates of K+ uptake. Tris-(hydroxymethyl)aminomethane, routinely used for resuspending the cells, was apparently taken up by the cells at pH >7.

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