Cation Transport in Serratia marcescens and Serratia marinorubra

Abstract

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 Mg 2+ contents of both microorganisms were found to be dependent on the ionic strength of the growth or suspending medium. The Mg 2+ 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 p H optimum of 5.5 to 6.1 for S. marcescens , and the K m for K + was approximately 1.6 m m . Na + and Mg 2+ were not taken up by the cells, although the presence of Mg 2+ tended to decrease rates of K + uptake. Tris-(hydroxymethyl)aminomethane, routinely used for resuspending the cells, was apparently taken up by the cells at p H >7.