Effect of different seawaters on the development of biochemically deficient mutants of Serratia marinorubra.

The effect of different seawaters on survival and growth of biotin-, isoleucine-, and uracil-requiring mutants of the marine bacterium, Serratia marinorubra, has been investigated. Samples of seawater were collected from coastal waters, the California Current, and central North Pacific waters at depths of 1, 25, 50, 100, 250, and 500 m. The growth or survival of the test bacterium in basal medium prepared in these seawater samples was determined. The control water was synthetic or charcoal-treated natural seawater. In several experiments, the metabolite required by the bacterium was added to the basal medium 24 hr after inoculation, and the growth response was determined. Depending on the source, the seawater samples were both stimulating and inhibitory. Surface waters were more inhibitory than those taken at depth, where, in some cases, bacterial growth occurred. Seawater inhibition was related more to station depth than to the location of the station. The most toxic effects were found against the uracil-requiring mutant; the least, against the isoleucine-requiring mutant. The results of these studies and some laboratory experiments indicate that seawater toxicity is not primarily associated with the physical and biological properties of a particular water mass and that the same factor(s) may be responsible for the rapid death of bacteria in all waters.