Seasonal changes in antibacterial activity of North Sea water

During 1969 and 1970, the antibacterial activity of North Sea water was investigated at Helgoland (southern North Sea). Tests were performed with resting cells of Escherichia coli, Staphylococous aureus and Serratia marinorubra, inoculated in freshly sampled sea water used raw or after filter sterilization. Simultaneously, growth of indigenous bacterial populations which occurred in the presence, as well as in the absence (only 1970), of test bacteria was controlled. Seasonal changes in inactivation of test cells and multiplication of marine bacteria were correlated with the life cycles of several diatom species. Breakdown of phytoplankton flowerings produced the most pronounced influence on antibacterial activity of sea water. Sometimes, enhancement of kill rate could be established during growth periods of various algal species, too. From the results obtained, it is concluded that the inactivation capacity of sea water depends, to a considerable degree, on the availability of nutritive organic matter, the concentration of which changes according to phytoplankton development. Strain-specific differences in resistance to inimical action of sea water are, in part, correlated with the ability of test cells to use, and to compete with, marine bacteria for nutrients from the sea. A somewhat modified interpretation of antibacterial activity of sea water is presented.