Stimulatory Properties of Filtrate From the Green Alga Hormotila Blennista. I. Description1,2

SUMMARY A laboratory phenomenon involving autostimulation of growth by filtrates of the green alga Hormotila blennista is described, and stimulation attributed primarily to the secretion of organic metabolites. Filtrates obtained from actively growing cultures 1 through 4 weeks old showed maximum growth rate stimulation values in excess of 100%. Stimulatory properties of filtrate were heat labile, were not closely controlled by the starting pH within the limits normally encountered in culture, and did not result from depletion of essential nutrients. Concomitant with growth rate stimulation, filtrates characteristically extended the lag phase of culture growth. H. blennista filtrate can support bacterial growth and selectively stimulate or inhibit 2 planktonic green algae. It was suggested that extracellular organic products secreted by H. blennista during active growth could be of survival value to the organism, and could also play regulatory roles among other microorganisms in nature.