Application of a growth-promoting bacteria for stable mass culture of three marine microalgae

Abstract

The practical mass culture of marine microalgae, faces occasionally unexpected problems or collapse. The effect of a marine bacterium, Flavobacterium sp., which was found to promote growth of a marine diatom Chaetoceros gracilis in the axenic culture condition, was examined on the mass cultures of three marine microalgae.

Three marine microalgae (C. gracilis, Isochrysis galbana, and Pavlova lutheri) were mass cultured in 3 1 flatbottom flasks (2.5 1 capacity of culture medium), in an indoor culture room at a commercial pearl oyster hatchery. The microalgal cells and the bacterium were inoculated at the same time, in the culture media. The specific growth rate and maximal cell density were determined in treated cultures (with added bacterial strain) and in controls (without added bacterial strain). The specific growth rate of C. gracilis in treated cultures was significantly higher than that of control cultures, and the stationary growth phase in the treated cultures lasted longer till the end of the culture period. However, the bacterium had no apparent effect on the exponential growth phase of two phytoflagellates, I. galbana and P. lutheri, but kept longer the high cell density in the stationary growth phases. The added bacterial strain (Flavobacterium sp.) was the dominant species (more than 45%) among the bacterial flora during the culture period.