(56e) The Growth Promoting Effect of Symbiont Bacteria On Chlorella Vulgaris

Symbioses between microalgae and bacteria are common in nature but are usually a complex phenomena. Other works have shown that algal-bacterial system have many interactions such as the microalgae producing O₂ which is necessary for bacterial aerobic respiration while at the same time, CO₂ from bacteria can be utilized by microalgae to perform photosynthesis. Some bacteria excrete phytohormone like indole-3-acetic acid which can induce algal cell division while microalgae also secrete extracellular compounds which can similarly enhance the bacterial activity. However, not all the interactions between algae and bacteria are synergistic. Microalgae can produce and accumulate bactericides, such as chlorellin, which can inhibit bacterial growth while toxic algaecide released from bacteria can affect the growth of algae. Recent studies confirmed that some small molecule modulators from algae can control the algal-bacterial symbiosis.

Here, we report the growth promoting effect of a symbiont bacteria isolated from a chlorella vulgaris culture. The algae culture ran for about one year and were found to be growing with other microorganisms to form the algae-bacterial system in our photobioreactor. Several bacteria strains were then isolated based on the agar plate culture method. The symbiont bacteria were co-cultured with axenic chlorella vulgaris and growth promoting effects on the microalgae were found. The number of bacteria increased over several days before remaining constant during the culture period. The findings that synergistic interaction between chlorella vulgaris and the symbiont bacteria could aid our understanding of algal-bacterial symbiosis in nature.