Algae-bacteria consortia promote the cell growth of marine microalgae Phaeodactylum tricornutum and Chrysotila roscoffensis

The commercial exploitation of Phaeodactylum tricornutum and Chrysotila roscoffensis is hampered by their low biomass productivity. Microalgae-bacteria co-cultivation (MBC), as an emerging approach designed to boost microalgal growth, has recently gained considerable attention. Nevertheless, studies focusing on MBC with these two microalgae remain scarce. In this study, six bacterial strains were isolated from xenic microalgal cultures. Subsequent co-cultivation trials revealed two strains of Bacillus spp. and one of Agrobacterium sp. were found to promote the growth of axenic C. roscoffensis and P. tricornutum. Biochemical analysis, encompassing macromolecules, pigments, and fatty acids, indicated that the addition of these beneficial bacteria did not weaken the quality of microalgal biomass, but substantially increased the productivity of bioactive substances. To assess the feasibility of employing these bacteria in large-scale microalgal cultivation, further MBC trials using xenic microalgal cultures were conducted. The results confirmed that the beneficial bacteria were also effective in a non-axenic MBC context.