Growth promotion of Chlorella ellipsoidea by co-inoculation with Brevundimonas sp isolated from the microalga

Eight bacterial strains identified as P1, P2, Y1, Y2, W1, W2, G, and R were isolated from a long-term laboratory culture of the green alga Chlorella ellipsoidea. Although it is unknown how these bacterial strains have been maintained with the C. ellipsoidea culture, all appeared to promote the growth of C. ellipsoidea. Co-inoculation of each bacterial strain with C. ellipsoidea resulted in 0.5-3 times greater algal growth than that of C. ellipsoidea alone. The most effective bacterium (i.e., strain P1) was selected and further characterized. Biochemical analysis and transmission electron microscopy revealed that strain P1 is closely related to the genus Brevundimonas. Sequence analysis of the 16S rRNA of strain P1 showed 99.9 and 99.4% nucleotide sequence identity to that of B. nasdae and B. vesicularis, respectively. In addition to the growth promotion of C. ellipsoidea by strain P1, the growth of strain P1 was also significantly enhanced by co-culturing with C. ellipsoidea, indicating a symbiotic relationship between the bacterium and alga. Scanning electron microscopy showed the direct adhesion of strain P1 cells to the surface of C. ellipsoidea cells, as well as the development of abundant crinkles on the surface of co-cultured C. ellipsoidea cells.