A Novel Strain of the Cyanobacterial Growth-promoting Bacterium, Rhodococcus sp. AF2108, Enhances the Growth of Synechococcus elongatus.

To enhance the growth of the cyanobacterium Synechococcus elongatus, the present study conducted direct screening for cyanobacterium growth-promoting bacteria (CGPB) using co-cultures. Of the 144 strains obtained, four novel CGPB strains were isolated and phylogenetically identified: Rhodococcus sp. AF2108, Ancylobacter sp. GA1226, Xanthobacter sp. AF2111, and Shewanella sp. OR151. A co-culture of S. elongatus with the most effective CGPB strain, Rhodococcus sp. AF2108, achieved a 8.5-fold increase in the chlo-rophyll content of cyanobacterial cells over that in a monoculture. A flow cytometric ana-lysis showed a 3.9-fold increase in the number of S. elongatus cells in the co-culture with Rhodococcus sp. AF2108. These results were attributed to increases in forward scattering and chlo-rophyll fluorescence intensities. The new Rhodococcus strain appears to be one of the most effective CGPBs described to date.