Growth inhibition of harmful cyanobacterium Microcystis by picocyanobacterium Cyanobium: transcriptome-based interaction analysis

The occurrence and collapse of cyanobacterial blooms, particularly those caused by Microcystis, are influenced by interactions with a variety of microorganisms. Recent studies have revealed that Microcystis is affected not only by heterotrophic bacteria but also by interactions with picocyanobacteria. This study investigated how and under what conditions the picocyanobacterium Cyanobium impacts Microcystis growth, suggesting potential mechanisms of these interactions based on transcriptome analysis. Cyanobium gracile A950 exhibited a stronger inhibitory effect on the growth of Microcystis aeruginosa KW at higher temperature. In a co-culture experiment, M. aeruginosa KW downregulated photosynthesis-related genes, including psaC and psaE, which impaired energy production and light harvesting. Reduced expression of phosphate uptake genes, such as phoU and pstA, suggests that M. aeruginosa KW was disadvantaged in nutrient uptake compared to C. gracile A950. In contrast, C. gracile A950 rapidly upregulated photosynthesis-related and ATP synthase genes within 2 h of co-culture, allowing it to gain an early competitive advantage over M. aeruginosa KW. These findings indicate that the inhibitory effect of C. gracile A950 on M. aeruginosa KW was mainly due to the unbalanced expression changes in photosynthesis-related genes between the two species.