Abstract
The marine cyanobacterium Synechococcus sp. PCC 7002 (Syn7002) is a model organism that lacks the gene cluster required for vitamin B(12) biosynthesis, necessitating cooperative interactions with other microbes. In this study, we established a synthetic microbial consortium by co-culturing Syn7002 with a bloom-forming Microcystis community, followed by purification, and subsequently investigated the interactions between Syn7002 and the associated microbial community. Electron microscopy revealed numerous rod-shaped bacteria clustered around Syn7002 cells, indicating close spatial associations between species. Metagenomic analysis showed that the early-stage community consisted mainly of Syn7002, Mesorhizobium sp. TaiHu (MesTH) and Pseudomonas sp. TaiHu (PseTH), although the abundance of PseTH declined after community stabilization. Investigation of vitamin B(12) regulation between MesTH and Syn7002 through metatranscriptomic analysis revealed upregulation of nitrogen metabolism-related genes in the microbial community. Transcriptomic data further indicated that vitamin B(12) biosynthesis and transport genes were significantly upregulated in MesTH. Combined with vitamin B(12)-positive control experiments, these results confirm potential vitamin B(12) complementarity between the two strains. The results further suggest that MesTH promotes the growth of Syn7002 in the community by providing the small amount of vitamin B(12) needed for its growth. These findings provide new insights into vitamin-mediated microbial interactions and reveal additional transcriptional features of the synthetic community.