Vitamin B<sub>12</sub>-associated interactions between <i>Mesorhizobium</i> sp. TaiHu and <i>Synechococcus</i> sp. PCC 7002 revealed by multi-omics analysis
Abstract
The marine cyanobacterium <i>Synechococcus</i> sp. PCC 7002 (Syn7002) is a model organism that lacks the gene cluster required for vitamin B<sub>12</sub> biosynthesis, necessitating cooperative interactions with other microbes. In this study, we established a synthetic microbial consortium by co-culturing Syn7002 with a bloom-forming <i>Microcystis</i> 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, <i>Mesorhizobium</i> sp. TaiHu (MesTH) and <i>Pseudomonas</i> sp. TaiHu (PseTH), although the abundance of PseTH declined after community stabilization. Investigation of vitamin B<sub>12</sub> 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<sub>12</sub> biosynthesis and transport genes were significantly upregulated in MesTH. Combined with vitamin B<sub>12</sub>-positive control experiments, these results confirm potential vitamin B<sub>12</sub> 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<sub>12</sub> needed for its growth. These findings provide new insights into vitamin-mediated microbial interactions and reveal additional transcriptional features of the synthetic community.