Data from: Macroalgal-bacterial interactions: role of dimethylsulfoniopropionate in microbial gardening by Ulva (Chlorophyta)

The marine macroalga Ulva mutabilis (Chlorophyta) develops into callus-like colonies consisting of undifferentiated cells and abnormal cell walls under axenic conditions. U. mutabilis is routinely cultured with two bacteria, the Roseovarius sp. MS2 strain and the Maribacter sp. MS6 strain, which release morphogenetic compounds and ensure proper algal morphogenesis. Using this tripartite community as an emerging model system, we tested the hypothesis that the bacterial-algal interactions evolved as a result of mutually taking advantage of signals in the environment. Our study aimed to determine whether cross-kingdom cross-talk is mediated by the attraction of bacteria through algal chemotactic signals. Roseovarius sp. MS2 senses the known osmolyte dimethylsulfoniopropionate (DMSP) released by Ulva into the growth medium. Roseovarius sp. is attracted by DMSP and takes it up rapidly. Therefore, the compound can only be determined in axenic growth media. As DMSP did not promote bacterial growth under the tested conditions, Roseovarius benefited solely from glycerol as the carbon source provided by Ulva. Roseovarius quickly catabolized DMSP into methanethiol (MeSH) and dimethylsulfide (DMS). We conclude that many bacteria can use DMSP as a reliable signal indicating a food source and promote the subsequent development and morphogenesis in Ulva.

无菌培养条件下，海洋大型藻类变异石莼（Ulva mutabilis，绿藻门（Chlorophyta））会形成由未分化细胞与异常细胞壁构成的愈伤组织样菌落。常规培养流程中，变异石莼需与两种细菌共培养：玫瑰杆菌属（Roseovarius）菌株MS2与海杆菌属（Maribacter）菌株MS6，这两类细菌可分泌形态发生化合物，保障藻类正常形态发生。本研究以该三方群落作为新兴模型系统，验证了“细菌-藻类互作是通过相互利用环境信号演化而来”这一假说。本研究旨在探究跨界信号互作是否由藻类释放的趋化信号介导细菌趋化过程所实现。玫瑰杆菌属菌株MS2可感知石莼释放至培养基中的已知渗透保护剂二甲基巯基丙酸内盐（dimethylsulfoniopropionate, DMSP）。该菌株可被DMSP吸引并快速摄取该物质，因此该化合物仅能在无菌培养培养基中被检测到。在本次实验设置的条件下，DMSP并未促进细菌生长，因此玫瑰杆菌属菌株仅能利用石莼提供的甘油作为碳源获取营养。玫瑰杆菌属菌株可快速将DMSP分解为甲硫醇（methanethiol, MeSH）与二甲基硫（dimethylsulfide, DMS）。综上，诸多细菌可将DMSP作为指示食物来源的可靠信号，并以此促进石莼的后续生长与形态发生。