Diazotrophic bacterium Azotobacter vinelandii as a mutualistic growth promoter of an aquatic plant: Lemna minor

Abstract Lemnaceae plants, commonly referred to as duckweeds, are small planktonic terrestrial freshwater plants that live in symbiosis with various microbial communities. These plants are model platforms for the study of host-microbe interactions (Yamakawa et al. 2018). Azotobacter vinelandii are typical free-living nitrogen fixing soil bacteria that indirectly benefit plants by providing nitrogen compounds. In this study, Lemna minor RDSC 5512 and A. vinelandii ATCC 12837 = NBRC 13581 were co-cultured under gnotobiotic conditions. The growth of L. minor colonized by A. vinelandii accelerated in both nitrogen-containing and nitrogen-free water conditions. Moreover, L. minor elevated the nitrogen fixing activity of A. vinelandii. Lastly, the cell number of A. vinelandii on L. minor increased continuously over 30 d. These observations indicated that L. minor provides a favorable environment for A. vinelandii colonization, allowing them to mutually benefit and flourish through syntrophism.