Growth promotion of synthetic microbial communities influenced by the function, diversity and interactions of their constituent strains and soil types.

The construction of efficient synthetic microbial communities (SMCs) is a major challenge for the scientific community. In this study, we constructed 15 SMCs with a diversity gradient of 1-4 by combining four strains with different functions, and investigated the effects of strain interactions, community diversity and in vitro functions on in vivo rice growth promotion in two soil types. The interactions between the 4 strains were tested using a modified dual culture plate assay. The in vitro functions (nitrogen fixation, phosphate and potassium solubilization, indoleacetic acid production, 1-aminocyclopropane-1-carboxylate (ACC) deaminase activity, siderophore production) of the 15 SMCs were measured by the biochemical assay. The in vivo growth promotion of the 15 SMCs was investigated in rice pot experiments in 2 different soils. The study showed that the in vivo functions of SMCs were related to the soils in which they were grown and their in vitro functions and diversity. The in vitro functions of SMCs were closely related to the functions (especially ACC deaminase producing capabilities), diversity, and interactions of the constituent strains. It was concluded that the plant growth promotion of SMCs was influenced by the function, diversity and interactions of their constituent strains and soil types. This not only advances our understanding of microbe-microbe-plant interactions, but also sheds light on the rational design of effective SMCs for environmentally friendly agriculture.