The legume species of Astragalus as traditional Chinese medicine source and environmental protection plants showed an extensive distribution in the arid region of northwestern China. However, few rhizobia associating with Astragalus have been investigated in this region so far. In this study, 78 endophytic bacteria were isolated from root nodules of 12 Astragalus species and characterized by the PCR-RFLP of 16S rRNA gene and symbiotic genes together with the phylogenetic analysis. Results showed that the majority (53%) of isolates are non-nodulating Agrobacterium sp. and the rest are Mesorhizobium genomic species (41%), Ensifer spp. and Rhizobium gallicum (6%), respectively. Mesorhizobium genomic species are broadly distributed in the Astragalus symbioses and most of them share similar symbiotic genes. It seems that horizontal gene transfer occurred frequently among different genomic species independent of their original hosts and sites. Astragalus adsurgens is nodulated by a widely range of rhizobial species in the nodulation test, revealing that it could play an important role in diversification of Astragalus symbionts and that might be a reason for its wide adaptation to diverse environments.

Algae are an attractive option for CO2 sequestration due to their natural ability to simultaneously fix CO2 and accumulate algal biomass for value-added products. However, the commercial implementation of such technology for efficient capture of CO2 from fossil-derived flue gases is not a reality yet due to several major challenges, such as low gas-liquid mass transport efficiency and relatively high light irradiance demand of algal growth. This study explored an algal-bacterial symbiotic system to utilize formate, a potential intermediate liquid compound of CO2, as carbon source to support microbial growth. The algal-bacterial assemblage, after an adaptive evolution using the formate medium, demonstrated a new route to assimilate CO2 without using high pH cultivations and promote biomass production under low light irradiance condition. The formate based culture system not only resolves CO2 mass transfer limitation, but also expels algae grazers in non-sterilized cultivation conditions. Continuous cultivation of the assemblage on formate led to a carbon capture efficiency of 90% with biomass concentration of 0.92 g/L and biomass productivity of 0.31 g/L/day, which is significantly better than the control cultivation on saturated CO2. In addition, isotope tracing and microbial community analysis offer new insights into formate metabolism and algal-bacterial symbiosis under light and carbon conditions. This study demonstrates a promising route of using electrochemical-derived formate to support algal biorefining.