Microbial Cross-Feeding and Its Effects on Cowpea (vigna Unguiculata) Plant Growth Promotion

Purpose: To evaluate the in vitro metabolic compartmentalization between strains of actinobacteria and rhizobia isolated from Brazilian semiarid soils and observe the effect of their coinoculation on the development of cowpea plants. Theoretical Framework: The study is based on the importance of microbial interactions in soil, such as metabolite and enzyme sharing, for nutrient cycling and plant growth promotion. Method: Twenty-six rhizobial strains and 23 actinobacteria were cocultured in vitro in media containing xylan, pectin and calcium phosphate. Strains were characterized regarding compatibility on different substrates. Two Streptomyces sp. strains and eight Bradyrhizobium sp. strains were selected and coinoculated in cowpea plants in a greenhouse to evaluate plant development and gas exchange. Results: Compatibility between strains varied significantly among the tested substrates, being higher in pectin and phosphate. Coinoculation resulted in increased values of several biometric parameters compared to standard treatments with only rhizobia or nitrogen fertilization. Conclusions: The association of microorganisms with distinct metabolic capabilities, such as enzyme production, promotes bacterial coexistence and facilitates plant development through complementarity mechanisms. Originality: There are scarce studies on metabolic interactions and growth promotion involving actinobacteria and rhizobia from semiarid soils.