Functional genomics and phenotypic characterization of PGP and biocontrol traits of rhizospheric Streptomyces spp. from Mexican milpa agroecosystem

Traditional Mesoamerican milpa is an ancient agroecosystem with actual cultural and economic importance, particularly for auto-consume agriculture. This agroecosystem includes several plants of American origin, establishing many beneficial ecological relationships among them and plant-microbe interactions. In this study, a collection of Streptomyces strains was isolated from the rhizosphere of native Cacahuacintle maize, squash, fava bean, and huauzontle, all of which exhibited various in vitro plant growth-promoting (PGP) activities such as ammonium production, phosphate solubilization, and siderophore production, moreover, Streptomyces sp. FR-108 from fava bean rhizosphere and Streptomyces griseus MR-45 from maize increased the maize biomass in a short-term greenhouse assay. Among other strains, Streptomyces sp. SR-10 from squash and Streptomyces albidoflavus MR-37 from maize expressed in vitro extracellular enzyme secretion and antagonistic activities against phytopathogenic fungi. Comparative and fuctional genomic analysis of these strains revealed extensive gene repertoires involved in plant growth promotion by nutrient acquisition, tolerance to osmotic, drought, chemical, and temperature stresses, mutualistic plant-microbe interactions, and fungi, bacteria, insects, and protist biocontrol. It is not common to find species of the genus Streptomyces as plant growth-promoting bacteria (PGPB) in agroecosystems; however, these findings highlight the untapped potential of milpa-associated members of this genus as bioinoculants for sustainable or extensive agriculture and underscore the importance of traditional agroecosystems as sources of beneficial microorganisms.