Endophytic Bacteria Isolated from Common Bean (Phaseolus vulgaris) Exhibiting High Variability Showed Antimicrobial Activity and Quorum Sensing Inhibition.

Endophytic bacteria play a key role in the biocontrol of phytopathogenic microorganisms. In this study, genotypic diversity was analyzed via repetitive element PCR (rep-PCR) of endophytic isolates of the phylum Actinobacteria that were previously collected from leaves of cultivars of common bean (Phaseolus vulgaris). Considerable variability was observed, which has not been reported previously for this phylum of endophytic bacteria of the common bean. Furthermore, the ethanol extracts from cultures of various isolates inhibited the growth of pathogenic bacteria in vitro, especially Gram-positive pathogens. Extracts from cultures of Microbacterium testaceum BAC1065 and BAC1093, which were both isolated from the 'Talismã' cultivar, strongly inhibited most of the pathogenic bacteria tested. Bean endophytic bacteria were also demonstrated to have the potential to inhibit the quorum sensing of Gram-negative bacteria. This mechanism may regulate the production of virulence factors in pathogens. The ability to inhibit quorum sensing has also not been reported previously for endophytic microorganisms of P. vulgaris. Furthermore, M. testaceum with capacity to inhibit quorum sensing appears to be widespread in common bean. The genomic profiles of M. testaceum were also analyzed via pulsed-field gel electrophoresis, and greater differentiation was observed using this method than rep-PCR; in general, no groups were formed based on the cultivar of origin. This study showed for the first time that endophytic bacteria from common bean plants exhibit high variability and may be useful for the development of strategies for the biological control of diseases in this important legume plant.