Endophytic microorganisms from Bauhinia monandra leaves: Isolation, antimicrobial activities and interaction with galactose-specific lectin BmoLL

Bauhinia monandra leaves are well known hypoglycemic agent in Brazilian popular medicine from which a galactose specific lectin (BmoLL) has been purified in milligram quantities. In this work, the antimicrobial activity of endophytes isolated from B. monandra leaves and the ability of BmoLL to agglutinate the microorganisms were evaluated. After disinfection, leaves of B. monandra were fragmented and distributed in Petri plates leading to isolation of fungi (37 strains) and both Gram-positive (26 strains) and negative bacteria (6 strains). A preliminary antimicrobial assay revealed that 62% of bacterial strains were active, while no antagonist action was detected with fungi. However, only 2 strains were able to excrete the antimicrobial compounds: Pseudomonas aeruginosa UFPEDA598 inhibited Aspergillus niger, Fusarium moniliform, Fusarium oxysporum, Micrococcus luteus, Staphylococcus aureus, Bacillus subtilis and PE(24)C1 inhibited Candida sp. strains, M. luteus and S. aureus. On the other hand, BmoLL did not show any antimicrobial action, but it was able to agglutinate the active strain P. aeruginosa UFPEDA598. The BmoLL-Pseudomonas interaction could promote a defense against the attack of phytopathogenic microorganisms in plants through a P. aeruginosa metabolic production mechanism. The lectins/endophytes interaction could be a new line to unravel defense mechanisms against phytopathogenic organisms.