Metabólitos vegetais e microbianos no controle de fitobactérias associadas à mandioca: Enterobacter cloacae E Xanthomonas phaseoli pv. manihotis

Abstract

Cassava (Manihot esculenta Crantz) is a crop of major socioeconomic importance, particularly for smallholder farming, but its production is severely constrained by bacterial diseases, including cassava bacterial blight caused by Xanthomonas phaseoli pv. manihotis (X2) and emerging soft rot associated with the Enterobacter cloacae complex (X6). Disease management relies mainly on copper-based compounds and antibiotics, whose effectiveness has been compromised by the emergence of resistant bacterial populations and environmental concerns, highlighting the need for sustainable alternatives. This study investigated plant- and microbial-derived metabolites as biocontrol agents against phytopathogenic bacteria. Initially, essential oils from different accessions of Lippia gracilis and their major constituents, thymol and carvacrol, were evaluated for their antimicrobial, antibiofilm, antivirulence activities and mechanisms of action against the Enterobacter cloacae complex. Subsequently, E. cloacae associated with cassava soft rot was isolated and characterized, followed by the evaluation of cell-free supernatants produced by Bacillus velezensis RT241 and Streptomyces sp. DN246. Antagonism assays, minimum inhibitory and bactericidal concentrations, growth kinetics, cell viability, biofilm formation and eradication, motility, DNA/RNA and protein leakage, hydrolytic enzyme production, and scanning electron microscopy were performed. Essential oils from L. gracilis exhibited pronounced antimicrobial and antibiofilm activities against the E. cloacae complex. Cell free supernatants of B. velezensis RT241 and Streptomyces sp. DN246 showed strong antibacterial activity, with growth inhibition of 90% against X2 and 87% against X6, reduced cell viability (80–87%), eradication of mature biofilms (98% for X2), increased DNA/RNA (58%) and protein (75%) leakage, and ultrastructural alterations consistent with severe membrane damage. Streptomyces sp. DN246 showed the greatest ability to prevent biofilm formation, reaching 93% inhibition against X2 and 82% against X6. Overall, the results demonstrate that metabolites produced by L. gracilis, B. velezensis, and Streptomyces represent promising candidates for the development of sustainable bioinputs for the management of cassava bacterial diseases and other phytopathogenic bacteria.