Bioprospecção de bactérias promotoras de crescimento do semiárido mineiro com potencial de tolerância ao déficit hídrico na cultura do café

Abstract

Plant growth-promoting bacteria (PGPB) constitute a sustainable biotechnological strategy to increase agricultural resilience to abiotic stresses such as water deficit and heat stress, which have been intensified by climate change. In Brazil, the world's largest coffee producer and exporter, with Minas Gerais accounting for a large share of Coffea arabica production, these bacteria have become increasingly relevant in view of harvests affected by droughts and high temperatures. The literature highlights the following mechanisms: ACC deaminase synthesis (reduces stress-induced ethylene), exopolysaccharide (EPS) production (improves water retention), osmoprotectant production (proline), and induction of the antioxidant system (SOD, CAT, APX). In C. arabica, which is sensitive to water deficit, stress causes stomatal closure, reduced photosynthesis, ROS accumulation, increased MDA, oxidative damage, and reduced growth and productivity. The study isolated 51 morphotypes (predominantly Bacillus cereus) from the rhizosphere, roots, and rhizomes of xerophytic plants from the Semiárido Mineiro (Calotropis procera and Smilax sp.). Functional characterization showed high EPS production (especially in sucrose), high ACC deaminase activity (with SE1M07 standing out), extreme osmotic tolerance (growth at Aw 0.844), and proline production (up to approximately 295 nmol/mg protein/h). MALDI-TOF confirmed the predominance of Bacillus spp., adapted to arid environments. Twenty isolates were inoculated into C. arabica seedlings under normal irrigation, promoting gains of up to 40% in height, greater number of leaves, stem diameter, chlorophyll/carotenoid contents, NDVI, and shoot biomass. Three isolates stood out (BAC1, BAC2, and BAC3) due to the balance between vigor and photoprotection. When tested under four levels of water stress (daily irrigation and irrigation every 2, 4, and 7 days), under mild to moderate stress, inoculation, especially BAC3, maintained better growth, preserved chlorophyll, reduced MDA and H₂O₂, and strongly activated the antioxidant system, particularly catalase (CAT). Under severe stress, the benefits were limited, but BAC3 maintained a distinct redox strategy (high CAT and lower APX). It is concluded that Bacillus isolates from the Semiárido Mineiro have high potential as bioinputs to increase the tolerance of coffee seedlings to moderate water deficit by modulating physiological and redox responses, contributing to a more resilient and sustainable coffee production system in southern Minas Gerais under climate change.