The stress-responsive alternative sigma factor SigB plays a positive role in the antifungal proficiency of Bacillus subtilis

BARTOLINI M.; BAUMAN C.; COGLIATI S.; RAMIREZ WALTER; VILETA D.; GRAU R.

APPLIED AND ENVIRONMENTAL MICROBIOLOGY

AMER SOC MICROBIOLOGY

Lugar: Washington; Año: 2019

0099-2240

Different Bacillus species with PGPR (plant growth-promoting rhizobacterium) activity produce potent biofungicides and stimulate plant defense responses against phytopathogenic fungi. However, very little is known about how these PGPRs recognize phytopathogens and process the antifungal response. Here, we report the antagonistic interaction between B. subtilis and the phytopathogenic fungus Fusarium verticillioides. We demonstrate that this bacterial-fungal interaction triggers the induction of the SigB transcription factor, the master regulator of B. subtilis stress adaptation. Dual-growth experiments performed with live or dead mycelia or cell-free supernatants of F. verticillioides showed that SigB was activated and required for the biocontrol of fungal growth. The use of different B. subtilis isogenic strains affected in the different pathways of SigB activation, showed that only the RsbP-dependent energetic route, and not the environmental and low-temperature routes, of SigB activation was responsible for fungal detection and the antagonistic response. The fungus-dependent activation of SigB increased the expression of the operon responsible for the production of the antimicrobial cyclic lipopeptide surfactin (the srfA operon). SigB-deficient B. subtilis cultures produced decreased amounts of surfactin, and B. subtilis cultures defective in surfactin production (ΔsrfA) were unable to control the growth of F. verticillioides. These findings provide the first evidence of the participation of the stress-responsive regulon of a PGPR Bacillus in the detection and biocontrol of a phytopathogenic fungus of agronomical importance.