Antagonistic effects of Bacillus subtilis subsp. subtilis and B. amyloliquefaciens against Macrophomina phaseolina: SEM study of fungal changes and UV-MALDI-TOF MS analysis of their bioactive compounds

M.J. TORRES,; C. PEREZ BRANDAN; G. PETROSELLI, ; M.C. AUDISIO; ERRA-BALSELLS, R; ROSA ERRA BALSELLS

MICROBIOLOGICAL RESEARCH

ELSEVIER GMBH

Año: 2016 vol. 182 p. 31 - 39

0944-5013

tThe antifungal effect of Bacillus subtilis subsp. subtilis PGPMori7 and Bacillus amyloliquefaciens PGPBacCA1was evaluated against Macrophomina phaseolina (Tassi) Goid. Cell suspension (CS), cell-free supernatant(CFS) and the lipopeptide fraction (LF) of PGPMori7 and PGPBacCA1 were screened against three differentM. phaseolina strains. CS exhibited the highest inhibitory effect (around 50%) when compared to thoseof CFS and LF, regardless of the fungal strain studied. The synthesis of lipopeptides was studied by UV-MALDI TOF. Chemical analysis of Bacillus metabolite synthesis revealed that surfactin and iturin weremainly produced in liquid medium. Potential fengycin was also co-produced when both Bacillus werecultivated in solid medium. In co-culture assays, the bacterial colony-fungal mycelium interface at theinhibition zone was evaluated by both scanning electron microscopy (SEM) and UV-MALDI TOF, theformer to determine the structural changes on M. phaseolina cells and the latter to identify the mainbioactive molecules involved in the inhibitory effect. PGPBacCA1 produced surfactin, iturin and fengycinin the inhibition zone while PGPMori7 only produced these metabolites within its colony and not in thenarrow inhibition zone. Interestingly, SEM revealed that PGPBacCA1 induced damage in M. phaseolinasclerotia, generating a fungicidal effect as no growth was observed when normal growth conditions werereestablished. In turn, PGPMori7 inhibited the growth of the Macrophomina mycelium without fungalinjury, resulting only in a fungistatic activity. From these results, it was determined that the two bacillisignificantly inhibited the growth of an important phytopathogenic fungus by at least two differentmechanisms: lipopeptide synthesis and competition among microorganisms.© 2015 Elsevier GmbH. All rights reserved.