Antimicrobial activity of Bacillus subtilis associated with Dactylellina gephyropaga against Arthrobotrys conoides isolated from nematode infested citrus rhizosphere

Abstract

ABSTRACT The direct and indirect modulating effects of two citrus soil bacteria, Bacillus thuringiensis and Bacillus subtilis, on the activity of two nematophagous fungi, Arthrobotrys conoides and Dactylellina gephyropaga, have been studied. Growth rates of A. conoides and D. gephyropaga, effect of D. gephyropaga on mycelial growth and conidial germination of A. conoides, antifungal activity of B. thuringiensis and B. subtilis against A. conoides and D. gephyropaga and other phytopathogenic fungal species were assessed. Characterisation of the bioactive molecules synthesised by B. subtilis and PCR amplification of Nonribosomal peptide synthetases (NRPS) genes encoding for lipopeptide synthesis were also performed. This study demonstrated that the growth of A. conoides was inhibited by D. gephyropaga strictly mediated by fungistatic substances secreted by its associated bacterium B. subtilis. Additionally, this bacterium showed strong mycelial growth inhibition of A. conoides, Fusarium sp., Penicillium italicum, P. digitatum and Phytophthora nicotianae. NRPS genes encoding for surfactin, mycosubtilin, fengycin, Kurstakine and bacillomycin synthesis were detected in B. subtilis. MALDI-TOF MS analysis of the lipopeptides identified the major fungistatic substances secreted by B. subtilis as surfactin and iturine C. This study extended our knowledge about the mechanism behind the complex interactions between the citrus soil bacteria and nematophagous fungi and revealed the bioactive molecules as key enzymes in the biocontrol.