Alcaligenes faecalis strain SASBG203: A novel biocontrol agent against Colletotrichum orbiculare

Abstract

Bottle gourd is one of the important cucurbitaceous vegetables widely consumed in Indian households. Many fungal diseases affect its cultivation and one among them is stem splitting caused by Colletotrichum orbiculare. This pathogen causes a range of symptoms, viz., leaf spots, vertical water-soaked streaks on petioles, stems, crotches and splitting of stem at crown region. Farmers resort to indiscriminate use of fungicides for controlling the disease which poses the threat of chemical residues in the produce. The aim of this study is to come out with ecofriendly approach like use of native bacterial endophyte from bottle gourd to manage the disease. Of the endophytes isolated, Alcaligenes faecalis strain SASBG203 performed well against the pathogen. The mycelial growth of Colletotrichum orbiculare was inhibited to the tune of 71.08 per cent in dual culture experiments compared to the mycelial growth in control plates. The profiling of soluble metabolites was performed through gas chromatography and mass spectrometry (GCMS) in control plates with fungus alone, the plates showing inhibition zone and from empty PDA plates. Twelve metabolites, viz., Shikimic acid; 2-Propenoic acid, 3-{[}5-(2-hydroxypropyl)-2,2-dimethyl-1,3dioxolan-4- yl]-, TBDMS derivative; dl-Mevalonic acid lactone; 4H-Pyran-4-one, 5-hydroxy-2(hydroxymethyl)-; 2,4-Hexadienoic acid, ethyl ester; Glycerin; Catechol; cis-Vaccenic acid; 9,12-Octadecadienoic acid (Z, Z)-; Ethanol, 2-{[}(2-aminoethyl) amino] and trans-1,10-Dimethyl-trans-9-decalinol were actively expressed in the interaction zone. The biosynthetic pathway topology and pathway impact assessment revealed glycerolipid metabolism and phenylalanine, tyrosine and tryptophan biosynthesis with impact values of 0.29 and 0.08 were unique in the interaction of Alcaligenes faecalis strain SASBG203 with C. orbiculare. The over representation analysis of soluble biomolecules from interaction zone against human metabolome suggested they were highly metabolized in bile acid biosynthesis, steroid biosynthesis and fatty acid metabolism. These compounds in interaction zone can be seen as potential antifungal agents against C. orbiculare in further studies.