Genotyping and identification of broad spectrum antimicrobial volatiles in black pepper root endophytic biocontrol agent, Bacillus megaterium BP17

• Bacillus megaterium BP17 is genetically divergent from clinical Bacillus strains.
• Bacillus megaterium BP17 is an endophytic colonist in diverse plant species.
• Bacillus megaterium BP17 showed volatiles mediated antimicrobial activity on plant pathogens.
• Antimicrobial activity of endophytic antagonist was attributed to Pyrazine group of chemicals.
• Pyrazine, 2-ethyl-3-methyl is identified as an antimicrobial compound against plant pathogens.

Black pepper root endophytic Bacillus BP17 was identified as Bacillus megaterium (BmBP17) by a panel of phenotypic and genotypic methods. BmBP17 was found genetically close to industrially significant B. megaterium WSH002 and divergent from clinical Bacillus strains. Tracking with genetically tagged BmBP17 revealed its endophytism in diverse plant species such as Piper nigrum, Zingiber officinale and Arabidopsis thaliana. BmBP17 released antimicrobial volatiles against several pathogens viz., Phytophthora capsici, Pythium myriotylum, Athelia rolfsii, Gibberella moniliformis, Colletotrichum gloeosporioides, Rhizoctonia solani, Magnaporthe oryzae, Ralstonia solanacearum, and Xanthomonas axonopodis pv. punicae. Chemical compounds belong to hydrocarbons, heterocyclics, esters and sulfoxides were dominantly present in solvent extracts of BmBP17 in GC/MS profile. Dynamic head space GC/MS analysis revealed broad spectrum antimicrobials such as Pyrazine, 2-ethyl-3-methyl-; Pyrazine, 2,5-dimethyl-; Pyrazine, ethyl-; and Pyrazine, methyl- in the volatiles of BmBP17. Pyrazine, 2-ethyl-3-methyl was found most inhibitory followed by Pyrazine, 2-ethyl-; Pyrazine, 2, 5-dimethyl and Pyrazine, 2-methyl which can be exploited for crop protection.

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