Characterization of jute endophytes with inhibiting activity against Macrophomina phaseolina

Abstract

An endophytic bacterium Burkholderia contaminans NZ; isolated from jute, an important fibre producing plant, shows significant growth promotion activity in in vivo pot experiments. Ability to fix nitrogen, production of indole acetic acid (IAA) and siderophore together with ACC (1-aminocyclopropane-1- carboxylate) deaminase activity make this endophyte a potent plant growth-promoting agent. Moreover, it proved to be an efficient bio control agent active against devastating plant pathogenic fungi Macrophomina phaseolina and several other fungi. Gas chromatography-mass spectroscopy (GC-MS) allowed the identification of some volatile biocontrol metabolites such as 2-bromo-2-cyano-N, N-dimethylacetamide, S-[4-cyanophenyl]-N, N-dimethylthiocarbamate and isoproturon that are known for their antimicrobial activities. The bacterium is also catalase, cellulase, lipase and protease positive which too could be responsible for the antifungal activity. The complete NZ genome analyses revealed the safe to use nature of this bacterium. It has been found to harbor multiple antimicrobial and plant growth promotion related genes but it lacks major virulence-related gene loci. For the better understanding of the mechanism of bacterium- fungi antagonism which should assist in the successful application of bacteria as biological control agents against fungal pathogens of plants, a combination of approaches including total fungal protein identification and comparative proteomics of bacteria-induced differential protein expression in M. phaseolina has been outlined in this study. Using the iTRAQ LC-MS/MS method for quantitative proteomics study, a comparative analysis of the whole proteome of M. phaseolina under both B. contaminans NZ challenged and unchallenged conditions were made and 2204 different proteins were identified of which 141 were considered to have significant deviation in expression. KEGG pathway analysis identified most of the upregulated proteins to be functionally related to energy production (26.11%), as well as defense and stress response (23.45%) while there was a significant down regulation in oxidative stress protection pathways (42.61%), growth and cell wall integrity (30.95%) and virulence (23.81%). A tough battle appears to ensue between the fungus and the bacterium, where B. contaminans NZ manages to arrest the growth of the fungus and decrease its pathogenicity but, the latter apparently survives under ‘hibernating’ conditions by up-regulating its energy metabolism. The findings of the study indicate that B. contaminans NZ can be considered as a completely safe, sustainable eco-friendly bioinoculant for crop improvement.