Bacterial strains integrated with surfactin molecules of Bacillus subtilis MTCC441 enrich nematocidal activity against Meloidogyne incognita.

Bacteria secrete lipopeptide (surfactin) molecules, which are known to act as natural antibiotics. Recently, research on lipopeptide molecules has grown because of their role in increasing resistance to plant pathogens. Isolated surfactin molecules at several concentrations, viz. 35, 25, 15 and 5 ppm, were used in an in vitro study for analysis of egg hatching inhibition and second-stage juvenile (J2) mortality of the nematode Meloidogyne incognita. Cell suspensions (1.2 × 108  cfu·ml-1 ) of both Bacillus subtilis (MTCC-441) and Pseudomonas putida (MTCC-102) were used in J2 inoculated tomato plants. Root-dip treatment of tomato seedlings with the crude lipopeptide (35 ppm) was also performed to analyse biocontrol potential. MALDI-TOF MS analysis was conducted to determine specific lipopeptide molecules. Data showed nematode egg mortality of 85% in the 35 ppm surfactin concentration 96 h after exposure. The maximum ovicidal activity was 83.97% after incubation with 35 ppm surfactin for the same exposure period. Plant growth attributes and biochemical parameters were significantly improved when bacterial cultures were applied before J2 inoculation of tomato seedlings. We also recorded a reduction in egg masses, nematode population and root galling. The J2 penetration into tomato roots was effective in the root-dip experiments. Surfactin mass peak was determined at m/z 1058 [M+Na]+ using MALDI-TOF MS. These results indicate that bacterial cell suspensions can be used as a potent and versatile source to deal with nematode infection and provide a rich source of bioactive compounds with antinematode activity.