Correction: Qualitative analysis of biosurfactants from Bacillus species exhibiting antifungal activity.

[This corrects the article DOI: 10.1371/journal.pone.0198107.].

Qualitative analysis of biosurfactants from Bacillus species exhibiting antifungal activity.

Bacillus spp. produce a broad spectrum of lipopeptide biosurfactants, among which surfactin, iturin and fengycin are widely studied families. The goals of this study were to characterize the biosurfactant activity of Bacillus spp. and to investigate their motility and biofilm formation capabilities. In addition, we extracted lipopeptides from these bacteria to assess their antifungal activities and analyzed these products by mass spectrometry (MS). B. amyloliquefaciens FZB42, Bacillus sp. NH 217 and B. subtilis NH-100 exhibited excellent biosurfactant and surface spreading activities, whereas B. atrophaeus 176s and Paenibacillus polymyxa C1225 showed moderate activity, and B. subtilis 168 showed no activity. Strains FZB42, NH-100, NH-217, 176s and CC125 exhibited excellent biofilm formation capabilities. Lipopeptide extracts displayed good antifungal activity against various phytopathogens and their associated diseases, such as Fusarium moniliforme (rice bakanae disease), Fusarium oxysporum (root rot), Fusarium solani (root rot) and Trichoderma atroviride (ear rot and root rot). Lipopeptide extracts of these strains also showed hemolytic activity, demonstrating their strong potential to produce surfactants. LCMS-ESI analyses identified the presence of surfactin, iturin and fengycin in the extracts of Bacillus strains. Thus, the strains assayed in this study show potential as biocontrol agents against various Fusarium and Trichoderma species.

Biocontrol activity of surfactin A purified from Bacillus NH-100 and NH-217 against rice bakanae disease.

The potential of the Bacillus genus to antagonize phytopathogens is associated with the production of cyclic lipopeptides. Depending upon the type of lipopeptide, they may serve as biocontrol agents that are eco-friendly alternatives to chemical fertilizers. This study evaluates the biocontrol activity of surfactin-producing Bacillus (SPB) strains NH-100 and NH-217 and purified surfactin A from these strains against rice bakanae disease. Biologically active surfactin fractions were purified by HPLC, and surfactin A variants with chain lengths from C12 to C16 were confirmed by LCMS-ESI. In hemolytic assays, a positive correlation between surfactin A production and halo zone formation was observed. The purified surfactin A had strong antifungal activity against Fusarium oxysporum, F. moniliforme, F. solani, Trichoderma atroviride and T. reesei. Maximum fungal growth suppression (84%) was recorded at 2000 ppm against F. moniliforme. Surfactin A retained antifungal activity at different pH levels (5-9) and temperatures (20, 50 and 121 °C). Hydroponic and pot experiments were conducted to determine the biocontrol activity of SPB strains and the purified surfactin A from these strains on Super Basmati rice. Surfactin production in the rice rhizosphere was detected by LCMS-ESI at early growth stages in hydroponics experiments inoculated with SPB strains. However, the maximum yield was observed with a consortium of SPB strains (T4) and purified surfactin A (T5) treatments in the pot experiment. The outcomes of the present study revealed that surfactin A significantly reduced rice bakanae disease by up to 80%. These findings suggest that purified surfactin A could be an effective biocontrol agent against bakanae disease in rice and should be incorporated into strategies for disease management.