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BackgroundTwo of our long term efforts are to discover compounds with synergistic antifungal activity from metabolites of marine derived microbes and to optimize the production of the interesting compounds produced by microorganisms. In this respect, new applications or mechanisms of already known compounds with a high production yield could be continually identified. Surfactin is a well-known lipopeptide biosurfactant with a broad spectrum of antimicrobial and antiviral activity; however, there is less knowledge on surfactin’s antifungal activity. In this study, we investigated the synergistic antifungal activity of C15-surfactin and the optimization of its production by the response surface method.Methodology/Principal FindingsUsing a synergistic antifungal screening model, we found that the combination of C15-surfactin and ketoconazole (KTC) showed synergistic antifungal effect on Candida albicans SC5314 when the concentrations of C15-surfactin and KTC were 6.25 µg/mL and 0.004 µg/mL, respectively. These concentrations were lower than their own efficient antifungal concentrations, which are >100 µg/mL and 0.016 µg/mL, respectively. The production of C15-surfactin from Bacillus amyloliquefaciens was optimized by the response surface methodology in shaker flask cultivation. The Plackett-Burman design found sucrose, ammonium nitrate and NaH2PO4.2H2O to have significant effects on C15-surfactin production. The optimum values of the tested variables were 21.17 g/L sucrose, 2.50 g/L ammonium nitrate and 11.56 g/L NaH2PO4·2H2O. A production of 134.2 mg/L, which were in agreement with the prediction, was observed in a verification experiment. In comparison to the production of original level (88.6 mg/L), a 1.52-fold increase had been obtained.Conclusion/SignificanceThis work first found that C15-surfactin was an efficient synergistic antifungal agent, and demonstrated that response surface methodology was an effective method to improve the production of C15-surfactin.

Strain 12A35 was isolated from a deep-sea sediment collected from the South China Sea and showed promising antibacterial activities. It was identified as Streptomyces sp. by the 16S rDNA sequence analysis. Bioassay-guided fractionation using HP20 adsorption, flash chromatography over silica gel and octadecylsilyl (ODS) and semi-preparative HPLC, led to the isolation and purification of five metabolites from the fermentation culture of 12A35. Two new spirotetronate antibiotics, lobophorins H (1) and I (2), along with three known analogues, O-β-kijanosyl-(1→17)-kijanolide (3), lobophorins B (4) and F (5) were characterized by 1D, 2D-NMR and MS data. These compounds exhibited significant inhibitory activities against Bacillus subtilis. Compounds 1 and 5 exhibited moderate activities against Staphylococcus aureus. In particular, the new compound lobophorin H (1) showed similar antibacterial activities against B. subtilis CMCC63501 to ampicillin.

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Certain species have the capacity to produce cyclic lipopeptides and these lipopeptides are promising determinants contributing to the biocontrol of plant diseases. In the current study, a cyclic lipopeptide plipastatin A1 was isolated from the fermentation broth of a marine sediment-derived SH-B74 by the combination of solid-phase extraction and reversed-phase high-performance liquid chromatography, and its structure was identified by tandem mass spectrometry, high-resolution electro-spray ionization mass spectrometry, and gas chromatography-mass spectrometry together with nuclear magnetic resonance analysis. Moreover, data from activity evaluation revealed that plipastatin A1 has excellent in vitro activity on the suppression of the conidia germination of ., the causal agent of gray mold disease in tomato. Furthermore, plipastatin A1 can successfully decrease the incidence of gray mold disease on tomato leaves at 50 µM concentration. This study indicates that . SH-B74 appears to be a potentially sustainable pesticide to control gray mold disease in tomato plants, and its cyclic lipopeptide plipastatin A1 plays an important role in the in vitro and biocontrol of. .