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This study demonstrates the use of Bacillus lipopeptides as both capping and stabilizing agents in the single-step synthesis of silver nanoparticles (Ag-NPs). With the aim to achieve a stable Ag-NP suspension, two methods of synthesis procedures, methods A and B, were tested and compared. In method A, the excess reactant sodium borohydride (NaBH4) was added to the limiting reactant silver nitrate (AgNO3), while in method B the limiting reactant was added to the excess reactant. It was found that, in both methods, the lipopeptide concentration significantly influenced the morphology and size of Ag-NPs. In case of method A, at low lipopeptide concentrations, Ag-NPs of uniform size distribution were synthesized, whereas at high concentration, incipient small nano-spheres of Ag-NPs were found concentrated at the vesicular surfaces during initial stage of reaction. However, at later stages, the smaller spherical particles radically changed into varied shapes and sizes and eventually detached from the vesicles completely. Ag-NPs of method B showed narrow size distribution. Stability studies revealed that Ag-NP suspension remained stable up to the sodium chloride, NaCl, concentration of 25 g/L. Steric and depletion types of stabilization were found to be the predominant mechanisms that imparted stability to the Ag-NPs. The particles were found to be stable up to test period of 6 months. Antimicrobial studies revealed that the lipopeptide-conjugated Ag-NPs with low lipopeptide were sensitive against all the tested organisms. [ABSTRACT FROM AUTHOR]

Poly(butylene adipate- co-terephthalate) (PBAT) nanocomposites films are prepared by a solution intercalation process using natural montmorillonite (MMT) and cetyltrimethylammonium bromide (CTAB)-modified montmorillonite (CMMT). Cation exchange technique has been used for modification of MMT by CTAB and characterized by Fourier transform infrared analysis, thermo-gravimetric analysis, and X-ray diffraction (XRD) studies. CMMT gives better dispersion in the PBAT matrix than MMT and is confirmed by XRD and transmission electron microscopy. Because of better compatibility of CMMT, water vapor transmission rate of PBAT decreases more in the presence of CMMT than MMT. The biodegradability of PBAT and its nanocomposite films are studied in compost and from the morphological analysis it is apparent that the PBAT/CMMT shows a lower biodegradation rate in comparison to the PBAT/MMT. The antimicrobial activity of PBAT and its nanocomposite films is tested by an inhibition zone method. Because of the presence of the quaternary ammonium group of CTAB-modified MMT, PBAT/CMMT nanocomposites show adequate antimicrobial activity. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014, 131, 40079. [ABSTRACT FROM AUTHOR]

This is for the first time that an attempt was made to enhance the performance of cross-flow ultrafiltration (CFUF) for the recovery and purification of lipopeptides by size-conditioning their micelles with Ca2+ ions and operating the system in diafiltration mode. In this study, polyether sulfone (PES) membranes with MWCOs 10, 30 and 50kDa were evaluated for recovery and purification of lipopeptides produced by Bacillus sp. CFUF studies performed under batch mode showed poor recovery (68±2%) of F2 fraction comprising Fengycin isoforms, whereas F1 fraction comprising a mixture of surfactin and iturin isoforms showed a moderate recovery of 83.5±2.4% in 50kDa MWCO membrane. To improve the recovery, lipopeptides were conditioned with Ca2+ ions. The CFUF purification of this size-conditioned lipopeptide solution under diafiltration mode was carried out in 50kDa PES membrane. Continuous irrigation of Ca2+ to lipopeptide solution under diafiltration mode of CFUF resulted in the increased recovery of lipopeptides, F1 (surfactin+iturin) fraction about 90.5±2.1% and F2 about 95.3±2.0%. Further, the colored impurities with MW range of 2334–3506Da were effectively removed from the solution. The results of CFUF purification of Ca2+conditioned lipopeptide solution under diafiltration mode indicate that this process can be readily scaled up to the commercial level, workable even with higher MWCO membranes. [ABSTRACT FROM AUTHOR]

BACKGROUND: Lipopeptide production is strongly influenced by trace metals. The availability of free Fe2+ in the media throughout the process of fermentation was found to be very critical. Since free Fe2+ was reported to be sequestered by the lipopeptide as it was produced, intermittent feeding of Fe2+ was strategized and optimized for enhanced lipopeptide production by marine Bacillus megaterium in glucose mineral salts medium (GMSM). RESULTS: Studies with the single-dose Fe2+ (0.48 mmol L−1) supplementation after 8 h of fermentation resulted in lipopeptide concentration of 3.3 ± 0.1 g L−1. Lipopeptide production was further enhanced to 4.2 ± 0.15 g L−1 by adopting a multi-dose Fe2+ feeding strategy. The maximum product yield ( Y P/ S) of 0.24 ± 0.02 g g−1 with specific product formation rate ( q p) of 0.124 ± 0.01 g g−1 h−1 was achieved when 0.48 mmol L−1 Fe2+ was fed intermittently at different times as per the designed strategy. CONCLUSION: Lipopeptide concentration was improved 4.7-fold by single-dosing and 5.8-fold by multiple dosing of Fe2+, when compared with GMSM without Fe2+ supplementation. Copyright © 2012 Society of Chemical Industry [ABSTRACT FROM AUTHOR]