Characterization of rhamnolipids produced by a Pseudomonas aeruginosa mutant strain grown on waste oils.

Pseudomonas aeruginosa EBN-8 mutant rhamnolipids produced on waste oils were investigated using normal-phase thin layer chromatography and fast atom bombardment mass spectrometry. Negative ion mode mass spectra yielded [M - H](-) ions and their fragment ions, which gave some indications on the sequence of rhamnolipid biosynthesis. Five rhamnolipid homologs [viz. RC(10)C(10) (m/z 503), RC(12)C(10) or RC(10)C(12) (531), RRC(10)C(8) or RRC(8)C(10) (621), RRC(10)C(10) (649) and RRC(12)C(10) or RRC(10)C(12) (677)] were detected in four rhamnolipid combinations under the different carbon sources. The prevalence of rhamnolipids was confirmed by Fourier transform infrared and one-dimensional proton nuclear magnetic resonance. We also observed some correlations between the tensioactive characteristics and structural chemistry of the rhamnolipid surfactants.

Polyelectrolyte Multicomponent Colloidosomes Loaded with Nisin Z for Enhanced Antimicrobial Activity against Foodborne Resistant Pathogens.

Food grade micro- or nano-carrier systems (NCS) are being developed to improve the controlled release of antimicrobial agents. To augment the stability of liposomal NCS and to overcome the limitations associated with the use of free bacteriocin (nisin) in the food system, multi-component colloidosomes (MCCS) were developed by electrostatic interactions between anionic alginate and cationic chitosan (multilayer) around phospholipids based liposomes (core). Zeta-sizer results revealed the average diameter of 145 ± 2 nm, 596 ± 3 nm, and 643 ± 5 nm for nano-liposome (NL), chitosomes (chitosan coated NL) and MCCS, respectively. Zeta potential values of NCS varied from -4.37 ± 0.16 mV to 33.3 ± 6 mV, thus both chitosomes (CS) and MCCS were positively charged. Microstructure analysis by scanning electron microscope (SEM) revealed relatively higher size of MCCS with smooth and round morphology. TGA and DSC based experiments revealed that MCCS were thermally more stable than uncoated liposomes. Encapsulation efficiency of nisin in MCCS was observed to be 82.9 ± 4.1%, which was significantly higher than NL (56.5 ± 2.5%). FTIR analyses confirmed the cross-linking between sodium alginate and chitosan layer. Both qualitative (growth kinetics) and quantitative (colony forming unit) antimicrobial assays revealed that nisin loaded MCCS have superior potential to control resistant foodborne pathogens including Staphylococcus aureus, Listeria monocytogenes, and Enterococcus faecalis, (5.8, 5.4, and 6.1 Log CFUmL-1 reduction, respectively) as compared to free nisin, loaded NL or CS. Controlled release kinetics data fitted with Korsmeyer-Peppas model suggested that nisin release from MCCS followed Fickian diffusion. Cytotoxic studies on human blood cells and HepG2 cell lines revealed hemocompatibility and non-toxicity of MCCS. Thus, due to enhanced controlled release, stability and biocompatibility; these multi-component colloidosomes can be useful for incorporating antimicrobial agents into functional foods, beverages and pharmaceutical products to combat pathogenic and spoilage bacteria.

Kinetics of p-nitrophenol degradation by Pseudomonas pseudomallei wild and mutant strains.

Pseudomonas pseudomallei EBN-10 strain, previously isolated from a local pharmaceutical industry's wastewater, was spontaneously adapted to higher p-nitrophenol (PNP) levels, which then was subjected to gamma ray-induced mutagenesis; the efficient isolates hence obtained were designated as EBN-11 and EBN-12, respectively. EBN-12 mutant strain could completely mineralize PNP (100 mg/L) on the minimal media in 24 h while, the parent strain utilized only 6% of it. Addition of glucose as co-substrate further increased the PNP degradation rate; however, phenol inclusion inhibited the degradation process. Ammonium sulphate was experienced as the best of the nitrogen sources used by EBN-12 mutant strain, while degrading PNP.

Physicochemical and surface-active properties of biosurfactant produced using molasses by a Pseudomonas aeruginosa mutant.

Production of a microbial surfactant was studied by growing Pseudomonas aeruginosa EBN-8 mutant on varying concentrations (on the basis of total sugars) of clarified blackstrap molasses as a sole carbon and energy source with or without auxiliary synthetic nitrogen source in 250 mL shake flasks. The progress of fermentation process was monitored by measuring the production of metabolites, and surface-active and emulsification properties of the cell-free culture broth. The biosurfactant was isolated from the supernatant by acid precipitation followed by solvent extraction. The amount of rhamnolipids produced was determined by the orcinol method. The highest dry cell biomass (1.67 g/L) and rhamnolipid (1.45 g/L) yields were observed, at 96 h of incubation on 2% total sugars-based molasses amended with sodium nitrate (at C:N, 20:1) with the product yield related to dry cell biomass (YP/X, g/g) of 0.869, specific product formation rate (V, h(-1)) of 0.295 and volumetric productivity rate (PV, g/L/h) of 0.015. The surface tension of this culture medium dropped to 28.0 from 50.0 mN/m.