Melanin-templated rapid synthesis of silver nanostructures

Background

As a potent antimicrobial agent, silver nanostructures have been used in nanosensors and nanomaterial-based assays for the detection of food relevant analytes such as organic molecules, aroma, chemical contaminants, gases and food borne pathogens. In addition silver based nanocomposites act as an antimicrobial for food packaging materials. In this prospective, the food grade melanin pigment extracted from sponge associated actinobacterium Nocardiopsis alba MSA10 and melanin mediated synthesis of silver nanostructures were studied. Based on the present findings, antimicrobial nanostructures can be developed against food pathogens for food industrial applications.

Results

Briefly, the sponge associated actinobacterium N. alba MSA10 was screened and fermentation conditions were optimized for the production of melanin pigment. The Plackett-Burman design followed by a Box-Behnken design was developed to optimize the concentration of most significant factors for improved melanin yield. The antioxidant potential, reductive capabilities and physiochemical properties of Nocardiopsis melanin was characterized. The optimum production of melanin was attained with pH 7.5, temperature 35°C, salinity 2.5%, sucrose 25 g/L and tyrosine 12.5 g/L under submerged fermentation conditions. A highest melanin production of 3.4 mg/ml was reached with the optimization using Box-Behnken design. The purified melanin showed rapid reduction and stabilization of silver nanostructures. The melanin mediated process produced uniform and stable silver nanostructures with broad spectrum antimicrobial activity against food pathogens.

Conclusions

The melanin pigment produced by N. alba MSA10 can be used for environmentally benign synthesis of silver nanostructures and can be useful for food packaging materials. The characteristics of broad spectrum of activity against food pathogens of silver nanostructures gives an insight for their potential applicability in incorporation of food packaging materials and antimicrobials for stored fruits and foods.

Production and characterisation of glycolipid biosurfactant by Halomonas sp. MB-30 for potential application in enhanced oil recovery

Biosurfactant-producing Halomonas sp. MB-30 was isolated from a marine sponge Callyspongia diffusa, and its potency in crude oil recovery from sand pack column was investigated. The biosurfactant produced by the strain MB-30 reduced the surface tension to 30 mN m(-1) in both glucose and hydrocarbon-supplemented minimal media. The critical micelle concentration of biosurfactant obtained from glucose-based medium was at 0.25 mg ml(-1) at critical micelle dilution 1:10. The chemical structure of glycolipid biosurfactant was characterised by infrared spectroscopy and proton magnetic resonance spectroscopy. The emulsification activity of MB-30 biosurfactant was tested with different hydrocarbons, and 93.1 % emulsification activity was exhibited with crude oil followed by kerosene (86.6 %). The formed emulsion was stable for up to 1 month. To identify the effectiveness of biosurfactant for enhanced oil recovery in extreme environments, the interactive effect of pH, temperature and salinity on emulsion stability with crude oil and kerosene was evaluated. The stable emulsion was formed at and above pH 7, temperature >80 °C and NaCl concentration up to 10 % in response surface central composite orthogonal design model. The partially purified biosurfactant recovered 62 % of residual crude oil from sand pack column. Thus, the stable emulsifying biosurfactant produced by Halomonas sp. MB-30 could be used for in situ biosurfactant-mediated enhanced oil recovery process and hydrocarbon bioremediation in extreme environments.

Biosurfactant production from marine bacteria associated with sponge Callyspongia diffusa

Marine-derived biosurfactants have gained significant attention due to their structural and functional diversity. Biosurfactant production was performed using bacteria associated with Callyspongia diffusa, a marine sponge inhabiting the southern coast of India. A total of 101 sponge-associated bacteria were isolated on different media, of which 29 isolates showed positive result for biosurfactant production. Among the 29 positive isolates, four were selected based on highest emusification activity and were identified based on 16S rDNA sequence analysis. These isolates were identified as Bacillus subtilis MB-7, Bacillus amyloliquefaciens MB-101, Halomonas sp. MB-30 and Alcaligenes sp. MB-I9. The 16S rDNA nucleotide sequences were deposited in GenBank with accession numbers KF493730, KJ540939, KJ414418 and KJ540940, respectively. Based on the highest oil displacement activity and effective surface tension reduction potential, the isolate B. amyloliquefaciens MB-101 was selected for further optimization and structural delineation. The production of biosurfactant by the isolate was significantly enhanced up to 6.76 g/l with optimal concentration values of 2.83 % for glycerol, 2.65 % for peptone, 20.11 mM for ferrous sulfate and 74 h of incubation by employing factorial design. The structural features of the purified biosurfactant from B. amyloliquefaciens MB-101 showed similarity with lipopeptide class of biosurfactant. In conclusion, the present study emphasizes the utilization of marine sponge-associated bacteria for the production of biosurfactant that may find various applications.

Monitoring surfactant mediated defence of gastrointestinal Proteus mirabilis DMTMMK1 against pathogenic consortia of Vibrio cholerae

Schematic representation of the biosurfactant production and evaluation of anti-pathogenic potential.