Abstract
An exopolymer producing bacterial strain was identified as Halomonas sp. S19 by 16S rRNA gene sequencing isolated from Mandapam, Southeast coast of India. Strain S19 produces a significant amount of exopolymer (320 mg L−1) in a medium optimized with 2.5 % glucose, 0.6 % peptone, 7.5 % salt and pH 7.5 at 35 °C. The exopolymer consists of total sugars (65 %), proteins (4.07 %), uronic acids (8.08 %) and sulphur contents (6.39 %). FT-IR and 1H NMR analysis revealed the presence of functional groups corresponding to carbohydrates, proteins and sulphates. The exopolymer of Halomonas sp. S19 emulsifies different oils. However, 10 % exopolymer shows 55.18, 55.18, 49.81 and 24.62 % of emulsifying activity for sesame oil, coconut oil, paraffin and kerosene. The present study was focused on optimisation of exopolymer production using Box–Behnken experimental design and its possibility for potential emulsification index.
Highlights
The genus Halomonas consists of a broad range of taxonomically and physiologically differed organisms growing at a diverse range of salinities (Kushner and Kamekura 1988)
Identification of exopolymer producing strain In the marine environment, most of the bacteria produce exopolymeric substances probably associated with the sticky texture
The blast similarity search and phylogenetic analysis of 16S rRNA sequence revealed that the isolated bacterial strain had close resemblance with Halomonas sp. (Accession no JX569798.1) (Fig. 1)
Summary
The genus Halomonas consists of a broad range of taxonomically and physiologically differed organisms growing at a diverse range of salinities (Kushner and Kamekura 1988). The exopolymeric substances are composed of sugars and non-sugar components (proteins, uronic acids, sulphates and acetyl group) (Llamas et al 2012). The presence of proteins, sulphates and uronic acids in bacterial exopolymeric substance confers anticancer, immune modulatory and emulsification activity Many microbial polysaccharides serve as emulsifiers due to their ability to stabilise emulsions between water and hydrophobic compounds. When compared with the chemically derived compounds, the bacterial exopolymeric substances were found to be stable in extreme conditions like temperature, pH and salinity (Banat et al 2000). Bioemulsifiers are essential in the formation and stabilisation of emulsion. It reduces the surface tension of oil Karuppiah et al Bioresour. Bioprocess. (2015) 2:48 and water interface by forming a protective layer around emulsion droplets and blocks coalescence by adsorbing with the oil/water interface
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