Characterisation of a carotenoid producing extremely halophilic archaeon Halorubrum sodomense MS5.1 isolated from a solar saltern in Tamil Nadu, South India

Abstract

A carotenoid producing extremely halophilic archaeon designated MS5.1 was isolated out of brine samples from a crystalliser pond of a marine solar saltern in Kanyakumari District, Tamil Nadu, South India. The red pigmented, long rod shaped haloarchaeon was found to be able to grow at temperature range of 20-40°C, salt concentration of 10-35% and pH range of 6 to 9 with optimum conditions for growth being 28°C; 30% salt and pH  7. The archaeal cells were found to be Gram negative and got lysed when placed in distilled water. Analysis of 16S rDNA sequence revealed that the isolate is phylogenetically related to species of the genus Halorubrum under the family Halobacteriaceae, with close relationship to Halorubrum sodomense. Further analyses of the phenotypic and biochemical characteristics of the isolate confirmed the identity of the organism as Halorubrum sodemense. The gene sequence of the strain was deposited in the NCBI GenBank with Accession No. MW332265. Polar lipid characterisation of the strain by thin layer chromatography (TLC) identified the major polar lipids as Phosphatidylglycerol (PG), Phosphatidylglycerol phosphate methyl ester (PGP-Me), Diglycosyl archaeol (DGA) and Sulfated diglycosyl archaeol (S-DGA). The strain was further screened for antibiotic sensitivity and found insensitive to antibiotics that target peptidoglycan layer and found sensitive only to Nitrofurantoin and Rifampicin, which works by inhibiting nucleic acid synthesis. As halophilic archaea are known natural sources of carotenoids, an attempt was made to extract these pigments from the cells and analysed by UV-VIS spectroscopy. Present study characterised the haloarchaeal strain H. sodomense MS5.1 isolated from a coastal solar saltern, optimised the growth conditions and the results clearly indicated that the strain is a potential source of carotenoids and halophilic enzymes.

Keywords: Carotenoid pigment, Haloarchaea, Halobacteriaceae, Manakudi salt pan, Polar lipids