65 Indian J. Fish., 68(1): 65-75, 2021 DOI: 10.21077/ijf.2021.68.1.109035-08 Characterisation of a carotenoid producing extremely halophilic archaeon Halorubrum sodomense MS5.1 isolated from a solar saltern in Tamil Nadu, South India K. P. NEETHU 1,4 , K. S. SOBHANA 1 , KEERTHI R. BABU 1,4 , S. JASMINE 2 , L. RANJITH 3 , H. JOSE KINGSLY 2 , K. K. JOSHI 1 AND A. GOPALAKRISHNAN 1 ICAR-Central Marine Fisheries Research Institute, Ernakulam North P. O., Kochi - 682 018, Kerala, India 2 Vizhinjam Research Centre of ICAR-Central Marine Fisheries Research Institute, Vizhinjam Thiruvananthapuram - 695 001, Kerala, India 3 Tuticorin Research Centre of ICAR-Central Marine Fisheries Research Institute, Thoothukudi - 628 001 Tamil Nadu, India 4 Cochin University of Science and Technology, Cochin University P.O., Kochi - 682 022, Kerala, India e-mail: sobhanapradeep11@gmail.com 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 confrmed the identity of the organism as H. 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) identifed 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 spectrophotometry. 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 Introduction Archaea are a group of atypical prokaryotic organisms originally called the archaebacteria and later the archaea (Jarrel et al., 1999). These are mostly distinct class of microbes with unique features, phylogenetically more similar to eukarya than bacteria. Unlike bacteria, achaeal membrane lacks peptidoglycan in their cell wall and have altered membrane lipid bonding (Ferokh and Nadia, 2016). Archaeal lipids have side chains comprising repeated units of isoprene and lack the fatty acids found in bacteria and eukaryotes. They are key players in the biogeochemical cycles in the ocean and many archaea are able to fx carbon from inorganic sources and thus infuence greenhouse gas emission (Offre et al., 2013). Aerobic halophilic archaeabacteria i.e. haloarchaea are halophiles par excellence and are the main component of microbial biomass in hypersaline environments. Hypersaline environments such as soda lakes, salt lakes and solar salterns are the common sources for isolation of haloarchaea. Haloarchaea have also been isolated from salt fermented seafood (Roh et al., 2007; Roh and Bae, 2009). Extremely halophilic archaea are well adapted to saturated NaCl concentrations and grow optimally at salt concentrations above 3.4-5.1 M or 20-30% NaCl (McGenity and Grant, 1995). Adaptation to such high salt containing environments has evolved unique properties in these microorganisms with considerable biotechnological potential. They have several novel molecular characteristics, particularly for their enzymes