ORIGINAL ARTICLE Exploration of a haloarchaeon, Halostagnicola larsenii, isolated from rock pit sea water, West Coast of Maharashtra, India, for the production of bacteriorhodopsin P.P. Kanekar 1 , S.O. Kulkarni 1 , S.P. Kanekar 2 , Y. Shouche 3 , K. Jani 3 and A. Sharma 3 1 Department of Biotechnology, Modern College of Arts, Science and Commerce, Pune, India 2 Microbial Sciences Divison, MACS-Agharkar Research Institute, Pune, India 3 Microbial Culture Collection (MCC), National Centre for Cell Science (NCCS), Pune, India Keywords bacteriorhodopsin, haloarchaea, Halostagnicola larsenii, low saline environment, red rock, rock pit sea water. Correspondence Pradnya P. Kanekar, Department of Biotech- nology, Modern College of Arts, Science and Commerce, Shivajinagar, Pune 411005, India. E-mail: kanekarpp@gmail.com 2014/2597: received 16 December 2014, revised 24 February 2015 and accepted 24 February 2015 doi:10.1111/jam.12784 Abstract Aims: The aim of the present investigation was to isolate haloarchaea from rock pit sea water, West Coast of India and to explore their potential in the production of bacteriorhodopsin (BR) which converts light energy into electrical energy. Methods and Results: Haloarchaeal strains were isolated from rock pit sea water samples collected from Rock garden, Malvan, West Coast of India. Based on morphological, physiological and biochemical characteristics, and 16S rRNA gene sequencing, all the 11 strains were identified as Halostagnicola larsenii. All the strains require at least 15 mol l 1 NaCl for growth; grow optimally in the range of 35–52 mol l 1 NaCl. BR was detected in all the strains ranging from 0035 to 0258 g l 1 . All 11 strains showed conversion of light energy into electrical energy in the range of 07–442 mV, when exposed to sunlight. Conclusions: A haloarchaeon, Hst. larsenii is isolated from rock pit sea water and demonstrated to have BR that converted light energy into electrical energy. Significance and Impact of the Study: The present investigation is presumably the first report of the isolation of Hst. larsenii from low salinity environment and its potential in production of BR. The haloarchaeon could be explored for the generation of electrical energy. Introduction With the ever depleting sources of natural oil and gas, nonconventional biological resources are being looked upon as the future energy stores. Micro-organisms with their amazing features have attracted the attention of researchers all over the world to explore them for the generation of energy. Anaerobic micro-organisms pro- duce energy in form of hydrogen and methane, classically termed as bioenergy. Among the natural microbial resources, extremophiles that thrive in harsh environmen- tal conditions are believed to be a treasure of novel bio- molecules, biomaterials and secondary metabolites. Bacteriorhodopsin (BR) is one such novel biomolecule of halophilic Archaea. It acts as a light-driven proton pump and can be used for the conversion of light energy into electrical energy (Keszthelyi et al. 1990). Halophiles are micro-organisms that live in extreme sal- ine environments. Depending upon their requirement of salt concentration, they are classified as slightly halophilic (which grow optimally at 02–085 mol l 1 NaCl), moder- ately halophilic (which grow optimally at 085–34 mol l 1 NaCl) and extremely halophilic (which grow optimally at 34–51 mol l 1 NaCl). The halotolerant micro-organisms can grow at <02 mol l 1 NaCl but tolerate high concen- tration of Nacl thus distinguished from halophiles (DasS- arma and Arora 2001). The halophiles are isolated from marine salterns, salt crystals, hypersaline lakes and rarely Journal of Applied Microbiology 118, 1345--1356 © 2015 The Society for Applied Microbiology 1345 Journal of Applied Microbiology ISSN 1364-5072