SHORT NOTE M. K. Chattopadhyay á M. V. Jagannadham Maintenance of membrane ¯uidity in Antarctic bacteria Accepted: 9 January 2001 / Published online: 21 February 2001 Ó Springer-Verlag 2001 Abstract Increase in the synthesis of membrane-¯uidiz- ing such as unsaturated) fatty acids in cold-adapted bacteria is well documented. More recently, a polar carotenoid was found to rigidify synthetic membranes in an in vitro study. Enhanced biosynthesis of some fatty acids that increase membrane ¯uidity, and also of polar carotenoids has been evidenced in one Gram-positive and one Gram-negative psychrotrophic bacterium, iso- lated from Antarctic soil. A role of carotenoids in ho- meoviscous adaptation of membrane ¯uidity has been postulated. Antarctic microorganisms provide an attractive model for studies on biological aspects of cold adaptation. Several clues to the understanding of the mechanism of cold-adaptation have been obtained from investigations on some psychrotrophic bacterial strains, isolated from the Schirmacher oasis of Antarctica see references in Chattopadhyay 2000). Lowering of temperature leads to the formation of a close array of acyl chains of fatty acids in the bacterial cytoplasmic membrane. The resultant restriction of molecular motion imposes a gelling eect on the lipid bilayer. Under this stress condition, maintenance of an optimum membrane ¯uidity becomes a crucial challenge for the microorganisms in survival at low temperature. Studies on other cold-adapted bacteria have revealed several strategies adopted by the microorganisms to maintain the cell membrane within a narrow range of viscosity or within a liquid crystalline phase. Conversion of saturated fatty acids into unsaturated fatty acids which have a ¯uidizing eect on the membrane) by cold-inducible desaturases is well known. Other mecha- nisms of maintaining an optimum ¯uidity involve reduction in the acyl chain length and synthesis of branched-chain fatty acids Suutari and Laakso 1994; Klein et al. 1999). It was observed that when two strains of Listeria monocytogenes were grown at low tempera- ture, there was a dominance of anteiso pentadecanoic acid in the fatty acid production pro®le. In two cold- sensitive mutants, a marked de®ciency of this branched chain fatty acid was also evidenced Annous et al. 1997). Bacteria in the deep-sea environment are adapted to high pressure and low temperature. Recently, the im- portance of monounsaturated fatty acids for growth has been demonstrated in a deep-sea isolate of Photo- bacterium Allen et al. 1999). Carotenoid pigments, present in a wide variety of bacteria, algae, fungi and plants, have been shown to play important biological roles Bramley and MacKenzie 1988). In photosynthetic bacteria, they help in harvesting light energy as accessory antenna pigments Sie®rmann- Harms 1985) and in protection of the photosynthetic apparatus against photodynamic killing Wloch and Wieckowski 1982; Krinsky 1989; Sandmann et al. 1993). In non-photosynthetic bacteria, they provide protection against ultraviolet UV) radiation Goodwin 1980; Bec- ker-Hapak et al. 1997). They are known to protect the neighbouring biomolecules against oxidative damage Di Mascio et al. 1989; Miller et al. 1996). They also stabilize the native conformation of functional pigment proteins Kuhlbrandt et al. 1994; Moskalenko and Karapetyan 1996). Possible role of carotenoids in regulation of membrane ¯uidity was demonstrated earlier in some in vitro studies Subczynski et al. 1992; Gabrielska and Gruszecki 1996). In bacterial systematics, carotenoids are useful as important chemotaxonomic markers Holmes et al. 1984; Kocur 1986). Bacterial carotenoids are believed to play a similar role as that played by cholesterol in eukaryotic cells as a membrane-spanning agent Rohmer et al. 1979; Sub- czynski et al. 1992). In our laboratory, studies on the bacterial species of Antarctica revealed a preponderance of pigmented bacteria Sarita and Shivaji 1994). During Polar Biol 2001) 24: 386±388 DOI 10.1007/s003000100232 M. K. Chattopadhyay &) á M. V. Jagannadham Centre for Cellular and Molecular Biology, Hyderabad 500 007, India E-mail: mkc@ccmb.ap.nic.in Tel.: +91-40-7172241 Fax: +91-40-7171195