Fatty Acid and Hopanoid Adaption to Cold in the Methanotroph Methylovulum psychrotolerans

Abstract

Three strains of aerobic psychrotolerant methanotrophic bacteria <i>Methylovulum psychrotolerans</i>, isolated from geographically remote low-temperature environments in Northern Russia, were grown at three different growth temperatures, 20, 10 and 4°C and were found to be capable of oxidizing methane at all temperatures. The three <i>M. psychrotolerans</i> strains adapted their membranes to decreasing growth temperature by increasing the percent of unsaturated fatty acid (FAs), both for the bulk and intact polar lipid (IPL)-bound FAs. Furthermore, the ratio of βOH-C_16:0 to <i>n</i>-C_16:0 increased as growth temperature decreased. The IPL head group composition did not change as an adaption to temperature. The most notable hopanoid temperature adaptation of <i>M. psychrotolerans</i> was an increase in unsaturated hopanols with decreasing temperature. As the growth temperature decreased from 20 to 4°C, the percent of unsaturated <i>M. psychrotolerans</i> bulk-FAs increased from 79 to 89 % while the total percent of unsaturated hopanoids increased from 27 to 49 %. While increased FA unsaturation in response to decreased temperature is a commonly observed response in order to maintain the liquid-crystalline character of bacterial membranes, hopanoid unsaturation upon cold exposition has not previously been described. In order to investigate the mechanisms of both FA and hopanoid cold-adaption in <i>M. psychrotolerans</i> we identified genes in the genome of <i>M. psychrotolerans</i> that potentially code for FA and hopanoid desaturases. The unsaturation of hopanoids represents a novel membrane adaption to maintain homeostasis upon cold adaptation.