The modification of the membrane of Oceanomonas baumannii T when subjected to both osmotic and organic solvent stress

Abstract

Oceanomonas baumannii(T) is a novel halotolerant bacterium which wasisolated from the estuary of the river Wear (Sunderland, UK). When grownin tryptone soya broth it can tolerate high levels of phenol, which isnot utilised as a carbon source in this medium. However, the level oftolerance was reduced from 35 mM to 3 mM phenol as salinity increasedfrom 1% to 12% NaCl (w/v). Increasing salinity up to 12% NaCl alsodecreased the growth rate 8-fold and caused modifications to thecytoplasmic membrane particularly anionic phosphatidylglycerol levels,which doubled at the expense of zwitterionic phosphatidylethanolamine.In addition, changes in the phospholipid fatty acid composition werenoted, cis-vaccenic acid decreased significantly at higher salinities.Intracellular solute levels also increased with increasing salinity andthere was an accumulation of the compatible solutes ectoine, glycinebetaine and glutamate. The addition of phenol to osmotically compromisedcultures led to a further modification of the cytoplasmic membranephospholipid composition, in particular, that the decrease inzwitterionic phosphatidylethanolamine and the increase of anionicphospholipid species was much less pronounced. A further decrease inunsaturation, particularly in the proportion of cis-vaccenic acid, andthe mean chain length of the fatty acids suggested that this responsewas important in maintaining membrane integrity in the presence ofphenol. (C) 2000 Federation of European Microbiological Societies.Published by Elsevier Science B.V. All rights reserved.