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

Abstract

Oceanomonas baumanniiT is a novel halotolerant bacterium which was isolated from the estuary of the river Wear (Sunderland, UK). When grown in tryptone soya broth it can tolerate high levels of phenol, which is not utilised as a carbon source in this medium. However, the level of tolerance was reduced from 35 mM to 3 mM phenol as salinity increased from 1% to 12% NaCl (w/v). Increasing salinity up to 12% NaCl also decreased the growth rate 8-fold and caused modifications to the cytoplasmic membrane particularly anionic phosphatidylglycerol levels, which doubled at the expense of zwitterionic phosphatidylethanolamine. In addition, changes in the phospholipid fatty acid composition were noted, cis-vaccenic acid decreased significantly at higher salinities. Intracellular solute levels also increased with increasing salinity and there was an accumulation of the compatible solutes ectoine, glycine betaine and glutamate. The addition of phenol to osmotically compromised cultures led to a further modification of the cytoplasmic membrane phospholipid composition, in particular, that the decrease in zwitterionic phosphatidylethanolamine and the increase of anionic phospholipid species was much less pronounced. A further decrease in unsaturation, particularly in the proportion of cis-vaccenic acid, and the mean chain length of the fatty acids suggested that this response was important in maintaining membrane integrity in the presence of phenol. ß

Solvent Stress Response of the Denitrifying Bacterium “ Aromatoleum aromaticum ” Strain EbN1

“…Only betaine aldehyde dehydrogenase (BetB), catalyzing the last biosynthetic reaction of osmotically active betaine, displayed a 3.5-fold increase in abundance during growth with 0.74 mM toluene. Osmotically stressed cells of Oceanomonas baumannii also increased betaine synthesis when they were treated with phenol (7).…”

Potassium uptake and retention by Oceanomonas baumannii at low water activity in the presence of phenol

“…This retention of K in the face of increasing external phenol concentrations is correlated with signi¢cant changes in the cell envelope. O. baumannii unlike P. putida P8 does not convert cis-unsaturated fatty acids to the trans isomers [16], instead the ratio of saturated to unsaturated fatty acids increased dramatically, from 0.47 in 4 mM phenol to 1.44 in 10 mM. In addition, the ratio of zwitterionic to anionic phospholipid decreased from 2.23 to 1.22.…”

Stress-Induced Changes of Phospholipids in Betaproteobacterium <i>Aromatoleum aromaticum</i> Strain EbN1 due to Alkylbenzene Growth Substrates

“…Systematic changes in membrane lipid composition of bacteria in response to ambient environmental conditions have been described in numerous studies [e.g., Brown et al, 2000;Cullis et al, 1996;Dowhan, 1997;Guckert et al, 1985;Rudolph et al, 1986;Russell and Fukunaga, 1990;Weber and de Bont, 1996;Yano et al, 1998]. They gave evidence that significant adaptation in membrane constituents occurs due to enhanced stress by, e.g.…”