Altered Phospholipid Composition in Mutants of Escherichia coli Sensitive or Resistant to Organic Solvents

Abstract

Mutants of Escherichia coli with altered resistance to low molecular weight organic solvents were isolated. Solvent-resistant mutants showed a decrease in the ratio of phosphatidylethanolamine to the anionic phospholipids (phosphatidylglycerol and cardiolipin) relative to the wild-type, whereas solvent-sensitive strains showed an increase. Reversion studies on representative mutants demonstrated that the phenotypic response to solvents and the changes in phospholipid composition were genetically associated. The fatty acid and lipopolysaccharide compositions of the various mutants showed no significant differences from the parental strain. The lesions in two of the solvent-sensitive mutants (DC7 and DC9) and one of the resistant mutants (DC11) were mapped by cotransduction with phage P1 and shown to lie very close to thepss locus at 56 min on the Escherichia coli map. I N T R O D U C T I O NAlcohols and other low molecular weight solvents have long been known to inhibit the growth of bacteria (Dagley et al., 1950). Low concentrations of solvents are reversible in action whereas higher concentrations are lethal (Harold, 1970). The target for solvents appears to be the lipid bilayer of the cell membranes (Hugo, 1967). Low concentrations of solvents dissolve into lipid bilayers, increasing the bilayer fluidity (Hill, 1974), whereas higher concentrations cause irreversible disruption and, eventually, lysis (Harold, 1970;Hugo, 1967). These observations suggested that mutants with an altered sensitivity to organic solvents might have an altered lipid composition which would change their membrane fluidity. We therefore isolated mutants of Escherichia coli K12 with altered sensitivity to ethanol and examined their lipid compositions. METHODSBacterial strains and media. Bacterial strains are listed in Table 1. Strain UB1005 is a spontaneous nalidixic acid-resistant derivative of W1655F- (Bachmann, 1972) and is the parent of mutants DC7 to DCl1. Strain KY2670 and its phenylethyl alcohol-resistant/azide-sensitive derivative KY2671 were received from D r T. Yura (Kyoto University, Japan).The nutrient broth has been described previously (Beard & Conolly, 1975 It was supplemented with necessary L-amino acids at 20 pg ml-I. Solid media contained 1.65 yo (w/v) agar. Mutagenesis and isolation of mutants. Mutagenesis was performed with

Survey of Extreme Solvent Tolerance in Gram-Positive Cocci: Membrane Fatty Acid Changes in Staphylococcus haemolyticus Grown in Toluene

“…All of these responses, both short and long term, result in a less fluid cellular membrane. Regarding phospholipids, the gram-negative organisms P. putida and E. coli have been shown to respond to the presence of toluene by decreasing the membrane content of phosphatidylethanolamine and increasing the content of phosphatidylglycerol and diphosphatidylglycerol, also known as cardiolipin (4,20). After toluene addition, 90% of the de novo phospholipid synthesis is diphosphatidylglycerol synthesis (23).…”

In Vitro and In Vivo Activities of AM-112, a Novel Oxapenem

“…Mueller-Hinton agar was used for MIC determination. The initial inoculum was 10 5 CFU/ml. The activities of ceftazidime, cefepime, ceftriaxone, and cefoperazone against a panel of ␤-lactamase-producing strains were determined alone and in combination at either a 1:1 (ceftazidime) or 2:1 (all agents) ratio with AM-112.…”

ORIGINAL RESEARCH: Determining the effects of inositol supplementation and theopi1mutation on ethanol tolerance ofSaccharomyces cerevisiae

“…On this basis, it stands to reason that cells with an increased content of PI, as in the case of opi1, would have a higher resistance to ethanol. Additionally, altering the ratio of charged head groups has been discussed as a possible mechanism for increased ethanol tolerance 16 . Since PI is the major anionic phospholipid in yeast, it is possible that alterations in membrane charge are responsible for the increased tolerance in PI-enriched cells.…”

“…It has been suggested that altering the ratio of charged head groups can affect ethanol tolerance. Clark and Beard 16 found that decreasing the ratio of anionic-to-zwitterionic phospholipids in E. coli, by increasing PE content, rendered yeasts cells less tolerant to organic solvents. Additional reports find reduced ATPase inhibition by ethanol in cells containing higher proportions of PS 9 or PI 12 .…”