The effect of growth rate and other growth conditions on the lipid composition of Escherichia coli

Fatty acid compositions in growing and resting cells of several strains of Pseudomonas putida (P8, NCTC 10936, and KT 2440) were studied, with a focus on alterations of the saturation degree, cis-trans isomerization, and cyclopropane formation. The fatty acid compositions of the strains were very similar under comparable growth conditions, but surprisingly, and contrary to earlier reports, trans fatty acids were not found in either exponentially growing cells or stationary-phase cells. During the transition from growth to the starvation state, cyclopropane fatty acids were preferentially formed, an increase in the saturation degree of fatty acids was observed, and larger amounts of hydroxy fatty acids were detected. A lowered saturation degree and concomitant higher membrane fluidity seemed to be optimal for substrate uptake and growth. The incubation of cells under nongrowth conditions rapidly led to the formation of trans fatty acids. We show that harvesting and sample preparation for analysis could provoke the enzyme-catalyzed formation of trans fatty acids. Freezethawing of resting cells and increased temperatures accelerated the formation of trans fatty acids. We demonstrate that cis-trans isomerization only occurred in cells that were subjected to an abrupt disturbance without having the possibility of adapting to the changed conditions by the de novo synthesis of fatty acids. The cis-trans isomerization reaction was in competition with the cis-to-cyclopropane fatty acid conversion. The potential for the formation of trans fatty acids depended on the cyclopropane content that was already present.The bacterial cytoplasmic membrane is an important target and/or receptor for stress factors. As a response to permanent physical and chemical changes in the cell environment, several protective mechanisms and metabolic adaptation reactions have evolved (10,52,56). At the level of membrane lipids and fatty acids, these processes are often referred to as homeoviscous adaptation (57). Cells control the fluidity of their membranes by altering the lipid composition to compensate for changes in fluidity induced by certain environmental factors, such as temperature or the presence of toxic, membrane-active compounds. In most cases, however, microorganisms are not able to compensate for externally induced fluidity changes with 100% efficacy (7,37,38). They can tolerate and maybe even need a wider range of different lipid compositions to establish homeostasis, especially during growth. Lipids can coexist in physically separated microdomains with more or less fluid-or gel-phase behavior, and membrane functions are locally influenced by many factors other than fluidity (20, 43). These are the reasons for attempts to enlarge the term homeoviscous adaptation (to maintain membrane fluidity) by use of the term homeophasic adaptation (to adjust membrane fluidity).At the level of lipid membrane composition, the predominant response of many bacteria to environmental perturbations is the alteration of lipid acyl chain structures by ...

Section: Resultssupporting

confidence: 90%

Formation of trans Fatty Acids Is Not Involved in Growth-Linked Membrane Adaptation of Pseudomonas putida

Härtig

Loffhagen

Harms

2005

“…Also, Chang and Cronan (10) demonstrated that cfa transcription in E. coli increased when cells were adapted to mildly acidic conditions. On the other hand, Arneborg et al (2) found that E. coli MT102 grown at pH 6.4 had lower proportions of unsaturated and cyclopropane fatty acids than did the same strain grown at pH 8.4. They demonstrated that E. coli increases the synthesis of saturated fatty acyl chains at the expense of both unsaturated and cyclopropane fatty acyl chains as a response to lower pH.…”

Section: Resultsmentioning

confidence: 97%

Adaptation of Escherichia coli O157:H7 to pH Alters Membrane Lipid Composition, Verotoxin Secretion, and Resistance to Simulated Gastric Fluid Acid

Yuk

Marshall

2004

140

The influence of adaptation to pH (from pH 5.0 to 9.0) on membrane lipid composition, verotoxin concentration, and resistance to acidic conditions in simulated gastric fluid (SGF) (pH 1.5, 37°C) was determined for Escherichia coli O157:H7 (HEC, ATCC 43895), an rpoS-deficient mutant of ATCC 43895 (HEC-RM, FRIK 816-3), and nonpathogenic E. coli (NPEC, ATCC 25922). Regardless of the strain, D values (in SGF) of acid-adapted cells were higher than those of non-acid-adapted cells, with HEC adapted at pH 5.0 having the greatest D value, i.e., 25.6 min. Acid adaptation increased the amounts of palmitic acid (C16:0) and decreased cis-vaccenic acid (C18:17c) in the membrane lipids of all strains. The ratio of cis-vaccenic acid to palmitic acid increased at acidic pH, causing a decrease in membrane fluidity. HEC adapted to pH 8.3 and HEC-RM adapted to pH 7.3 exhibited the greatest verotoxin concentrations (2,470 and 1,460 ng/ml, respectively) at approximately 10 8 CFU/ml. In addition, the ratio of extracellular to intracellular verotoxin concentration decreased at acidic pH, possibly due to the decrease of membrane fluidity. These results suggest that while the rpoS gene does not influence acid resistance in acid-adapted cells it does confer decreased membrane fluidity, which may increase acid resistance and decrease verotoxin secretion.

“…Homoviscous adaptation of the cytoplasmic membrane through alteration of membrane lipid composition maintains bacterial membranes in a functional, liquid crystalline state during heat stress (5,20,39). To determine whether an altered profile of membrane lipids contributes to the heat resistance of E. coli AW1.7, the membrane fatty acid composition of late-exponential-phase and heat-stressed cultures was compared to that of E. coli GGG10 ( Table 2).…”

Section: Resultsmentioning

confidence: 99%

Solute Transport Proteins and the Outer Membrane Protein NmpC Contribute to Heat Resistance of Escherichia coli AW1.7

Ruan

Pleitner

Gänzle

et al. 2011

This study aimed to elucidate determinants of heat resistance in Escherichia coli by comparing the composition of membrane lipids, as well as gene expression, in heat-resistant E. coli AW1.7 and heat-sensitive E. coli GGG10 with or without heat shock. The survival of E. coli AW1.7 at late exponential phase was 100-fold higher than that of E. coli GGG10 after incubation at 60°C for 15 min. The cytoplasmic membrane of E. coli AW1.7 contained a higher proportion of saturated and cyclopropane fatty acids than that of E. coli GGG10. Microarray hybridization of cDNA libraries obtained from exponentially growing or heat-shocked cultures was performed to compare gene expression in these two strains. Expression of selected genes from different functional groups was quantified by quantitative PCR. DnaK and 30S and 50S ribosomal subunits were overexpressed in E. coli GGG10 relative to E. coli AW1.7 upon heat shock at 50°C, indicating improved ribosome stability. The outer membrane porin NmpC and several transport proteins were overexpressed in exponentially growing E. coli AW1.7. Sodium dodecyl sulfate-polyacrylamide gel electrophoresis analysis of membrane properties confirmed that NmpC is present in the outer membrane of E. coli AW1.7 but not in that of E. coli GGG10. Expression of NmpC in E. coli GGG10 increased survival at 60°C 50-to 1,000-fold. In conclusion, the outer membrane porin NmpC contributes to heat resistance in E. coli AW1.7, but the heat resistance of this strain is dependent on additional factors, which likely include the composition of membrane lipids, as well as solute transport proteins.Escherichia coli is a common contaminant of the food supply. The majority of the strains of this species are not pathogenic; however, their relatively high resistance to environmental insults and the occurrence of virotypes with a low infectious dose, particularly enterohemorrhagic E. coli, make E. coli an organism of major concern in the production of minimally processed foods, particularly produce and fresh beef (11).Most strains of E. coli have a D 60 value (the duration of heat treatment at 60°C required to reduce the number of microorganisms to 1/10 of the initial value) of less than 1 min. However, the heat resistance of E. coli is highly variable among different strains and individual strains exhibit D 60 values of up to 6.5 min (8,21,25,37). The heat resistance of individual strains of E. coli relates to their ability adapt to heat stress by the homoviscous adaptation of the plasma membrane, as well as the synthesis of heat shock proteins (20, 43). The 32 -induced expression of heat shock proteins after sublethal thermal stress increases resistance to lethal heat treatment (43; for a review, see reference 6). Increased basal expression of the heat shock proteins DnaK, Lon, and ClpX was linked to the increased heat resistance of E. coli mutants LMM1010, LMM1020, and LMM 1030 (1, 21). The S -mediated general stress response additionally contributes to acid, heat, pressure, and salt resistance in E. coli (2,14,22,3...