Alterations in normal fatty acid composition in a temperature-sensitive mutant of a thermophilic bacillus

Microbial fatty acids and thermal adaptation

The existing literature on the role of fatty acids in microbial temperature adaptation is reviewed. Several modes of change of cellular fatty acids at varying environmental temperatures are shown to exist in yeasts and fungi, Gram-negative bacteria, and bacteria containing iso- and anteiso-branched fatty acids, as well as in a few Gram-positive bacteria. Consequently, the degree of fatty acid unsaturation and cyclization, fatty acid chain length, branching, and cellular fatty acid content increase, decrease, or remain unaltered on lowering the temperature. Moreover, microorganisms seem to be able to change from one mode or alter the cellular fatty acid profile temperature dependently to another on lowering the temperature, as well as even within the same growth temperature range, depending on growth conditions. Therefore, the effect of the temperature on cellular fatty acids appears to be more complicated than known earlier. However, similarities found in the modes of change of cellular fatty acids at varying environmental temperatures in several microorganisms within the above mentioned groups support the existence of a limited amount of common regulatory mechanisms. The models presented enable the prediction of temperature-induced changes occurring in the fatty acids of microorganisms, and enzymatic steps of the fatty acid biosynthesis that possibly are under temperature control.

Composition of polar lipid acyl chains of Bacillus stearothermophilus as affected by temperature and calcium

Bacillus stearothermophilus was grown within the temperature range of 48 to 68 degrees C in a complex medium and in the range of 45 to 72 degrees C in the presence of 2.5 mM Ca2+. The main fatty acids of lipid extracts contain 15 to 17 carbon atoms, mostly branched-chain species. The most prevalent saturated straight-chain fatty acid is n-C16. The total amount of branched-chain species decreases with increasing temperature of growth from 48 to 68 degrees C, whereas the straight-chain species increase. Thus, n-C16 almost doubles while i-C16, i-C17 and a-C17 decrease by 41.2, 28.9 and 41.9%, respectively. In the presence of Ca2+, the lipid metabolism favours the biosynthesis of straight-chain fatty acids with depression of branched-chain species, especially at lower temperatures. At high temperatures, Ca2+ has a less pronounced effect in the lipid biosynthesis. However, above 68 degrees C, a significant decrease is observed among the branched-chain fatty acids i-C15, i-C17 and a-C17 with a consequent increase in n-C16. Furthermore, a remarkable increase is observed in oleic acid (from 2.7% at 68 degrees C to 11.5% at the extreme 72 degrees C.

Chlorinated fatty acid distribution in Mycobacterium convolutum phospholipids after growth on 1-chlorohexadecane

The composition of phospholipids from Mycobacterium convolutum R22 was determined after growth at two temperatures (20 and 30 degrees C) with 1-chlorohexadecane as the substrate. Comparisons were made with the phospholipids of cells grown on n-hexadecane. Phosphatidylinositolmannosides and phosphatidylethanolamine (PE) were the major phospholipids in n-hexadecane-grown cells. In 1-chlorohexadecane-grown cells, phosphatidylinositolmannosides were approximately half of the total phospholipids, with lesser amounts of PE and cardiolipin (CL). The relative level of PE was greater at 20 degrees C (versus that at 30 degrees C) after growth on either substrate. A determination was made of structure and positional distribution of constituent fatty acid in both CL and PE. The relative amount of unsaturated fatty acid was higher at 20 degrees C. There were two C16:1 fatty acids (C16:1 delta 9 and C16:1 delta 11), and these had positional preferences in both CL and PE. The positional sites of chlorinated fatty acids differed in both CL and PE at the two temperatures. The results confirm that microorganisms can specifically distribute chlorinated fatty acids into cellular phospholipids.

Phospholipid surface bilayers at the air-water interface. III. Relation between surface bilayer formation and lipid bilayer assembly in cell membranes

Lipid bilayer assembly in cell membranes has been simulated with total lipid extracts from human red blood cells and from mesophilic and thermophilic bacteria grown at several temperatures. Aqueous dispersions of these natural lipid mixtures form surface bilayers, a single bimolecular lipid state, but only at the growth temperature of the source organism. Thus, a single isolated bilayer state forms spontaneously in vitro from lipids that are available in vivo at the growth temperature of the cell. Surface bilayers form at a specific temperature that is a function of hydrocarbon chain length and degree of fatty acid unsaturation of the phospholipids; this property is proposed as an essential element in the control of membrane lipid composition.

Temperature-dependent lipid content and fatty acid composition of three thermophilic bacteria

The lipid content and fatty acid composition of a strain of Bacillus caldolyticus and of two facultative thermophiles (B. flavothermus and strain NZ-2) were analysed after growth at different temperatures. In all three strains the amount of membrane, as a fraction of total cellular dry mass, was found to increase with temperature, however, in varying degrees. Changes of lipid content and protein/lipid ratio in B. caldolyticus between 60 degrees C and 100 degrees C and in strain NZ-2 between 45 degrees C and 70 degrees C were minor; in B. flavothermus the alterations in the 50 degrees C-70 degrees C range were more pronounced. The same was found for changes observed in the phospholipid/total lipid and phospholipid/membrane ratios, and also in the amounts of individual phospholipids. The alterations of the fatty acid composition were most significant in B. caldolyticus, especially between 80 degrees C and 95 degrees C. In contrast, the main changes in B. flavothermus and NZ-2 were found to occur between 30 degrees C and 50 degrees C, and between 45 degrees C and 60 degrees C, respectively. Based on these data, strain NZ-2 could be characterized as the least and B. flavothermus as the most versatile of the three organisms.

Effects of temperature and sodium chloride concentration on the phospholipid and fatty acid compositions of a halotolerant Planococcus sp

The phospholipid headgroup composition and fatty acid composition of a gram-positive halotolerant Planococcus sp. (strain A4a) were examined as a function of growth temperature (5 to 35 degrees C) and NaCl content (0 to 1.5 M) of the growth medium. When the growth temperature was decreased, the relative amount of mono-unsaturated branched-chain fatty acids increased. When Planococcus sp. strain A4a was grown in media containing high NaCl concentrations, the relative amount of the major fatty acid, Ca15:0, increased. The relative amount of anionic phospholipid also increased when the NaCl concentration of the growth medium was increased. The increase in anionic phospholipid content resulted from a decrease in the relative mole percent content of phosphatidylethanolamine and an increase in the relative mole percent content of cardiolipin.

Changes in enzyme stability and fatty acid composition of Streptomyces sp., a facultative thermophilic actinomycete

The thermostability of several enzymes from the facultative thermophilic actinomycete Streptomyces sp., derived from cells grown in the temperature range from 37 degrees C to 60 degrees C, has been examined. A correlation between the growth temperature of the cultures and the heat stability of the enzymes could be demonstrated for alanine dehydrogenase, isocitrate dehydrogenase, myokinase and pyruvate kinase. Except for the isocitrate dehydrogenase, which showed a linear increase of its stability throughout the entire temperature range, all enzymes exhibited a steep increase of the heat stability up to about 50 degrees C, but no further increase in the higher growth range, suggesting, that from 50 degrees C upward a shift to the exclusive production of thermostable protein occurs. Furthermore, the stability of alanine dehydrogenase and pyruvate kinase was found to increase substantially in presence of their substrates. In contrast, substrate-mediated stabilization was very weak with glucose-6-phosphate dehydrogenase and totally absent with acetate kinase, isocitrate dehydrogenase and myokinase. A comparison with previous observations with the same enzymes from Bacillus flavothermus showed, that enzymes from different organisms can have different thermal properties. Determination of the fatty acid composition of Streptomyces sp. cells, grown at different temperatures, showed relatively small alterations, with the main changes occurring between 37 degrees C and 40 degrees C.

Ethanol-induced changes in the membrane lipid composition of Clostridium thermocellum

When ethanol is added to the growth medium of Clostridium thermocellum ATCC 27405 and C9, a different membrane composition is observed after the period of growth arrest. Changes in fatty acid composition and some unsaturated, branched hydrocarbons have been monitored by GLC-MS. There is a marked increase in normal and anteiso-branched fatty acids at the expense of isobranched fatty acids and an increase in short and unsaturated fatty acids. Thus, an adaptive response to growth in the presence of ethanol induces a membrane containing fatty acids with lower melting points and produces a more 'fluid' membrane. The suggestion is made that these membrane changes may be maladaptive to the performance of C. thermocellum.

Effect of restrictive temperature on cell wall synthesis in a temperature-sensitive mutant of Bacillus stearothermophilus

A temperature-sensitive mutant of Bacillus stearothermophilus, TS-13, was unable to grow above 58 degrees C, compared to 72 degrees C for the wild type. Actively growing TS-13 cells lysed within 2 h when exposed to a restrictive temperature of 65 degrees C. Peptidoglycan synthesis stopped within 10 to 15 min postshift before a shut down of other macromolecular syntheses. Composition of preexisting peptidoglycan was not altered, nor was new peptidoglycan of aberrant composition formed. No significant difference in autolysin activity was observed between the mutant and the wild type at 65 degrees C. Protoplasts of TS-13 cells were able to synthesize cell wall material at 52 degress C, but not at 65 degrees C. This wall material remained closely associated with the cell membrane at the outer surface of the protoplasts, forming small, globular, membrane-bound structures which could be visualized by electron microscopy. These structures reacted with fluorescent antibody prepared against purified cell walls. Production of this membrane-associated wall material could be blocked by bacitracin, which inhibited cell wall synthesis at the level of transport through the membrane. The data were in agreement with previous studies showing that at the restrictive temperature this mutant is unable to alter its membrane fatty acid and phospholipid composition with temperature such that it is not able to maintain a membrane lipid composition which permits normal membrane function at the restrictive temperature.

Development of ethanol tolerance in Clostridium thermocellum: effect of growth temperature

The growth of Clostridium thermocellum ATCC 27405 and of C9, an ethanol-resistant mutant of this strain, at different ethanol concentrations and temperatures was characterized. After ethanol addition, cultures continued to grow for 1 to 2 h at rates similar to those observed before ethanol was added and then entered a period of growth arrest, the duration of which was a function of the age of inocula. After this period, cultures grew at an exponential rate that was a function of ethanol concentration. The wild-type strain showed a higher energy of activation for growth than the ethanol-tolerant derivative. The optimum growth temperature of the wild type decreased as the concentration of the ethanol challenge increased, whereas the optimum growth temperature for C9 remained constant. The results are discussed in terms of what is known about the effects of ethanol and temperature on membrane composition and fluidity.

Orientational order of unsaturated lipids in the membranes of Acholeplasma laidlawii as observed by 2H-NMR

Oleic acid specifically deuterated at fifteen different positions along the chain, including the double bond, was biosynthetically incorporated into the membrane lipids of the microorganism Acholeplasma laidlawii B. A detailed study of the dynamic conformation of these chains was carried out using deuterium nuclear magnetic resonance. The deuterium spectra fourteen different samples were recorded as a function of temperature over the range 0-41 degrees C. Spectra were obtained down to -52 degrees C for the sample enriched with oleic acid deuterated at the C-12' position. Above 20 degrees C, where the lipids are in the liquid crystal phase, a single quadrupolar powder pattern was observed for each C2H2 segment, except for the C-2' position which gave rise to a three-component spectrum characteristic for this position in both model and biological membranes. Simulation of this spectrum indicates that there are two conformations of the lipid molecule in the region of the C-2' segment of the sn-2 chain. The orientationa fluctuations of the fatty acid chain segments in the A. laidlawii membranes are described by the deuterium order parameters, and a striking similarity is shown to exist between the oleate chain conformation of the A. laidlawii membrane and a phospholipid model membrane. Remarkable similarities are also demonstrated in the A. laidlawii membrane enriched in palmitic and oleic fatty acids when the order parameter profiles are plotted at the same reduced temperature. Below 15 degrees C a second component, due to gel phase lipid, starts to appear in the spectra. This broad gel phase component grows at the expense of the liquid crystal phase component as the temperature is reduced. The spectra indicate that the center of the phase transition is at about -12 degrees C, in good agreement with DSC studies.

Change in chemical composition of membrane of Bacillus caldotenax after shifting the growth temperature

Membranes from Bacillus caldotenax contain neutral lipids and phospholipids such as phosphatidyl-ethanolamine, phosphatidyl glycerol and cardiolipin. Each of the lipids has almost the same fatty acid composition. When the growth temperature decreases, not only the fatty acid composition but also the lipid composition changes such that the membrane fluidity increases, and the composition of membrane-bound proteins also changes. On shifting the growth temperature from 65 degrees to 45 degress C, the bacterium grows immediately with a doubling time at 45 degrees C, but the compositions of proteins and lipids in membranes gradually change and reach the compositions typical of cells growing at 45 degrees C one doubling time after the temperature shift, respectively. It is concluded that the change in chemical composition of membrane of the bacterium on the temperature shift from 65 degrees to 45 degrees C is not prerequisite for growth at 45 degrees C.

Stability of bacterial messenger RNA in mesophiles and thermophiles

The decay of [3H]uridine-labeled mRNA was measured in the mesophile, Bacillus licheniformis (grown at 37 degrees C and 46 degrees C), and in the thermophile, Bacillus stearothermophilus (grown at 46 degrees C and 55 degrees C). For each organism, the half-life of the mRNA decreased as the growth temperature was increased. The stability index (half-life of mRNA/doubling time of cells), however, was remarkably constant for each organism regardless of the growth temperature. It is concluded that these results support the concept that kinetic considerations play a significant role in the explanation of thermophily.

Lipid and protein composition of membranes of Bacillus megaterium variants in the temperature range 5 to 70 degrees C

Membranes were prepared from four temperature range variants of Bacillus megaterium: one obligate thermophile, one facultative thermophile, one mesophile, and one facultative psychrophile, covering the temperature interval between 5 and 70 degrees C. The following changes in membrane composition were apparent with increasing growth temperatures: (i) the relative amount of iso fatty acids increased and that of anteiso acids decreased, the ratio of iso acids to anteiso acids being 0.34 at 5 degrees C and 3.95 at 70 degrees C, and the pair iso/anteiso acids thus seemed to parallel the pair saturated/unsaturated acids in their ability to regulate membrane fluidity; (ii) the relative/unsaturated acids in their ability to regulate membrane fluidity; (ii) the relative amount of long-chain acids (C16 to C18) increased fivefold over that of short-chain acids (C14 and C15) between 5 and 70 degrees C; (iii) the relative amount of phosphatidylethanolamine increased, and this phospholipid accordingly dominated in the thermophilic strains, whereas diphosphatidylglycerol was predominant in the two other strains; and (iv) the ratio of micromoles of phospholipid to milligrams of membrane protein increased three-fold between 5 and 70 degrees C. Moreover, a quantitative variation in membrane proteins was evident between the different strains. Briefly, membrane phospholipids with higher melting points and packing densities appeared to be synthesized at elevated growth temperatures.

Effect of growth substrate on thermal death of thermophilic bacteria

The heat sensitivity of gram-negative, hydrocarbon-utilizing thermophilic bacteria was altered by a change in growth substrate. Thermophilic strains CC-6, BI-1, and LEH-1, grown with acetate or n-heptadecane as the carbon source, had a higher survival rate when incubated 5 degrees C above their maximum growth temperature than cells of the same organism after growth on glucose or glycerol. There was a correlation between the growth substrated, heat resistance, and the ratios of cellular n-hexadecanoic acid/branched hexadecanoic acid and n-heptadecanoic acid/branched heptadecanoic acid. The bacterial cells that were more heat resistant had ratios of straight-chain/branched-chain fatty acids above 1.0, whereas the heat-sensitive cells had ratios below 0.6.

Temperature range variants of Bacillus megaterium

Facultatively and obligately thermophilic variants were isolated from 3 out of 12 tested mesophilic Bacillus megaterium strains. The variants occurred at a frequency of 10(-8)-10(-9). The ability to grow at elevated temperatures was cured by means of treatment with acridine orange. Stable revertants were isolated from facultatively and obligately thermophilic variants. An unknown type of megacin was produced by the facultative thermophiles. This megacin attacked mesophilic and obligately thermophilic strains. The thermophiles displayed a few divergent taxonomic characteristics but a close relationship between the strains was indicated by the megacin spectrum and sensitivity to phage. Arrhenius plots revealed that the strains could be considered as temperature range variants and that the temperature characteristic increased with growth at a higher temperature range. The case for a plasmid involvement in the phenomenon is discussed.

The relationship between environmental temperature, cell growth and the fluidity and physical state of the membrane lipids in Bacillus stearothermophilus

A definite and characteristic relationship exists between growth temperature, fatty acid composition and the fluidity and physical state of the membrane lipids in wild type Bacillus stearothermophilus. As the environmental temperature is increased, the proportion of saturated fatty acids found in the membrane lipids is also markedly increased with a concomitant decrease in the proportion of unsaturated and branched chain fatty acids. The temperature range over which the gel to liquid-crystalline membrane lipid phase transition occurs is thereby shifted such that the upper boundary of this transition always lies near (and usually below) the temperature of growth. This organism thus possesses an effective and sensitive homeoviscous adaptation mechanism which maintains a relatively constant degree of membrane lipid fluidity over a wide range of environmental temperatures. A mutant of B. stearothermophilus which has lost the ability to increase the proportion of relatively high melting fatty acids in the membrane lipids, and thereby increase the phase transition temperature in response to increases in environmental temperature, is also unable to grow at higher temperatures. An effective homeoviscous regulatory mechanism thus appears to extend the growth temperature range of the wild type organism and may be an essential feature of adaptation to temperature extremes. Over most of their growth temperature ranges the membrane lipids of wild type and temperature-sensitive B. stearothermophilus cells exist entirely or nearly entirely in the liquid-crystalline state. Also, the temperature-sensitive mutant is capable of growth at temperatures well above those at which the membrane lipid gel to liquid-crystalline phase transition is completed. Therefore, although other evidence suggests the existence of an upper limit on the degree of membrane fluidity compatible with cell growth, the phase transition is completed. Therefore, although other evidence suggests the existence of an upper limit on the degree of membrane fluidity compatible with cell growth, the phase transition upper boundary itself does not directly determine the maximum growth temperature of this organism. Similarly, the lower boundary does not determine the minimum growth temperature, since cell growth ceases at a temperature at which most of the membrane lipid still exists in a fluid state. These observations do not support the suggestion made in an earlier study, which utilized electron spin resonance spectroscopy to monitor membrane lipid lateral phase separations, that the minimum and maximum growth temperatures of this organism might directly be determined by the solid-fluid membrane lipid phase transition boundaries. Evidence is presented here that the electron spin resonance techniques used previously did not in fact detect the gel to liquid-crystalline phase transition of the bulk membrane lipids, which, however, can be reliably measured by differential thermal analysis.

Changes in muscle lipid composition and resistance adaptation to temperature in the freshwater crayfish, Austropotamobius pallipes

The phospholipid and fatty acid composition of muscle lipid extracts from crayfish acclimated to 4 C and 25 C (18 hr-light photoperiod) were analyzed. The phospholipid content and class distribution, and cholesterol content were unaffected by the acclimation treatment. Unsaturation of muscle phosphoglycerides was higher in cold acclimated crayfish. Serine/inositol phosphoglycerides from cold-acclimated animals showed somewhat higher proportions of mono- and polyunsaturated fatty acids, whereas choline and ethanolamine phosphoglycerides were less affected. This was correlated with a decreased resistance of cold-acclimated crayfish to lethal high temperature. Acclimation at 4 C under an 8 hr-light photoperiod caused an increased fatty acid unsaturation of the total phospholipid fraction compared to the 4 C, 18 hr-light photoperiod acclimated animals. The resistance of 4 C acclimated crayfish to lethal high temperature, however, was unaffected by daylength treatment. The resistance of freshwater crayfish to lethal high temperature is not simply related to the degree of saturation of the muscle phospholipids. It is suggested that a breakdown in the integrity of a bulk-lipid bilayer is not involved in the process of heat death; rather, that a membrane-bound protein factor, whose thermal sensitivity is modified by changes in its phospholipid environment during temperature adaptation but not during photoperiod adaptation, is the primary site of heat injury.

Altered phospholipid metabolism in a temperature-sensitive mutant of a thermophilic bacillus

The phospholipid metabolism of a temperature-sensitive mutant of a thermophilic bacillus was studied after the shift from a permissive (58 degrees C) to a restrictive (65 degrees C) growth temperature. During the short period of growth of the mutant at 65 degrees C, the proportions of cardiolipin and its 3-acyl derivative (lyso-cardiolipin) increased, and the proportions of phosphatidylglycerol and phosphatidylethanolamine decreased on cell dry weight basis. In 32P incorporation and turnover experiments, phosphatidylglycerol showed the most rapid uptake and loss of the label. Turnover of cardiolipin, limited to a short period, ceased 18 min after the shift, as did the turnover of phosphatidylethanolamine. In the absence of net phospholipid synthesis, there was a quantitative conversion of phosphatidylglycerol to cardiolipin and an increase in the proportion of lyso-cardiolipin. Chloramphenicol, added to the medium at the time of the shift, reduced the rate of phospholipid synthesis, prevented the increase in the proportions of cardiolipin and lyso-cardiolipin, and slowed the decrease in the proportions of the other two phospholipids. The results indicated a defect in the regulatory mechanism(s) of phospholipid metabolism in the mutant at the restrictive temperature.

Lipid metabolism during bacterial growth, sporulation, and germination: differential synthesis of individual branched- and normal-chain fatty acids during spore germination and outgrowth of Bacillus thuringiensis

The biosynthesis of individual branched- and normal-chain fatty acids during Bacillus thuringiensis spore germination and outgrowth was studied by comparing pulsed and continuous labeling of these fatty acids with [U-14C]acetate. The relative specific activity of each fatty acid varies with time as the cell progresses through outgrowth. However, fatty acid synthesis does occur in two distinct phases. Upon germination, acetate is incorporated only into the iso-isomers i-C13, i-C14, and i-C16; no normal or anteiso synthesis occurs. Subsequent to T30, the full complement of branched- and normal-chain homologues is formed and there is a dramatic enhancement in the overall rate of fatty acid synthesis. Significantly, this rate increase coincides with a marked shift from the synthesis of short-chain to long-chain fatty acids. These findings illustrate a dichotomy in synthesis that may result from initial fatty acid formation by preexisting spore fatty acid biosynthetic enzymes in the absence of de novo protein synthesis. Elucidation of the timing and kinetics of individual fatty acid formation provides a biochemical profile of activities directly related to membrane differentiation and cellular development.

Correlation between thermal death and membrane fluidity in Bacillus stearothermophilus

Paramagnetic resonance spectra of spin labels partitioned into spheroplast membranes of Bacillus stearothermophilus indicate lateral lipid phase separations. Cells adjust their lipid composition in response to temperature changes so that the same change of state in membrane phospholipids is achieved at the respective growth temperature. A temperature-sensitive mutant that fails to change its lipid composition above a certain temperature can survive only up to the higher temperature boundary for lateral phase separation. These data are interpreted to indicate that the maximal and minimal growth temperatures of thermophiles are regulated by the onset and conclusion of phase separations of the particular lipid composition they synthesize. It is suggested that isolated lipid domains are required for functional membrane assembly.