Formation of trans fatty acids is not involved in growth-linked membrane adaptation of Pseudomonas putida

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. Freeze-thawing 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.     

Effect of ammonium ions on spiramycin biosynthesis in Streptomyces ambofaciens

The physiological significance of trans unsaturated fatty acids, which are constituents of membrane lipids of the phenol-degrading bacterium Pseudomonas putita P8, was studied. The addition of phenol or phenol derivatives to the cells induced the formation of trans unsaturated fatty acids, yielding an overall maximal amount of 41.3% of total fatty acids. The inhibition of de-novo lipid synthesis by cerulenin prevented the change in the degree of saturation in the lipids. However, the cells could still respond to phenols with an amplified conversion of cis into trans unsaturated fatty acids, which is apparently a post-synthesis mechanism of isomerization of the double bond. The cis/trans conversion correlated with growth inhibition induced by toxic concentrations of 4-chlorophenol, whereas only growing cells were able to change the degree of saturation. In cells that were protected against phenol by immobilization in calcium alginate, the conversion of cis into trans fatty acids occurred at higher toxin concentrations compared with free cells. Cells entering the stationary growth phase increased the prodortion of saturated to unsaturated fatty acids but maintained a constant trans/cis ratio.P. putida P8 reacted to an increase or decrease in the growth temperature with an appropriate change in the ratio of saturated to unsaturated fatty acids and in cells inhibited by cerulenin with a change in the trans/cis ratio. This study shows that the physiological role of the cis/trans conversion is probably the regulation of membrane fluidity when the most important mechanism for this, the modification of the degree of saturation, cannot by used by the cells due to inhibition of growth and lipid biosynthesis. Correspondence to: H. Keweloh     

cis/trans Isomerase of Unsaturated Fatty Acids of Pseudomonas putida P8: Evidence for a Heme Protein of the Cytochrome c Type

From a pool of 600 temperature-sensitive transposon mutants of Pseudomonas putida P8, 1 strain was isolated that carries a mini-Tn5 insertion within the cytochrome c operon. As a result, genes involved in the attachment of heme to cytochrome c-type proteins are turned off. Accordingly, cytochrome c could not be detected spectrophotometrically. The mutant also exhibited a remarkable reduction of cis-trans isomerization capability for unsaturated fatty acids. Consistent with the genetic and physiological data is the detection of a cytochrome c-type heme-binding motif close to the N terminus of the predicted polypeptide of the cis/trans isomerase (cti) gene (CVACH; conserved amino acids in italics). The functional significance of this motif was proven by site-directed mutagenesis. A possible mechanism of heme-catalyzed cis-trans isomerization of unsaturated fatty acids is discussed.     

S-Adenosylmethionine,cyclopropane fatty acid synthase,and the production of lactobacillic acid in Lactobacillus plantarum

S-Adenosylmethionine (AdoMet) levels in Lactobacillus plantarum were found to increase concomitantly with the production of membrane cyclopropane fatty acids under normal growth conditions. This increase in AdoMet did not occur when the pH of the culture medium (initially pH 6.5) was not allowed to fall (pH 4 or lower) during growth. When the culture medium was maintained at pH 6.5, cyclopropane fatty acid synthesis also remained low. While the activity of cyclopropane fatty acid synthase is increased as the pH decreases, the activity of AdoMet synthetase is largely unaffected by the variation of pH of the culture medium. The production of cyclopropane fatty acids is also dependent upon continued protein synthesis; in the presence of chloramphenicol cyclopropane fatty acid synthase activity is decreased, resulting in a lowered production of cyclopropane fatty acids. A dramatic increase in AdoMet levels occurs in the presence of chloramphenicol. It is proposed that AdoMet levels, in conjunction with cyclopropane fatty acid synthase activities, regulate cyclopropane fatty acid synthesis in L. plantarum.     

Temperature- and growth-phase-regulated changes in lipid fatty acid structures of psychrotolerant groundwater Proteobacteria

Cellular fatty acid compositions of five psychrotolerant groundwater isolates representing alpha- and beta-Proteobacteria were studied at temperatures ranging from 8 to 25 degrees C. Unsaturation of straight-chain fatty acids was the most common response to decreasing temperature and was detected in four of the isolates. On solid media, decrease of temperature resulted in a decrease of cyclopropane fatty acids in beta-proteobacterial isolates. The formation of cyclopropane fatty acids depended, however, to a greater extent on the growth phase than the temperature and increased drastically as the cells entered stationary phase. The alpha-proteobacterial isolates contained a branched C(19:1) fatty acid. The formation of the branched C(19:1) increased during growth in the same way as the cyclopropane fatty acids in beta-proteobacterial strains, indicating possibly an analogous formation of the branched fatty acid by methylation of the 18:1 fatty acid. Sphingomonas sp. K6 possessed a novel temperature-induced modification of lipid fatty acids. As temperature decreased from 25 to 8 degrees C, the fatty acid composition shifted from predominantly even-carbon fatty acids to odd-carbon fatty acids. The results show completely different fatty acid modifications in two strains of the same genus Sphingomonas.     

Relation between Cyclopropane Fatty Acid Formation and Saturation of Phospholipid Species in Escherichia coli K-12

Alterations in the degrees of saturation of phosphatidylethanolamine, phosphatidylglycerol and cardiolipin of Escherichia coli K–12 were determined after raising or lowering the growth temperature during the exponential growth phase. After raising the growth temperature from 17 to 42°C, the cells continued to grow with increasing degrees of saturation of the three phospholipids. cis-9,10-Methylenehexadecanoic acid increased only in phosphatidylethanolamine. During growth after lowering the growth temperature from 42 to 17°C, no increase was found in cyclopropane fatty acid content of phosphatidylethanolamine, in which cis-vaccenic acid increased. Significance of cyclopropane fatty acid formation in phospholipids was discussed.     

Biotransformation of Unsaturated Long-Chain Fatty Acids by Eubacterium lentum

Eubacterium lentum (33 strains) isomerized the 12-cis double bond of C₁₈ fatty acids with cis double bonds at C-9 and C-12 into an 11-trans double bond before reduction of the 9-cis double bond. The 14-cis double bond of homo-γ-linolenic acid was isomerized by 29 strains into a 13-trans double bond. The same strains isomerized the 14-cis double bond of arachidonic acid into a 13-trans double bond and then isomerized the 8-cis double bond into a 7-trans double bond; the 13-cis double bond of 10-cis, 13-cis-nonadecadienoic acid was isomerized into a 12-trans double bond. None of these isomerization products was further reduced. Studies with resting cells showed optimal isomerization velocity at a linoleic acid concentration of 37.5 μM; higher concentrations were inhibitory. The pH optimum for isomerization was 7.5 to 8.5. The isomerase was inhibited by the sulfhydryl reagents iodoacetamide, bromoacetate, and N-ethylmaleimide and by the chelators EDTA and 1,10-phenanthroline.     

Cellular fatty acid patterns inPseudomonas sp. CF600 during catechol and phenol degradation in media supplemented with glucose as an additional carbon source

Fatty acid composition inPseudomonas sp. CF600 during degradation of catechol and phenol individually and their mixture was investigated. Moreover, the influence of glucose as an additional, easily degradable carbon source on fatty acid profiling in bacteria grown on these aromatic substrates was studied. Both catechol and phenol treatments caused in bacterial cells crucial changes in the distribution of tested groups of fatty acids. The major changes included the increase of fatty acid saturation, decrease in the percentage of cyclopropane fatty acid 17:0cy and the appearance of branched and hydroxy fatty acids. Under catechol, phenol and their mixture exposure saturated/unsaturated ratio showed the value 6.5, 5.68 and 6.38 whereas in control cells this ratio reached the value 3.05. As a response to aromatic compounds bacteria formed fatty acids that were not detected in control cells growing on glucose. It has been demonstrated that the supplementation of cultured media containing single aromatic substrates or/and their mixture with glucose resulted in changes in degradation rates of catechol and phenol. It seemed that glucose influenced some metabolic pathways responsible for the assimilation of aromatic compounds. The incubation of cells in the presence of aromatic compounds and glucose rapidly led to alterations of whole-cell derived fatty acid composition. The most important changes were associated with saturation level of fatty acids and cyclopropane fatty acid contents.     

Competition between cis,trans and Cyclopropane Fatty Acid Formation and its Impact on Membrane Fluidity

The impact of cis, trans and cyclopropane fatty acids on membrane fluidity was investigated using batch‐grown Pseudomonas putida P8 and Comamonas testosteroni ATCC 17454. A major difference observed between the two investigated strains is the absence of the ability to synthesize trans‐unsaturated fatty acids in Comamonas. When grown exponentially at 30 °C, a shift to 35 °C increased the trans/cis ratios of the fatty acids of P. putida P8 from 0 to 0.81 and 0 to 1.07, in lipid extracts and cell hydrolyzates, respectively. After prolonged growth followed by nutrient deprivation for 48 h, both at 30 °C, trans fatty acids were absent, but the cyclo/cis ratios rose from 0.1 to 1.55 in lipid extracts, and from 0.1 to 1.54 in cell hydrolyzates. C. testosteroni ATCC 17454 contained no cyclo fatty acids when harvested in the exponential phase after 6 h, whereas after 72 h cultivation, the cyclo/cis ratios rose to 0.49 and 0.47, in lipid extracts and cell hydrolyzates, respectively. Trans fatty acids were never observed in this strain. Increased cyclo/cis and trans/cis ratios correlated with decreased fluidity measured by the fluorescence anisotropy of 1,6‐diphenyl‐1,3,5‐hexatriene (DPH) intercalated in the bilayers of liposomes and by Fourier Transform Infrared (FTIR) spectroscopy of lipids prepared from the cells. The specific effect of cyclopropane fatty acids on membrane fluidity was much smaller than that of trans fatty acids. FTIR‐measurements of intact cells of P. putida P8 confirmed the high potency of trans fatty acids to decrease the fluidity. In cells with induced cyclopropane fatty acid synthesis, the membranes remained more fluidized, indicating the lower importance of these fatty acids for homeoviscosis.     

The glycerophospholipid inventory of Pseudomonas putida is conserved between strains and enables growth condition‐related alterations

Microorganisms, such as Pseudomonas putida, utilize specific physical properties of cellular membrane constituents, mainly glycerophospholipids, to (re‐)adjust the membrane barrier to environmental stresses. Building a basis for membrane composition/function studies, we inventoried the glycerophospholipids of different Pseudomonas and challenged membranes of growing cells with n‐butanol. Using a new high‐resolution liquid chromatography/mass spectrometry (LC/MS) method, 127 glycerophospholipid species [e.g. phosphatidylethanolamine PE(32:1)] with up to five fatty acid combinations were detected. The glycerophospholipid inventory consists of 305 distinct glycerophospholipids [e.g. PE(16:0/16:1)], thereof 14 lyso‐glycerophospholipids, revealing conserved compositions within the four investigated pseudomonads P. putida KT2440, DOT‐T1E, S12 and Pseudomonas sp. strain VLB120. Furthermore, we addressed the influence of environmental conditions on the glycerophospholipid composition of Pseudomonas via long‐time exposure to the sublethal n‐butanol concentration of 1% (v/v), focusing on: (i) relative amounts of glycerophospholipid species, (ii) glycerophospholipid head group composition, (iii) fatty acid chain length, (iv) degree of saturation and (v) cis/trans isomerization of unsaturated fatty acids. Observed alterations consist of changing head group compositions and for the solvent‐sensitive strain KT2440 diminished fatty acid saturation degrees. Minor changes in the glycerophospholipid composition of the solvent‐tolerant strains P. putida S12 and Pseudomonas sp. VLB120 suggest different strategies of the investigated Pseudomonas to maintain the barrier function of cellular membranes.     

Changes in fatty acid composition of Pseudomonas aeruginosa ATCC 15442 induced by growth conditions: consequences of resistance to quaternary ammonium compounds

The effects of changes in the fatty acid composition of Pseudomonas aeruginosa induced by growth conditions on its resistance to two quaternary ammonium compounds (QAC) were investigated. The temperature and growth phase were the most influential parameters affecting the fatty acid composition of this bacterium. Furthermore, the formation of saturated fatty acids and cyclopropane fatty acids was stimulated by increasing the temperature, whereas the proportion of unsaturated fatty acids fell. The degree of saturation and the proportion of cyclopropane fatty acids increased in the course of the exponential and stationary phases. These modifications mostly concerned the inner membrane of the bacterium. Resistance of P. aeruginosa to both QAC tested was not significantly influenced by temperature and growth phase variations. Thus, resistance to the two QAC did not seem to be dependent on modifications of the fatty acid composition of the inner membrane.     

Thiol-catalyzed cis-trans isomerization of oleic acid

Various thiols were found to catalyze the geometrical isomerization of oleic acid to trans-Δ⁹-octadecenoic acid. The reaction proceeds in neutral aqueous solution at mild temperatures and at relatively low thiol concentration, 5–20 meq/liter. Hydrogen from the medium was not incorporated into the product, and no trace of Δ⁸ or Δ¹⁰ octadecenoic acid could be detected among the products. The reaction is proposed to involve the formation of a mixed micelle of fatty acid and thiol, nucleophilic attack of the double bond by the thiol, rotation about the former double bond, and elimination of the thiol to produce the thermodynamically more stable trans isomer. The cationic reagent, 2-mercaptoethylamine, was the most efficient catalyst tested. This system should prove to be useful for the preparation of labeled trans unsaturated fatty acids.     

Light,temperature and nitrogen starvation effects on the total lipid and fatty acid content and composition ofSpirulina platensis UTEX 1928

The total lipid and fatty acid content ofSpirulina platensis UTEX 1928 was 7.2 and 2.2% respectively of cellular dry weight under controlled conditions supporting high growth rates. With increases in irradiance from 170 to 870 μmol photon m^?2 s^?1, growth rate increased, total lipid decreased, and fatty acid composition was unaffected. At 1411 μmol photon m^?2 s^?1, total lipid increased slightly and percent composition of the fatty acid gamma linolenic acid increased. Growth and total lipid content ofS. platensis were affected by changes in growth temperature from 25 to 38 °C. With increased growth rate, total lipid content increased. This suggests that the storage of carbon increases at temperatures supporting high growth rates. The degree of saturation increased with temperature. Although the percent composition of gamma linolenic acid was higher at lower growth temperature, production was still primarily a function of growth rate. The effect of temperature on fatty acid content and degree of saturation was of secondary importance. Nitrogen starvation increased total lipid content but decreased fatty acid content as a percentage of dry weight; composition of the fatty acids was unaffected. N-starvation appeared to suspend synthesis of long chain fatty acids inS. platensis, suggesting that some other compound stores fixed carbon when nitrogen is limiting. It was concluded that fatty acid production inS. platensis is maximized by optimizing culture conditions for growth.     

Invertase and auxin-induced elongation in internodal segments of Phaseolus vulgaris

A close positive correlation was observed between segment elongation and the specific activity of soluble acid invertase in stem segments of P. vulgaris incubated for 21 hr in the presence of IAA or of several synthetic auxins and auxin analogues. Optimum concentrations for the stimulation of growth and invertase activity were similar and varied from 10^?6 M (2,4-D) through 10^?5 M (IAA, IBA, α-NAA, β-NAA) to greater than 10^?4 (IPA, PoAA, trans-cinnamic acid). The weak activity of trans-cinnamic acid, a competitive inhibitor of auxin action, may have resulted from cis-trans isomerization during incubation. The concentration of hexose sugars in the segments fell during incubation in the presence of auxin, the greatest decline in hexose concentration occurring in the presence of compounds exhibiting the greatest stimulation of growth.     

Maleylacetoacetate cis-trans isomerase: One-step double cis-trans isomerization of monomethyl muconate and the enzyme's probable role in benzene metabolism

Maleylacetoacetate cis-trans isomerase together with glutathione has been found to isomerize cis-trans isomers of monomethyl muconate. Isomerization about a single double bond and concerted double isomerization of the diene unit occurs. In addition to the variations in substrate structure previously identified the current results demonstrate that a cis,cis diene skeleton and a conjugated ester function are accepted by the enzyme. The present work and the fiding of trans,trans-muconic acid in the urine of benzene-fed mice ([16.] Xenobiotica 15, 211) suggest that maleylacetoacetate cis-trans isomerase may be responsible for the geometrical isomerization. However, cis,cis-muconaldehydic acid rather than cis,cis-muconic acid is suggested to be the early intermediate in benzene metabolism capable of rapid enzyme-catalyzed cis-trans isomerization.     

Conjugated Linoleic Acid Accumulation via 10-Hydroxy-12-Octadecaenoic Acid during Microaerobic Transformation of Linoleic Acid by Lactobacillus acidophilus

Specific isomers of conjugated linoleic acid (CLA), a fatty acid with potentially beneficial physiological and anticarcinogenic effects, were efficiently produced from linoleic acid by washed cells of Lactobacillus acidophilus AKU 1137 under microaerobic conditions, and the metabolic pathway of CLA production from linoleic acid is explained for the first time. The CLA isomers produced were identified as cis-9, trans-11- or trans-9, cis-11-octadecadienoic acid and trans-9, trans-11-octadecadienoic acid. Preceding the production of CLA, hydroxy fatty acids identified as 10-hydroxy-cis-12-octadecaenoic acid and 10-hydroxy-trans-12-octadecaenoic acid had accumulated. The isolated 10-hydroxy-cis-12-octadecaenoic acid was transformed into CLA during incubation with washed cells of L. acidophilus, suggesting that this hydroxy fatty acid is one of the intermediates of CLA production from linoleic acid. The washed cells of L. acidophilus producing high levels of CLA were obtained by cultivation in a medium containing linoleic acid, indicating that the enzyme system for CLA production is induced by linoleic acid. After 4 days of reaction with these washed cells, more than 95% of the added linoleic acid (5 mg/ml) was transformed into CLA, and the CLA content in total fatty acids recovered exceeded 80% (wt/wt). Almost all of the CLA produced was in the cells or was associated with the cells as free fatty acid.     

Purification and characterization of 9-hexadecenoic acid cis-trans isomerase from Pseudomonas sp. strain E-3

A 9-hexadecenoic acid cis-trans isomerase (9-isomerase) that catalyzed the cis-to-trans isomerization of the double bond of free 9-cis-hexadecenoic acid [16:1(9c)] was purified to homogeneity from an extract of Pseudomonas sp. strain E-3 and characterized. Electrophoresis of the purified enzyme on both incompletely denaturing and denaturing polyacrylamide gels yielded a single band of a protein with a molecular mass of 80 kDa, suggesting that the isomerase is a monomeric protein of 80 kDa. The 9-isomerase, assayed with 16:1(9c) as a substrate, had a specific activity of 22.8 μmol h^–1 (mg protein)^–1 and a K _m of 117.6 mM. The optimal pH and temperature for catalysis were approximately pH 7–8 and 30° C, respectively. The 9-isomerase catalyzed the cis-to-trans conversion of a double bond at positions 9, 10, or 11, but not that of a double bond at position 6 or 7 of cis-mono-unsaturated fatty acids with carbon chain lengths of 14, 15, 16, and 17. Octadecenoic acids with a double bond at position 9 or 11 were not susceptible to isomerization. These results suggest that 9-isomerase has a strict specificity for both the position of the double bond and the chain length of the fatty acid. The enzyme catalyzed the cis-to-trans isomerization of fatty acids in a free form, and in the presence of a membrane fraction it was also able to isomerize 16:1(9c) esterified to phosphatidylethanolamine. The 9-isomerase was strongly inhibited by catecholic antioxidants such as α-tocopherol and nordihydroguaiaretic acid, but was not inhibited by 1,10-phenanthroline or EDTA or under anoxic conditions. Based on these results, the possible mechanism of catalysis by this enzyme is discussed. Received: 21 May 1997 / Accepted: 5 September 1997     

Pseudomonas putida NCTC 10936 balances membrane fluidity in response to physical and chemical stress by changing the saturation degree and the trans/cis ratio of fatty acids

This study explored the capability of Pseudomonas putida NCTC 10936 to maintain homeoviscosity after changing the growth temperature, incubating resting cells at different temperatures or at a constant temperature in the presence of 4-chlorophenol (4-CP). After raising the growth temperature from 20 to either 30 or 35 degrees C, the degree of saturation of the organism's fatty acids increased and the ratio of trans to cis unsaturated fatty acids decreased somewhat. In contrast, after the incubation temperature of resting cells was raised (grown at 30 degrees C) from 20 to 30 or 35 degrees C the degree of saturation of the fatty acids remained nearly constant, while the ratio of trans to cis unsaturated fatty acids increased. Incubating resting cells (grown at 30 degrees C) at 20 degrees C in the presence of 4-CP again caused no major changes in the degree of saturation, but cis to trans conversion of unsaturated fatty acids was induced, with a corresponding increase in the trans/cis ratios. Increases in both the saturation degree of the fatty acids and the trans/cis ratio of the unsaturated fatty acids correlated with increases in the fluorescence anisotropy of 1,6-diphenyl-1,3,5-hexatriene intercalated in the bilayers of liposomes prepared from the cells of P. putida NCTC 10936. Electron transport phosphorylation (ETP) could be stabilized by adaptive adjustments in the fluidity of the cytoplasmic membrane mediated by changes in fatty acid composition such as those observed. Whether changes in the degree of saturation or in the trans/cis ratio are more effective can be decided by studying P. putida NCTC 10936.     

Changes in fatty acid profiles of thermo-intolerant and thermo-tolerant marine diatoms during temperature stress

Fatty acid composition and degree of fatty acid saturation during temperature stress in thermo-intolerant (Phaeodactylum tricornutum) and thermo-tolerant (Chaetoceros muelleri) marine diatoms were investigated. A greater number of fatty acids were observed in C. muelleri than in P. tricornutum regardless of treatment. The major fatty acids detected were 14:0, 16:0, 16:1, 16:2, 16:3, 18:0, 18:1(n-9)c, 18:2(n-6) and 20:5(n-3) with additional fatty acids 18:1(n-9)t and 20:4(n-6) detected in C. muelleri. Short duration (2 h) temperature increase above optimal growth temperature had a greater effect on fatty acid composition in C. muelleri than in P. tricornutum and the degree of fatty acid saturation was affected more by temperature in C. muelleri than in P. tricornutum during both short and long duration (24 h) treatments. Total protein assay results suggest that P. tricornutum, but not C. muelleri, was undergoing stress under our growing conditions although lipids in both diatoms were affected by increased temperature. Immunodetection of proteins with anti-rubisco indicates that the rubisco large subunit was undergoing greater turnover in C. muelleri than in P. tricornutum. However, the integrity of rubisco as a suitable indicator of lipid status needs further study. This work supports the hypothesis that a particular temperature, and not treatment duration, has the greater effect on changes in fatty acid composition. Furthermore, changes in fatty acid composition and degree of fatty acid saturation occurred more quickly in the diatoms in response to increased temperature than previously observed in nutrient starvation studies. Since diatom lipids represent an important resource for growth and reproduction of marine animals, the rapid alteration of their lipid composition under temperatures normally encountered in marine environments warrants further study.     

Stability of Lactic Acid Bacteria to Freezing as Related to Their Fatty Acid Composition

The viability of Streptococcus lactis and Lactobacillus sp. A-12 after freezing at -17°C for 48 h was better preserved when the cells were grown in medium supplemented with oleic acid or Tween 80 (polyoxyethylene sorbitan monooleate). A pronounced change in the cellular fatty acid composition was noted when the bacteria were grown in the presence of Tween 80. In S. lactis the ratio of unsaturated to saturated fatty acids increased from 1.18 to 2.55 and in Lactobacillus sp. A-12 it increased from 0.85 to 1.67 when Tween 80 was added to the growth medium. The antibiotic cerulenin markedly inhibited the growth of lactic acid bacteria in tomato juice (TJ) medium but had almost no effect on the growth of the bacteria in TJ medium containing Tween 80 (or oleic acid). The antibiotic inhibited markedly the incorporation of [1-¹⁴C]acetate but had no inhibitory effect on the incorporation of exogenous [1-¹⁴C]oleate (or [1-¹⁴C]palmitate) into the lipid fractions of lactic acid bacteria. Thus, the fatty acid composition of lactic acid bacteria, inhibited by the antibiotic cerulenin, can be modulated by exogenously added oleic acid (or Tween 80) without the concurrent endogenous fatty acid synthesis from acetate. The data obtained suggest that cerulenin inhibits neither cyclopropane fatty acid synthesis nor elongation of fatty acid acyl intermediates. The radioactivity of cells grown in the presence of [1-¹⁴C]oleate and cerulenin was associated mainly with cyclopropane Δ19:0, 20:0 + 20:1, and 21:0 acids. As a consequence, cerulenin caused a decrease in the ratio of unsaturated to saturated fatty acids in lactic acid bacteria as compared with cells grown in TJ medium plus Tween 80 but without cerulenin. Cerulenin caused a decrease in the viability of S. lactis and Lactobacillus sp. A-12 after freezing at -17°C for 48 h only when Tween 80 was present in the growth medium. We conclude that the sensitivity of lactic acid bacteria to damage from freezing can be correlated with specific alterations in the cellular fatty acids.