Changes in Ribonucleic Acid Turnover During Aerobic and Anaerobic Growth in Rhodopseudomonas spheroides

Differences in the rate and extent of degradation of ribonucleic acid (RNA) labeled by a 30-sec pulse in aerobically or anaerobically grown Rhodopseudomonas spheroides have been studied by using rifampin to block RNA synthesis. In anaerobic cultures, unstable RNA is degraded with a half-life of 1.25 to 2.0 min, and about 40% of the pulse-labeled RNA is stable. In aerobic cultures, the half-life of unstable RNA is increased to 2.5 to 4.0 min, and 50% of the RNA is stable. When aerobic cultures are transferred to anaerobic conditions, there is a rapid drop in half-life and in the proportion of stable RNA. When anaerobic cultures are made aerobic, the reverse changes occur after a lag of about 30 min. Addition of puromycin to either aerobic or anaerobic cultures caused the pulse-labeled RNA to be degraded at the same rate and to the same extent as the RNA in an anaerobic control culture. In contrast, addition of chloramphenicol enhanced the difference in RNA half-life and increased the proportion of stable RNA by about 10% in each case. It is concluded that there is a difference in the stability of an RNA component under aerobic and anaerobic conditions.     

Effect of yeast growth conditions on yeast-mycelial transition in Candida albicans

When grown and induced to form germ tubes in liquid defined media, yeast cells of Candida albicans must reach stationary phase before acquiring ability to carry out the yeast-mycelial transition. This study examined the effect of the carbon source utilized for yeast growth on the inducibility of stationary phase yeast. When grown to the same stationary phase cell density as glucose cultures, cultures grown on citrate were fully inducible while cultures grown on galactose and mannose showed a small reduction. Cultures grown on ethanol were reduced 80% in morphological conversion. When glucose grown cells were induced in the presence of these carbon sources, hexoses supported full induction while ethanol reduced induction 80%. Induction in the presence of carboxylic acids was similar to induction in the absence of added carbon source. When induced on the same source used in yeast growth, germ tube formation was reduced for all carbon sources except hexoses. When induced in the absence of added carbon source, yeasts grown on citrate and ethanol were inhibited 80-100%. Cultures starved for glucose were more inhibited than cultures starved for NH4Cl when induced without added carbon source. These observations suggest that the metabolic state of the stationary phase cell is an important factor in the ability to respond to conditions inducing germ tube formation.     

Effect of glucose and long-chain fatty acids on synthesis of long-chain alcohols by Candida albicans

Candida albicans, grown aerobically in glucose-containing media, produced C14, C16 and C18 saturated long-chain alcohols only after the end of exponential growth. Contents of C14 alcohols were always lowest, and C16 and C18 alcohol contents about equal. Contents of all three classes of alcohol increased as the concentration of glucose in aerobic cultures harvested after 168 h incubation was raised from 1.0 to 30.0% (w/v). However, in 168 h anaerobic cultures, greatest long-chain alcohol contents in organisms were obtained using media containing 10% (w/v) glucose. Substituting glucose (10%, w/v) with the same concentration of galactose in aerobic cultures greatly decreased contents of long-chain alcohols, while inclusion of 10% (w/v) glycerol virtually abolished their synthesis. Supplementing anaerobic cultures with odd-chain fatty acids induced synthesis of odd-chain alcohols. Maximum conversion of fatty acid to the corresponding long-chain alcohol was observed with heptadecanoic acid. The effect of glucose on production of heptadecanol from exogenously provided heptadecanoic acid was similar to that observed on synthesis of the three major even-chain alcohols in media lacking a fatty-acid supplement. Cell-free extracts of organisms catalysed in vitro conversion of palmitoyl-CoA to 1-hexadecanol.     

In Vitro Effect of Rifampin on Mycobacteria

Rifampin inhibited 20 strains of Mycobacterium tuberculosis in concentrations of 0.005 to 0.02 mug/ml in 7H-9 broth with Tween 80 and killed all or nearly all of the inoculum in four to eight times greater concentrations. In the same medium without Tween 80, as well as on 7H-10 agar, about 16 to 64 times these amounts were required to produce the same effect. Rifampin was also active against M. kansasii and some of the nonchromogenic mycobacteria. The incidence of mycobacterial cells resistant to rifampin within the cultures studied was in the range of one to four per 10(8) to 10(9) colony-forming units with concentrations of 4 to 125 mug of rifampin per ml. Only one of the Battey cultures and that of M. fortuitum yielded cells resistant to rifampin at 125 mug/ml but not at 500 mug/ml. The same strains yielded more than double that number of organisms resistant to streptomycin and up to 100 times more organisms resistant to isoniazid. All three drugs stopped the growth or reduced the mycobacterial population in growing cultures after contact for 24 to 48 hr. Complete inhibition of growth was produced by rifampin at 1.0 mug/ml in an average of 6 days and by streptomycin at 5.0 mug/ml in 3 days. After an average contact of 10.7 days with rifampin, five of seven strains resumed growth and all strains began regrowth after exposure to streptomycin for 9.4 days. The marked susceptibility of M. tuberculosis and of atypical mycobacteria to rifampin in vitro and the relatively low incidence of resistant mutants suggests that this agent may have clinical usefulness in the treatment of tuberculosis and some other mycobacterioses.     

Involvement of an ATP-dependent carboxylase in a CO2-dependent pathway of acetone metabolism by Xanthobacter strain Py2.

The metabolism of acetone by the aerobic bacterium Xanthobacter strain Py2 was investigated. Cell suspensions of Xanthobacter strain Py2 grown with propylene or glucose as carbon sources were unable to metabolize acetone. The addition of acetone to cultures grown with propylene or glucose resulted in a time-dependent increase in acetone-degrading activity. The degradation of acetone by these cultures was prevented by the addition of rifampin and chloramphenicol, demonstrating that new protein synthesis was required for the induction of acetone-degrading activity. In vivo and in vitro studies of acetone-grown Xanthobacter strain Py2 revealed a CO2-dependent pathway of acetone metabolism for this bacterium. The depletion of CO2 from cultures grown with acetone, but not glucose or n-propanol, prevented bacterial growth. The degradation of acetone by whole-cell suspensions of acetone-grown cells was stimulated by the addition of CO2 and was prevented by the depletion of CO2. The degradation of acetone by acetone-grown cell suspensions supported the fixation of 14CO2 into acid-stable products, while the degradation of glucose or beta-hydroxybutyrate did not. Cultures grown with acetone in a nitrogen-deficient medium supplemented with NaH13CO3 specifically incorporated 13C-label into the C-1 (major labeled position) and C-3 (minor labeled position) carbon atoms of the endogenous storage compound poly-beta-hydroxybutyrate. Cell extracts prepared from acetone-grown cells catalyzed the CO2- and ATP-dependent carboxylation of acetone to form acetoacetate as a stoichiometric product. ADP or AMP were incapable of supporting acetone carboxylation in cell extracts. The sustained carboxylation of acetone in cell extracts required the addition of an ATP-regenerating system consisting of phosphocreatine and creatine kinase, suggesting that the carboxylation of acetone is coupled to ATP hydrolysis. Together, these studies provide the first demonstration of a CO2-dependent pathway of acetone metabolism for a strictly aerobic bacterium and provide direct evidence for the involvement of an ATP-dependent carboxylase in bacterial acetone metabolism.     

Demonstration of anaerobic catalase synthesis in the cz1 mutant of Saccharomyces cerevisiae.

Anaerobic synthesis of catalase T (a typical oxygen-inducible haem containing enzyme) in the cz1 mutant of yeast was demonstrated. The synthesis of catalase T in anaerobically grown mutant cells is stimulated by haemin under carbon-derepressed conditions of growth (galactose as carbon source) but not in glucose repressed cultures. Haem is practically undetectable in the anaerobically grown glucose repressed wild type strain and its level in derepressed cells amounts to 3% of the fully derepressed aerobically grown cells. In the cz1 mutant cultures grown in anoxia both on galactose and glucose the haem level usually exceeds 10% of that in the aerobic control.     

Effect of Tween 80 on glucosyltransferase production in Streptococcus mutans.

Glucan production from sucrose by Streptococcus mutans OMZ 176 was stimulated approximately threefold in the presence of 0.1% Tween 80. When OMZ 176 was grown in a medium containing glucose, the glucosyltransferase level in the medium was also increased about fivefold in the presence of 0.1% Tween 80. The glucosyltransferase level increased in proportion to the logarithm of the concentration of Tween 80 in the glucose medium. Tween 80 affected neither bacterial growth nor the activity of glucosyltransferase. The appearance of glucosyltransferase in the glucose medium was inhibited immediately by chloramphenicol and actinomycin D and, after a lag, by rifampin as well. It was observed that the fatty acid composition of the cells grown with Tween 80 was altered. These results suggest that Tween 80 stimulates glucosyltransferase synthesis either directly, or indirectly by promoting glucosyltransferase secretion.     

Influence of oxygen availability on physiology, verocytotoxin expression and adherence of Escherichia coli O157

A strain of Escherichia coli serotype O157 was grown in steady state chemostat culture under aerobic, oxygen-limited and anaerobic conditions. The growth and metabolic efficiency of oxygen-limited and anaerobic cultures was impaired, with biomass yield and the molar growth yield for glucose, Yglucose, reduced markedly in comparison with aerobic cultures. Steady state cells were typically short rods 2-3 microns long, and were encapsulated by a layer of extracellular material. The majority of cells were non-flagellated and fimbriae were not observed. Chemostat-grown cells were significantly more adhesive for HEp-2 monolayers than cells grown in aerobic batch culture. Furthermore, oxygen-limited and anaerobic cultures were significantly more adhesive for Hep-2 cells when compared with cells grown in aerobic chemostat culture, possibly reflecting increased pathogenicity associated with the induction of novel adhesins. Type 1 pili were not responsible for increased adherence. Verocytotoxins, VT1 and VT2, were expressed constitutively and were not influenced by oxygen availability. This study demonstrates that E. coli O157 is a versatile micro-organism, which responds to environmental conditions likely to be encountered during infection by inducing a phenotype which is more adhesive for human epithelial cells.     

Differential adaptation of membranes of two osmotolerant fungi,Aspergillus chevalieri and Penicillium expansum to high sucrose concentrations

Aspergillus chevalieri and Penicillium expansum were able to tolerate sucrose concentrations in the growth media up to 80% (w/v). At 50% sucrose the growth rate is approximately 1.4 and 1.2 times, respectively, higher than in the control. While at 80% sucrose it drops to 35% and 45% of the control level for both fungi. Lipids and proteins in plasma membranes increased with increasing sucrose concentrations in the growth medium. Phospholipid content in membranes of both organisms being also increased, phosphatidyl glycerol was the major detected phospholipid and represented the highest increase. The fatty acid composition of fraction enriched plasma membrane of both fungi changed when they were grown in high sucrose concentrations. Some fatty acids which had not been detected in control cultures were present and the proportions of other fatty acids changed. At 50% sucrose the unsaturation index of membranes decreased by 20-25% in both fungi, indicating that the plasma membrane is less fluid at this concentration. At 80% sucrose a similar trend was observed for P. expansum but for A. chevalieri the unsaturation index was little changed compared with the control. The fluorescence polarization values of 1,6-diphenyl 1,3,5-hexatriene (DPH) in membranes of both fungi grown at 80% sucrose increased, indicating a decrease in membrane fluidity. At 50% sucrose the increase in saturation of membrane fatty acids would tend to reduce membrane fluidity but in A. chevalieri at 80% sucrose fatty acids did not become more saturated. In this case the marked increase in sterols at this sucrose concentration may be responsible for low membrane fluidity.     

Oxygen toxicity in Streptococcus mutans: manganese, iron, and superoxide dismutase.

When cultured anaerobically in a chemically defined medium that was treated with Chelex-100 to lower its trace metal content, Streptococcus mutans OMZ176 had no apparent requirement for manganese or iron. Manganese or iron was necessary for aerobic cultivation in deep static cultures. During continuous aerobic cultivation in a stirred chemostat, iron did not support the growth rate achieved with manganese. Since the dissolved oxygen level in the chemostat cultures was higher than the final level in the static cultures, manganese may be required for growth at elevated oxygen levels. In medium supplemented with manganese, cells grown anaerobically contained a low level of superoxide dismutase (SOD) activity; aerobic cultivation increased SOD activity at least threefold. In iron-supplemented medium, cells grown anaerobically also had low SOD activity; aerobic incubation resulted in little increase in SOD activity. Polyacrylamide gel electrophoresis of the cell extracts revealed a major band and a minor band of SOD activity in the cells grown with manganese; however, cells grown with iron contained a single band of SOD activity with an Rf value similar to that of the major band found in cells grown with manganese. None of the SOD activity bands were abolished by the inclusion of 2 mM hydrogen peroxide in the SOD activity strain. S. mutans may not produce a separate iron-containing SOD but may insert either iron or manganese into an apo-SOD protein. Alternatively, iron may function in another activity (not SOD) that augments the defense against oxygen toxicity at low SOD levels.     

Cell aggregation in cultures of Micrococcus luteus studied by dynamic light scattering

Cell aggregation was studied using the method of dynamic light scattering in the course of growth of Micrococcus luteus cultures in a liquid medium. The method detects particles ranging in size from 0.5 to 1000 microm in samples containing no more than 10(5) cells/ml. When grown in liquid media, M. luteus forms aggregates; during the lag phase, 80% of the cells are found in aggregates of 10 to 1000 microm, only minor amounts being represented by single cells. With the onset of exponential growth, the aggregates were decomposed, and single cells became prevalent in the culture liquid. This observation confirms that the aggregation of the cells during the lag phase is prerequisite to the initiation of bacterial growth. The method may be used in biotechnology for monitoring the state of bacterial cultures.     

Effect of chlorate,molybdate, and shikimic acid on Salmonella enterica serovar Typhimurium in aerobic and anaerobic cultures

Experiments were conducted to determine factors that affect sensitivity of Salmonella enterica serovar Typhimurium to sodium chlorate (5 mM). In our first experiment, cultures grown without chlorate grew more rapidly than those with chlorate. An extended lag before logarithmic growth was observed in anaerobic but not aerobic cultures containing chlorate. Chlorate inhibition of growth during aerobic culture began later than that observed in anaerobic cultures but persisted once inhibition was apparent. Conversely, anaerobic cultures appeared to adapt to chlorate after approximately 10 h of incubation, exhibiting rapid compensatory growth. In anaerobic chlorate-containing cultures, 20% of total viable counts were resistant to chlorate by 6 h and had propagated to 100% resistance (>10⁹ CFU mL^?1) by 24 h. In the aerobic chlorate-containing cultures, 12.9% of colonies had detectable resistance to chlorate by 6 h, but only 1% retained detectable resistance at 24 h, likely because these cultures had opportunity to respire on oxygen and were thus not enriched via the selective pressure of chlorate. In another study, treatment with shikimic acid (0.34 mM), molybdate (1 mM) or their combination had little effect on aerobic or anaerobic growth of Salmonella in the absence of added chlorate. As observed in our earlier study, chlorate resistance was not detected in any cultures without added chlorate. Chlorate resistant Salmonella were recovered at equivalent numbers regardless of treatment after 8 h of aerobic or anaerobic culture with added chlorate; however, by 24 h incubation chlorate sensitivity was completely restored to aerobic but not anaerobic cultures treated with shikimic acid or molybdate but not their combination. Results indicate that anaerobic adaptation of S. Typhimurium to sodium chlorate during pure culture is likely due to the selective propagation of low numbers of cells exhibiting spontaneous resistance to chlorate and this resistance is not reversible by molybdenum supplementation.     

Fatty Acid and Sterol Composition of Mucor genevensis in Relation to Dimorphism and Anaerobic Growth

Fatty acid and sterol content and composition were determined for the dimorphic mold, Mucor genevensis, grown under a variety of experimental conditions. Fatty acids account for 6 to 9% of the dry weight of aerobically grown mycelium, and 70 to 80% of these are unsaturated. The organism contains γ-linolenic acid which is characteristic for Phycomycetes, and in sporangiospores this compound represents 40% of the total fatty acids. Of the sterols found in mycelium, 80% is ergosterol, and stigmasterol was positively identified as one of the minor components. In anaerobically grown yeastlike cells, sterol content is less than 10% of the level found in aerobically grown cells, and fatty acids amount to less than 2% of the dry weight. These fatty acids are predominantly short chain and less than 10% are unsaturated. Yeastlike cells obtained under aerobic conditions by growth in the presence of phenethyl alcohol have fatty acid and sterol compositions characteristic of aerobically grown mycelium. It is concluded that the dimorphology of the organism is not directly related to lipid composition.     

Oxygen requirements of the food spoilage yeast Zygosaccharomyces bailii in synthetic and complex media

Most yeast species can ferment sugars to ethanol, but only a few can grow in the complete absence of oxygen. Oxygen availability might, therefore, be a key parameter in spoilage of food caused by fermentative yeasts. In this study, the oxygen requirement and regulation of alcoholic fermentation were studied in batch cultures of the spoilage yeast Zygosaccharomyces bailii at a constant pH, pH 3.0. In aerobic, glucose-grown cultures, Z. bailii exhibited aerobic alcoholic fermentation similar to that of Saccharomyces cerevisiae and other Crabtree-positive yeasts. In anaerobic fermentor cultures grown on a synthetic medium supplemented with glucose, Tween 80, and ergosterol, S. cerevisiae exhibited rapid exponential growth. Growth of Z. bailii under these conditions was extremely slow and linear. These linear growth kinetics indicate that cell proliferation of Z. bailii in the anaerobic fermentors was limited by a constant, low rate of oxygen leakage into the system. Similar results were obtained with the facultatively fermentative yeast Candida utilis. When the same experimental setup was used for anaerobic cultivation, in complex YPD medium, Z. bailii exhibited exponential growth and vigorous fermentation, indicating that a nutritional requirement for anaerobic growth was met by complex-medium components. Our results demonstrate that restriction of oxygen entry into foods and beverages, which are rich in nutrients, is not a promising strategy for preventing growth and gas formation by Z. bailii. In contrast to the growth of Z. bailii, anaerobic growth of S. cerevisiae on complex YPD medium was much slower than growth in synthetic medium, which probably reflected the superior tolerance of the former yeast to organic acids at low pH.     

Effect of aerobically generated inoculum on xylose fermentation by an ethanologenic recombinantE. coli

Summary The anaerobic conversion of xylose to ethanol by a genetically engineredE. coli B (pLOI297) was investigated using anaerobically and aerobically grown cultures as inocula. Using anaerobically grown cells, an increase in the inoculation density from 50 to 340 mg dry wt. cells/L resulted in an increase in the overall volumetric productivity from 0.57 to 0.71 g/L/h. At the higher inoculation density, substitution of the anaerobic inoculum by aerobically grown cells resulted in a 15% reduction in volumetric productivity (0.61 g/L/h) that was caused by the introduction of a lag period during which the aerobic inoculum adapted to the anaerobic environment. In all cases, the ethanol yield from xylose approached the theoretical maximum and seemed unaffected by the physiological history of the inoculum with respect to aeration. It is concluded that aeration should be avoided in the production of high performance starter cultures.     

Physiological studies on the growth and utilization of sugars by Listeria species

Experiments, relevant to growth in milk, were done to delineate the aerobic and anaerobic growth of Listeria species on selected sugars in several media. All species grew on glucose aerobically, forming lactic acid and (or) acetic acid. Anaerobically, only lactic acid was formed; cell yields were 80% of those obtained aerobically. When incubated aerobically, small amounts (1.5 microns/mL) of isovaleric acid, 2-hydroxyisovaleric acid, and trace amounts of isobutyric acid were formed. These products were characteristically formed by 26 strains representing all the species of Listeria. Added leucine stimulated isovaleric acid formation. Anaerobic fermentations of glucose could be followed by 60 to 80% cell lysis; less lysis occurred in air. Anaerobically, only hexoses and pentoses supported growth; aerobically, maltose and lactose supported growth of some strains, but sucrose did not support growth of any strain tested. Listeria grayi and Listeria murrayi utilized the galactose and glucose moieties of lactose for growth; Listeria monocytogenes and Listeria innocua used only the glucose moiety. Glucosamine and N-acetylglucosamine supported aerobic and anaerobic growth as well as glucose, and their presence stimulated the utilization of lactose by "lactose-negative" strains. Analyses of cultures grown at 5 degrees C in sterile milk treated with glucose oxidase supported the conclusion that the glucose of the milk was the major, if not the limiting, substrate that supported growth.     

Ribonucleic Acid from Aerobically and Anaerobically Grown Rhodopseudomonas spheroides: Comparison by Hybridization to Chromosomal and Satellite Deoxyribonucleic Acid

Ribonucleic acid (RNA) species from aerobically and anaerobically grown Rhodopseudomonas spheroides were compared via hybridization to deoxyribonucleic acid (DNA). Both long-labeled and stable RNA bound to chromosomal DNA to the same extent, regardless of derivation. About 4% of the chromosomal DNA hybridized with total cell RNA and about 0.08% with stable RNA. About 4% of the mixed satellite DNA could be hybridized to total cell RNA from aerobic or anaerobic cultures, whereas essentially no stable RNA formed a hybrid with this DNA. Hybridization competition experiments with aerobic and anaerobic pulse-labeled RNA and chromosomal or satellite DNA demonstrated that no qualitative differences existed between the RNA species. It is concluded that identical species of RNA in the same relative amounts are synthesized by R. spheroides during aerobic or anaerobic growth on the same medium.     

Effects of growth conditions on mitochondrial morphology inSaccharomyces cerevisiae

Effects of growth conditions on mitochondrial morphology were studied in livingSaccharomyces cerevisiae cells by vital staining with the fluorescent dye dimethyl-aminostyryl-methylpyridinium iodine (DASPMI), fluorescence microscopy, and confocal-scanning laser microscopy. Cells from respiratory, ethanol-grown batch cultures contained a large number of small mitochondria. Conversely, cells from glucose-grown batch cultures, in which metabolism was respiro-fermentative, contained small numbers of large, branched mitochondria. These changes did not significantly affect the fraction of the cellular volume occupied by the mitochondria. Similar differences in mitochondrial morphology were observed in glucose-limited chemostat cultures. In aerobic chemostat cultures, glucose metabolism was strictly respiratory and cells contained a large number of small mitochondria. Anaerobic, fermentative chemostat cultivation resulted in the large, branched mitochondrial structures also seen in glucose-grown batch cultures. Upon aeration of a previously anaerobic chemostat culture, the maximum respiratory capacity increased from 10 to 70 µmole.min^–1.g weight^–1 within 10 h. This transition resulted in drastic changes of mitochondrial number, morphology and, consequently, mitochondrial surface area. These changes continued for several hours after the respiratory capacity had reached its maximum. Cyanide-insensitive oxygen consumption contributed ca. 50% of the total respiratory capacity in anaerobic cultures, but was virtually absent in aerobic cultures. The response of aerobic cultures to oxygen deprivation was qualitatively the reverse of the response of anaerobic cultures to aeration. The results indicate that mitochondrial morphology inS. cerevisiae is closely linked to the metabolic activity of this yeast: conditions that result in repression of respiratory enzymes generally lead to the mitochondrial morphology observed in anaerobically grown, fermenting cells.     

Interactions between respiration and denitrification during growth of Thiosphaera pantotropha in continuous culture

Abstract The effects of oxygen on the use of nitrate as an electron acceptor by the denitrifying bacterium Thiosphaera pantotropha were investigated during growth on acetate. In batch cultures under aerobic conditions nitrate was not utilised and the growth rate constant was 0.55 h⁻¹. The corresponding value for growth on nitrate under anoxic conditions was 0.37 h⁻¹. In acetate-limited continuous cultures with feedback control of the dissolved oxygen concentration, nitrate utilisation was totally inhibited by the lowest concentration of oxygen tested (22 μM). Carbon conversion efficiencies with acetate increased from 0.28 with nitrate to 0.44 with oxygen. The rates of nitrification calculated from nitrogen balance studies were not greater than 1.5% of the rate of anoxic denitrification.     

Comparative fatty acid profiling of Mucor rouxii under different stress conditions

To understand the relationship between fatty acid metabolism and the growth morphology of Mucor rouxii, fatty acid profiling was studied comparatively in cells grown under conditions which included different atmospheric conditions or the addition of phenethyl alcohol (PEA). The significant difference in fatty acid profiles from M. rouxii grown under aerobic or anaerobic conditions was not found to be directly related to morphological growth. Oxygen limitation, which induced the formation of pure multipolar budding yeasts, led to a decrease in long-chain fatty acids-- particularly unsaturated fatty acids-- and an increase in medium-chain saturated fatty acids, a finding which contrasted with the aerobic cultures, including mycelia and PEA-induced bipolar budding cells. High levels of C18 : 1Delta(9) were found in aerobic yeast cultures with additional PEA when compared to that in the aerobically grown mycelia. The identification of unusual fatty acids in Mucor in response to alcoholic and hypoxic stresses - including odd-numbered fatty acids and 7-hydroxy dodecanoic acid (7-OH C12 : 0) in addition to the more common fatty acids - implied that an important role existed for these unusual fatty acids.