Anaerobic Degradability of Alcohol Ethoxylates and Related Non-Ionic Surfactants

The anaerobic degradability of alcohol ethoxylates with various degrees of branching and several related substances was studied. Different inocula were employed in order to increase the probability of obtaining capable bacteria, and the degradation assays were fed with several small doses of the test substances in order to avoid inhibition by too high initial concentrations. Mineralization was quantified by monitoring the biogas production and inorganic carbon concentration in the liquid phase. Almost complete mineralization was achieved in the assays with linear alcohol ethoxylate, poly(ethylene glycol), dodecanol, 2-ethyl-hexanoic acid and 3-methyl-valeric acid. No significant degradation was detected in the assays with highly branched alcohol ethoxylate, 2-butyl-branched alcohol ethoxylate, alcohol alkoxylate, poly(propylene glycol) and iso-tridecanol. A 2-ethyl-branched alcohol ethoxylate was transformed to (2-ethyl-hexyloxy)-acetate, which was not further degraded. Apparently already the first step of anaerobic degradation of alcohol ethoxylates, the ethoxylate chain shortening, is sterically hindered by the alkyl branching. Alkyl branching in alcohol ethoxylates and the inclusion of propylene oxide units in alcohol alkoxylates seem to have a clearly more detrimental effect on anaerobic degradability than on aerobic degradability.     

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.     

The effect of propionic to acetic acid ratio on anaerobic-aerobic (low dissolved oxygen) biological phosphorus and nitrogen removal

In this paper, three lab-scale sequencing batch reactors (SBR-A, B, and C) operated with anaerobic/aerobic (low dissolved oxygen, 0.15-0.45 mg L(-1)) configuration were long-term cultured, respectively with single acetic acid and propionic/acetic acid of 1/1 and 2/1 (carbon molar ratio), and the comparisons of anaerobic and aerobic transformations of phosphorus and nitrogen among them were made. With the increase of propionic/acetic acid, lower anaerobic phosphorus release and higher phosphorus release to short-chain fatty acids uptake ratio were observed, and less anaerobic and aerobic transformations of glycogen and poly-3-hydroxybutyrate as well as total polyhydroxyalkanoates occurred, but the transformations of poly-3-hydroxyvalerate and poly-3-hydroxy-2-methyvalerate increased. The phosphorus removal efficiency was respectively 81, 94 and 97% in SBR-A, B and C. Almost all ammonium was removed and no significant nitrite was accumulated at different propionic/acetic acid ratios. However, the nitrate accumulation and total nitrogen removal were observed to be affected by propionic/acetic acid ratio. The total nitrogen removal efficiency was 61, 68 and 82%, and the aerobic end nitrate concentration was 8.05, 6.40 and 3.54 mg L(-1) in three SBRs, respectively. All the above studies indicated that the sole acetic acid caused more nitrate accumulation than propionic and acetic acids mixture, and a pertinent increase of wastewater propionic/acetic acid ratio was of benefit to both nitrogen and phosphorus removal in an anaerobic/aerobic (low dissolved oxygen) biological wastewater treatment process.     

Anaerobic removal of linear alcohol ethoxylates

The present paper deals with a laboratory-scale study of anaerobic treatment of two commercial mixtures (LS2, LT7) of alcohol ethoxylates with 8-14 carbon atoms and 2 and 7 ethoxy groups. Tests were carried out in batch, with a 2 g l(-1) single dose, and in semibatch, with daily 0.2 g l(-1) doses. The behaviour of the tested mixtures was different: anaerobic sludge adsorption was the main removal process for LS2, while adsorption was less significant and biodegradation was more important for LT7. These differences appeared to be mainly related to the ethoxy portion length determining the extent of biodegradability and adsorption.     

Potential for Aerobic and Anaerobic Biodegradation of Petroleum Hydrocarbons in Boreal Subsurface

We studied the role of aerobic and anaerobic petroleum hydrocarbon degradation at a boreal, light-weight fuel and lubrication oil contaminated site undergoing natural attenuation. At the site, anoxic conditions prevailed with high concentrations of CH4 (up to 25% v/v) and CO2 (up to 18% v/v) in the soil gas throughout the year. Subsurface samples were obtained mainly from the anoxic parts of the site and they represented both the unsaturated and saturated zone. The samples were incubated in microcosms at near in situ conditions (i.e. in situ temperature 8 degrees C, aerobic and anaerobic conditions, no nutrient amendments) resulting in the removal of mineral oil (as determined by gas chromatography) aerobically as well as anaerobically. In the aerobic microcosms on average 31% and 27% of the initial mineral oil was removed during a 3- and 4-month incubation, respectively. In the anaerobic microcosms, on average 44% and 15% of the initial mineral oil was removed during a 12- and 10-month anaerobic incubation, respectively, and e.g. n-alkanes from C11 to C15 were removed. A methane production rate of up to 2.5 microg CH4 h(-1) g(-1) dwt was recorded in these microcosms. In the aerobic as well as anaerobic microcosms, typically 90% of the mineral oil degraded belonged to the mineral oil fraction that eluted from the gas chromatograph after C10 and before C15, while 10% belonged to the fraction that eluted after C15 and before C40. Our results suggest that anaerobic petroleum hydrocarbon degradation, including n-alkane degradation, under methanogenic conditions plays a significant role in the natural attenuation in boreal conditions.     

Anaerobiosis and Release from Dormancy in Apple Embryos: Leaching of (+/-) [C]Abscisic Acid and its Metabolites under Aerobic and Anaerobic Conditions

An anaerobic treatment released Pyrus malus L. cv Golden Delicious embryos from their primary dormancy. It also suppressed the inhibitory effect induced by exogenous abscisic acid (ABA) on after-ripened embryos. For the study of ABA metabolism, a two-step culture method was developed. Embryos in primary dormancy were cultivated aerobically in the presence of [¹⁴C]ABA (first culture). Some were directly analyzed to evaluate metabolism of absorbed ABA. The remaining embryos were cultivated on moist cotton without ABA, either in aerobic or anaerobic conditions (second culture). The amounts of ABA and its metabolites were measured both in the embryos and the water-leachates. After the second culture, the embryos showed a spectacular decrease in ABA content, with no difference between anaerobic and aerobic cultures. The amount of ABA glucose ester increased slightly in aerobiosis but diminished markedly in anaerobiosis. Radioactivity of the butanol fraction, which corresponded to polar conjugates, decreased considerably in anaerobiosis, whereas it increased in aerobiosis.

Analysis of the water-leachates indicated that, compared to aerobic conditions, anaerobiosis increased total leaching of radioactive materials (× 4.2) as well as leaching of ABA (× 1.4). In addition, anaerobiosis induced leaching of conjugates, such as ABA glucose ester and butanol-soluble metabolites. We concluded that the anaerobic treatment affects mainly membrane permeability.

     

Aerobic phosphorus release linked to acetate uptake in bio-P sludge: process modeling using oxygen uptake rate

The main processes involved in enhanced biological phosphorus removal (EBPR) under anaerobic and subsequently aerobic conditions are widely described in the literature. Polyphosphate accumulating organisms (PAO) are the organisms responsible for this process. However, the mechanisms of PAO are not fully established yet under conditions that differ from the classical anaerobic/aerobic conditions. In this work, we made a comparison between the behavior of PAO under classical EBPR conditions and its behavior when consuming substrate under only aerobic conditions. In addition, oxygen uptake rate (OUR) was measured in the set of experiments under aerobic conditions to improve the characterization of the process. A kinetic and stoichiometric model based on Activated Sludge Model No.2 (ASM2) and including glycogen economy (AnOx model), calibrated for classical anaerobic/aerobic conditions, was not able to describe the experimental data since it underestimated the acetate consumption, the PHB storage, and the OUR. Two different hypotheses for describing the experimental measurements were proposed and modeled. Both hypotheses considered that PAO, under aerobic conditions, uptake acetate coupled to PHB storage, glycogen degradation, and phosphorus release as in anaerobic conditions. Moreover, the first hypothesis (PAO-hypothesis) considered that PAO were able to store acetate as PHB linked to oxygen consumption and the second one (OHO hypothesis) considered that this storage was due to ordinary heterotrophic organisms (OHO). Both hypotheses were evaluated by simulation extending the AnOx model with additional equations. The main differences observed were the predictions for PHB degradation during the famine phase and the OUR profile during both feast and famine phases. The OHO hypothesis described the experimental profiles more accurately than the PAO hypothesis.     

Variability of Wax Ester Fermentation in Natural and Bleached Euglena gracilis Strains in Response to Oxygen and the Elongase Inhibitor Flufenacet

ABSTRACT. Euglena gracilis is able to synthesize adenosine triphosphate under anaerobic conditions through a malonyl-independent fatty acid synthesis leading to wax ester fermentation. Mitochondrial fatty acid synthesis uses acetyl-CoA and propionyl-CoA as C2- and C3-donors for de novo synthesis of even- and odd-numbered fatty acids, respectively. Euglena' s wax ester fermentation has only been described in the E. gracilis strain 1224-5/25 Z. Here we investigate eight E. gracilis strains isolated in 1932–1958 from different localities in Europe and two bleached substrains of E. gracilis 1224-5/25, obtained by treatment with streptomycin and ofloxacin, and examine their anaerobic growth, wax ester fermentation, and wax ester composition. Under ambient oxygen levels, all strains accumulated wax esters in concentrations between 0.3% and 3.5% of the dry weight, but the strains revealed marked differences in wax ester accumulation with respect to anaerobic growth. Most fermenting strains tested showed increased wax ester synthesis under anaerobic conditions as well as the increased synthesis of odd-numbered fatty acids and alcohols suggesting an activation of the mitochondrial fatty acid biosynthesis pathway. Addition of the elongase inhibitor flufenacet to the growth medium specifically reduced the accumulation of odd-numbered fatty acids and alcohols and tended to increase the overall yield of anaerobic wax esters.     

Cytolysin gene expression in<Emphasis Type="Italic"> Enterococcus faecalis</Emphasis> is regulated in response to aerobiosis conditions

Here we investigate the expression of cylL(L)and cylL(S), the genes that encode the structural subunits of the cytolysin/haemolysin of Enterococcus faecalis, in response to aerobiosis conditions. Haemolysis assays of E. faecalis strains cultured under aerobic and anaerobic conditions revealed three different haemolytic phenotypes, one of which exhibited greater haemolysis under anaerobic conditions than under aerobic conditions, and was shown to be associated with the presence of the cyl genes. Reporter gene studies revealed that cylL(L) L(S) promoter activity was significantly greater (up to 8.6-fold) under anaerobic compared to aerobic conditions throughout batch growth, demonstrating that these genes are regulated in response to the degree of aerobiosis. Band shift assays confirmed the binding of a protein factor to the region between 202 and 37 bp upstream of the cylL(L)start codon, and a higher level of binding was observed with anaerobically derived cell-free extracts than with extracts of aerobically grown cells. This is the first report of an oxygen-regulated virulence factor in E. faecalis (that is distinct from the quorum-sensing regulatory system reported previously), and may be of in vivo relevance for the bacterium in biofilms and other environments characterised by oxygen gradients.     

Absence of carotenes and presence of a tertiary methoxy group in a carotenoid from a thermophilic filamentous photosynthetic bacterium Roseiflexus castenholzii.

We identified pigments in a thermophilic filamentous photosynthetic bacterium Roseiflexus castenholzii strain HL08. We detected neither bacteriochlorophyll (BChl) c nor carotenes in this bacterium cultured under the aerobic dark and the anaerobic light conditions, which may correspond to its lack of chlorosomes. In the cells cultured under the aerobic dark conditions, the carotenoids were derivatives of keto-gamma-carotene, and the major ones were methoxy-keto-myxocoxanthin and keto-myxocoxanthin glucoside fatty acid ester. Although the tertiary methoxy group at C-1' and the double bond at C-3',4' in the psi end group of carotenoid, such as spirilloxanthin, have only been found in purple bacteria, this was the first such report in other bacterial groups. The fatty acid moiety was composed of iso fatty acids, which were rare in the cellular lipids. In the cells cultured under the anaerobic light conditions, in addition to these keto-carotenoids, we also found non-oxidized carotenoids (derivatives of gamma-carotene). Concerning the esterifying alcohol of BChl a, we found a substantial amount of geranylgeraniol, although the major component was phytol. The existence of these pigments makes this bacterium unique among the known species in CHLOROFLEXACEAE.     

The physiological role of oxygen-sensitive pyruvate dehydrogenase in mitochondrial fatty acid synthesis in Euglena gracilis

In Euglena gracilis a malonyl-CoA-independent fatty acid-synthetic system, in which fatty acids are synthesized directly from acetyl-CoA as both primer and C2 donor, occurs in mitochondria, and the system contributes to the wax ester fermentation. The activity of fatty acid synthesis in the mitochondrial system was enhanced about six times when an artificial acetyl-CoA-regenerating system was present, indicating that the fatty acid-synthetic activity is controlled by the ratio of acetyl-CoA against CoA. When fatty acids were synthesized using pyruvate instead of acetyl-CoA as substrate, a high activity, about 30 times higher than that from acetyl-CoA, was found under anaerobic conditions (below 10(-5) M oxygen), while in aerobiosis fatty acids were not synthesized at all. CoA, NADH, and NADP+ were required as cofactors for fatty acid synthesis from pyruvate. It was indicated that high activity of fatty acid synthesis from pyruvate due to the high ratio of acetyl-CoA against CoA was maintained by the action of the oxygen-sensitive pyruvate dehydrogenase found in Euglena mitochondria. When [2-14C]pyruvate was fed into intact mitochondria under anaerobic conditions, radioactive fatty acids were formed in the presence of malate, which provided reducing power for the matrix.     

Characterization of E. coli MG1655 and frdA and sdhC mutants at various aerobiosis levels

Depending on the availability of oxygen, Escherichia coli is able to switch between aerobic respiratory metabolism and anaerobic mixed acid fermentation. An important, yet understudied, metabolic mode is the micro-aerobic metabolism at intermediate oxygen availabilities. The relationship between oxygen input, physiology and gene expression of E. coli MG1655 and two isogenic mutants lacking succinate dehydrogenase (SDH) and fumarate reductase (FRD) activities was analyzed at different aerobiosis levels. Growth rate and cell yield were very similar to the parent strain. By-product formation was altered in the sdhC mutant to higher acetic acid and glutamate production in batch cultures. In continuous cultures with defined oxygen input gene expression analysis revealed a dependency of many catabolic genes to aerobiosis. Acetate excretion was still detectable under aerobic conditions in the sdhC mutant; the frdA mutant lacked anaerobic succinate excretion. Anaerobic repression of the sdh operon was diminished in the frdA strain, possibly to allow SDH to partially replace FRD. The experiments illustrate the remarkable adaptability of E. coli physiology—to compensate for the absence of important metabolic genes by altering carbon flux and/or gene expression such that there are only minor changes in growth capability across the aerobiosis range.     

Metabolism of long-chain alcohols in cell suspension cultures of soya and rape

Heterotrophic cell suspension cultures of soya (Glycine max) and photomixotrophic cell suspension cultures of rape (Brassica napus) were incubated with cis-9-[1-¹⁴C]octadecenol for 3–48 h. It was found that under aerobic conditions large proportions of the alcohol are oxidized to oleic acid, which is incorporated predominantly into phospholipids, whereas up to 30% of the substrate is esterified to wax esters. This is true for both the heterotrophic and the photomixotrophic cell suspension cultures, but the metabolic rates are much higher in the latter. Under anaerobic conditions only small proportions of the radioactively labeled alcohol are oxidized to oleic acid, whereas a major portion of the alcohol is esterified to wax esters both in heterotrophic and photomixotrophic cultures. Incubations of homogenates of photomixotrophic rape cells with labeled cis-9-octadecenol showed that pH 6 is optimum for the formation of wax esters. This monounsaturated alcohol is preferred as a substrate over saturated longchain alcohols, whereas short-chain alcohols, cholesterol, and glycerol are not acylated. Incubations of an enzyme concentrate from a homogenate of rape cells with unlabeled cis-9-octadecenol and [1-¹⁴C]oleic acid, or [1-¹⁴C]stearoyl-CoA, or di[1-¹⁴C]palmitoyl-sn-glycero-3-phosphocholine showed that acylation of the longchain alcohol proceeds predominantly through acyl-CoA. Direct esterification of the alcohol with fatty acid as well as acyl transfer from diacylglycerophosphocholine could be demonstrated to occur to a much smaller extent.     

Influence of glycerol production on the aerobic and anaerobic growth of the wine yeast Candida stellata

Candida stellata is frequently found in wine fermentations and may be used as a yeast starter in beverage production. In order to acquire additional knowledge on the physiology of C. stellata, a study on sugar metabolism in aerobic and anaerobic conditions was carried out. We found that under anaerobic conditions the low growth rate and biomass yield of C. stellata were due to the diversion of carbon flux from ethanol to glycerol. C. stellata had lower ADHI (alcohol dehydrogenase) activity (3-4 fold) and higher GPDH (glycerol-3-phosphate dehydrogenase) activity (40 and 15 times higher in anaerobiosis and aerobiosis respectively) than that of a Saccharomyces cerevisiae control strain. In aerobic sugar-limited chemostat culture C. stellata exhibited lower maximum biomass concentration [5.23 gl(-1) (dry weight)] than other respirofermentative yeasts at very low dilution rates (up to D = 0.042 h(-1)). While glycerol was constantly produced, ethanol and sugar residue appeared at D = 0.042 h(-1) and D = 0.065 h(-1) respectively. The tendency of C. stellata to form glycerol is probably the main cause of its very low growth and fermentation rates.     

The Role of Particulate Organic Matter and Acetic Acid in the Removal of Phosphate in Anaerobic/Aerobic Activated Sludge Processes

Acetic acid is thought to be an important substrate for the removal of phosphate in anaerobic/aerobic activated sludge (AS) processes. However, the acetic acid content in municipal sewage is low, and the main organic compounds in such sewage are particulate organic matters (POM) that are converted to endogenous substrates (E(ntrapped) POM, i.e., EPOM) in AS processes. Thus, the question arises whether it is really acetate or POM, which is important for the removal of phosphate in full‐scale AS plants. AS was harvested from a full‐scale anaerobic/aerobic AS plant. The amount of phosphate released after the addition of acetic acid depends on the AS conditions, particularly the influent sewage quality. However, the amount of phosphate released by EPOM was not affected by the AS conditions, and the amount of phosphate released per AS concentration and per unit of time was calculated to be about 0.86 mg PO₄‐P/g MLSS/hour. When the AS concentration is 2.5 g/L and the mixed‐liquor retention time is 2 hours in the anaerobic zone, about 4 mg/L PO₄‐P is released from EPOM. Under these conditions, phosphate in such sewage is removed by full‐scale AS plants without using acetic acid. In the case of carbon deficiency, the introduction of primary sludge to the anaerobic zone promoted the release of phosphate.     

The use of fatty acid methyl esters as biomarkers to determine aerobic, facultatively aerobic and anaerobic communities in wastewater treatment systems

The use of fatty acid methyl esters (FAME) as biomarkers to identify groups of microorganisms was studied. A database was constructed using previously published results that identify FAME biomarkers for aerobic, anaerobic and facultatively aerobic bacteria. FAME profiles obtained from pure cultures were utilized to confirm the predicted presence of biomarkers. Principal component analysis demonstrated that the FAME profiles can be used to determine the incidence of these bacterial groups. The presence of aerobic, anaerobic and facultatively aerobic bacteria in the communities, in four bioreactors being used to treat different wastewaters, was investigated by applying FAME biomarkers.     

Constitutive and Inducible Aerobic and Anaerobic Stress Proteins in the Echinochloa Complex and Rice

Anaerobic stress resulted in a change in the protein accumulation patterns in shoots of several Echinochloa (barnyard grass) species and Oryza sativa (L.) (rice) as resolved by two-dimensional gel electrophoresis. Of the six Echinochloa species investigated, E. phyllopogon (Stev.) Koss, E. muricata (Beauv.) Fern, E. oryzoides (Ard.) Fritsch Clayton, and E. crus-galli (L.) Beauv. are tolerant of anaerobiosis and germinate in the absence of oxygen, as does rice. In contrast, E. crus-pavonis (H.B.K.) Schult and E. colonum (L.) Link are intolerant and do not germinate without oxygen. Computer analysis of the protein patterns from the four tolerant species and rice indicated that the anaerobic response is of five classes: class 1 proteins, enhanced under anaerobiosis (9 to 13 polypeptides ranging from 16-68 kD); class 2 proteins, unique to anaerobiosis (1 to 5 polypeptides ranging from 17-69 kD); class 3 proteins, remained constant under aerobiosis and anaerobiosis; class 4 proteins, prominent only in air and repressed under anoxia (3 to 7 polypeptides ranging from 19-45 kD); and class 5 proteins, unique to aerobiosis (1 to 4 polypeptides ranging from 18-63 kD). In the intolerant species, E. colonum and E. crus-pavonis, no polypeptides were enhanced or repressed under anoxia (class 1 and class 4, respectively), whereas in the tolerant Echinochloa species and rice, a total of at least 9 to 13 anaerobic stress proteins and 4 to 7 "aerobic" proteins were noted. Immunoblotting identified two of the major anaerobic stress proteins as fructose-1,6-bisphosphate aldolase and pyruvate decarboxylase. Based on the differential response of the intolerant species to anaerobiosis, we suggest that another set of genes, whose products may not necessarily be among the major anaerobic stress polypeptides, might confer tolerance in Echinochloa under prolonged anaerobic stress.     

Inhibitors of cholesterol biosynthesis. Further studies of the metabolism of 5 alpha-cholest-8(14)-en-3 beta-ol-15-one in rat liver preparations

5 alpha-Cholest-8(14)-en-3 beta-ol-15-one is a potent inhibitor of sterol biosynthesis in mammalian cells in culture and has significant hypocholesterolemic activity upon oral administration to rodents and non-human primates. The conversion of the 15-ketosterol to cholesterol upon incubation with the 10,000 x g supernatant fraction of rat liver homogenate preparations under aerobic conditions has been reported (D.J. Monger, E.J. Parish and G.J. Schroepfer, Jr. (1980) J. Biol. Chem. 255, 11122-11129). Presented herein are results of studies of the metabolism of [2,4-3H]5 alpha-cholest-8(14)-en-3 beta-ol-15-one obtained upon incubation with the microsomal, cytosolic and the 10,000 x g supernatant fractions of liver homogenates of female rats under a variety of conditions. The results of these studies indicated metabolism of the 15-ketosterol to materials with the chromatographic properties of fatty acid esters of the 15-ketosterol, fatty acid esters of C27-monohydroxysterols, a component similar to the 15-ketosterol (possibly an isomer of the delta 8(14)-15-ketosterol), and a polar component. Detailed studies of the C27-monohydroxysterols obtained from incubation of the 15-ketosterol under anaerobic conditions indicated the formation of labeled 5 alpha-cholesta-8,14-dien-3 beta-ol and 5 alpha-cholest-7-en-3 beta-ol which were characterized by their behavior on silicic acid column chromatography, by the behavior of their acetate derivatives on medium pressure liquid chromatography on alumina-AgNO3 columns, and by co-crystallization of the labeled sterols with authentic unlabeled standards. The identification of 5 alpha-cholesta-8,14-dien-3 beta-ol and 5 alpha-cholest-7-en-3 beta-ol as metabolites of the 15-ketesterol, coupled with previous studies of the metabolism of 5 alpha-cholesta-8,14-dien-3 beta-ol and of 5 alpha-cholest-8(14)-ene-3 beta, 15 alpha-diol and 5 alpha-cholest-8(14)-ene-3 beta, 15 beta-diol has permitted the formulation of a scheme for the overall metabolism of the 15-ketosterol to cholesterol.     

Anaerobic production of polyunsaturated fatty acids by Shewanella putrefaciens strain ACAM 342

Abstract The fatty acid composition of cultures of Shewanella putrefaciens strain ACAM 342 grown aero-bically and anaerobically at 15°C and 25°C were analysed by capillary gas chromatography. The bacterium was found to produce the polyunsaturated fatty acids (PUFA) 18:2ω3, 18:3ω3 and 20:5ω3 under aerobic and anaerobic conditions at both growth temperatures. This result suggests that the bacterium possesses both the aerobic and anaerobic pathways for unsaturated fatty acid synthesis, where an alternate terminal electron acceptor(s) is utilised in the absence of oxygen.     

Mechanism of biosynthesis of unsaturated fatty acids in Pseudomonas sp. strain E-3, a psychrotrophic bacterium.

Biosynthesis of palmitic, palmitoleic, and cis-vaccenic acids in Pseudomonas sp. strain E-3 was investigated with in vitro and in vivo systems. [1-14C]palmitic acid was aerobically converted to palmitoleate and cis-vaccenate, and the radioactivities on their carboxyl carbons were 100 and 43%, respectively, of the total radioactivity in the fatty acids. Palmitoyl coenzyme A desaturase activity was found in the membrane fraction. [1-14C]stearic acid was converted to octadecenoate and C16 fatty acids. The octadecenoate contained oleate and cis-vaccenate, but only oleate was produced in the presence of cerulenin. [1-14C]lauric acid was aerobically converted to palmitate, palmitoleate, and cis-vaccenate. Under anaerobic conditions, palmitate (62%), palmitoleate (4%), and cis-vaccenate (34%) were produced from [1-14C]acetic acid, while they amounted to 48, 39, and 14%, respectively, under aerobic conditions. In these incorporation experiments, 3 to 19% of the added radioactivity was detected in released 14CO2, indicating that part of the added fatty acids were oxidatively decomposed. Partially purified fatty acid synthetase produced saturated and unsaturated fatty acids with chain lengths of C10 to C18. These results indicated that both aerobic and anaerobic mechanisms for the synthesis of unsaturated fatty acid are operating in this bacterium.