Hydroxylation of oleic acid by cell-free extracts of a species of torulopsis

Sophorolipid production by Candida bombicola: Medium composition and culture methods

Candida bombicola is able to produce sophorolipid molecules with surfactant properties when grown in a medium composed of two different carbon sources (usually sugar and oil) and a nitrogen source (frequently yeast extract). In this work, the composition of the medium and the culture method employed have been studied. The influences of glucose concentration, properties of oil and yeast extract concentration have been taken into account. Accordingly, a production medium composition is proposed (100 g/l glucose, 100 g/l sunflower oil and 1 g/l yeast extract). The most frequent culture methods reported in literature, i.e. batch, medium pulse mode and resting-cell methods, have been tested. The resting-cell method was found to produce the highest final concentration of sophorolipid, obtaining a good yield of carbon sources in a relatively short time. Under the best operational conditions and using the resting-cell method, 120 g/l sophorolipid was obtained in 8 d, with a carbon source yield of 0.60. Product distribution has also been investigated and the sophorolipid molecular structure of opened or cycled molecules has been determined under different operational conditions. Low yeast extract concentration and long fermentation time enhance the production of cycled structures by all the production methods studied.

Cytochromes P450 in fungi

The article gives an overview on the history of the discovery of P450 cytochromes and on their occurrence in nature, especially on their interactions with metabolic pathways in fungi. The significance of the P450 cytochromes in the ergosterol synthesis as well as in the inhibitory mechanisms caused by imidazole and triazole antimycotics is described in detail.

Oleate 6-hydroxylase activity in the membrane fraction from an oleaginous fungus, Mortierella ramanniana var. angulispora

Conversion of [1-14C]oleoyl-CoA (OA-CoA) in subcellular fractions of an oleaginous fungus, Mortierella ramanniana var. angulispora (IFO 8187) was investigated. The membrane fraction actively catalyzed the transformation of OA-CoA into one metabolite, which was identified as 6-hydroxy oleic acid (6-HOOA) by GC-MS analysis. The enzyme activity to form 6-HOOA was dependent on OA-CoA concentrations and increased linearly with incubation time and protein concentrations under appropriate experimental conditions. Since the enzyme activity required molecular oxygen and reduced pyridine nucleotides (NADH and NADPH), it was most probable that the formation of 6-HOOA was ascribed to direct hydroxylation to the C6 position, oleate 6-hydroxylase. 6-HOOA was formed from free oleic acid (OA) and OA-NH4 salt as substrate as well as OA-CoA, but not from OA covalently bound to phosphatidylcholine or triacylglycerol. Since CoA stimulated the hydroxylation of free OA and OA-NH4 salt but not that of OA-CoA, OA may be converted to OA-CoA and then hydroxylated. The enzyme activity was distinctly reduced by addition of lysophosphatidic acid, phosphatidic acid and dithiothreitol. Since hydroxy fatty acids are very minor components in this fungus, it may raise the possibility that the 6-hydroxylase activity works for other functions such as comprising one step for desaturation as well as forming the hydroxy fatty acids.

Cytochromes P450 of the sophorose lipid-producing yeast Candida apicola: heterogeneity and polymerase chain reaction-mediated cloning of two genes

Candida apicola belongs to a group of yeasts producing high amounts of surface-active extracellular glycolipids consisting of sophorose and long-chain-omega- and (omega-1)-hydroxy fatty acids. The involvement of cytochrome P450 in the synthesis of sophorose lipid by the hydroxylation of long-chain fatty acids was suggested from a simultaneous increase of cellular P450 content. Hydroxylation studies indicated the existence of multiple P450 forms capable of hydroxylating not only long-chain fatty acids, but also n-alkanes. In this report, two different P450 DNA fragments amplified in a polymerase chain reaction with heterologous primers and chromosomal DNA of Candida apicola were used as homologous probes for the isolation of full-length clones from a genomic library. The open reading frames of both genes encode proteins of 519 amino acids with calculated molecular weights of 58,656 and 58,631, respectively, that contain N-terminal membrane anchor sequences and hallmark residues, in common with other eukaryotic P450s. The deduced amino acid sequences of the C. apicola P450 genes are 84.4% identical. They share 34.5 to 44.1% identity with the proteins of the yeast family CYP52 and about 25% identity with fatty acid hydroxylases of higher eukaryotes (family CYP4A) and of Bacillus megaterium (CYP102). Southern hybridization experiments revealed the existence of further P450-related genes in C. apicola. According to the P450 nomenclature system, the cloned genes were named CYP52E1 and CYP52E2, establishing a new subfamily in yeast family CYP52.

Formation and physiological role of biosurfactants produced by hydrocarbon-utilizing microorganisms

Microbial growth on water-insoluble carbon sources such as hydrocarbons is accompanied by metabolic and structural alterations of the cell. The appearance of surface-active compounds (biosurfactants) in the culture medium or attached to the cell boundaries is often regarded as a prerequisite for initial interactions of hydrocarbons with the microbial cell. Under this point of view, biosurfactants produced by hydrocarbon-utilizing microorganisms, their structures and physico-chemical properties are reviewed. The production of such compounds is mostly connected with growth limitation in the late logarithmic and the stationary growth phase, in which specific enzymes are induced or derepressed. Addition of purified biosurfactants to microbial cultures resulted in inhibitory as well as in stimulatory effects on growth. Therefore, a more differentiated view of microbial production of surface-active compounds is proposed. Biosurfactants should not only be regarded as prerequisites of hydrocarbon uptake, but also as secondary metabolic products.

Lipid metabolism in fungi

So far, reviews that have appeared on fungal lipids present data mainly on the lipid composition of these organisms and the influence of lipids on their physiology. These reviews provide little information about the enzymes of lipid metabolism in these organisms and it is assumed, by most workers, that lipid synthesis in all fungi takes place as in Saccharomyces cervesiae, the only fungus in which the complete pathways of phospholipid biosynthesis have been worked out. During the last few years, literature has accumulated on lipid metabolic enzymes of other fungi, as investigators became increasingly interested in this area of research. The present review, after an introduction, will be divided into different sections and each section will deal, comparatively, with various aspects of fungal lipid metabolism and physiology. This review will, therefore, bring out the differences or similarities of lipid metabolism in diverse fungal species.

Effect of inhibitors on omega- and (omega-1)-hydroxylation of lauric acid by frog liver microsomes

To investigate the involvement of different cytochrome P-450 monooxygenases in fatty acid hydroxylation in frog liver microsomes, the effect of various inhibitors of cytochrome P-450 monooxygenases on the omega- and (omega-1)-hydroxylation of laurate was examined. The omega/omega-1-hydroxylation ratios were changed significantly by various levels of carbon monoxide (CO) inhibition; the formation of omega-hydroxylaurate was more sharply inhibited by various levels of CO than was the formation of (omega-1)-hydroxylaurate. On the contrary, metyrapone inhibited only the formation of (omega-1)-hydroxylaurate and stimulated the formation of omega-hydroxylaurate, 7,8-Benzoflavone as well as CO was more inhibitory to the omega-hydroxylation of laurate. At low concentrations of KCN (0.2 and 0.1 mM), the (omega-1)-hydroxylase activity was stimulated, but both the omega- and (omega-1)-hydroxylase activities were inhibited at the higher concentrations (5-10 mM). The effect of drugs and hydroxylaurate isomers on the omega- and (omega-1)-hydroxylation was also examined. Aminopyrine showed a stimulative effect on omega-hydroxylase activity and no effect on the (omega-1)-hydroxylase activity, while p-nitroanisole inhibited the (omega-1)-hydroxylase activity and showed almost no effect on the omega-hydroxylase activity. 12-Hydroxylaurate inhibited both the omega- and (omega-1)-hydroxylase activities, but the omega-hydroxylase activity was inhibited to a much greater extent. 11-Hydroxylaurate had no effect on either hydroxylation. These findings strongly support the hypothesis that different cytochrome P-450 species are involved in the hepatic microsomal hydroxylation of laurate at omega- and (omega-1)-positions in the frog.

Regulation of the biosynthesis of cytochrome P-450 in brewer's yeast. Role of cyclic AMP

The drug metabolising enzyme cytochrome P-450 has been studied in great detail in mammalian systems and its presence in microorganisms is also well established. However, neither its function nor its means of control in brewer's yeast, Saccharomyces cerevisiae, has been investigated. We demonstrate here using yeast protoplasts that it is the intracellular concentration of cyclic AMP which controls, by repression, the de novo synthesis of the enzyme, and also that cyclic AMP concentrations are in turn inversely related to the concentration of glucose in the yeast growth medium.