Fatty acids in yeasts

From the work of Kock and his associates, together with the data compiled by Rattray (1988), the following very general conclusions can be advanced regarding the occurrence of fatty acids in yeasts. 

Oleic acid (18 1) is usually the most abundant fatty acid in yeasts except for those where 16 1 is the major fatty acid. Contents in some species, e.g. Schizosaccharomyces spp, may be over 80% (Viljoen et al., 1986) and over 70% in a small number of taxonomically disparate yeasts (Rattray, 1988). 

Although the extent of stearic acid accumulation was not as high as had been achieved with the genetic programme (compare Table 9.6 to Table 9.5), nevertheless the total saturated fatty acid content (16 0, 18 0, 20 0 and 24 0) was over 50% of the total. This is a remarkable achievement considering the usual predominance of unsaturated fatty acids in yeasts (Table 9.2). In this work of the New Zealand group, the overall performance of the yeast at the low OUR values was only slightly less than at... 

There is considerable interest in the role of formic acid and other volatile fatty acids in the early diagnosis of organic matter in lacustrine and marine sediments. Formic acid is an important fermentation product or substrate for many aerobic and anaerobic bacteria and for some yeasts, hi the atmosphere, formic acid is an important product in the photochemical oxidation of organic matter. 

After sterilization, yeast is added to initiate fermentation. McConnell and Schramm (1995) recommend inoculation with no less than 10% by volume. Moreover, as the pH of honey is naturally low and because it is poorly buffered, the pH of must may drop during fermentation to a point limiting yeast efficiency. pH reduction can result from the synthesis of acetic and succinic acids by the yeast cells (Sroka and Tuszynski, 2007). While a rapid decline in pH inhibits undesirable microbial activity (Sroka and Tuszynski, 2007), it also reduces the dissociation of fatty acids in the wort, potentially slowing yeast metabolic action. For this, addition of a buffer is important to maintain the pH within a range of 3.7-4.0 throughout fermentation (McConnell and Schramm, 1995). Calcium carbonate, potassium carbonate, potassium bicarbonate, and tartaric acid are potential candidates. However, as some of these salts can add a bitter-salty... 

Yeast strain, and nutrient status of the must and fermentation conditions, many of which affect growth or induce physiological stress, modulate the accumulation of acetic and other fatty acids in wine. Reported factors include must sugar concentration, nutrient balance, inoculum level, fermentation temperature, pH and aeration (Delfini and Costa 1993 Henschke and Jiranek 1993 Shimazu and Watanabe 1981). The effects of osmotic stress, as induced by sugar concentration, on acetic acid production are discussed in Sect. 8D.3.2. 

Candida strains convert ricinoleic acid into If-decalactone, which displays the fatty, fruity aroma typical of peaches. Ricinoleic acid (12-hydroxy octadec-9-enoic acid) is the major fatty acid in castor oil (approx. 80 %). The yeast can lipolyze castor oil glycerides and the liberated ricinoleic acid is subsequently metabolized via d-oxidation and eventually converted to 4-hydroxy-decanoic acid (Figure 5). Recently a European patent has been filed (20) essentially covering the same procedure. Shake culture fermentations were carried out on 100 ml scale for one week. The 4-hydroxydecanoic acid formed was converted to )f-decalactone by boiling the crude, acidified (pH 1.5) fermentation broth for a period of 10 minutes. The lactone was isolated via solvent extraction and a yield of some 5 g/1 was obtained. The same lactone was detected as the major volatile component formed when the yeast, Sporobolomyces odorus was grown in standard culture medium (21). Although the culture medium displayed an intense fruity, typical peach-like odor, the concentration of y-decalactone amounted to no more than 0.5 mg/1. 

Fatty acid distributions can be affected by microbial oxidation in sediments, so care must be exercised when certain components are used as source indicators. For example, (3-hydroxy fatty acids are produced from (3-oxidation of saturated fatty acids. In addition, C0-oxidation of saturated fatty acids to CO-hydroxy acids and of CO-hydroxy acids to a,CO-diacids is performed by yeasts (unicellular fungi, mainly belonging to the as-comycetes) and bacteria. Consequently, while the long-chain (>C22) CO-hydroxy acids are reliable indicators of higher plant sources, the short-chain components... 

Several yeasts are able to assimilate fatty acids. In the /I-oxidation pathway of unsaturated fatty acids, NADPH-dependent 2,4-dienoyl-CoA reductase is needed for double-bond hydrogenation. The respective 2,4-dienoyl-CoA reductase has been partially purified from oleate-grown Candida tropicalis. It catalyzes one step in the degradation of oleic acid, namely the transformation of 2-trc/ s--4-c s-decadienoyl-CoA to 3-ttww-decadienoyl-CoA87. 

Thioacylated proteins contain fatty acids in thioester linkage to cysteine residues [7-9] (Fig. lA). Protein thioacylation is frequently referred to as palmitoylation, although fatty acids other than palmitate are found on thioacylated proteins. Membrane proteins as well as hydrophilic proteins are thioacylated, the latter, in many cases, acquiring the modification when they become associated with a membrane compartment as a result of initial N-myristoylation or prenylation. Examples include G-protein coupled receptors, the transferrin receptor, the cation-dependent mannose-6-phosphate receptor, and hydrophilic proteins such as members of the Src family of protein tyrosine kinases (e.g., p59h " and p56 ) as well as H-Ras, N-Ras, and the synaptic vesicle protein SNAP-25. The yeast palmitoyl proteome, i.e., the collection of all S-acylated proteins in yeast, was recently defined via a comprehensive proteomics approach (A.F. Roth, 2006). It consists of 50 proteins including... 

Davoli, R, Mierau, V., and Weber, R.W.S. 2004. Carotenoids and fatty acids in red yeasts Sporobolomyces roseus and Rhodotonda glutinis. Appl Biochem Microbiol 40 392-397. 

Besides the production of biomass, the investigators are also trying to produce interesting intermediate products. Thus, the production of fatty acids has been intensively investigated by the preparation of definite fatty-acid samples. Yeasts grown on media which do not contain hydrocarbons contain fatty acids whose C chains are practically all even-numbered. Quantitatively detectable differences in the fatty acid sample can be attributed to nutrient combination which obviously exerts a decisive influence. 

This means that molecular oxygen Is required, and, when availability of oxygen Is denied. It Is obvious that neither sterol nor unsaturates can be formed. By operating anaerobically we can therefore dictate what sterol Is In the cells simply by adding the sterol of our choice to the medium. Andreasen and Stier (11) were the first to demonstrate that this could be done and they were the first also to show that without sterol (11) and unsaturated fatty acid (15) yeast will not grow. This was an elegant demonstration that these lipids play a vital role. 

The concept of a peroxisome being a closed compartiment also requires transport systems for fatty acids which undergo oxidation in the peroxisome. Since oxidation of fatty acids in peroxisomes is incomplete, the peroxisome must also have systems to allow export of chain-shortened fatty acids. Recent evidence notably in yeast suggests that... 

Fatty acids in plants are synthesized by a series of reactions similar to those for fatty acid biosynthesis in animals, yeasts, bacteria, and other organisms. The synthetases of prokaryotic cytoplasmic systems are freely soluble and readily separable as discrete proteins those in mammalian systems are localized in the cytoplasm as large soluble synthetase complexes. The exact nature of association of the enzymes in plants is unknown (Ohlrogge et al., 1993). The reactions of plant fatty acid biosynthesis are catalyzed by individual polypeptides (Somerville and Browse, 1991) once organelles are disrupted, the enzymes also are soluble and may be isolated (Somerville and Browse, 1991 Stumpf, 1976). In contrast to mammalian systems, plant fatty acid synthetases are plastid localized. 

There is ample evidence for hydroxy fatty acids in other yeasts. Saccharomycopsis malanga (Ascomycota, Saccharomycetales, Saccharomyco-psidaceae) forms 3-hydroxypalmitic acid [31] while trihydroxy acids are formed in Picia sydowiorum (Ascomycota, Saccharomycetales, Saccharomycetaceae) [32] and an unidentified yeast [33]. 2-Hydroxy long-chain fatty acids are found in S. cerevisiae [34]. The production of 2-hydroxyhexadecanoic acid in P. sydowiorum was increased in the presence of the mycotoxin fumonisin B, and a cyt P-450 mechanism of production suggested [32]. In many cases, these compounds are esterified in wall or membrane fractions but they may also occur as free acids. Unfortunately, none of these oxylipins has been linked to a specific regulatory function. 

Prior to about 1982 it was often assumed that the enzymes of the chloroplast fatty acid synthase would be organized into some sort of multienzyme complex even though the absolute requirement of all known plant fatty acid synthase (FAS) preparations for added acyl carrier protein (ACP) precluded the type of complex observed in yeast and mammalian cells. Then in 1982 three laboratories [1-3] independently showed that the FAS consisted of individual proteins that were readily separable by conventional gel filtration techniques i.e. the plant synthase was of the prokaryotic type, similar to that in E. coli. After that, the concept of a multienzyme complex synthesizing fatty acids in chloroplasts was effectively in limbo. 

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