Microbial lipids

Schweizer E (1989) Biosynthesis of fatty acids and related compounds. In Ratledge C, Wilkinson SG (eds), Microbial lipids, vol. 2. Academic Press, London, p 3 -50... 

Dudd, S.N., Regert, M. and Evershed, R.P. (1998). Assessing microbial lipid contributions during laboratory degradations of fats and oils and pure triacylglycerols absorbed in ceramic potsherds. Organic Geochemistry 29 1345-1354. 

S. G. Wilkinson, in C. Ratledge and S. G. Wilkinson (Eds.,) Microbial Lipids, Vol. 1, Gram-Negative Bacteria, p. 299. Academic Press, London/San Diego, 1988. 

Ratledge, C., and S.G. Wilkinson, eds. 1988. Microbial Lipids. New York Academic Press. 

Alicyclic hydrocarbons are saturated carbon chains that form ring structures. Naturally occurring alicyclic hydrocarbons are common (Chap. 1). For example, alicyclic hydrocarbons are a major component of crude oil, comprising 20-67 vol.%. Other examples of complex, naturally occurring alicyclic hydrocarbons include camphor (a plant terpene) and cyclohexyl fatty acids (components of microbial lipids). Anthropogenic sources of alicyclic hydrocarbons to the environment include fossil-fuel processing and oil spills, as well as the use of such agrochemicals as the pyrethrin insecticides (Chap. 1, and references therein). 

NKT cells express T-cell receptors as well as receptors commonly found on NK cells. NKT cells recognize microbial lipid antigens... 

The usual diet of ruminants consists of fresh and preserved herbage and cereals. As a result of microbial activity in the rumen, esterified dietary fatty acids are hydrolyzed, short chain fatty acids are produced by fermentation of cellulose and other polysaccharides, unsaturated fatty acids are hydrogenated and/or converted to geometric (trans) and positional isomers, and microbial lipids are synthesized. These activities account in part for the enormous diversity of fatty acids in milk and the unique features short-chain and a high proportion of long chain saturated fatty acids. (Patton and Jensen, 1976 Christie, 1979B). 

Hay and Morrison (1971) did not neglect the alkyl and alkenyl ethers in milk phospholipids, finding 4% of the latter in phosphatidylethanolamine and 1.3% in phosphatidylcholine. Trans isomers were not found. The authors postulated that the branched chain compounds in the alkenyl ethers were derived from rumen microbial lipids. 

Natural killer T (NKT) cells are T cells that express T cell receptors as well as the NK1.1 receptors commonly found on NK cells. NKT cells recognize microbial lipid antigens presented by a unique class of MHC-like molecules known as CD1. They have been implicated in host defense against microbial agents, autoimmune diseases, and tumors. 

Solid-state NMR has done much to dispel the mysteries of humin compositions, and significant advances have recently been made using proton NMR in the liquid state (see Section 15.3.3 of Chapter 15). Based on solid-state 13C NMR spectra, Hatcher et al. (1980) concluded that a repeating aliphatic structural unit, possibly attributable to branched and cross-linked algal or microbial lipids, is common to both soil and sediment humin samples. Hatcher et al. (1983) viewed the increase in humin relative to the other humic fractions as a selective preservation of the aliphatic compounds of the sediments and did not support condensation theories. 

The principles of sonochemistry can also be applied to disrupt different species of oil-bearing microalgae cells. Detailed experimental results are necessary to support the cost-effectiveness and industrial scale applicability of ultrasound for microbial lipid extraction, and subsequent biodiesel production in comparison to conventional methods (Mata et al., 2010). 

Alicyclic hydrocarbons are major components of petroleum (comprising from 20% to 67% of its volume) as well as components of plant oils and paraffins, microbial lipids, and pesticides. They range from simple molecules (e.g., cyclopentane and cyclohexane) to complex molecules (e.g., the pesticides aldrin and kepone shown in Figure 9.4). 

New (de novo) fatty acids are synthesized from two-carbon acetyl units produced during metabolism. Two enzyme complexes, acetyl-coenzyme A carboxylase and fatty acid synthetase, work in concert to build up fatty acid chains, two carbons at a time, until released by the complex. The primer in plants and animals is essentially a two-carbon acetyl group and the fatty acid chains have even numbers of carbons. If the primer is a three-carbon propionate group, odd-number carbon chains result. Odd-number fatty acids are common in microbial lipids and also are synthesized de novo from propionic VFA by rumen bacteria and deposited in adipose tissue. The length of the fatty acid synthesized depends on the tissue. Palmitic acid is produced in the liver and adipose tissue, and shorter-chain fatty acids are also produced in the mammary glands (49). 

Hatcher et al. (1981) pointed out that the aliphatic region of terrestrial humic acids is very similar to that of marine humic acids and that the only difference is the presence of aromatic bands in the terrestrial humic acid spectra. In previous work, Hatcher (1980) and Hatcher et al. (1980b) concluded from the H/C ratio of 1.5 and presence of a strong terminal methyl band at 0.9 ppm that marine humic acids have highly branched and cross-linked paraffinic carbon atoms. These structures appear to arise from algal and microbial lipids. The similarity in the aliphatic region in terrestrial humic acids suggests that soil microbial lipids may be the source of the aliphatic structures in terrestrial humic acids. 

Abraham WR, Hesse C, Pelz O (1998) Ratios of carbon isotopes in microbial lipids as an indicator of substrate usage. Appl Environ Microbiol 64 4202-4209 Abrajano Jr. TA, Murphy DE, Fang J, Comet P, Brooks JM (1994) ratios in individual fatty acids... 

Volkman JK, Johns RB, Gillan FT (1980) Microbial lipids of an intertidal sediment I. fatty acids and hydrocarbons. Geochim Cosmochim Acta 44(8) 1133-... 

Beligon, V, Christophe, G., Fontanille, P., and Larroche, C. (2016) Microbial lipids as potential source to food supplements. Curr. Opin. Food Sci., 7, 35-42. 

Microbial lipid production has been known for more than a century however, the economics of microbial oil production utilizing yeasts and fungi could not compete with that of plant-derived oils for commodity products. Therefore the concept of commodity oil production by fermentation was generally abandoned. ... 

Incorporation of K -acetate into microbial lipids is a simple, yet useful technique for measuring heterotrophic microbial activity. The rate of acetate incorporation into microbial phospholipids has been shown to be an accurate and sensitive measure of growth in sediment samples [37]. The technique has been used to measure activity in sewsige sludge [38], marine sediments [39], antarctic rock microbiota [40], and soils [41]. Acetate incorporation has also been used to sussess the effects of toxicants, both inorgsmic and organic, on microbial metabolic activity [42]. 

Microbial Lipids Productioii J t fuel by Deoxygenation Polymers... 

Losel, D.M. 1988. Fungal lipids, in Ratledge, C., Wilkinson, S.G. (eds) Microbial Lipids Vol. 1. Academic Press London, pp. 669-806. 

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