# Nutritional and Medicinal Properties of Microbial Oil
## 5 Composition and Properties of Microbial Oil  
All microorganisms are capable of synthesizing lipids, but only those referred to as oleaginous can accumulate significant amounts of them. Single-cell oils, or so-called microbial oils, are lipids produced by microorganisms, including bacteria, yeasts, molds, and algae [33; 68; 69; 70; 71; 72; 73; 74]. Their properties and composition depend entirely on the microorganisms involved in their biosynthesis. The fatty acid composition of microbial oils typically consists of mainly palmitic and oleic fatty acids, with other common acids like myristic, palmitoleic, stearic, and linoleic, as well as \(\alpha\)- and \(\gamma\)-linolenic acids, while the oils obtained from algae may be a source of other polyunsaturated fatty acids, like EPA (eicosapentaenoic acid, C20:5) and DHA (docosahexaenoic acid, C22:6) [27]. Bacteria belonging to the _Rhodococcus_ genus are one of the most frequently studied prokaryotes capable of synthesizing lipids [75]. According to the data shown in Table 1, it can be seen that _R. opacus_, as well as _R. jostii_ and _R. rhodocrotus_, have the potential to produce microbial oil with an unusual fatty acid composition. In the studies of [PERSON] et al. [68] and [PERSON] et al. [69], the bacteria of the _Rhodococcus_ genus produced significant amounts of odd-chain fatty acids, where both saturated and unsaturated odd-chain acids were achieved. The most common fatty acids in these papers were pentadecanoic (C15:0), heptadecanoic (C17:0), and heptadecenoic (C17:1) acids. In the case of _R. opacus_ PD630, which grew on a mixture of glucose and 1-propanol, about 48% of the cell dry weight consisted of microbial lipids, whereas approximately 69% of the obtained fatty acids were those with an odd number of carbon atoms in the molecule [68]. A wide range of substrates can be converted in nitrogen-limited conditions by _Rhodococcus_ strains into triacylglycerglycerols. [PERSON] et al. [69] confirmed such possibilities using gluconate, benzoate, hexadecane, and even naphthalene and naphthyl-1-dodecanoate. During the cultivation with gluconate and benzoate as the main carbon sources, _Rhodococcus_ sp. 602 was able also to biosynthesize polyhydroxyalkanoate, i.e., 3-hydroxybutyrate and 3-hydroxyvalerate, which may find its application in the polymer industry. Moreover, the capability of metabolizing and converting hydrocarbons into lipids in nitrogen-deficient conditions may be significant in its potential use in the bioremediation processes of pollutant-contaminated soils [68; 69]. Yeasts are used for the biosynthesis of microbial oil from waste substrates such as waste cooking oils, palm oil or olive oil wastewaters, fish waste, pork lard, and other animal-based fats [31; 32]. For example, a culture of _Y. lipolytica_ W29 in a medium with eucalyptus bark hydrolysate with a high concentration of glucose and xylose allows for the production of lipids-rich biomass. A biosynthesis yield of 26% (5.6 g/L) can be achieved, and the lipids consist of more than 85% of unsaturated fatty acids, including oleic acid (48.4%), palmitoleic (20.2%), linoleic (17.1%), and palmitic acids (14.3%) [71]. In the case of using hydrophobic substrates, [PERSON] et al. [70] evaluated the possibility of using hexadecane as the main carbon source in the culture of _Y. lipolytica_ CBS 2075. The authors confirmed that, in yeast cells, alkanes are oxidized to fatty alcohols. Then, through aldehydes, finally become fatty acids, which, in favorable culture conditions, are stored in the lipid bodies as triacylglycerols and steryl esters. As _Y. lipolytica_ yeasts are strictly aerobic, the agitation rate and, thus, the dissolved oxygen in the medium was crucial for the highest lipid accumulation. Moreover, the low ratio of C/N is also considered a limiting factor in microbial oil synthesis, and the authors also observed that nitrogen-deficient media are suitable for the outstanding yield of microbial oil syntheses.