The utilisation of used and other fats by fungi

English: In 1997, Jeffery and co-workers discovered that when Mucor circinelloides t. circinelloides CBS 108.16 was cultivated on 30g/1 sunflower oil and 10g/1 sodium acetate, an improved utilisation of the oil, doubling of the biomass production and enhancement of the intracellular polyunsaturated y-linolenic acid (GLA) content occurred as compared to when this fungus was cultivated on only 40g/1 sunflower oil as sole carbon source. Consequently, the aim of this study became to further explore this phenomenon (hypothesis) in selected members of the zygomycotan fungi as well as yeasts when cultivated on various fat and oil substrates in the presence and absence of acetate. The ultimate aim was to identify those taxa that can be further explored for the transformation of edible and tall oils to high value lipids in the presence and absence of acetate. In this study, similar trends were observed in Mucor circinelloides f circinelloides CBS 108.16 as that found by Jeffery et al when cultivated on sunflower oil in the presence and absence of acetate. A similar pattern was also found when this fungus was grown on used cooking oil and tall oil. The enhancing effect of acetate was not generally observed in the other fungi and on some other fats and oils tested. Most fungi, including the yeasts, could grow on fats and oils provided in the presence or absence of acetate. Exceptions to the rule were MorfierelIa alpina MUFS Mo058 and Lipomyces starkeyi CBS 1807 T that were unable to grow. Schizosaccharomyces pombe var. pombe CBS 0356 T could also not grow on linseed oil. The presence of acetate had in many cases a stimulatory effect on growth. In some cases, the addition of acetate had an inhibitory effect on growth. With a few exceptions, most mucoralean fungi, when cultivated on various fats and oils, became oleaginous (i.e. contain ≥ 20% lipids) in the presence or absence of acetate. However, when these fungi were cultivated on linseed ail in the presence or absence of acetate they were unable to accumulate more than 20% lipids according to biomass. Less yeasts became oleaginous when cultivated on various fat and oil substrates when compared to the mucoralean fungi tested. The non-oleaginous yeasts i.e. Kluyveromyces, Saccharomyces, Schizosaccharomyces, Schwanniomyces and Yarrowia became oleaginous when cultivated on various fats and oils in the presence of acetate. In most mucoralean fungi and yeasts, the presence of acetate had an effect on cellular lipid content. The enhancing effect of acetate addition on cellular lipid content was experienced especially on GongronelIa, Mucor circinelloides t. circinelloides CBS 108.16 and Thamnostylum when cultivated on various fats and oils. On the other hand, the addition of acetate had a negative effect on cellular lipid accumulation in some mucoralean fungi and yeasts. In general, both the mucoralean fungi and yeasts utilised different fats and oils [(i.e. containing saturated fatty acids (FAs) and polyunsaturated fatty acids (PUFAs)] as carbon sources in the presence or absence of acetate. MortierelIa and Lipomyces could not utilise any of these fats and oils. The presence of acetate had a positive effect on fat and oil utilisation by most mucaralean fungi and some yeasts. In most cases, a pH increase was observed probably due to acetic acid utilisation during cultivation. In the presence or absence of acetate, most mucoralean fungi and yeasts showed a high preference towards the utilisation of PUFAs present in the residual oil fractions. The addition of acetate had both a positive and negative effect on the degree of preference towards PUFAs in the residual lipids. In most cases (in both mucoralean fungi and yeasts) lower amounts of PUFAs in the cellular lipid fractions in the presence or absence of acetate were found when compared to the oil substrate fed. This is probably due to the utilisation of these FAs through β-oxidation for the production of energy. No general pattern was observed regarding the effect of acetate addition on cellular PUFA content. Many mucoralean fungi when cultivated on various fats and oils (except soap skimmings) could produce GLA in the presence or absence of acetate. All the yeasts in this study could not produce GLA when cultivated on any lipid substrate in the presence or absence of acetate. This is probably due to the lack of a ∆6 desaturase enzyme. The addition of acetate improved GLA production in most mucoralean fungi when cultivated on sunflower oil and used cooking oil. Those fungi capable of producing GLA in this study should now be explored in the transformation of edible fats and oils to high value lipids containing GLA.