Abstract
The oleaginous fungus, Mucor circinelloides, is one of few fungi that produce high amounts of γ-linolenic acid (GLA); however, it usually only produces <25% lipid. Nevertheless, a new strain (WJ11) isolated in this laboratory can produce lipid up to 36% (w/w) cell dry weight (CDW). We have investigated the potential mechanism of high lipid accumulation in M. circinelloides WJ11 by comparative biochemical analysis with a low lipid-producing strain, M. circinelloides CBS 277.49, which accumulates less than 15% (w/w) lipid. M. circinelloides WJ11 produced more cell mass than that of strain CBS 277.49, although with slower glucose consumption. In the lipid accumulation phase, activities of glucose-6-phosphate dehydrogenase and 6-phosphogluconate dehydrogenase in strain WJ11 were greater than in CBS 277.49 by 46% and 17%, respectively, and therefore may provide more NADPH for fatty acid biosynthesis. The activities of NAD+:isocitrate dehydrogenase and NADP+:isocitrate dehydrogenase, however, were 43% and 54%, respectively, lower in WJ11 than in CBS 277.49 and may retard the tricarboxylic acid cycle and thereby provide more substrate for ATP:citrate lyase (ACL) to produce acetyl-CoA. Also, the activities of ACL and fatty acid synthase in the high lipid-producing strain, WJ11, were 25% and 56%, respectively, greater than in strain CBS 277.49. These enzymes may therefore cooperatively regulate the fatty acid biosynthesis in these two strains.
Highlights
The interest of microbial oils has increased as they are used as commercial sources of several nutritionally-important polyunsaturated fatty acids (PUFAs) [1]
M. circinelloides strain WJ11 isolated in this laboratory produced up to 36% lipid (w/w, cell dry weight (CDW)), which is higher than that of strain CBS 108.16 (25% lipid, w/w, CDW), a model organism for lipid accumulation studies, and much higher than strain CBS 277.49 (15% lipid, w/w, CDW)
The molecular mechanism for the differential lipid accumulation in this fungus was investigated through comparative biochemical analysis of the key pathways involved lipid metabolism
Summary
The interest of microbial oils has increased as they are used as commercial sources of several nutritionally-important polyunsaturated fatty acids (PUFAs) [1]. They are being considered as potential sources of biofuels [2]. Amounts of cellular lipid vary between 20% (w/w) cell dry weight and more than 80% (w/w) [2,3]. The lipid content of Mucor circinelloides CBS 108.16 and Mortierella alpina CBS 696.70 are 25% and 40% of their cell dry weight, respectively, under the same cultivation conditions [6]. Lipid in the bacterium, Rhodococcus opacus PD630, can account for up to 87% of its cell dry weight [7]
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