Lipid Biosynthesis In Some Oleaginous Yeasts

Microbial oil is one of renewable resources, with great potential in manyindustrial fields, especially for biodiesel production. Oleaginous yeast has gained moreand more attention, for its relatively larger biomass and broad material utilization.However, microbial oil production has not been employed for industry use so far.There are still some defects limiting the development of microbial oil intocommercialization as limited knowledge of regulation in lipid metabolism, highmaterial cost, and low lipid production. Based on the problems mentioned above, lipidbiosynthesis and secretion in some yeasts were studied in this study.The MIG1gene in the oleaginous yeast Yarrowia lipolytica ACA-DC50109wasdisrupted. It was found that the cells of the disruptant M25had more lipid bodies thanthose of its parent yeast. The disruptant M25contained48.7%(w/w) of oil based onits cell weight while the parent yeast only contained36.0%(w/w) of oil. Transcriptlevels of many genes relevant to lipid biosynthesis in the disruptant M25wereenhanced compared to those of the same genes in the parent yeast. However,transcript level of the MFE1gene, one of the genes relevant to fatty acid degradationwas reduced in the disruptant M25compared to that of the same gene in the parentyeast. Such changes in gene expression pro file may cause the increased lipidbiosynthesis in the disruptant M25. Biosynthesis of C18:1fatty acid in the disruptantM25was greatly enhanced compared to that in the parent yeast. All the resultsilluminated that MIG1gene indeed was associated with regulation of lipid metabolismRhodosporidium toruloides has been widely used to accumulate lipid fromdifferent carbon sources. An inulinase-producing yeast strain2F5of R. toruloides wasobtained. It was found that the yeast strain2F5could produce higher amount of oilfrom inulin and larger lipid bodies in its cells than any other yeast strains tested in thisstudy. Under the optimal conditions,62.14%(w/w) of lipid based on cell dry weightand15.82g/l of the dry cell mass were produced from6.0%(w/v) inulin at flask level,leaving0.92%(w/v) of total sugar in the fermented medium. During2-l fermenter, 70.36%(w/w) of lipid based on cell dry weight and15.64g/l of the dry cell masswere produced from6.0%(w/v) inulin, leaving0.58%(w/v) of total sugar in thefermented medium within96h. Therefore, the lipid titer was11.7g/l, the yield was0.22g/g and the productivity was0.12g/l/h. Over99.09%of the fatty acids from theyeast strain2F5grown in the oil production.In this study, Rhodosporidium paludigenum p1721isolated from mangroveecosystems was found to be able to produce high level of both intracellular andextracellular lipid. Under the microscope, many lipid particles released from the cellswere observed. Under the optimal conditions,15.2g/l extracellular lipid,9.6g/lintracellular lipid,15.2g/l biomass and63.2%(w/w) lipid were produced within168h while17.0g/l extracellular lipid,19.3g/l biomass,12.1g/l intracellular lipid,62.7%(w/w) lipid were obtained within108h during the10l-fermentation, causing0.5g/l reducing sugar left in the fermented medium. GC-MS analysis showed that theextracellular lipids contained3-OH-myristic acid (C14:0)(1.2%),3-OH-palmitic acid(C16:0)(29.8%),3-OH-stearic acid (C18:0)(33.4%), palmitic acid (C16:0)(8.1%),palmitoleic acid (C16:1)(13.4%), oleic acid (C18:1)(10.1%), linoleic acid(C18:2)(4.1%) while the intracellular lipids contained C14:0(1.1%), C14:1(1.0%),C16:0(27.2%), C18:0(4.5%), C18:1(46.1%), C18:2(15.1%) and C18:2(2.4%) fattyacids, suggesting that only the extracellular lipids contain3-OH-fatty acids. The3-OH-fatty acids synthesized may be linked to xylitol or mannitol or sorbitol by esterlinkage. As biosynthesis of the extracellular lipid, especially3-OH-fatty acids wasobviously inhibited by triclosan sodium and thioglycolate and DNA fragments relatedto polyketide synthase (PKS) pathway could not be PCR-amplified, a biosyntheticpathway for3-OH-fatty acids was proposed.