Zhi-Peng Wang

Disruption of the MIG1 gene enhances lipid biosynthesis in the oleaginous yeast Yarrowia lipolytica ACA-DC 50109.

In this study, the MIG1 gene in the oleaginous yeast Yarrowia lipolytica ACA-DC 50109 (the parent yeast) was disrupted and the disruptant M25 obtained could grow in yeast nitrogen base-N5000 medium without uracil or the medium with 2-deoxy-D-glucose. It was found that the cells of the disruptant M25 had more lipid bodies than those of its parent yeast. The disruptant M25 contained 48.7% (w/w) of oil based on its cell weight while the parent yeast only contained 36.0% (w/w) of oil. Transcript levels of many genes relevant to lipid biosynthesis in the disruptant M25 were enhanced compared to those of the same genes in the parent yeast. However, transcript level of the MFE1 gene, one of the genes relevant to fatty acid degradation was reduced in the disruptant M25 compared to that of the same gene in the parent yeast. Such changes in gene expression profile may cause the increased lipid biosynthesis in the disruptant M25. Biosynthesis of C18:1 fatty acid in the disruptant M25 was greatly enhanced compared to that in the parent yeast.

High level lipid production by a novel inulinase-producing yeast Pichia guilliermondii Pcla22.

In this study, an inulinase-producing yeast strain Pcla22 of Pichia guilliermondii was identified. It was found that the yeast strain Pcla22 could produce higher amount of oil and more lipid bodies in its cells than any other yeast strains tested in this study. Under the optimal conditions, 60.6%(w/w) of lipid based on cell dry weight, 20.4 g/l of the dry cell mass, SCO produced per g of consumed sugar of 0.19 g/g and biomass produced per g of consumed sugar of 0.32 g/g were obtained in the culture of the yeast strain Pcla22 after 96 h of the fed-batch fermentation. Over 79.8% of the fatty acids from the yeast strain Pcla22 grown in the oil production medium containing inulin was C(16:0) and C(18:1), especially C(18:1) (57.9%). The biodiesel obtained from the produced lipid could be burnt well.

Taxonomy of Aureobasidium spp. and biosynthesis and regulation of their extracellular polymers

Abstract The genus Aureobasidium spp. have been divided into three species, A. pullulans. A. leucospermi and A. proteae, and A. pullulans has been known to have five varieties. However, after analysis of many strains of this yeast isolated from different environments, they do not belong to any of the three species or the five varieties. Although pullulan produced by A. pullulans has been widely used in different fields in industry and different strains of this yeast has been known to produce poly(β-L-malic acid) (PMA), heavy oils and β-1,3-glucan, it is still unknown how the black yeast synthesizes and secretes the extracellular polymers at molecular level. In this review article, new biosynthetic pathways of pullulan, PMA and heavy oils, the enzymes and their genes related to their biosynthesis and regulation are proposed. Furthermore, some enzymes and their genes related to pullulan biosynthesis in A. pullulans have been characterized. But it is completely unknown how pullulan is secreted and how PMA, heavy oils and β-1,3-glucan are synthesized and secreted. Therefore, there is much work to be done about taxonomy and biosynthesis, secretion and regulation of pullulan, PMA, heavy oils and β-1,3-glucan at molecular levels in Aureobasidium spp.

Yeast killer toxins, molecular mechanisms of their action and their applications

Abstract Killer toxins secreted by some yeast strains are the proteins that kill sensitive cells of the same or related yeast genera. In recent years, many new yeast species have been found to be able to produce killer toxins against the pathogenic yeasts, especially Candida albicans. Some of the killer toxins have been purified and characterized, and the genes encoding the killer toxins have been cloned and characterized. Many new targets including different components of cell wall, plasma membrane, tRNA, DNA and others in the sensitive cells for the killer toxin action have been identified so that the new molecular mechanisms of action have been elucidated. However, it is still unknown how some of the newly discovered killer toxins kill the sensitive cells. Studies on the killer phenomenon in yeasts have provided valuable insights into a number of fundamental aspects of eukaryotic cell biology and interactions of different eukaryotic cells. Elucidation of the molecular mechanisms of their action will be helpful to develop the strategies to fight more and more harmful yeasts.

Cloning, characterization and heterelogous expression of the INU1 gene from Cryptococcus aureus HYA.

The INU1 gene (Accession number: JX073660) encoding exo-inulinase from Cryptococcus aureus HYA was cloned and characterized. The gene had an open reading frame (ORF) of 1653 bp long encoding an inulinase. The coding region of the gene was not interrupted by any intron. It encoded 551 amino acid residues of a protein with a putative signal peptide of 23 amino acids and the calculated molecular mass of 59.5 kDa. The protein sequence deduced from the inulinase structural gene contained the inulinase consensus sequences (WMNDPNGL), (RDP), ECP, FS and Q. It also had two conserved putative N-glycosylation sites. The inulinase from C. aureus HYA was found to be closely related to that from Kluyveromyces marxianus and Pichia guilliermondii. The inulinase gene without the signal sequence was subcloned into pPICZaA expression vector and expressed in Pichia pastoris X-33. The expressed fusion protein was analyzed by SDS-PAGE and western blotting and a specific band with molecular mass of about 60 kDa was found. Enzyme activity assay verified the recombinant protein as an inulinase. A maximum inulinase activity of 16.3±0.24 U/ml was obtained from the culture supernatant of P. pastoris X-33 harboring the inulinase gene. The optimal temperature and pH for action of the enzyme were 50 °C and 5.0, respectively. A large amount of monosaccharides were detected after the hydrolysis of inulin with the purified recombinant inulinase.

Direct conversion of inulin into cell lipid by an inulinase-producing yeast Rhodosporidium toruloides 2F5

In this study, an inulinase-producing yeast strain 2F5 of Rhodosporidium toruloides was obtained. It was found that the yeast strain 2F5 could produce higher amount of oil from inulin and larger lipid bodies in its cells than any other yeast strains tested in this study. Under the optimal conditions, 62.14% (w/w) of lipid based on cell dry weight and 15.82g/l of the dry cell mass were produced from 6.0% (w/v) inulin at flask level, leaving 0.92% (w/v) of total sugar in the fermented medium. During 2-l fermentation, 70.36% (w/w) of lipid based on cell dry weight and 15.64g/l of the dry cell mass were produced from 6.0% (w/v) inulin. Over 99.09% of the fatty acids from the yeast strain 2F5 grown on inulin was C16:0, C18:0, C18:1 and C18:2, especially C18:1 (52.2%). The biodiesel prepared using the lipids produced by the yeast strain 2F5 could be burnt well.

Occurrence and Diversity of Yeasts in the Mangrove Ecosystems in Fujian, Guangdong and Hainan Provinces of China

Mangrove wetland is a unique ecosystem and has rich bioresources. In this article, the roots, stems, branches, leaves, barks, fruits, and flowers from 12 species of the mangrove plants and six species of the accompanying mangrove plants, seawater and sediments in mangrove ecosystems in China were used as sources for isolation of yeasts. A total of 269 yeasts strains were obtained from the samples. The results of routine identification and phylogenetic analysis showed that they belonged to 22 genera and 45 species. Of all the 269 strains, Candida spp. was predominant with the proportion of 44.61%, followed by Kluyveromyces spp. (8.55%), Pichia spp. (7.44%), Kodamaea ohmeri (5.58%), Issatchenkia spp. (4.83%) and Debaryomyces hansenii (4.46%). We also found that strains N02-2.3 and ST3-1Y3 belonged to the undescribed species of Pichia sp. and Trichosporon sp. respectively while strain HN-12 was not related to any known yeast strains. This means that different yeast strains of Candida spp. especially C. tropicalis were widely distributed in the mangrove ecosystems and may have an important role in the mangrove ecosystems. The results also showed that some of them may have potential applications.

High-level production of calcium malate from glucose by Penicillium sclerotiorum K302.

In this study, after screening of 9 fungal strains for their ability to produce calcium malate, it was found that Penicillium sclerotiorum K302 among them could produce high-level of calcium malate. Under the optimal conditions, the titer of calcium malate in the supernatant was 88.6 g/l at flask level. During 10-l fermentation, the titer of 92.0 g/l, the yield of 0.88 g/g of glucose and the productivity of 1.23 g/l/h were reached within 72 h of the fermentation, demonstrating that the titer, yield and productivity of calcium malate by this strain were very high and the fermentation period was very short. After analysis of the partially purified product with HPLC, it was found that the main product was calcium malate. The results showed that P. sclerotiorum K302 obtained in this study was suitable for developing a novel one-step fermentation process for calcium malate production from glucose on large scale.