The effects of the concentration of the medium components and other cultural conditions on the total cell number and on the lipid content (mg of total lipid/108 cells) of the fat yeast Lipomyces starkeyi were examined. The no addition and deficiency of NH4+, K+, Mgt, P043-, SO42-, Zn2+, Fe3+, or Mn2+ decreased the total cell number. Mn2+ sufficiency increased the total cell number by a factor of 1.5 to 1.7, as compared with that of the standard concentration. The lipid content of the yeast was affected by six (NH4+, K+, Cat +, Zn2+, Fe3+, and Mn2+) ion concentrations. The no addition and deficiency of Zn2+ increased the lipid content by a factor ranging from 2.4 to 2.8 in comparison with that of the standard concentration. The concentration of Zn2+ also altered the lipid yield (g of lipid/100 g of glucose consumed) considerably. The concentration of Nat, Cl-, Cue, B033-, I-, Mo042-, and biotin had almost no effect on the total cell number, lipid content, and lipid yield of L. starkeyi. The cultural temperature and the initial pH value of the medium affected the total cell number and lipid content; the optimum temperature ranged from 25.5 to 29.5°C, and the optimum pH value was 4.9. A low concentration of dissolved oxygen decreased both the total cell number and lipid content. D-Glucose, D-mannose, D-galactose, Dlevulose, sucrose, D-xylose, and L-arabinose proved to be usable carbon sources for the growth and the lipid accumulation of L. starkeyi.Some yeasts accumulate a large amount of lipid in the cells. Although studies on lipid accumulation of microorganisms have been conducted since 1878, few reports on the physiological factors of lipid accumulation of yeasts have been published (1-4). The previous research conducted at our laboratory suggested that only a few trace elements affect the growth and the intracellular lipid (mainly 29

Lipomyces starkeyi is an oleaginous yeast, and has been classified in four distinct groups, i.e., sensu stricto and custers α, β, and γ. Recently, L. starkeyi clusters α, β, and γ were recognized independent species, Lipomyces mesembrius, Lipomyces doorenjongii, and Lipomyces kockii, respectively. In this study, we investigated phylogenetic relationships within L. starkeyi, including 18 Japanese wild strains, and its related species, based on internal transcribed spacer sequences and evaluated biochemical characters which reflected the phylogenetic tree. Phylogenetic analysis showed that most of Japanese wild strains formed one clade and this clade is more closely related to L. starkeyi s.s. clade including one Japanese wild strain than other clades. Only three Japanese wild strains were genetically distinct from L. starkeyi. Lipomyces mesembrius and L. doorenjongii shared one clade, while L. kockii was genetically distinct from the other three species. Strains in L. starkeyi s.s. clade converted six sugars, D-glucose, D-xylose, L-arabinose, D-galactose, D-mannose, and D-cellobiose to produce high total lipid yields. The Japanese wild strains in subclades B, C, and D converted D-glucose, D-galactose, and D-mannose to produce high total lipid yields. Lipomyces mesembrius was divided into two subclades. Lipomyces mesembrius CBS 7737 converted D-xylose, L-arabinose, D-galactose, and D-cellobiose, while the other L. mesembrius strains did not. Lipomyces doorenjongii converted all the sugars except D-cellobiose. In comparison to L. starkeyi, L. mesembrius, and L. doorenjongii, L. kockii produced higher total lipid yields from D-glucose, D-galactose, and D-mannose. The type of sugar converted depended on the subclade classification elucidated in this study.

No abstract

We studied how to control the ability of Lipomyces starkeyi cells to grow and accumulate lipid by adding inorganic elements. Adding Zn2 +, Mn2 +, and monopotassium phosphate at a stationary phase of growth caused rapid changes. However, adding these elements individually did not induce any marked changes in the cell growth and lipid accumulation. When these elements were added simultaneously, the yeast underwent a second logarithmic growth and the respiration rate increased. Concurrently, this addition stopped the normal increase in the amount of lipid in the culture (mg of lipid ml of culture), and decreased the lipid content of the cells (mg of lipid/108 cells). The periods of second logarithmic growth and the cessation of lipid accumulation were shortened when monopotassium phosphate was not added. The function of monopotassium phosphate was replaced by another buffer chemical.Artificial modification of the physiological conditions of growing microorganisms has often been used as a way to control metabolite production. In Lipomyces starkeyi grown in batch cultures, cell growth and lipid accumulation gradually change with the progress of the growth phases (1, 2). If the progress of the growth phases can be artificially controlled, cells with different abilities can be easily obtained. Development of such a control method enables us to study the metabolism of lipid accumulation in the yeast.In our earlier report, we showed that the concentration of certain inorganic micro-ions seriously affect the cell growth and the lipid accumulation (3). That raised the possibility that these changes, which accompany the progress of growth phases, could be controlled artificially by changing the concentration of inorganic elements midway in the culture. In the present study, this possibility was examined.

No abstract