Presentation Information
[2BRBP-14]Ammonium ion concentration-dependent production of extracellular polysaccharides from glycerol by an oleaginous yeast Rhodotorula toruloides: Visualization of the producer cells
Soyoka Takegawa1, Chiaki Matsuzaki1, Hikosaka Taiki2, Kazuhiro Hamamoto2, ○Shigeyuki Kawai1 (1. Ishikawa Prefectural University (Japan), 2. Miyoshi Oil & Fat Co., Ltd. (Japan))
Keywords:
Rhodotorula toruloides,extracellular polysaccharide,oleochemical industrial waste,lipid droplet,transmission electron microscopy
[Background]
In the oleochemical industry, a fat-splitting process is used to generate a methanol-free byproduct, oleochemical industrial waste, that includes crude glycerol. While there have been many efforts to utilize biodiesel-derived crude glycerol, few studies have explored the utilization of oleochemical industrial waste. The oleaginous yeast Rhodotorula toruloides is a nonconventional yeast that is well known for its industrial potential as a producer of lipids, carotenoids, and enzymes. Extracellular polysaccharides (EPSs) are of increasing interest due to their many applications. We found that the R. toruloides NBRC 8766 strain produced mannose-rich and high-molecular-weight EPSs with a mannose content (mol%) exceeding 90% and an estimated molecular weight greater than 10,000 k from oleochemical industrial waste crude glycerol or pure glycerol. Components in the industrial waste increased EPS production. The molecular mechanisms underlying the production of EPS from glycerol has remained to be elucidated.
[Results]
To elucidate the mechanism, a key factor responsible for the production of EPS was investigated. Through the comparison of the composition of culture media, the concentration of NH4+ ions in the culture medium was identified as a key factor in discriminating cells producing the abovementioned EPSs (EPS-producing cells) from EPS-nonproducing cells. Fluorescent and transmission electron microscopic analyses of the two cell types revealed differences; the EPS-producing cells had immature lipid droplets and marked two-layered cell walls, where the outer layer was darker and looked like it was wearing “fuzz”, which was assumed to be the EPSs released from the cells. The EPS-nonproducing cells had clear lipid droplets, one-layered cell walls without obvious fuzz-like structures, and more abundant intracellular polysaccharide granules.
[Conclusion]
The identification of the concentration of NH4+ ions in the culture medium as a key factor in discriminating EPS-producing cells from EPS-nonproducing cells and the morphological observations of the cells presented here will provide a basis for understanding the molecular mechanism underlying the production of mannose-rich and high-molecular-weight EPS, as well as clues for artificially increasing the amounts of EPSs and lipids produced.
In the oleochemical industry, a fat-splitting process is used to generate a methanol-free byproduct, oleochemical industrial waste, that includes crude glycerol. While there have been many efforts to utilize biodiesel-derived crude glycerol, few studies have explored the utilization of oleochemical industrial waste. The oleaginous yeast Rhodotorula toruloides is a nonconventional yeast that is well known for its industrial potential as a producer of lipids, carotenoids, and enzymes. Extracellular polysaccharides (EPSs) are of increasing interest due to their many applications. We found that the R. toruloides NBRC 8766 strain produced mannose-rich and high-molecular-weight EPSs with a mannose content (mol%) exceeding 90% and an estimated molecular weight greater than 10,000 k from oleochemical industrial waste crude glycerol or pure glycerol. Components in the industrial waste increased EPS production. The molecular mechanisms underlying the production of EPS from glycerol has remained to be elucidated.
[Results]
To elucidate the mechanism, a key factor responsible for the production of EPS was investigated. Through the comparison of the composition of culture media, the concentration of NH4+ ions in the culture medium was identified as a key factor in discriminating cells producing the abovementioned EPSs (EPS-producing cells) from EPS-nonproducing cells. Fluorescent and transmission electron microscopic analyses of the two cell types revealed differences; the EPS-producing cells had immature lipid droplets and marked two-layered cell walls, where the outer layer was darker and looked like it was wearing “fuzz”, which was assumed to be the EPSs released from the cells. The EPS-nonproducing cells had clear lipid droplets, one-layered cell walls without obvious fuzz-like structures, and more abundant intracellular polysaccharide granules.
[Conclusion]
The identification of the concentration of NH4+ ions in the culture medium as a key factor in discriminating EPS-producing cells from EPS-nonproducing cells and the morphological observations of the cells presented here will provide a basis for understanding the molecular mechanism underlying the production of mannose-rich and high-molecular-weight EPS, as well as clues for artificially increasing the amounts of EPSs and lipids produced.
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