IMPROVEMENT OF YEAST STRAINS TROUGH IRRADIATION AND FAST ADAPTATIONFOR BIOETHANOL FERMENTATION OF KAPPAPHYCUSALVAREZrr

Abstract

Kappaphycusalvarezii has polysaccharides which consist of galactose as monomer unit. After acid hydrolysis, galactose can be lIsed as carbon and energy SOllrce by Pachysolentannophilus IPBCC YIII149 and Saccharomyces cerevisiae IPBCC Y03545, but the ability of these strains to convert K alvareziihydrolysates into bioethanol was low. Those strains have to be improved to achieve beller pelformance of substrate and fermentation efficiency. The research aimed to get improved strains of s. cerevisiae IPBCC Y03545 and P. tannophilZls IPBCC YIII149 which had beller activity in KappaphyclIsalvareziihydrolysate. Strain improvement methods were gamma irradiation andfast adaptation on Yeast Malt Peptone Galactose (YMP-galactose) broth. Gamma irradiation was done at 10 Gy, followed by adaptation on YMP-galactose for 9 times. Strains improvement throllgh fast adaptation was done by growing the wild strains in Fesh YMP-galactose (0.1% galactose) medium for 264 times. Subculturing was done every 4 hours, when the cells were at lag phase. Gamma irradiation (10 Gy) resulted in I isolate of P. tannophilus which had higher substrate efficiency (37.12%) andfermentation efficiency {I. 16%) than its wild type (24.31% and 0.39%, respectively). While for S. cerevisiae isolates, ethanol production and substrat efficiency on K. alvareziihydrolisate were relatively the same as its wild type. Improved isolates of P. tannophilus were varied in their galactose fermentation ability, while S. cerevisiae's pelformance was increased with the increase of adaptation cycles. The fermentation characteristics of all improved isolates in YMP-galac/ose media were in accordance with their fermentation ability on K. alvareziihydrolysate. P. tannophilus isolate of 88 adaptation cycles was beller than other isolates and wild strains /0 ferment K. alvareziihydrolysates. All adapted S. cerevisiae isolales, had better jermentation characteristics than its wild strain, except for fermentation efficiency. The shape of P. lannophillls cell was similar with the wild type, butfor S. cerevisiae, the cell shape became oval-like and had bigger size.