Reducing glucoamylase usage for commercial-scale ethanol production from starch using glucoamylase expressing Saccharomyces cerevisiae

Abstract

The development of yeast that converts raw corn or cassava starch to ethanol without adding the exogenous α-amylase and/or glucoamylase would reduce the overall ethanol production cost. In this study, two copies of codon-optimized Saccharomycopsis fibuligera glucoamylase genes were integrated into the genome of the industrial Saccharomyces cerevisiae strain CCTCC M94055, and the resulting strain CIBTS1522 showed comparable basic growth characters with the parental strain. We systemically evaluated the fermentation performance of the CIBTS1522 strain using the raw corn or cassava starch at small and commercial-scale, and observed that a reduction of at least 40% of the dose of glucoamylase was possible when using the CIBTS1522 yeast under real ethanol production condition. Next, we measured the effect of the nitrogen source, the phosphorous source, metal ions, and industrial microbial enzymes on the strain’s cell wet weight and ethanol content, the nitrogen source and acid protease showed a positive effect on these parameters. Finally, orthogonal tests for some other factors including urea, acid protease, inoculum size, and glucoamylase addition were conducted to further optimize the ethanol production. Taken together, the CIBTS1522 strain was identified as an ideal candidate for the bioethanol industry and a better fermentation performance could be achieved by modifying the industrial culture media and condition.

Effect of glucose levels on carbon flow rate, antioxidant status, and enzyme activity of yeast during fermentation

“…The ethanol content in culture medium is an important indicator of yeast metabolism. 38 As shown in Fig. 5, the high glucose group contained more ethanol in the culture medium, and the ethanol content of different groups demonstrated significant differences.…”

“…The ethanol content in culture medium is an important indicator of yeast metabolism 38 . As shown in Fig.…”

Research progress of glucoamylase with industrial potential

“…Glucoamylase can improve the fermentation rate and ethanol production, but it will increase the cost of ethanol production. To reduce the cost of ethanol production, the glucoamylase synthesis genes were integrated into industrial yeast by Wang et al (2021), and a recombinant strain CIBTS1522 was obtained, which can reduce the addition of glucoamylase by about 40%. The use of strains that can produce glucoamylase in the process of ethanol fermentation, which reduces the addition of glucoamylase and the cost of ethanol production effectiveness (Favaro et al, 2015; Kobayashi & Nakamura, 2004; Viswanathan et al, 2021).…”

“…A synthetic gene for a tolerant glucoamylase was isolated from Aspergillus flavus NSH9 and expressed successfully in P. pastoris GS115 , and a recombinant glucoamylase strain (rGA2) was obtained by Kmr et al (2019). Based on the research of Favaro et al (2012), the optimizing glucoamylase synthetic genes were integrated into industrial S. cerevisiae by Wang et al (2021) and found that the recombinant strain could reduce the exogenous Saccharomyces adds by over 40% in actual ethanol production.…”

“…The size of the nodes represents the frequency of the cited articles; Lines between nodes represents the connection of cited articles; the color-coded bar key on the right represents 1991-2021 from bottom to top F I G U R E 8 Co-cited references with a burst strength of glucoamylase research was isolated from Aspergillus flavus NSH9 and expressed successfully in P. pastoris GS115, and a recombinant glucoamylase strain (rGA2) was obtained by Kmr et al (2019). Based on the research of Favaro et al (2012), the optimizing glucoamylase synthetic genes were integrated into industrial S. cerevisiae byWang et al (2021) and found that the recombinant strain could reduce the exogenous Saccharomyces adds by over 40% in actual ethanol production.3.6.2 | Aspergillus Niger glucoamylaseA. niger is common filamentous fungi with a wide range of industrial applications because of its unique strain morphology and biochemical characterization.…”