Enhancement of Galactose Uptake from Kappaphycus alvarezii Using Saccharomyces cerevisiae through Deletion of Negative R
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Enhancement of Galactose Uptake from Kappaphycus alvarezii Using Saccharomyces cerevisiae through Deletion of Negative Regulators of GAL Genes In Yung Sunwoo 1,2 & Pailin Sukwong 1 & Yu Rim Park 1 Soo Rin Kim 3 & Gwi-Teak Jeong 1 & Sung-Koo Kim 1
3
& Deok Yeol Jeong &
Received: 1 July 2020 / Accepted: 29 September 2020/ # Springer Science+Business Media, LLC, part of Springer Nature 2020
Abstract
This study was aimed at enhancing galactose consumption from the red seaweed Kappaphycus alvarezii. The optimal pretreatment condition of thermal acid hydrolysis was treated with 350 mM HNO3 for 60 min at 121 °C. The enzymatic saccharification with a 1:1 mixture of Celluclast 1.5 L and Viscozyme L showed the maximum yield of glucose; 42-g/L monosaccharide concentration was obtained with the highest yield of pretreatment and enzymatic saccharification (EPS) and the lowest inhibitory compound concentration. The deletion of the GAL80, MIG1, CYC8, or TUP1 gene was performed to improve the galactose consumption rate. The strains with the deletion of the MIG1 gene (mig1Δ) showed higher galactose consumption rate and ethanol yield than other strains. High transcription levels of regulatory genes revealed that the mig1Δ relieved glucose repression. These results show that the mig1Δ enhances galactose consumption rate from K. alvarezii. Keywords Kappaphycus alvarezii . Fermentation . CRISPR/Cas9 . MIG1 . Ethanol
Introduction Biofuels, such as bioethanol, biodiesel, biogas, and biobutanol, are currently produced globally as ecofriendly and sustainable sources of energy [1]. Bioethanol is the most widely used biofuel as fuel for engines and fuel additives [2]. Commercial bioethanol production has been
* Sung-Koo Kim [email protected]
1
Department of Biotechnology, Pukyong National University, Busan 48513, Republic of Korea
2
Department of Chemistry, Umeå University, SE-90187 Umeå, Sweden
3
School of Food Science and Biotechnology, Kyungpook National University, Daegu 41566, Republic of Korea
Applied Biochemistry and Biotechnology
prohibited due to the use of edible feed stock, such as sugarcane, corn, and lignocellulosic biomass (1st and 2nd generation biomass) [3]. Seaweeds are receiving considerable global attention as the primary source of energy. The major advantages of the use of seaweed are no agricultural land requirement and no recalcitrant compounds, such as lignin [4]. These advantages indicate that seaweed has considerable prospects as an ecofriendly and sustainable feedstock for bioethanol production. Considering monosaccharide constituents in seaweed hydrolysate, the major monosaccharide in K. alvarezii is galactose. However, S. cerevisiae utilizes galactose slower than it utilizes glucose [5]. Therefore, development of yeasts that utilize and convert various monosaccharides into ethanol is warranted. The scheme for glucose repression of the GAL genes is shown in Fig. 1. The induction of the GAL system requires intracellular galactose which acts as a signal molecule by an ATP-dependent mechanism [6]. Intra
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