Abstract
BackgroundThe development of biorefinery systems that use lignocellulosic biomass as a renewable carbon source to produce fuels and chemicals is attracting increasing attention. The process cost of enzymatic saccharification of biomass is a major challenge for commercialization. To decrease this cost, researchers have proposed on-site solid-state fermentation (SSF). This study investigated the feasibility of using Aspergillus oryzae as a host microorganism for SSF recombinant enzyme production with ammonia-treated rice straw as model biomass. Eight A. oryzae strains were tested, all of which are used in the food industry. We evaluated the effects of acetic acid, a fermentation inhibitor. We also developed a platform strain for targeted recombinant enzyme production by gene engineering technologies.ResultsThe SSF validation test showed variation in the visibility of mycelium growth and secreted protein in all eight A. oryzae strains. The strains used to produce shoyu and miso grew better under test conditions. The ammonia-treated rice straw contained noticeable amounts of acetic acid. This acetic acid enhanced the protein production by A. oryzae in a liquid-state fermentation test. The newly developed platform strain successfully secreted three foreign saccharifying enzymes.ConclusionsA. oryzae is a promising candidate as a host microorganism for on-site SSF recombinant enzyme production, which bodes well for the future development of a more cost-efficient saccharifying enzyme production system.
Highlights
The development of biorefinery systems that use lignocellulosic biomass as a renewable carbon source to produce fuels and chemicals is attracting increasing attention
Because ammonia-treated rice straw contains noticeable amounts of acetic acid, a fermentation inhibitor, we evaluated the effect of acetic acid [44, 45] on the protein production by the selected A. oryzae strains
The glucan content of the two types of biomass was comparable, ammonia-treated rice straw had more than twice xylan content compared to dilute sulfuric acid-treated corn stover
Summary
The development of biorefinery systems that use lignocellulosic biomass as a renewable carbon source to produce fuels and chemicals is attracting increasing attention because of the social need for replacing fossil fuel resources and decreasing carbon dioxide emissions [1, 2]. Residual ammonia can be neutralized by acid chemicals, such as sulfuric acid, and can be used as a nutrient by fermenting microorganisms growing on the pretreated biomasses or their hydrolysates in a subsequent process. These versatile processing options of aqueous ammonia provide strong advantages compared with other alkaline reagents
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