Abstract
Alginate is a linear polyuronate in brown macroalgae. It is also a promising marine biopolymer that can be degraded by exo-type alginate lyase into an unsaturated uronate that is non-enzymatically or enzymatically converted to 4-deoxy-l-erythro-5-hexoseulose uronate (DEH). In a bioengineered yeast Saccharomyces cerevisiae (DEH++) strain that utilizes DEH, DEH is not only an important physiological metabolite but also a promising carbon source for biorefinery systems. In this study, we uncovered the essential chemical nature of DEH. In particular, we showed that DEH non-enzymatically reacts with specific amino groups in Tris, ammonium salts [(NH4)2SO4 and NH4Cl], and certain amino acids (e.g., Gly, Ser, Gln, Thr, and Lys) at 30 °C and forms other compounds, one of which we tentatively named DEH-related product-1 (DRP-1). In contrast, Asn, Met, Glu, and Arg were almost inert and Ala, Pro, Leu, Ile, Phe, Val, and Asp, as well as sodium nitrate (NaNO3), were inert in the presence of DEH. Some of the above amino acids (Asn, Glu, Ala, Pro, Phe, and Asp) were suitable nitrogen sources for the DEH++ yeast strain, whereas ammonium salts and Ser, Gln, and Thr were poor nitrogen sources owing to their high reactivity to DEH. Nutrient-rich YP medium with 1% (w/v) Yeast extract and 2% (w/v) Tryptone, as well as 10-fold diluted YP medium, could also be effectively used as nitrogen sources. Finally, we identified DRP-1 as a 2-furancarboxylic acid and showed that it has a growth-inhibitory effect on the DEH++ yeast strain. These results show the reactive nature of DEH and suggest a basis for selecting nitrogen sources for use with DEH and alginate in biorefineries. Our results also provide insight into the physiological utilization of DEH. The environmental source of 2-furancarboxylic acid is also discussed.
Highlights
Brown macroalgae have attracted attention as a promising marine biomass for the production of biofuels and chemicals in biorefinery applications[1]
We evaluated the reactivity of amino acids to deoxy-l-erythro-5-hexoseulose uronate (DEH) and found that DEH reacted with Gly, Ser, Gln, Thr, and Lys, clearly formed DEH-related product-1 (DRP-1), and disappeared from the chromatogram; Asn, Met, Glu, and Arg were almost inert in the presence of DEH, and Asn, Glu, and Arg formed slight DRP-1 spots (Fig. 2A)
We described the reactive nature of DEH in the utilization of alginate
Summary
Brown macroalgae have attracted attention as a promising marine biomass for the production of biofuels and chemicals in biorefinery applications[1]. Alginate can be degraded by exo-type alginate lyase into an unsaturated uronate that is non-enzymatically or enzymatically converted to 4-deoxy-l-erythro-5-hexoseulose uronate (DEH)[6,7,8,9]; DEH is an important intermediate in the physiological metabolism of alginate. 27 27 28 28 alginate via exo-type alginate lyase expressed on the cell surface[14]. In these bioengineered yeast strains, DEH is transported into cells via a fungal DEH transporter and reduced to 2-keto-3-deoxy-d-gluconate by a bacterial reductase. DEH is an important intermediate in the physiological metabolism of alginate and a promising carbon source for the production of biofuels and chemicals. We determined the properties of DEH that contribute to the utilization of DEH and alginate
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