Recently, the utilization of renewable biomass instead of fossil fuels for producing fuels and chemicals has received much attention due to the global climate change. Among renewable biomass, marine algae are gaining importance as third generation biomass feedstocks owing to their advantages over lignocellulose. Particularly, red macroalgae have higher carbohydrate contents and simpler carbohydrate compositions than other marine algae. In red macroalgal carbohydrates, 3,6-anhydro-L-galactose (AHG) is the main sugar composing agarose along with D-galactose. However, AHG is not a common sugar and is chemically unstable. Thus, not only AHG but also red macroalgal biomass itself cannot be efficiently converted or utilized. Here, we biologically upgraded AHG to a new platform chemical, its sugar alcohol form, 3,6-anhydro-L-galactitol (AHGol), an anhydrohexitol. To accomplish this, we devised an integrated process encompassing a chemical hydrolysis process for producing agarobiose (AB) from agarose and a biological process for converting AB to AHGol using metabolically engineered Saccharomyces cerevisiae to efficiently produce AHGol from agarose with high titers and yields. AHGol was also converted to an intermediate chemical for plastics, isosorbide. To our knowledge, this is the first demonstration of upgrading a red macroalgal biomass component to a platform chemical via a new biological route, by using an engineered microorganism.

中文翻译：

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3,6-脱水-L-半乳糖从琼脂糖升级为新型平台化学品

近来，由于全球气候变化，利用可再生生物质代替化石燃料来生产燃料和化学品受到了广泛关注。在可再生生物质中，海藻由于其比木质纤维素的优势而作为第三代生物质原料正变得越来越重要。特别地，红色大型藻类具有比其他海洋藻类更高的碳水化合物含量和更简单的碳水化合物组成。在红色大藻糖中，3,6-脱水-L-半乳糖（AHG）是构成琼脂糖和D的主要糖-半乳糖。但是，AHG不是常见的糖，化学上不稳定。因此，不仅不能有效地转化或利用AHG，而且不能有效地转化或利用红色大型藻类生物质本身。在这里，我们将AHG生物升级为一种新的平台化学品，其糖醇形式为3,6-脱水L-半乳糖醇（AHGol），一种脱水己糖醇。为实现此目的，我们设计了一个集成过程，包括从琼脂糖生产琼脂二糖（AB）的化学水解过程和使用代谢工程酿酒酵母将AB转化为AHGol的生物过程。以高滴度和高产率从琼脂糖高效生产AHGol。AHGol还转化为塑料的中间化学品异山梨醇。据我们所知，这是使用工程微生物通过新的生物途径将红色大型藻类生物质组分升级为平台化学品的首次演示。