Cyanobacteria show great promise as autotrophic hosts for the renewable biosynthesis of useful chemicals from CO2 and light. While they can efficiently fix CO2, cyanobacteria are generally outperformed by heterotrophic production hosts in terms of productivity and titer. Photomixotrophy, or co-utilization of sugars and CO2 as carbon feedstocks, has been implemented in cyanobacteria to greatly improve productivity and titers of several chemical products. We introduced xylose photomixotrophy to a 2,3-butanediol producing strain of Synechococcus elongatus PCC 7942 and characterized the effect of gene knockouts, changing pathway expression levels, and changing growth conditions on chemical production. Interestingly, 2,3-butanediol production was almost completely inhibited in the absence of added CO2. Untargeted metabolomics implied that RuBisCO was a significant bottleneck, especially at ambient CO2 levels, restricting the supply of lower glycolysis metabolites needed for 2,3-butanediol production. The dependence of the strain on elevated CO2 levels suggests some practical limitations on how xylose photomixotrophy can be efficiently carried out in S. elongatus.

中文翻译：

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木糖的高效利用需要在 Synechococcus elongatus PCC 7942 中固定 CO2


蓝细菌作为自养宿主显示出巨大的前景，可以从 CO2 和光中可再生地合成有用的化学物质。虽然蓝藻可以有效地固定 CO2，但在生产率和滴度方面通常优于异养生产宿主。光混合营养，或糖和 CO2 作为碳原料的共利用，已在蓝藻中实施，以大大提高几种化学产品的生产率和滴度。我们将木糖光混合营养引入 Synechococcus elongatus PCC 7942 的 2,3-丁二醇生产菌株中，并表征了基因敲除、改变途径表达水平和改变生长条件对化学生产的影响。有趣的是，在没有添加 CO2 的情况下，2,3-丁二醇的产生几乎完全受到抑制。非靶向代谢组学表明 RuBisCO 是一个重要的瓶颈，尤其是在环境 CO2 水平下，限制了 2,3-丁二醇生产所需的低糖酵解代谢物的供应。菌株对升高的 CO 2 水平的依赖性表明，如何在 S. elongatus 中有效地进行木糖光混合营养存在一些实际限制。