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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木糖的有效利用需要细长聚球藻 PCC 7942 中的 CO2 固定


蓝藻作为自养宿主，在利用二氧化碳和光进行有用化学物质的可再生生物合成方面显示出巨大的前景。虽然蓝藻可以有效地固定二氧化碳，但在生产力和效价方面，蓝藻通常优于异养生产宿主。光混合营养，即糖和二氧化碳作为碳原料的共同利用，已在蓝细菌中得到应用，大大提高了多种化学产品的生产力和效价。我们将木糖光混合营养引入细长聚球藻 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，在不添加 CO2 的情况下，2,3-丁二醇的生产几乎完全受到抑制。非靶向代谢组学表明，RuBisCO 是一个重大瓶颈，尤其是在环境二氧化碳水平下，限制了 2,3-丁二醇生产所需的较低糖酵解代谢物的供应。该菌株对升高的 CO2 水平的依赖性表明，如何在 S. elongatus 中有效进行木糖光混合营养存在一些实际限制。