Effects of Reduced and Enhanced Glycogen Pools on Salt-Induced Sucrose Production in a Sucrose-Secreting Strain of Synechococcus elongatus PCC 7942
Effects of Reduced and Enhanced Glycogen Pools on Salt-Induced Sucrose Production in a Sucrose-Secreting Strain of Synechococcus elongatus PCC 7942
复制标题
糖原池减少和增加对细长聚球藻 PCC 7942 蔗糖分泌菌株中盐诱导的蔗糖生产的影响
DOI：
10.1128/aem.02023-17
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发表时间：
2018-01-01
影响因子：
4.4
通讯作者：
Lu, Xuefeng
中科院分区：
文献类型：
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作者：
Qiao, Cuncun;Duan, Yangkai;Lu, Xuefeng
蓝藻中蔗糖和糖原的合成都有一个共同的前体葡萄糖-1-磷酸。一般认为，降低糖原合成可以驱动更多的碳向蔗糖合成，可以诱导盐胁迫蓝藻之间。通过使用茶碱依赖的核糖开关系统，在糖原合成中的关键基因glgC的表达，在细长聚球藻PCC 7942的蔗糖分泌菌株中以定量的方式下调。我们观察到，逐步抑制糖原合成限制，而不是刺激蔗糖生产的盐胁迫细胞，表明糖原可以作为一个碳库的蔗糖合成。因此，我们产生了糖原过量生产菌株，但增加的糖原库单独不刺激蔗糖生产，表明替代步骤限制了蔗糖合成的碳通量。与先前的研究表明蔗糖磷酸合酶（SPS）催化蔗糖合成中的限速步骤相一致，糖原过量生产和SPS过表达的组合导致蔗糖产量增加。我们的研究结果表明，在细长聚球藻PCC 7942中，糖原和蔗糖池是紧密相连的，我们提出，在存在强蔗糖合成库的情况下，提高糖原池可能是提高蓝藻蔗糖产量的一个有前途的策略。重要意义许多蓝藻在NaCl胁迫下自然合成和积累蔗糖，这为通过蓝细菌工程化获得糖原料提供了新的可能性。据推测，糖原合成与蔗糖合成竞争碳通量。然而，我们的研究结果表明，糖原合成的抑制减少，而不是刺激蔗糖分泌菌株细长聚球藻PCC 7942的蔗糖生产。这一结果表明，糖原可以作为一个支持性的，而不是竞争性的碳库蔗糖的合成，提供了新的见解糖原合成和蔗糖合成之间的关系在蓝藻。这一发现也有助于指导代谢工程工作，以优化蓝藻生产蔗糖和可能的其他产品。
Sucrose and glycogen syntheses in cyanobacteria share the common precursor glucose-1-phosphate. It is generally assumed that lowering glycogen synthesis could drive more carbon toward sucrose synthesis that can be induced by salt stress among cyanobacteria. By using a theophylline-dependent riboswitch system, the expression of glgC, a key gene in glycogen synthesis, was downregulated in a quantitative manner in a sucrose-secreting strain of Synechococcus elongatus PCC 7942. We observed that the stepwise suppression of glycogen synthesis limited rather than stimulated sucrose production in the salt-stressed cells, suggesting that glycogen could serve as a carbon pool for the synthesis of sucrose. Accordingly, we generated glycogen-overproducing strains, but the increased glycogen pool alone did not stimulate sucrose production, indicating that alternative steps limit the carbon flux toward the synthesis of sucrose. Consistent with previous studies that showed that sucrose-phosphate synthase (SPS) catalyzes the rate-limiting step in sucrose synthesis, the combination of glycogen overproduction and sps overexpression resulted in increased sucrose production. Our results indicate that the glycogen and sucrose pools are closely linked in Synechococcus elongatus PCC 7942, and we propose that enhancing the glycogen pool could be a promising strategy for the improvement of sucrose production by cyanobacteria in the presence of a strong sucrose synthesis sink.IMPORTANCE Many cyanobacteria naturally synthesize and accumulate sucrose when stressed by NaCl, which provides novel possibilities for obtaining sugar feedstock by engineering of cyanobacteria. It has been assumed that glycogen synthesis competes with sucrose synthesis for the carbon flux. However, our results showed that the suppression of glycogen synthesis decreased rather than stimulated sucrose production in a sucrose-secreting strain of Synechococcus elongatus PCC 7942. This result suggests that glycogen could serve as a supportive rather than a competitive carbon pool for the synthesis of sucrose, providing new insights about the relation between glycogen synthesis and sucrose synthesis in cyanobacteria. This finding is also useful to guide metabolic engineering work to optimize the production of sucrose and possibly other products by cyanobacteria.