Selão Tiago Toscano, Jebarani Jasmin, Ismail Nurul Aina, Norling Birgitta, Nixon Peter Julian
School of Biological Sciences, Nanyang Technological University, Singapore, Singapore.
Department of Life Sciences, Imperial College London, London, United Kingdom.
Front Plant Sci. 2020 Jan 31;10:1700. doi: 10.3389/fpls.2019.01700. eCollection 2019.
Cyanobacteria are promising chassis strains for the photosynthetic production of platform and specialty chemicals from carbon dioxide. Their efficient light harvesting and metabolic flexibility abilities have allowed a wide range of biomolecules, such as the bioplastic polylactate precursor D-lactate, to be produced, though usually at relatively low yields. In order to increase photosynthetic electron flow towards the production of D-lactate, we have generated several strains of the marine cyanobacterium sp. PCC 7002 (Syn7002) with deletions in genes involved in cyclic or pseudo-cyclic electron flow around photosystem I. Using a variant of the D-lactate dehydrogenase (LDH, engineered to efficiently utilize NADPH ), we have shown that deletion of either of the two flavodiiron homologs (involved in pseudo-cyclic electron transport) or the Syn7002 homolog (proposed to be a vital part of the cyclic electron transport pathway) is able to increase D-lactate production in Syn7002 strains expressing LDH and the LldP (lactate permease), especially at low temperature (25°C) and 0.04% (v/v) CO, though at elevated temperatures (38°C) and/or high (1%) CO concentrations, the effect was less obvious. The Δ background seemed to be particularly beneficial at 25°C and 0.04% (v/v) CO, with a nearly 7-fold increase in D-lactate accumulation in comparison to the wild-type background (≈1000 vs ≈150 mg/L) and decreased side effects in comparison to the deletion strains. Overall, our results show that manipulation of photosynthetic electron flow is a viable strategy to increase production of platform chemicals in cyanobacteria under ambient conditions.
蓝细菌是利用二氧化碳光合生产平台化学品和特殊化学品的理想底盘菌株。它们高效的光捕获能力和代谢灵活性使其能够生产多种生物分子，如生物塑料聚乳酸的前体D-乳酸，不过产量通常相对较低。为了增加光合电子流以用于D-乳酸的生产，我们构建了几株海洋蓝细菌聚球藻属PCC 7002（Syn7002）菌株，这些菌株中参与围绕光系统I的循环或伪循环电子流的基因被敲除。通过使用一种经过工程改造以有效利用NADPH的D-乳酸脱氢酶（LDH）变体，我们发现敲除两个黄素二铁同源物（参与伪循环电子传递）或Syn7002同源物（被认为是循环电子传递途径的重要组成部分）中的任何一个，都能够增加表达LDH和LldP（乳酸通透酶）的Syn7002菌株中D-乳酸的产量，特别是在低温（25°C）和0.04%（v/v）CO₂条件下，不过在高温（38°C）和/或高（1%）CO₂浓度下，这种效果不太明显。Δ背景在25°C和0.04%（v/v）CO₂条件下似乎特别有益，与野生型背景相比，D-乳酸积累量增加了近7倍（约1000 vs约150 mg/L），并且与敲除菌株相比副作用减少。总体而言，我们的结果表明，在环境条件下，操纵光合电子流是提高蓝细菌中平台化学品产量的可行策略。
