Nano Electrochemistry Laboratory, College of Engineering, University of Georgia, Athens, Georgia.
Biosynthetic Engineering and Biocatalysis Laboratory, College of Engineering, University of Georgia, Athens, Georgia.
Biotechnol Bioeng. 2018 May;115(5):1361-1366. doi: 10.1002/bit.26542. Epub 2018 Feb 7.
Cyanobacteria are used as anode catalysts in photo-bioelectrochemical cells to generate electricity in a sustainable, economic, and environmental friendly manner using only water and sunlight. Though cyanobacteria (CB) possess unique advantage for solar energy conversion by virtue of its robust photosynthesis, they cannot efficiently perform extracellular electron transfer (EET). The reasons being, unlike dissimilatory metal reducing bacteria (that are usually exploited in microbial fuel cells to generate electricity), (1) CB do not possess any special features on their outer membrane to carry out EET and, (2) the electrons generated in photosynthetic electron transport chain are channeled into competing respiratory pathways rather than to the anode. CB, genetically engineered to express outer membrane cytochrome S (OmcS), was found to generate ∼nine-fold higher photocurrent compared to that of wild-type cyanobacterium in our previous work. In this study, each of the three respiratory terminal oxidases in Synechococcus elongatus PCC7942 namely bd-type quinol oxidase, aa -type cytochrome oxidase, and cbb -type cytochrome oxidase was knocked-out one at a time (cyd , cox , and cco respectively) and its contribution for extracellular ferricyanide reduction and photocurrent generation was investigated. The knock-out mutant lacking functional bd-type quinol oxidase (cyd ) exhibited greater EET by reducing more ferricyanide compared to other single knock-out mutants as well as the wild type. Further, cyd omcs (the cyd mutant expressing OmcS) was found to generate more photocurrent than the corresponding single knock out controls and the wild-type. This study clearly demonstrates that the bd-quinol oxidase diverted more electrons from the photosynthetic electron transport chain towards respiratory oxygen reduction and knocking it out had certainly enhanced the cyanobacterial EET.
蓝藻被用作光电生物电化学电池中的阳极催化剂，仅利用水和阳光以可持续、经济和环保的方式发电。虽然蓝藻 (CB) 凭借其强大的光合作用具有独特的太阳能转换优势，但它们不能有效地进行细胞外电子转移 (EET)。原因是，与通常在微生物燃料电池中用于发电的异化金属还原细菌 (dissimilatory metal reducing bacteria) 不同，(1) CB 在外膜上没有任何特殊特征来进行 EET，并且 (2) 在光合电子传递链中产生的电子被引导到竞争呼吸途径而不是阳极。在我们之前的工作中，我们发现经过基因工程表达外膜细胞色素 S (OmcS) 的 CB 产生的光电流比野生型蓝藻高约九倍。在这项研究中，逐个敲除了 Synechococcus elongatus PCC7942 中的三种呼吸末端氧化酶，即 bd 型醌氧化酶、aa 型细胞色素氧化酶和 cbb 型细胞色素氧化酶 (cyd 、cox 和 cco 分别)，并研究了它们对细胞外铁氰化物还原和光电流产生的贡献。缺乏功能性 bd 型醌氧化酶 (cyd ) 的敲除突变体与其他单敲除突变体以及野生型相比，通过还原更多的铁氰化物表现出更大的 EET。此外，cyd omcs（表达 OmcS 的 cyd 突变体）产生的光电流比相应的单敲除对照和野生型多。这项研究清楚地表明，bd-醌氧化酶将更多的电子从光合作用电子传递链转移到呼吸氧还原中，敲除它肯定增强了蓝藻的 EET。
