Eutrophication and deoxygenation possibly occur in coastal waters due to excessive nutrients from agricultural and aquacultural activities, leading to sulfide accumulation. Cyanobacteria, as photosynthetic prokaryotes, play significant roles in carbon fixation in the ocean. Although some cyanobacteria can use sulfide as the electron donor for photosynthesis under anaerobic conditions, little is known on how they interact with sulfide under aerobic conditions. In this study, we report that Synechococcus sp. strain PCC7002 (PCC7002), harboring an sqr gene encoding sulfide:quinone oxidoreductase (SQR), oxidized self-produced sulfide to S0, present as persulfide and polysulfide in the cell. The Δsqr mutant contained less cellular S0 and had increased expression of key genes involved in photosynthesis, but it was less competitive than the wild type in cocultures. Further, PCC7002 with SQR and persulfide dioxygenase (PDO) oxidized exogenous sulfide to tolerate high sulfide levels. Thus, SQR offers some benefits to cyanobacteria even under aerobic conditions, explaining the common presence of SQR in cyanobacteria.IMPORTANCE Cyanobacteria are a major force for primary production via oxygenic photosynthesis in the ocean. A marine cyanobacterium, PCC7002, is actively involved in sulfide metabolism. It uses SQR to detoxify exogenous sulfide, enabling it to survive better than its Δsqr mutant in sulfide-rich environments. PCC7002 also uses SQR to oxidize endogenously generated sulfide to S0, which is required for the proper expression of key genes involved in photosynthesis. Thus, SQR has at least two physiological functions in PCC7002. The observation provides a new perspective for the interplays of C and S cycles.

中文翻译：

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粘球菌 菌株PCC7002使用硫化物：奎宁氧化还原酶将外源性硫化物解毒，并将内源性硫化物转化为细胞中的硫化物硫。

由于农业和水产养殖活动产生的过量养分，沿海地区可能发生富营养化和脱氧，导致硫化物积聚。蓝细菌作为光合作用的原核生物，在海洋碳固定中起着重要作用。尽管某些蓝细菌可以在厌氧条件下将硫化物用作光合作用的电子供体，但对于它们如何在需氧条件下与硫化物相互作用的了解甚少。在这项研究中，我们报告说Synechococcus sp。菌株PCC7002（PCC7002），带有编码硫化物：醌氧化还原酶（SQR）的sqr基因，将自生的硫化物氧化为SO，以过硫化物和多硫化物的形式存在于细胞中。Δsqr突变体含有较少的细胞S0，并且具有参与光合作用的关键基因的表达增加，但是在共培养中，它的竞争力不如野生型。此外，具有SQR和过硫化物双加氧酶（PDO）的PCC7002氧化了外源性硫化物以耐受高含量的硫化物。因此，即使在有氧条件下，SQR对蓝细菌也有一些好处，这说明了SQR在蓝细菌中的普遍存在。重要信息蓝细菌是通过海洋中的光合作用进行初级生产的主要力量。海洋蓝细菌PCC7002积极参与硫化物代谢。它使用SQR解毒外源性硫化物，使其在富含硫化物的环境中比其Δsqr突变体存活得更好。PCC7002还使用SQR将内生的硫化物氧化为S0，这是正确参与光合作用的关键基因表达所必需的。因此，SQR在PCC7002中至少具有两个生理功能。