Interdisciplinary Centre of Marine and Environmental Research (CIIMAR), University of Porto, Matosinhos 4450-208, Portugal.
Faculty of Biotechnology, Catholic University of Portugal, Porto 4169-005, Portugal.
FEMS Microbiol Lett. 2023 Jan 17;370. doi: 10.1093/femsle/fnad047.
Deep-sea mining may lead to the release of high concentrations of metals into the surrounding seabed, which can disturb important ecosystem functions provided by microbial communities. Among these, the production of N2O and its reduction to N2 is of great relevance since N2O is an important greenhouse gas. Metal impacts on net N2O production by deep-sea bacteria are, however, currently unexplored. Here, we evaluated the effects of cadmium (Cd) on net N2O production by a deep-sea isolate, Shewanella loihica PV-4. We performed a series of Cd exposure incubations in oxic conditions and determined N2O fluxes during induced anoxic conditions, as well as the relative expression of the nitrite reductase gene (nirK), preceding N2O production, and N2O reductase gene (nosZ), responsible for N2O reduction. Net N2O production by S. loihica PV-4 exposed to Cd was strongly inhibited when compared to the control treatment (no metal). Both nirK and nosZ gene expression were inhibited in reactors with Cd, but nirK inhibition was stronger, supporting the lower net N2O production observed with Cd. The Cd inhibition of net N2O production observed in this study poses the question whether other deep-sea bacteria would undergo the same effects. Future studies should address this question as well as its applicability to complex communities and other physicochemical conditions, which remain to be evaluated.
深海采矿可能导致金属大量释放到周围海底，从而干扰微生物群落提供的重要生态系统功能。其中，N2O 的产生及其还原为 N2 具有重要意义，因为 N2O 是一种重要的温室气体。然而，目前尚未研究金属对深海细菌净 N2O 产生的影响。在这里，我们评估了镉 (Cd) 对深海分离株希瓦氏菌 PV-4 净 N2O 产生的影响。我们在好氧条件下进行了一系列 Cd 暴露培养，并在诱导缺氧条件下测定了 N2O 通量，以及在 N2O 产生之前负责 N2O 还原的亚硝酸盐还原酶基因 (nirK) 和 N2O 还原酶基因 (nosZ) 的相对表达。与对照处理（无金属）相比，暴露于 Cd 的 S. loihica PV-4 的净 N2O 产生受到强烈抑制。Cd 抑制了反应器中 nirK 和 nosZ 基因的表达，但 nirK 的抑制更强，这支持了在 Cd 存在下观察到的净 N2O 产生减少。本研究中观察到的 Cd 对净 N2O 产生的抑制提出了一个问题，即其他深海细菌是否会经历同样的影响。未来的研究应该解决这个问题及其在复杂群落和其他物理化学条件下的适用性，这些条件仍有待评估。
