Cadmium effects on net N(2)O production by the deep-sea isolate Shewanella loihica PV-4

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 N(2)O and its reduction to N(2) is of great relevance since N(2)O is an important greenhouse gas. Metal impacts on net N(2)O production by deep-sea bacteria are, however, currently unexplored. Here, we evaluated the effects of cadmium (Cd) on net N(2)O production by a deep-sea isolate, Shewanella loihica PV-4. We performed a series of Cd exposure incubations in oxic conditions and determined N(2)O fluxes during induced anoxic conditions, as well as the relative expression of the nitrite reductase gene (nirK), preceding N(2)O production, and N(2)O reductase gene (nosZ), responsible for N(2)O reduction. Net N(2)O 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 N(2)O production observed with Cd. The Cd inhibition of net N(2)O 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.