The effect of pH on Marinobacter hydrocarbonoclasticus denitrification pathway and nitrous oxide reductase
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ORIGINAL PAPER
The effect of pH on Marinobacter hydrocarbonoclasticus denitrification pathway and nitrous oxide reductase Cíntia Carreira1,2 · Rute F. Nunes1 · Olga Mestre1 · Isabel Moura2 · Sofia R. Pauleta1 Received: 27 March 2020 / Accepted: 12 August 2020 © Society for Biological Inorganic Chemistry (SBIC) 2020
Abstract Increasing atmospheric concentration of N 2O has been a concern, as it is a potent greenhouse gas and promotes ozone layer destruction. In the N-cycle, release of N 2O is boosted upon a drop of pH in the environment. Here, Marinobacter hydrocarbonoclasticus was grown in batch mode in the presence of nitrate, to study the effect of pH in the denitrification pathway by gene expression profiling, quantification of nitrate and nitrite, and evaluating the ability of whole cells to reduce NO and N2O. At pH 6.5, accumulation of nitrite in the medium occurs and the cells were unable to reduce N2O. In addition, the biochemical properties of N 2O reductase isolated from cells grown at pH 6.5, 7.5 and 8.5 were compared for the first time. The amount of this enzyme at acidic pH was lower than that at pH 7.5 and 8.5, pinpointing to a post-transcriptional regulation, though pH did not affect gene expression of N 2O reductase accessory genes. N 2O reductase isolated from cells grown at pH 6.5 has its catalytic center mainly as CuZ(4Cu1S), while that from cells grown at pH 7.5 or 8.5 has it as CuZ(4Cu2S). This study evidences that an in vivo secondary level of regulation is required to maintain N2O reductase in an active state. Graphic abstract
Keywords Denitrification · Nitrous oxide reductase · “CuZ” center · Acidic pH · Marinobacter hydrocarbonoclasticus · Marine bacteria Electronic supplementary material The online version of this article (https://doi.org/10.1007/s00775-020-01812-0) contains supplementary material, which is available to authorized users. * Sofia R. Pauleta [email protected] Extended author information available on the last page of the article
Introduction Nitrous oxide (N2O) has an estimated half-life of 120 years in the atmosphere, being one of the major contributors to the greenhouse effect [1, 2]. Global analysis of N2O emissions
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highlights that there has been an enhancement of this gas in the atmosphere in the last century due to biomass burning, combustion of fossil fuel and in particular from agriculture through the use of synthetic nitrogenous fertilizers [3–5]. In fact, 60% of N2O emissions come from soils [5]. Nevertheless, a perturbation in nitrogen balance of marine systems has also been observed due to the increase presence of fertilizers in drainage waters and inorganic nitrogen leaching to coastal seawaters and oceans [2, 6]. An increase in nitrogen-based compounds together with low oxygen tensions in these environments induce anaerobic metabolic processes, such as denitrification and anammox (pathways of the nitrogen cycle). In fact, many bacteria can switch from respiring oxygen to respiring nitrate ( NO3−) and using N2O as
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