Microbial abundance and activity of nitrite/nitrate-dependent anaerobic methane oxidizers in estuarine and intertidal wetlands: Heterogeneity and driving factors
Authors: Chen Feiyang , Zheng Yanling , Hou Lijun 
Published: March 2022

&lt;p&gt;Nitrite/nitrate-dependent anaerobic methane oxidation (n-DAMO) is a crucial link between carbon and nitrogen cycles in estuarine and coastal ecosystems. However, the factors that affect the heterogeneous variability in n-DAMO microbial abundance and activity across estuarine and intertidal wetlands remain unclear. This study examined the spatiotemporal variations in n-DAMO microbial abundance and associated activity in different estuarine and intertidal habitats via quantitative PCR and &lt;sup&gt;13&lt;/sup&gt;C stable isotope experiments. The results showed that &lt;em&gt;Candidatus '&lt;/em&gt;Methylomirabilis oxyfera&lt;em&gt;' &lt;/em&gt;(&lt;em&gt;M. oxyfera&lt;/em&gt;)-like DAMO bacteria and &lt;em&gt;Candidatus '&lt;/em&gt;Methanoperedens nitroreducens&lt;em&gt;' &lt;/em&gt;(&lt;em&gt;M. nitroreducens&lt;/em&gt;)-like DAMO archaea cooccurred in estuarine and intertidal wetlands, with a relatively higher abundance of the &lt;em&gt;M. oxyfera&lt;/em&gt;-like bacterial &lt;em&gt;pmoA&lt;/em&gt; gene (4.0&amp;#215;10&lt;sup&gt;6&lt;/sup&gt;-7.6&amp;#215;10&lt;sup&gt;7&lt;/sup&gt; copies g&lt;sup&gt;-1&lt;/sup&gt; dry sediment) than the &lt;em&gt;M. nitroreducens&lt;/em&gt;-like archaeal &lt;em&gt;mcrA&lt;/em&gt; gene (4.5&amp;#215;10&lt;sup&gt;5&lt;/sup&gt;-9.4&amp;#215;10&lt;sup&gt;7 &lt;/sup&gt;copies g&lt;sup&gt;-1&lt;/sup&gt; dry sediment). The abundance of the &lt;em&gt;M. oxyfera&lt;/em&gt;-like bacterial &lt;em&gt;pmoA&lt;/em&gt; gene was closely associated with sediment pH and ammonium (&lt;em&gt;P&lt;/em&gt;&lt;0.05), while no significant relationship was detected between &lt;em&gt;M. nitroreducens&lt;/em&gt;-like archaeal&lt;em&gt; mcrA&lt;/em&gt; gene abundance and the measured environmental parameters (&lt;em&gt;P&lt;/em&gt;&gt;0.05). High n-DAMO microbial activity was observed, which varied between 0.2 and 84.3 nmol &lt;sup&gt;13&lt;/sup&gt;CO&lt;sub&gt;2&lt;/sub&gt; g&lt;sup&gt;-1&lt;/sup&gt; dry sediment day&lt;sup&gt;-1 &lt;/sup&gt;for nitrite-DAMO bacteria and between 0.4 and 32.6 nmol &lt;sup&gt;13&lt;/sup&gt;CO&lt;sub&gt;2&lt;/sub&gt; g&lt;sup&gt;-1&lt;/sup&gt; dry sediment day&lt;sup&gt;-1 &lt;/sup&gt;for nitrate-DAMO archaea. The total n-DAMO potential tended to be higher in the warm season and in the upstream freshwater and low-salinity estuarine habitats and was significantly related to sediment pH, total organic carbon, Fe(II), and Fe(III) contents (&lt;em&gt;P&lt;/em&gt;&lt;0.05). In addition to acting as an important methane (CH&lt;sub&gt;4&lt;/sub&gt;) sink, n-DAMO microbes had the potential to consume a substantial amount of reactive N in estuarine and intertidal environments, with estimated nitrogen elimination rates of 0.5-224.7 nmol N g&lt;sup&gt;-1&lt;/sup&gt; dry sediment day&lt;sup&gt;-1&lt;/sup&gt;. Overall, our investigation reveals the distribution pattern and controlling factors of n-DAMO bioprocesses in estuarine and intertidal marshes and gains a better understanding of the coupling mechanisms between carbon and nitrogen cycles.&lt;/p&gt;