Anaerobic methane oxidation coupled to denitrification is the dominant methane sink in a deep lake

Abstract

Anaerobic methane oxidation coupled to denitrification, also known as "nitrate/nitrite-dependent anaerobic methane oxidation" (n-damo), was discovered in 2006. Since then, only a few studies have identified this process and the associated microorganisms in natural environments. In aquatic sediments, the close proximity of oxygen-and nitrate-consumption zones can mask n-damo as aerobic methane oxidation. We therefore investigated the vertical distribution and the abundance of denitrifying methanotrophs related to Candidatus Methylomirabilis oxyfera with cultivation-independent molecular techniques in the sediments of Lake Constance. Additionally, the vertical distribution of methane oxidation and nitrate consumption zones was inferred from high-resolution microsensor profiles in undisturbed sediment cores. M. oxyfera-like bacteria were virtually absent at shallow-water sites (littoral sediment) and were very abundant at deep-water sites (profundal sediment). In profundal sediment, the vertical distribution of M. oxyfera-like bacteria showed a distinct peak in anoxic layers that coincided with the zone of methane oxidation and nitrate consumption, a strong indication for n-damo carried out by M. oxyfera-like bacteria. Both potential n-damo rates calculated from cell densities (660-4,890 μmol CH 4 ·m ) were sufficiently high to prevent methane release from profundal sediment solely by this process. Additionally, when nitrate was added to sediment cores exposed to anoxic conditions, the n-damo zone reestablished well below the sediment surface, completely preventing methane release from the sediment. We conclude that the previously overlooked n-damo process can be the major methane sink in stable freshwater environments if nitrate is available in anoxic zones.n-damo | M. oxyfera-like bacteria | NC-10 bacteria | microsensor profiles |

Nitrite-dependent anaerobic methane oxidizing bacteria along the water level fluctuation zone of the Three Gorges Reservoir

“…In the samples taken from six elevations at two different sampling times, molecular evidence showed n-damo bacteria were more likely to be observed at lower elevations, suggesting the lower sites which endured longer flooding time and as a consequence anoxic conditions could be a preferred habitat for M. oxyfera-like bacteria. The results were consistent with previous studies showing that the distribution of M. oxyfera-like bacteria was restricted by the presence of O 2 in natural ecosystems and higher abundances in deeper sediments (Deutzmann et al 2014;Kojima et al 2012) and deep wetland soils Wang et al 2012;Zhou et al 2014;Zhu et al 2015). Unlike other studies, nitrite was not detected in our samples.…”

“…The pmoA gene-based analyses showed that all the sequences from the WLFZ of the TGR clustered together with the sequences from natural environment such as lake sediment Zhu et al 2015) and paddy soil (Wang et al 2012), distantly related to the sequences from culture environments either in China or The Netherlands (Wang et al 2012). Compared with the pmoA sequences from The Netherlands (Zhu et al 2012) and Germany (Deutzmann et al 2014), sequences obtained in this study were more likely to cluster with the environmental samples from China (Shen et al 2015;Zhou et al 2014;Zhu et al 2015).…”

“…oxyfera-like bacteria have been demonstrated to be widely distributed in stable environments such as freshwater sediment (Deutzmann et al 2014;Hu et al 2014a;Norði and Thamdrup 2014) and WWTP sludge Luesken et al 2011). Here, we conducted a study in a water-level fluctuation zone of a reservoir with seasonal flooding.…”

High rates of anaerobic methane oxidation in freshwater wetlands reduce potential atmospheric methane emissions

“…In contrast, a dominant electron acceptor for freshwater AOM has not been identified. Experimental evidence suggest sulphate is not the sole electron acceptor for AOM in freshwater sediments and peat 2,9,15,20 , and AOM in low-sulphate environments has been linked to the reduction of nitrate, nitrite, iron and manganese 4,5,12,13,16,33 . The geochemical and rate profiles in the wetlands studied here support a linkage between SR and AOM.…”

“…Yet, despite low sulphate concentrations, FWW support a dynamic sulphur cycle and high rates of sulphate reduction 9 (SR) are maintained by rapid recycling of reduced sulphur species 10 . Moreover, studies of freshwater AOM have indicated several electron acceptors for methane oxidation, including sulphate 11 , nitrate/nitrite 5,[12][13][14][15] , iron 16 and manganese 17 . Geochemical profiles 4,18,19 , stable isotope geochemistry 16,18,19 , potential methane oxidation assays 2,4,5,20 and long-term enrichments 4 have provided tantalizing evidence of AOM in FWW, but environmentally relevant, in vitro, rate measurements are rare 9 .…”