Page 263 - Microbial methane cycling in a warming world From biosphere to atmosphere Michiel H in t Zandt

also found a link between MOB and iron-cycling partners (Geothrix and Geobacter). We also observed aerobic methanotrophs in anoxic thermokarst lake sediments (Chapter 7), which could be rapidly reactivated upon the addition of oxygen and CH4.
Methane-oxidizing bacteria can also thrive under extremely low oxygen conditions by coupling fermentative metabolism to nitrate reduction (Kits et al. 2015; Kits, Klotz and Stein 2015; Oswald et al. 2016; Gilman et al. 2017). In addition, a switch to mixed-acid fermentation and H2 production, as observed in Methylobacter species, provides a potential adaptation to oxygen limitation (van Grinsven et al. 2020). In our co-cultivation experiment of Methylocystaceae (Methylosinus sporium and Methylocystis sp.) with Methanosarcina barkeri under oxygen- limited conditions, we observed the potential of Methylocystaceae to metabolize acetate (Chapter 10). Interestingly, the Methylocystis sp. in the co-culture was most identical to M. rosea. A study of Im et al. (2011) showed that M. rosea strain SB2 was able to grow on acetate. However, this trait seems to be highly strain-specific, as it was not observed for M. rosea strain SV97T.
A study by Zheng et al. (2020) demonstrated CH4-dependent ferrihydrite reduction in Methylosinus (Alphaproteobacteria) and Methylomonas (Gammaproteobacteria). The use of minerals as alternative electron acceptors likely provides an important survival strategy under anoxic conditions. Interestingly, in our study on permafrost soils (Chapter 9), the relatively high concentrations of Fe(II) and Fe(III) could additionally provide alternative electron acceptors for aerobic methanotrophs.
Under these anoxic survival strategies, aerobic methanotrophs do likely not oxidize CH4. Therefore, an increase in anoxic conditions will likely strongly increase CH4 fluxes (Conrad 2020b; Zhao et al. 2020). However, these findings highlight the flexibility of methanotrophic bacteria, which are able to rapidly adapt to changing environmental conditions. Within the bigger picture, this implies that aerobic methanotrophs can quickly regain metabolic activity when facing high substrate availability.
Current sequencing methods and efforts need to be critically evaluated
Sequencing stands at the basis of most current environmental microbial studies, from ecosystem dynamics to pure culture work. In order to make sure we obtain the required answers through sequencing efforts, we have to constantly evaluate our current sequencing approaches and
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