Abstract
Soil microorganisms require metabolic strategies to cope with the significant variations in oxygen availability that occur in soil over a range of time scales. Characterised ammonia-oxidisers within Thaumarchaeota Groups 1.1a and 1.1b are aerobic, but the oxygen preference and metabolic potential of deeply-rooted Thaumarchaeota remain unknown, with several studies providing evidence for both aerobic and anaerobic metabolisms. This study therefore aimed to determine the influence of oxygen on the mesophilic Group 1.1c and Group 1.3 thaumarchaeotal community in controlled microcosm experiments conducted using oxic and anoxic Scottish pine forest soils, incubated under oxic or anoxic conditions. While we expected more anaerobic growth metabolism in those peatland soils, we demonstrated growth of multiple aerobic clusters within Group 1.1c Thaumarchaeota and anaerobic growth within Group 1.3 Thaumarchaeota. These findings extend our understanding of the physiology of deeply-rooted mesophilic Thaumarchaeota and provide the first detailed qualitative and quantitative assessment of their growth in soil.
Highlights
Determining the potential of uncultivated soil microorganisms for aerobic and anaerobic metabolism is important for an understanding of ecosystem function in environments with variable oxygen availability (Laanbroek, 2010; Offre et al, 2013)
Temporal changes and growth of these lineages were assessed in two soils incubated under oxic and anoxic conditions, using MiSeq sequencing and quantitative PCR (qPCR) quantification of the thaumarchaeotal 16S rRNA genes
A phylogenetic tree recon structed from 16S rRNA gene sequences of thaumarchaeotal mesophilic clades (Fig. 1) provided strong phylogenetic support for the majority of the nodes, and phylogenetic affiliations were broadly congruent with those previously described (Vico-Oton et al, 2016), with the exception of clades G3.4 to G3.7, which grouped with Bathyarchaeota rather than
Summary
Determining the potential of uncultivated soil microorganisms for aerobic and anaerobic metabolism is important for an understanding of ecosystem function in environments with variable oxygen availability (Laanbroek, 2010; Offre et al, 2013). Oxygen availability is influenced in terrestrial ecosystems by soil depth and water content and oxygen has been advanced as a critical environmental factor leading to niche specialisation and evolution of different soil microorganisms, including Haloarchaea (Nelson-Sathi et al, 2012) and Thaumarchaeota (Ren et al, 2019). Deeply rooted Thaumarchaeota are known to be non-ammonia oxidisers (Weber et al, 2015; Ren et al, 2019) and their metabolism remains underex plored, with availability of a few genomes and a single enrichment culture (Gubry-Rangin et al, 2018; Kato et al, 2019). Other environmental char acteristics, such as pH (Gubry-Rangin et al, 2015), influenced further niche specialisation and evolution of terrestrial ammonia-oxidising Thaumarchaeota
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