4.5. Bathy-6 is the dominant subgroup in paddy soils with broad
environmental adaptation
Bathy-6 exhibits a widespread presence in terrestrial
environments, including soil, freshwater sediments, and mangrove
sediments (Pan et al. 2019; Xiang et al. 2017; Zou et al. 2020),
although it has also been detected in certain marine sediments (Yu et
al. 2018). In numerous prior studies, Bathyarchaeia were
primarily observed in anaerobic sediments, characterizing their
anaerobic lifestyle. Notably, Lazar et al. identified genes
encoding enzymes responsible for responding to oxidative stress inBathy-6 (AD8–1), suggesting that Bathy-6 members possess
an ability to adapt to fluctuations in oxygen levels (Lazar et al.
2016). Additionally, Pan et al . reported the presence of
oxygen-dependent metabolic pathways within certain Bathy-6genomes, hinting at a microaerophilic lifestyle for Bathy-6 (Pan
et al. 2020). In our study, the results underscored that Bathy-6stands as the predominant subgroup within the Bathyarchaeia in
all the paddy soils (see Fig. 3a). Flooded paddy soils are characterized
by microaerophilic conditions due to the presence of dissolved oxygen in
soil porewater and oxygen released by rice roots (Chen et al. 2008; Li
et al. 2007). This microoxic nature of paddy soil could elucidate why
the anaerobic Bathyarchaeia subgroups are less prevalent, whileBathy-6 becomes dominant in these environments. Collectively,
these findings collectively indicate that Bathy-6 possesses
wide-ranging environmental adaptability, accommodating both microoxic
and anaerobic conditions. This suggests that Bathy-6 may
potentially play a distinctive role in the evolutionary transition of
life from anaerobic to aerobic environments. Further investigations are
necessary to unravel the mechanisms underpinning the high prevalence of
Bathy-6 in paddy soils.
Furthermore, beyond adapting to diverse oxygen conditions, certainBathy-6 ASVs exhibit the capability to thrive across a broad pH
range from 5 to 8. Bathy-6 demonstrates resilience not only in
oligotrophic marine sediments (Yu et al. 2018) but also in eutrophic
paddy soils with elevated TC. Our network analysis indicated thatBathy-6 members are subdivided into several groups. These results
collectively underscore that Bathy-6 possesses versatile
metabolic capabilities, thrives in diverse habitats, and exhibits varied
lifestyles, consistent with genomic predictions (Pan et al. 2020).
In addition, genomic analyses have revealed the presence of genes
encoding flagella within Bathy-6 (Lazar et al. 2016). All of these
attributes associated with Bathy-6 suggest that it may symbolize
the transition of Bathyarchaeia from a marine to a terrestrial
ecosystem. Moving forward, the comprehensive characterization and
potential role of Bathy-6 in paddy soils and even within the
global ecosystem warrant further research.