Effect of salt stress on aerobic methane oxidation and associated methanotrophs; a microcosm study of a natural community from a non-saline environment

We investigated the response of aerobic methane oxidation and the associated methanotrophs to salt-stress in a NaCl gradient ranging from 0 M (un-amended reference) to 0.6 M NaCl (seawater salinity) using a rice paddy soil as a model system. Salt-stress significantly inhibited methanotrophic activity at > 0.3 M NaCl; at 0.6 M NaCl amendment, methanotrophic activity fully ceased. MiSeq sequencing of the pmoA gene and group-specific qPCR analyses revealed that type Ia methanotroph (Methylobacter) appeared to be favored under salinity up to 0.3 M NaCl, increasing in numerical abundance, while the type Ib was adversely affected. This suggests niche differentiation within members of the gammaproteobacterial methanotrophs. Overall, rice paddy soil methanotrophs showed remarkable resistance to salt-stress.