Uncultivated Methylocystis Species in Paddy Soil Include Facultative Methanotrophs that Utilize XXXX .

@entity577 @entity579 @entity598
Methanotrophs are crucial in regulating @entity577 emission from @entity579 field systems. Type II methanotrophs in particular are often observed in high abundance in paddy soil. Some cultivated species of Methylocystis are able to grow on @entity598 in the absence of @entity577 . We hypothesize that the dominant type II methanotrophs in paddy soil might facultatively utilize @entity598 for growth, which we evaluate in the present study. The measurement of @entity577 oxidation rates showed that the methanotrophic activity in paddy soil was inhibited by the addition of @entity598 compared to the continuous supplementation of @entity577 , but the paddy soil maintained the @entity577 oxidation capacity and recovered following @entity577 supplementation. Terminal restriction fragment length polymorphism analysis (T-RFLP) combined with cloning and sequencing of pmoA genes showed that Methylocystis was enriched after incubation with added @entity598 , while the type I methanotrophs Methylocaldum/Methylococcus and Methylobacter were enriched by @entity577 supplementation. A comparison of pmoA sequences obtained in this study with those in the public database indicated that they were globally widespread in paddy soils or in associated with @entity579 roots. Furthermore, we performed stable isotope probing (SIP) of pmoA messenger RNA (mRNA) to investigate the assimilation of (13)C-acetate by paddy soil methanotrophs. RNA-SIP revealed that Methylocystis-related methanotrophs which shared the same genotype of the above enriched species were significantly labelled. It indicates that these methanotrophs actively assimilated the labelled @entity598 in paddy soil. Altogether, these results suggested that uncultivated Methylocystis species are facultative methanotrophs utilizing @entity598 as a secondary carbon source in paddy soil.
