Succession of methanotrophs in oxygen–methane counter-gradients of flooded rice paddies

Little is known about population dynamics and contribution of specific taxa to methane oxidation in flooded rice paddies. In this article we investigate the succession of methanotrophs in oxygen–methane counter-gradients. We used a gradient microcosm system that simulates oxic–anoxic interfaces of a water-saturated paddy soils, and measured pmoA-based (gene encoding particulate methane monooxygenase) terminal restriction fragment length polymorphism (T-RFLP) profiles at both the transcription (mRNA) and the population (DNA) levels. The DNA T-RFLP profiles indicated that the methanotrophic community present clearly differed from the active methanotrophic community. We observed a succession of the methanotrophic community over time without any direct effect of pore water chemistry on the community structure. Both the total population and the active subpopulation changed with time, whereas methane oxidation rates remained nearly constant. Hence, we suggest that a diverse microbial seed bank of methanotrophs is important in maintaining the function in a dynamic ecosystem.