Aquatic plant surface as a niche for methanotrophs

This study investigated the potential local CH(4) sink in various plant parts as a boundary environment of CH(4) emission and consumption. By comparing CH(4) consumption activities in cultures inoculated with parts from 39 plant species, we observed significantly higher consumption of CH(4) associated with aquatic plants than other emergent plant parts such as woody plant leaves, macrophytic marine algae, and sea grass. In situ activity of CH(4) consumption by methanotrophs associated with different species of aquatic plants was in the range of 3.7–37 μmol·h(−1)·g(−1) dry weight, which was ca 5.7–370-fold higher than epiphytic CH(4) consumption in submerged parts of emergent plants. The qPCR-estimated copy numbers of the particulate methane monooxygenase-encoding gene pmoA were variable among the aquatic plants and ranged in the order of 10(5)–10(7) copies·g(−1) dry weight, which correlated with the observed CH(4) consumption activities. Phylogenetic identification of methanotrophs on aquatic plants based on the pmoA sequence analysis revealed a predominance of diverse gammaproteobacterial type-I methanotrophs, including a phylotype of a possible plant-associated methanotroph with the closest identity (86–89%) to Methylocaldum gracile.