Selective grazing of methanotrophs by protozoa in a rice field soil

Abstract

Biological methane oxidation is a key process in the methane cycle of wetland ecosystems. The methanotrophic biomass may be grazed by protozoa, thus linking the methane cycle to the soil microbial food web. In the present study, the edibility of different methanotrophs for soil protozoa was compared. The number of methanotroph-feeding protozoa in a rice field soil was estimated by determining the most-probable number (MPN) using methanotrophs as food bacteria; naked amoebae and flagellates were the dominant protozoa. Among ten methanotrophic strains examined as a food source, seven yielded a number of protozoa comparable with the yield with Escherichia coli [10(4) MPN (g soil dry weight)(-1)], and three out of four Methylocystis spp. yielded significantly fewer numbers [10(2)-10(3) MPN (g soil dry weight)(-1)]. The lower edibility of the Methylocystis spp. was not explained either by their growth phase or by harmful effects on protozoa. Incubation of the soil under methane resulted in a higher number of protozoa actively grazing on methanotrophs, especially on the less-edible group. Protozoa isolated from the soil demonstrated a grazing preference on the different methanotrophs consistent with the results of MPN counts. The results indicate that selective grazing by protozoa may be a biological factor affecting the methanotrophic community in a wetland soil.

Termites Facilitate Methane Oxidation and Shape the Methanotrophic Community

“…However, it is unclear if activity was confined to specific areas in the mound, but there was a tendency for higher activity in the active nest area. While the responses of methanotrophs to N amendments, methane, oxygen, and copper have been widely documented (7,38,59,60), their responses to biotic factors are less well known (8,61). Exemplifying the interaction of methanotrophs with their biotic environment, we provide a first insight into the methanotroph community and evidence for termite-facilitated selection/enrichment of the methanotroph community in M. falciger mounds.…”

Phylogenetic evidence for a new genotype of Acanthamoeba (Amoebozoa, Acanthamoebida)

“…'polyphaga' ATCC 30872, from freshwater (Alves et al 2000); Acanthamoeba sp. strains SE2-6F, E-5C and OB3b-3A, from rice soil (Murase and Frenzel 2008); and Acanthamoeba sp. strain MSG27, from marine sediment (Liu et al 2006).…”

Methanotrophic bacteria in oilsands tailings ponds of northern Alberta

“…Grazing by amoebae has previously been observed in soils with elevated methanotroph populations (Murase and Frenzel, 2008). These two heavily grazed SIP experiments were not included in Supplementary Table S3, as the methanotroph species ratios may have been affected by selective grazing.…”