1998 Volume 69 Issue 6 Pages 570-575
The population of methanotrophs in paddy soils and rice roots was investigated. The most probable number method was carried out by measuring the carbon dioxide production by methanotrophs instead of methane consumption. The number of methanotrophs detected was in the range of 10^5-10^6 MPN g^<-1> dry soil both in flooded rice soil and drained rice soil. Similar or a larger density of methanotrophs was also enumerated in the rice roots. All of the isolated methanotrophs from rice soils were catalase and oxidase-positive, gramnegative, straight rod-shaped and vibrio-shaped bacteria which formed exospores. The methanotrophs could grow in the absence of copper and fixed nitrogen, and possessed a type II intracytoplasmic membrane structure. Type II methanotrophs seem to be dominant in rice soils under copper-deficient, low-oxygen and high-methane conditions.
