IN-SITU LOCALIZATION OF 2 METHANOTROPHIC STRAINS IN THE RHIZOSPHERE OF RICE PLANTS

Methanotrophic bacteria play an important role in regulating the metha ne flux from rice fields to the atmosphere. The abundance of methane-o xidizing bacteria is very heterogeneous along the rice root as reveale d by most probable number (MPN) counts and by scanning confocal laser microscopy (SCLM). Two methanotrophic strains. Rp1 and Rp2, were isola ted from high dilutions of MPN counts from the rhizoplane of rice root s grown in natural rice field soil. We used monoxenically grown rice p lants to relocalize these strains on and in rice roots by means of pol yclonal antisera and 16S rRNA probes. Strain Rp1 was even detected in xylem vessels. The two isolates also were able to recolonize roots gro wn in natural soil under competitive conditions. We found large coloni es in deep grooves on the root surface between iron oxide precipitates . Some cells also were observed in the root cortex. The distribution o f methane-oxidizing bacteria probably reflects the changing availabili ty of methane and oxygen in the rhizosphere. (C) 1998 Federation of Eu ropean Microbiological Societies. Published by Elsevier Science B.V.