The plasmid pSa was found to mobilize the genes for simazine degradation (smz) of the rhizosphere bacterium Herbaspirillum sp.В601 by forming hybrid pSa-Smz plasmids. Independent migration of smz genes into various loci of genome during transfer and elimination of the hybrid plasmids indicated that the genes were parts of a «catabolic island» which could be unstable under certain conditions.

Keywords: Herbaspirillum, simazine, biodegradation, smz genes, catabolic island.