Some physiological properties and a number of heterotrophic bacteria inhabiting the surface of the root system of the common reed (Phragmites australis [Cav.] Trin. ex Steudel) were studied in two different types of bottom sediments (sandy and silty), and the bacteria were identified. For comparative purposes, samples of the bottom sediments from the sites where the reed grew were subjected to microbiological tests. It was found that the number of bacteria growing on the root system of the common reed and those inhabiting the types of bottom sediments tested increased from spring to summer and then decreased in autumn. On the surface of the rhizomes of the reed growing in silty sediments, a higher number of bacteria was always noted than on the surface of rhizomes growing in sandy sediments. Also, the number of heterotrophic bacteria in samples of bottom sediments was always higher in silty sediments than in sandy sediments. Lipo-, proteo- and amylolytic bacteria and bacteria capable of producing ammonia from organic compounds were dominant among all the isolated strains. The lowest numbers were found of chitinolytic bacteria and those that form hydrogen sulphide from organic compounds. Strains isolated in spring - both from the root system of the plant and from the samples of sediments - were potentially the most active physiologically. As a result of the identification of the isolated bacterial strains, it was found that bacteria from the Arthrobacter-Corynebacterium group and the Achromobacter genus are dominant in the root system of the common reed and in sandy and silty sediments.