Studies on a Bacterial Community in a River, with Special Reference to an Epilithon Bacterial Community on Riverbed Stones

KAZUKO MORIKAWA
1988 Bulletin of Japanese Society of Microbial Ecology  
A river is an excellent open flow system where water flows continuously. Nevertheless, a comparatively stable microbial layer (epilithon) forms and adheres to stones in the riverbed. The bacterial population in the epilithon is known to play an important role in the river ecosystem, and clarification of the bacterial generic composition is the first step in understanding the mechanism of this role. An urban river supplies many kinds of organic substances for heterotrophic bacteria; however, in
more » ... teria; however, in upper regions substrate for bacterial growth seems to be limited primarily to materials derived from algae. The sunny open riverbed of the Tamagawa River at Unazawa was therefore chosen as the main study site for this investigation. The epilithon of the riverbed increases and exfoliates. The number of bacteria and the amount of chlorophyll a in the epilithon showed a high correlation coefficient; thus, the bacteria and algae seemed to coexist. Three predominant bacterial groups were distinguished at Unazawa. One of them, Cytophaga sp. seemed to increase in accordance with the growth of specific algae. Three categories of generic groups were recognized: (i) those bacteria existing primarily in river water, (ii) those mainly inhabiting the epilithon, and (iii) those consistently isolated from both epilithon and river water. Changes in the bacterial generic composition were studied in the process of biofilm formation on an artificial substrata submerged in the river water. Greater variation in generic composition in platable colonies was obtained on the upper surface of this substratum than on the lower surface; this variation corresponded to the variation in algal biomass. Accompanying the
doi:10.1264/microbes1986.2.67 fatcat:vrmoupidszf6rkguoiuju5bkna