FEEDING-BEHAVIOR AND GRAZING IMPACTS OF A EUPLOTES SP. ON ATTACHED BACTERIA

The locomotory and feeding responses of a Euplotes sp. to attached pop ulations of Vibrio natriegens and Pseudomonas fluorescens in a continu ous flow system were analyzed by computer image analysis of video micr oscopy recordings. Upon entry into the chamber, the ciliates moved in long continuous arcs 300 mu m in length during which time no bacteria were consumed. As feeding began, the average path length shortened, th e arcs became tighter, and the ciliates changed direction more frequen tly. The feeding activity of the Euplotes appeared to be gregarious, b eing concentrated in patches within the biofilm of attached bacteria. It was also noted that the feeding effort targeted patches previously visited by other Euplotes, despite reduced bacterial density relative to the surrounding field of attached bacteria. This focused and intens e feeding activity resulted in localized zones of nearly complete clea rance within the attached bacterial populations. Loss of bacteria and averaged ciliate presence within feeding patches were determined from digitized time series images and discrimination thresholds for particl e size. These data were used to determine grazing rates indicating tha t Euplotes sp. removed 120 V. natriegens cells.ciliate(-1).h(-1) and u p to 882 P. fluorescens cells.ciliate(-1).h(-1). However, surface clea rance rates for Euplotes sp. grazing on V. natriegens and P. fluoresce ns were 0.02 and 0.03 mm(2.)ciliate(-1).h(-1), respectively, indicatin g that surface grazing pressure was fairly consistent within the patch es of intense feeding activity. The effect of such intense localized f eeding behaviour on attached or biofilm bacteria would be to increase spatial and temporal heterogeneity within biofilms.