ROLE OF PORE-SIZE LOCATION IN DETERMINING BACTERIAL-ACTIVITY DURING PREDATION BY PROTOZOA IN SOIL

The Predation of a luminescence marked strain of Pseudomonas fluoresce ns by the soil ciliate Colpoda steinii was studied in soil microcosms, Bacterial cells were introduced in either small (neck diameter, <6 mu m) or intermediate-sized (neck diameter, 6 to 30 mu m) pores in the s oil by inoculation at appropriate matric potentials, and ciliates were introduced into large pores (neck diameter, 30 to 60 mu m). Viable ce ll concentrations of bacteria introduced into intermediate-sized pores decreased at a greater rate than those in small pores, with reduction s in bacterial populations being accompanied by an increase in viable cell numbers of the ciliate, The data indicate that the location of ba cteria in small pores provides significant protection from predation. In the absence of C. steinii, the level of metabolic activity of the b acterial population, measured by luminometry, decreased at a greater r ate than cell number, and the Level of luminescence cell(-1) consequen tly decreased. The decrease in levels of luminescence indicates a loss of activity due to starvation, During predation by C. steinii, the le vel of the activity of cells introduced into small pores fell in a sim ilar manner, The level of cell activity was, however, significantly gr eater for cells introduced into intermediate-sized pores, despite thei r greater susceptibility to predation, The data suggest that increased activity arises from a release of nutrients by the predator and the g reater accessibility of bacteria to nutrients in larger pores, Nutrien t amendment of microcosms resulted in increases in bacterial populatio ns to sustained, higher levels, while levels of luminescence increased transiently, The predation of cells introduced into intermediate-size d pores was greater, acid there was also evidence that the level of ac tivity of surviving bacteria was greater for bacteria in intermediate- sized but not small pores.