Growth of amoebae and flagellates on bacteria deposited on filters

Artificial bacterial biofilms were formed by making microwave-irradiated, d ual-radioisotope-labelled Vibrio bacteria adhere to 0.4 mu m pore size filt ers with albumin. The rate of release of H-3 from thymidine label in these bacteria into the surrounding seawater when protozoa were incubated with th e biofilm indicated the predator's grazing rate, and the rate of accumulati on of C-14 in the predators from leucine label in the bacteria indicated th e assimilation rate of the protozoa. The amoeba Vanella septentrionalis con sumed about 60% of the available bacteria between the 5th and 15th days of incubation with a gross growth efficiency of 22 +/- 6%, compared with about 75% consumption at 29 +/- 8% efficiency for the surface-feeding flagellate Caecitellus parvulus, and about 55% consumption at 16 +/- 5% efficiency fo r the suspension-feeding flagellate Pteridomonas danica. As a result of the ir grazing and metabolism these protozoa regenerated about 70-85% of the nu trients present in their food and released these nutrients in the immediate vicinity of the bacterial biofilm. The biomass of the amoeba Vanella was c alculated to be 166 pg protein cell(-1) during maximum growth and 93 pg pro tein cell(-1) in the stationary phase.