Growth of Amoebae and Flagellates on Bacteria Deposited on Filters

> Abstract Artificial bacterial biofilms were formed by making microwave-irradiated, dual-radioisotope-labelled Vibrio bacteria adhere to 0.4 µm pore size filters with albumin. The rate of release of 3H from thymidine label in these bacteria into the surrounding seawater when protozoa were incubated with the biofilm indicated the predator's grazing rate, and the rate of accumulation of 14C in the predators from leucine label in the bacteria indicated the assimilation rate of the protozoa. The amoeba Vanella septentrionalis consumed 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 for the suspension-feeding flagellate Pteridomonas danica. As a result of their grazing and metabolism these protozoa regenerated about 70-85% of the nutrients present in their food and released these nutrients in the immediate vicinity of the bacterial biofilm. The biomass of the amoeba Vanella was calculated to be 166 pg protein cell-1 during maximum growth and 93 pg protein cell-1 in the stationary phase.