Using a green fluorescent protein gene-labeled p-nitrophenol-degrading Moraxella strain to examine the protective effect of alginate encapsulation against protozoan grazing

A gfp-labeled p-nitrophenol-degrading Moraxella strain G21 was used to stud y grazing of a Tetrahymena thermophila strain in liquid medium. This allowe d visualization of the feeding process. Under an epifluorescent microscope, individual G21 fluorescent cells could be seen in vacuoles within the prot ozoans. Most of the G21 cells appeared to be lysed by T. thermophila and gr een fluorescent protein released from the bacteria yielded brightly fluores cent food vacuoles inside the protozoans. Examination of population dynamic s of a mixed culture of T. thermophila and Moraxella sp. G21 showed that th e protozoan reduced the bacterial density from 7.6 to 5.8 log CFU/ml in 2 d ays. Encapsulating the bacteria in alginate prevented grazing by the protoz oans and the density of G21 cells in the beads increased steadily from abou t 8.3 to 8.9 log CFU/ml in 15 days regardless of the presence of the protoz oans. (C) 2000 Elsevier Science B.V. All rights reserved.