Antagonistic association of the chlorellavorus bacterium (“Bdellovibrio” chlorellavorus) withChlorella vulgaris

The chlorellavorus bacterium (Bdellovibrio chlorellavorus Gromov and Mamkaeva 1972) attaches to (but does not enter) cells of the unicellular green alga,Chlorella, which is killed and the cell contents of which are digested. The bacterium is pleomorphic (vibrios 0.3 μm wide; cocci 0.6 μm wide), and it has a Gram-negative cell wall structure pili, and a single, unsheathed, polar flagellum. Division may occur only in bacterial cells attached to algal cells, an attachment mediated by a pad (245×36 nm) of unknown composition. Bacterial growth occurs only in the presence of liveChlorella cells, and not on various bacteriological culture media, killedChlorella cells, 4 strains ofPrototheca, or 24 strains of Gram-negative bacteria. The chlorellavorus bacterium may not require algal protein synthesis, since the bacterium grows on algae in the presence of cycloheximide (30 μg/ml). Although the DNA base composition of the chlorellavorus bacterium (50 mol % G+C) is in the same range asBdellovibrio bacteriovorus, its ultrastructure, developmental cycle, host range, and format of its intermicrobial association all distinguish the chlorellavorus bacterium from members of the genusBdellovibrio.