A New Method for Isolating Host-Independent Variants of Bdellovibrio bacteriovorus Using E. coli Auxotrophs

Bdellovibrios are Gram-negative bacteria that are characterized by predatory behavior. Although Bdellovibrios exhibit an obligatory parasitic life cycle, it is possible to isolate Bdellovibrio variants that no longer require host cells for their growth. In this study, a new method for isolating Bdellovibrio bacteriovorus host-independent (HI) variants was developed. Filtered B. bacteriovorus prey cells were cultured with E. coli diaminopimelic acid (DAP) auxotrophs as host cells. Thereafter, the lysate was plated on DAP minus media, allowing only HI colonies to develop. Using this method, we have isolated numerous HI variants and demonstrated that the emergence of HI variants may be occurring at a higher frequency than was previously suggested.