Lysis of Gram-Negative Bacteria by Host-Independent Ectoparasitic Bdellovibrio bacteriovorus Isolates

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Abstract
Methods of isolation and nutritional requirements of B. bacteriovorus strains capable of growth on host-free media are described. Such strains retained their parasitic capacities for various gram-negative bacteria after many transfers in host-free media. In parasite + host suspensions the spectrum of host specificity of various bdellovibrio strains was considerably wider than that obtained by examination for plaques on host lawns. The growth conditions therefore affect the capacity of the bdellovibrios to attach to and lyse host organisms. A proteolytic exoenzyme formed by certain bdellovibrio strains digested heat-killed, acid-treated or EDTA-treated host organisms, but did not affect intact host organisms. High phosphate concentrations inhibited exoenzyme activity. The morphological sequence of lysis induced by exoenzyme-forming parasitic bdellovibrio strains suggested that this lysis was a two-stage process: the first stage was specific attachment of bdellovibrios with damage to the cell wall of the host organisms; the second stage was non-specific digestion of cellular components by exoenzyme produced by the bdellovibrios.