|Abstract or Summary
- The genus Bdellovibrio is characterized by the unique ability to
parasitize and enter gram-negative host bacteria. This interaction
leads to the consumption and death of the host cell as the Bdellovibrio
grows and divides into progeny. Little is known about the metabolism
of host cell components by Bdellovibrio. The possibility that Bdellovibrio
utilizes host cell RNA, DNA, and protein was investigated.
Initial studies involved the growth of host-independent (H-I)
bdellovibrios in a growth limiting medium supplemented with a single
potential metabolite. Protein, host extracts, and autoclaved host
cells stimulated growth. Purified RNA or DNA in concentrations up
to 0. 5 mg/ml did not stimulate H-I Bdellovibrio growth as measured
by increase in viable count. Subsequent studies with labeled amino
acids and nucleosides indicated that Bdellovibrio does utilize these
substances. An amino acid mixture was incorporated into Bdellovibrio
macromolecules; from 1 to 4% of the added label was taken up and used anabolically. The amino acids glycine and aspartate are not
used for the synthesis of nucleic acid precursors, Although from 1%
to 10% of these added amino acids was incorporated into cold TCA
precipitable material, none of the label was hot TCA soluble. The
nucleosides, adenosine and guanosine, were incorporated into hot TCA
soluble material; from 8. 5% to 42. 7% of these nucleosides were
incorporated from the culture medium.
Exocellular enzymes of Bdellovibrio were briefly examined.
Exoproteases are well documented (7), but nuclease activity had not
been previously shown to exist. These enzymes were used to prepare
hydrolysates of host RNA, DNA, and protein.
Labeled RNA, DNA, and protein, prepared from host cells and
hydrolyzed by Bdellovibrio enzymes, were incorporated into Bdellovibrio
macromolecules, From 4% to 6% of the added protein hydrolysate
was incorporated into cold TCA precipitable material. From 8%
to 18% of the hydrolyzed RNA was utilized anabolically by Bdellovibrio.
Of the hydrolyzed DNA, 10% to 14% was incorporated by Bdellovibrio.
DNA-RNA hybridization studies have shown that during the
infectious life cycle prelabeled host cell RNA breaks down and
Bdellovibrio incorporates the products into its RNA. The specific
activity of the labeled RNA generally decreases throughout the life
cycle. At the beginning of the experiment no radioactive RNA binds to
the Bdellovibrio filters. At the completion of the burst (5 hours) almost as much RNA is homologous to Bdellovibrio DNA as had been
homologous to E. coli DNA at the start of infection. Concomitant with
this is the reduction of homologous RNA to E. coli DNA to about 1% of
the preinfection level.