Graduate Thesis Or Dissertation
 

Bdellovibrio metabolism of host macromolecules

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  • 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.
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Déclaration de droits
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