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20 Bdellovibrio: Lone Hunter “Cousin” of the “Pack Hunting” Myxobacteria, Page 1 of 2
< Previous page | Next page > /docserver/preview/fulltext/10.1128/9781555815677/9781555814205_Chap20-1.gif /docserver/preview/fulltext/10.1128/9781555815677/9781555814205_Chap20-2.gifAbstract:
This chapter describes about the isolation of Bdellovibrio and myxobacteria from similar soil environments, and the employment of an arsenal of hydrolytic enzymes to kill and digest other bacteria to provide for their own growth and division. It concentrates on the ecology and motility systems of Bdellovibrio, followed by an overview of the hydrolytic enzymes used in prey digestion. It is clear that the nonobligately symbiotic or parasitic, predatory bacteria like Bdellovibrio and Myxobacteria have large genomes akin to those of heterotrophs; thus, determining whether transfer of predatory gene islands is responsible for apparently quite diverse bacteria adapting to fit certain predatory niches is not trivial and can ultimately be answered only by full comparative analysis of multiple predatory genomes, although there is little evidence of recent horizontal gene transfer in the Bdellovibrio bacteriovorus HD100 genome. Gliding motility genes are implicated in myxococcal motility, but these systems seem to be not present in Bdellovibrio, or they were made redundant so long ago that the genes involved are no longer recognizable as such. Homology searches found no significant homologues of Myxococcus genes involved in gliding. Bdellovibrio preys upon only gram-negative bacteria, albeit a wide range of these, as it penetrates the outer layers and enters the periplasmic space of its prey. By far the largest group of hydrolases in both bacteria is proteases; this probably reflects the importance to predatory bacteria in breaking down prey proteins for uptake and consumption by the predator.
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The predatory life cycle and host-independent growth phases of Bdellovibrio.
Transmission electron micrographs of B. bacteriovorus attaching to E. coli DFB225 prey (A) and B. bacteriovorus forming a bdelloplast and preying upon E. coli DFB225 (B). Bars, 1 μm. Both stained with 1% phosphotungstic acid (pH7).
Ecological, genomic, and phylogenetic relationships between the type strains of Bdellovibrio and the myxobacteria.
Comparison of the operon structure of pil genes in Myxococcus and Bdellovibrio. (A) Organization of Myxococcus pil genes, taken from Wall and Kaiser, 1999 . (B) pil genes are scattered around the Bdellovibrio genome, but a Myxococcus-like, possibly ancestral, organization can be seen with the gene order being conserved. The starred annotated pilT within the operon is a good homologue, but Bd3852 on the left is a better homologue, suggesting a duplication event. Bdellovibrio does not have significant homologues of pilR2/S2.
Comparison (not to scale) of motility systems in Bdellovibrio (A) and myxobacterial (B) cells. The cytoplasm is shown in white and the periplasm in gray in each. EPS, extracellular polysaccharide.
Pilus genes found in Myxococcus compared to the Bdellovibrio genome, using reciprocal homology searches and protein level alignment to determine appropriate homologues
Predicted location and classes of Myxococcus and Bdellovibrio proteases a