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.

ABSTRACT Early electron microscopy and more recent studies in our laboratory of Bdellovibrio bacteriovorus cells indicated the presence of narrow fibers at the nonflagellar pole of this unusual predatory bacterium. Analysis of the B. bacteriovorus HD100 genome showed a complete set of genes potentially encoding type IV pili and an incomplete gene set for Flp pili; therefore, the role of type IV pili in the predatory life cycle of B. bacteriovorus HD100 was investigated. Alignment of the predicted PilA protein with known type IV pilins showed the characteristic conserved N terminus common to type IVa pilins. The pilA gene, encoding the type IV pilus fiber protein, was insertionally inactivated in multiple Bdellovibrio replicate cultures, and the effect upon the expression of other pilus genes was monitored by reverse transcriptase PCR. Interruption of pilA in replicate isolates abolished Bdellovibrio predatory capability in liquid prey cultures and on immobilized yellow fluorescent protein-labeled prey, but the mutants could be cultured prey independently. Expression patterns of pil genes involved in the formation of type IV pili were profiled across the predatory life cycle from attack phase predatory Bdellovibrio throughout the intraperiplasmic bdelloplast stages to prey lysis and in prey-independent growth. Taken together, the data show that type IV pili play a critical role in Bdellovibrio predation.

ABSTRACT In Helicobacter pylori 26695, a gene annotated HP1575 encodes a putative protein of unknown function which shows significant similarity to part of the C-terminal domain of the flagellar export protein FlhB. In Salmonella enterica , this part (FlhB CC ) is proteolytically cleaved from the full-length FlhB, a processing event that is required for flagellar protein export and, thus, motility. The role of FlhB (HP0770) and its C-terminal homologue HP1575 was studied in H. pylori using a range of nonpolar deletion mutants defective in HP1575, HP0770, and the CC domain of HP0770 (HP0770 CC ). Deletion of HP0770 abolished swimming motility, whereas mutants carrying a deletion of either HP1575 or HP0770 CC retained their ability to swim. An H. pylori strain containing deletions in both HP1575 and HP0770 CC was nonmotile and did not produce flagella, suggesting that at least one of the two proteins had to be present for flagellar assembly to occur. Indeed, motility was restored when HP1575 was reintroduced into this strain immediately downstream of, but not fused to, the truncated HP0770 gene. Thus, HP1575 can functionally replace HP0770 CC in this background. Like FlhB in S. enterica , HP0770 appeared to be proteolytically processed at a conserved NPTH processing site. However, mutation of the proline contained within the NPTH site of HP0770 did not affect motility and flagellar assembly, although it clearly interfered with processing when the protein was heterologously produced in Escherichia coli .

The predatory bacterium Bdellovibrio bacteriovorus swims rapidly by rotation of a single, polar flagellum comprised of a helical filament of flagellin monomers, contained within a membrane sheath and powered by a basal motor complex. Bdellovibrio collides with, enters and replicates within bacterial prey, a process previously suggested to firstly require flagellar motility and then flagellar shedding upon prey entry. Here we show that flagella are not always shed upon prey entry and we study the six fliC flagellin genes of B. bacteriovorus, finding them all conserved and expressed in genome strain HD100 and the widely studied lab strain 109J. Individual inactivation of five of the fliC genes gave mutant Bdellovibrio that still made flagella, and which were motile and predatory. Inactivation of the sixth fliC gene abolished normal flagellar synthesis and motility, but a disordered flagellar sheath was still seen. We find that this non-motile mutant was still able to predate when directly applied to lawns of YFP-labelled prey bacteria, showing that flagellar motility is not essential for prey entry but important for efficient encounters with prey in liquid environments.