Abstract
Bdellovibrio bacteriovorus is a Gram-negative bacterium that is a pathogen of other Gram-negative bacteria, including many bacteria which are pathogens of humans, animals and plants. As such Bdellovibrio has potential as a biocontrol agent, or living antibiotic. B. bacteriovorus HD100 has a large genome and it is not yet known which of it encodes the molecular machinery and genetic control of predatory processes. We have tried to fill this knowledge-gap using mixtures of predator and prey mRNAs to monitor changes in Bdellovibrio gene expression at a timepoint of early-stage prey infection and prey killing in comparison to control cultures of predator and prey alone and also in comparison to Bdellovibrio growing axenically (in a prey-or host independent “HI” manner) on artificial media containing peptone and tryptone. From this we have highlighted genes of the early predatosome with predicted roles in prey killing and digestion and have gained insights into possible regulatory mechanisms as Bdellovibrio enter and establish within the prey bdelloplast. Approximately seven percent of all Bdellovibrio genes were significantly up-regulated at 30 minutes of infection- but not in HI growth- implicating the role of these genes in prey digestion. Five percent were down-regulated significantly, implicating their role in free-swimming, attack-phase physiology. This study gives the first post- genomic insight into the predatory process and reveals some of the important genes that Bdellovibrio expresses inside the prey bacterium during the initial attack.
Highlights
Bdellovibrio bacteriovorus are predatory delta Proteobacteria which invade the periplasm of other Gram-negative bacteria and attach to their inner membrane forming an infective structure called a bdelloplast
In this structure the prey peptidoglycan is modified so the bdelloplast does not burst, but accommodates the growing predator; the cellular constituents of the prey bacterium are degraded to monomers which are taken up and used to fuel growth and division of the Bdellovibrio (Figure 1)
The gene products required for the initial invasive predatory processes have not been extensively studied but the genome sequencing of B. bacteriovorus HD100 [1] revealed a genome of 3.85Mb, including a core genome similar to that of non-predatory bacteria and some 40% of the genome comprising a potential predicted ‘‘predatosome’’ of genes, encoding both hydrolytic products that may be employed in prey degradation, and genes that may be required for host predation and are not conserved across the Proteobacteria
Summary
Bdellovibrio bacteriovorus are predatory delta Proteobacteria which invade the periplasm of other Gram-negative bacteria and attach to their inner membrane forming an infective structure called a bdelloplast. In this structure the prey peptidoglycan is modified so the bdelloplast does not burst, but accommodates the growing predator; the cellular constituents of the prey bacterium are degraded to monomers which are taken up and used to fuel growth and division of the Bdellovibrio (Figure 1). By combining careful semi-synchronous culturing of prey and predators with RNA preparations we have been able to study the transcriptome of Bdellovibrio at 30 minutes of predatory interaction, a key point in predation, as the Bdellovibrio enters the prey periplasm and establishes itself by attaching to the prey cytoplasmic membrane and killing the prey. We were able to define genes that were expressed in HI growth and not in either predatory attack phase or 30 minutes of prey-invasion
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