Abstract
Bdellovibrio bacteriovorus is a small Gram-negative predatory bacterium that attacks other Gram-negative bacteria, including many animal, human, and plant pathogens. This bacterium exhibits a peculiar biphasic life cycle during which two different types of cells are produced: non-replicating highly motile cells (the free-living phase) and replicating cells (the intracellular-growth phase). The process of chromosomal replication in B. bacteriovorus must therefore be temporally and spatially regulated to ensure that it is coordinated with cell differentiation and cell cycle progression. Recently, B. bacteriovorus has received considerable research interest due to its intriguing life cycle and great potential as a prospective antimicrobial agent. Although, we know that chromosomal replication in bacteria is mainly regulated at the initiation step, no data exists about this process in B. bacteriovorus. We report the first characterization of key elements of initiation of chromosomal replication – DnaA protein and oriC region from the predatory bacterium, B. bacteriovorus. In vitro studies using different approaches demonstrate that the B. bacteriovorus oriC (BdoriC) is specifically bound and unwound by the DnaA protein. Sequence comparison of the DnaA-binding sites enabled us to propose a consensus sequence for the B. bacteriovorus DnaA box [5′-NN(A/T)TCCACA-3′]. Surprisingly, in vitro analysis revealed that BdoriC is also bound and unwound by the host DnaA proteins (relatively distantly related from B. bacteriovorus). We compared the architecture of the DnaA–oriC complexes (orisomes) in homologous (oriC and DnaA from B. bacteriovorus) and heterologous (BdoriC and DnaA from prey, Escherichia coli or Pseudomonas aeruginosa) systems. This work provides important new entry points toward improving our understanding of the initiation of chromosomal replication in this predatory bacterium.
Highlights
Bdellovibrio are small intriguing Gram-negative predatory bacteria that enter and kill other Gramnegative bacteria, including many pathogens, such as Campylobacter, Helicobacter (Markelova, 2010), Escherichia (Varon and Shilo, 1968), Pseudomonas, Salmonella (Iebba et al, 2014), Fusobacterium nucleatum, and Aggregatibacter actinomycetemcomitans (Loozen et al, 2015)
Tiberius strains) and other species belonging to this genus, including Halobacteriovorax marinus SJ and B. exovorus JSS (B. exovorus JSS is not yet included in the DoriC data set created by Gao et al, 2013)
We know that chromosomal replication in bacteria is mainly regulated at the initiation step, nothing is known about this process in B. bacteriovorus
Summary
Bdellovibrio are small intriguing Gram-negative predatory bacteria that enter and kill other Gramnegative bacteria, including many pathogens, such as Campylobacter, Helicobacter (Markelova, 2010), Escherichia (Varon and Shilo, 1968), Pseudomonas, Salmonella (Iebba et al, 2014), Fusobacterium nucleatum, and Aggregatibacter actinomycetemcomitans (a member of oral microbial communities) (Loozen et al, 2015). B. bacteriovorus degrades the host’s macromolecules using different types of hydrolytic enzymes, allowing it to grow and replicate its chromosome (Rendulic et al, 2004). This chromosomal replication is not followed by cell division, but instead leads to the formation of a multinucleoid elongated filamentous. When the resources of the host cell are exhausted, the elongated filament synchronously septates to form usually three to six B. bacteriovorus progeny cells (Fenton et al, 2010) These progeny cells become motile, and are released into the environment through lysis of the host cell. To fully utilize B. bacteriovorus in any of these roles, we must better understand the cell biology of this pathogen at the molecular level
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