Revealing the roles of DnaA on the biological characteristics of Brucella and the inflammatory response to Brucella

The Brucella cell cycle, including chromosomal replication and cell
division, is coordinated with the virulence of the bacteria. DnaA, a
chromosomal replication initiator protein, is an essential regulator of
cell cycle progression and is tightly regulated both temporally and
spatially because it is activated only once per cell cycle in bacteria.
Although DnaA exists in many bacteria, the role of DnaA during Brucella
infection, with the exception of its induction of the initiation of
chromosome replication, remains unclear. Here, we generated a Brucella
strain in which the expression of DnaA was conditionally controlled via
anhydrotetracycline (ATc)-induced complementation of a deletion of the
dnaA gene encoding the DnaA protein. We found that DnaA is required for
Brucella division and activity to response various environmental stresses.
As demonstrated by RNA-seq, DnaA was found to be involved in physiological
processes, including the regulation of the cell cycle. Moreover, the
inactivation of DnaA can inhibit Brucella intracellular trafficking
through impaired replicative Brucella-containing vacuole (rBCV)
biogenesis. In RAW 264.7 cells, the mutant strain promoted secretion of
the proinflammatory cytokines interleukin 1β (IL-1β) and interleukin 6
(IL-6) and reduced survival. In addition, the inhibition of DnaA
expression also attenuated the virulence of Brucella, but the resultant
strain exhibited excellent immunogenicity to activate host immune
responses in a mouse model. Altogether, these findings show that DnaA is
involved in Brucella virulence in vitro and in vivo and could become a new
target for the development of a safer and more efficient live attenuated
Brucella vaccine.