PdeA is required for the rod shape morphology of Brucella abortus

Cyclic-di-GMP plays crucial role in the cell cycle regulation of the alpha-Proteobacterium Caulobacter crescentus. Here we investigated its role in the alpha-Proteobacterium Brucella abortus, a zoonotic intracellular pathogen. Surprisingly, deletion of all predicted cyclic-di-GMP synthesizing or degrading enzymes did not drastically impair the growth of B. abortus, nor its ability to grow inside cell lines. As other Rhizobiales, B. abortus displays unipolar growth from the new cell pole generated by cell division. We found that the phosphodiesterase PdeA, the ortholog of the essential polar growth factor RgsP of the Rhizobiale Sinorhizobium meliloti, is required for rod shape integrity but is not essential for B. abortus growth. Indeed, the radius of the pole is increased by 31 +/- 1.7% in a Delta pdeA mutant, generating a coccoid morphology. A mutation in the cyclic-di-GMP phosphodiesterase catalytic site of PdeA does not generate the coccoid morphology and the Delta pdeA mutant kept the ability to recruit markers of new and old poles. However, the presence of PdeA is required in an intra-nasal mouse model of infection. In conclusion, we propose that PdeA contributes to bacterial morphology and virulence in B. abortus, but it is not crucial for polarity and asymmetric growth.