Abstract
During evolution, some α-Proteobacteria like Brucella have become stealthy intracellular pathogens, not easily detected by the innate immune system. To gain knowledge into the emergence of this strategy and the virulence mechanisms of Brucella, we sought to compare phylogenetically close but biologically divergent bacteria. Accordingly, the aim of this work was to search for the genomic characteristics thatmight explain the biological differences between Brucella, a pathogen of livestock and humans, and the closely related genera Ochrobactrum and Pseudochrobactrum, which are mainly free-living bacteria and only occasionally opportunistic human pathogens. For this purpose, we focused the comparison on P. algeriensis, a recently described species isolated from lymph nodes of cattle. Genomic analyses suggest that Pseudochrobactrum, conserves the lipid A structure of Brucella LPS, a trait already observed in O. intermedium that could delay immunity activation and hamper a prompt clearance of the bacteria. In addition, P. algeriensis contains putative genes for free-lipid modifications, probably explaining its extreme resistance in vitro to cationic peptides that mimic the bactericidal peptides of innate immune system. Finally,P. algeriensis, unlike other Pseudochrobactrum species, presents the genomic capacity of producing a rhamnose based O-polysaccharide LPS, being in this regard similar to B. inopinata BO2, an early diverging Brucella strain. Likewise, P. algeriensis carries part of the operon coding for the Type IV secretion system (T4SS) that, while essential for intracellular multiplication of Brucella, has been described as involved in plasmid transfer in Ochrobactrum. This work supports the notion that lipid A and free-lipid modifications are conserved in Brucellaceae as mechanisms of resistance to cationic peptide antibiotics in soil or to their innate immunity counterparts, while the T4SS have diverged to different functions.References
Batut et al., (2004) ‘The evolution of chronic infection strategies in the α -proteobacteria’, Nature Reviews Microbiology. doi:10.1038/nrmicro1044.
Conde-Álvarez et al., (2012) ‘The lipopolysaccharide core of Brucella abortus acts as a shield against innate immunity recognition’, PLoS Pathogens. doi:10.1371/journal.ppat.1002675.
Loperena-Barber et al., (2022) ‘Pseudochrobactrum algeriensis sp. nov., isolated from lymph nodes of Algerian cattle’, Int J Syst Evol Microbiol. doi: 10.1099/ijsem.0.005223.
Celli et al., (2003) ‘Brucella evades macrophage killing via VirB-dependent sustained interactions with the endoplasmic reticulum’, J Exp Med. doi: 10.1084/jem.20030088.