The Role of the Flagellar Protein FlgJ in the Virulence of Brucella abortus

Abstract

Brucella abortus is a facultative intracellular pathogen that causes a zoonosis called brucellosis. This disease leads to abortion and infertility in cattle, and diverse complications in humans. B. abortus is a successful intracellular bacterium that has developed the ability to evade the host's immune system and it replicates in professional and non-professional phagocytic cells, persisting in the different tissues, and organs of its hosts. It has been described that Brucella expresses a polar flagellum under certain conditions, but its function is still unknown. In this study we evaluated the role of the FlgJ, a protein, presumably a peptidoglycan hydrolase involved in flagellum formation and in the virulence of B. abortus strain 2308. B. abortus 2308 flgJ mutant and complemented strains were constructed to study the function of the FlgJ protein in the context of the virulence of this pathogen in in vitro and in vivo assays. The results showed that the elimination of the flgJ gene delays the growth rate of B. abortus in culture, reduces its intracellular survival capacity in professional and non-professional phagocytic cells, rendering it unable to escape from the endocytic route and not reaching the endoplasmic reticulum. It also negatively affects their persistence in BALB/c mice. Functionally, the B. abortus 2308 flgJ gene restored motility to an E. coli flgJ mutant gene. Furthermore, it was discovered that the production of FlgJ protein is associated with the bacterial adherence by B. abortus. Therefore, although the specific function of the polar flagellum for Brucella is unknown, the data indicates that the flagellar flgJ gene and its product are required for full virulence of B. abortus 2308, since its deletion significantly reduces the fitness of this pathogen in vitro and in vivo.

Brucella and Its Hidden Flagellar System

“…As previously mentioned, the flagellar genes of B. abortus, present in its genome, are an interesting finding in relation to a bacterium described as non-motile [86]. This discovery may indicate that these proteins are involved in other vital functions for the establishment of bacterial infection, as in the case of the FlgJ protein, which, when encoded by the open reading frame BAB1_0260, participating in virulence and being mutated, limits the ability to form biofilms in vitro [69,88]. In E. coli, Salmonella, and other bacterial groups, this flagellar conformation and its subsequent formation begin with the action of the FlgJ protein.…”

“…The most important characteristic of Brucella is the ability to survive and multiply within both phagocytic and non-phagocytic cells [85]. There is also evidence that certain proteins that make up part of the flagellum participate in mechanisms that allow the bacterium to establish its replicative niche and its infective chronicity in the host [57,63,64,68,69]. These flagellar virulence factors have even been studied as immunogenic agents in murine models for the development of brucellosis vaccines [67].…”

“…Furthermore, PleA is required for flagellar assembly, indicating its involvement during flagellum formation [96]. B. abortus has a flagellar protein with hydrolase activity on peptidoglycan, the FlgJ protein (BAB1_0260) located in genomic island three (GI-3) (https://www.ncbi.nlm.nih.gov/protein/82615263, accessed on 15 November 2021), which may be involved in the virulence of this species [69]. Although the muramidase activity has not yet been studied in Brucella, its activity in that part of the PG is doubtful; however, the bioinformatic bases suggest an important role for FlgJ in the initial stages of flagellar genesis, due to its glucosaminidase activity (https: //www.kegg.jp/dbget-bin/www_bget?bmf:BAB1_0260, accessed on 15 November 2021).…”

Pangenome analysis and virulence profiling of Streptococcus intermedius

“…Flagella-related unique genes found in different studied strains include flgG, flgI, flgJ and flgk which play a major role in virulence, adhesion and motility. They are mostly involved in flagellum formation and also act as interface with other flagellar proteins [80][81][82][83]. The lnlK gene was reported in Listeria monocytogenes to help avoid autophagy while virB8 localizes to the inner membrane and is related to the export of alkaline phosphatase to the periplasm [84].…”

Design of a new multi-epitope vaccine against Brucella based on T and B cell epitopes using bioinformatics methods

“…In previous studies, a series of different proteins from Brucella has been used to identify immunodominant antigens against Brucella infection, including outer membrane proteins [12], flagellar proteins [13][14][15], L7/L12 ribosomal proteins [16] and Cu −Zn superoxide dismutase (Cu/Zn SOD) [17], etc. The Omp22 protein is an immunodominant antigen, belonging to the Omp25/Omp31 family of proteins.…”