The Predicted ABC Transporter AbcEDCBA Is Required for Type IV Secretion System Expression and Lysosomal Evasion by Brucella ovis

Abstract

Brucella ovis is a major cause of reproductive failure in rams and it is one of the few well-described Brucella species that is not zoonotic. Previous work showed that a B. ovis mutant lacking a species-specific ABC transporter (ΔabcBA) was attenuated in mice and was unable to survive in macrophages. The aim of this study was to evaluate the role of this ABC transporter during intracellular survival of B. ovis. In HeLa cells, B. ovis WT was able to survive and replicate at later time point (48 hpi), whereas an ΔabcBA mutant was attenuated at 24 hpi. The reduced survival of the ΔabcBA mutant was associated with a decreased ability to exclude the lysosomal marker LAMP1 from its vacuolar membrane, suggesting a failure to establish a replicative niche. The ΔabcBA mutant showed a reduced abundance of the Type IV secretion system (T4SS) proteins VirB8 and VirB11 in both rich and acid media, when compared to WT B. ovis. However, mRNA levels of virB1, virB8, hutC, and vjbR were similar in both strains. These results support the notion that the ABC transporter encoded by abcEDCBA or its transported substrate acts at a post-transcriptional level to promote the optimal expression of the B. ovis T4SS within infected host cells.

Meta-Analysis and Advancement of Brucellosis Vaccinology

“…For instance, we have recently developed a B . ovis attenuated mutant vaccine candidate strain that lacks an ABC transporter [36], which influences the virB -encoded Type IV secretion system [146] thus interfering with intracellular trafficking [147]. This vaccine strain provided only moderate protection in the mouse model, yielding a protection index of approximately 1.0 [120], whereas it surprisingly provided a very strong protection against experimental challenge in rams, preventing shedding of the wild type strain in the semen and urine, accumulation of inflammatory cells in the semen, and gross or microscopic lesions induced by wild type B .…”

Pathogenic potential of Brucella ovis field isolates with different genotypic profile and protection provided by the vaccine strain B. ovis ΔabcBA against B. ovis field isolates in mice

“…can adapt to the intracellular environment upon activation of expression of certain virulence factors (Kohler et al 2002). Different strains of a given Brucella species may exhibit different intracellular kinetics (Harmon et al 1988, Kohler et al 2002, Silva et al 2014. This may explain the differences in intracellular and in vivo survival and multiplication observed in this study, whereas in vitro growth on solid medium was remarkably similar among these isolates.…”

“…A previous study demonstrated that a B. ovis specific ABC transporter is required for B. ovis survival in vivo and evasion from phagosome/lysosome fusion (Silva et al 2011b, Macedo et al 2015. Additionally, B. ovis-specific ABC transporter is required for normal expression of the virB-encoded T4SS since in the absence of this ABC transporter there is a post-transcriptional impairement of expression of virB-encoded proteins (Silva et al 2014). Indeed, B. ovis mutant strains lacking a functional B. ovis-specific ABC transporter (Silva et al 2011b) or the virB-encoded T4SS (Sá et al 2012) have similar phenotypes.…”

“…A B. ovis-specific genomic island (Tsolis et al 2009), named BOPI-1 for B. ovis pathogenicity island 1 (Silva et al 2011b), encodes an ABC transporter that is essential for pathogenesis since the B. ovis ΔabcBA strain is strongly attenuated in vitro and in vivo so this genomic island has been named BOPI-1 for B. ovis pathogenicity island 1 (Silva et al 2011b). However, the substrates of this particular ABC transporter are still unkown (Silva et al 2014). In spite of its attenuation, B. ovis ΔabcBA triggers humoral and cellular immune responses in rams that are indistinguishable from those triggered by the wild-type parental strain (Silva et al 2013).…”

Protection Provided by an Encapsulated Live Attenuated ΔabcBAStrain of Brucella ovis against Experimental Challenge in a Murine Model

“…Although the substrate of this ABC transporter is not known, it is required for expression of B. ovis virulence proteins, including Omp31, Sod, and the virB-encoded type IV secretion system (23), which is required for B. ovis intracellular survival and in vivo persistence (17). Furthermore, a B. ovis ⌬abcBA strain is capable of triggering humoral and cellular immune responses like the wild-type strain in rams; importantly, however, the mutant strain is not excreted in semen and urine (24).…”