The Lon‐2 protease of Borrelia burgdorferi is critical for infection in the mammalian host

Abstract

Borrelia burgdorferi encodes a functional homolog of canonical Lon protease termed Lon-2. To date, the contribution of Lon-2 to B. burgdorferi fitness and infection remains unexplored. Herein, we showed that expression of lon-2 was highly induced during animal infection, suggesting that Lon-2 is important for B. burgdorferi infection. We further generated a lon-2 deletion mutant. Compared with that of wild-type (WT) strain, the infectivity of the mutant was severely attenuated in a murine infection model. Although no growth defect was observed for the mutant in normal BSK-II medium, resistance of the lon-2 mutant to osmotic stress was markedly reduced. In addition, when exposed to tert-Butyl hydroperoxide, survival of the lon-2 mutant was impaired. In addition, we found that the protein levels of RpoS and RpoS-dependent OspC were decreased in the mutant. All these phenotypes were restored to WT or near-WT levels when lon-2 mutation was complemented in cis. Taken together, these results demonstrate that Lon-2 is critical for B. burgdorferi to establish infection and to cope with environmental stresses. This study provides a foundation for further uncovering the direct link between the dual roles of Lon-2 in protein quality control and bacterial pathogenesis.

The Lon-1 Protease Is Required by Borrelia burgdorferi To Infect the Mammalian Host

“…Moreover, the ATP-dependent protease FtsH has been reported to be essential for B. burgdorferi infection (38). Additionally, we recently found that the Lon-2 protease is critical for B. burgdorferi to infect the mammalian host (11). This current study on Lon-1 thus provides further evidence for the implication of proteases as a previously unappreciated layer of control over virulence and pathogenesis in B. burgdorferi.…”

“…The Lon protease in Yersinia pestis has been reported to indirectly activate the expression of the important type III secretion system (TTSS) (25). Furthermore, we recently found that the protein levels of RpoS and OspC in B. burgdorferi were reduced in a lon-2 deficient mutant (11). As such, Lon-1 may directly or indirectly impact the expression of key virulence determinants.…”

“…By using a functional complementation assay, Coleman et al reported that introduction of B. burgdorferi Lon-2 into an E. coli lon mutant corrected phenotypes associated with lon deficiency, such as cell filamentation and cps dysregulation, suggesting that Lon-2 is a functional homolog of the E. coli Lon protease (8). Recently, we created a lon-2 deletion mutant and found that the infectivity of the mutant in mice was significantly attenuated, suggesting that Lon-2 is critical for infection of B. burgdorferi in the mammalian host (11). In contrast, B. burgdorferi Lon-1 was incapable of complementing the E. coli lon mutant.…”

DksA plays an essential role in regulating the virulence of Borrelia burgdorferi

“…This assay was performed as previously described (Curtis et al , 2018; Mason et al , 2020). In brief, B. burgdorferi was grown in BSK‐II until the late logarithmic phase.…”

“…qPCR was performed using the PowerUP SYBR Green Master Mix (Thermo Fisher Scientific). As previously described (Pal et al , 2004; 2008; Ouyang et al , 2012; Mason et al , 2020), the absolute quantification method was employed to calculate the copy number of murine β‐actin gene and B. burgdorferi flaB gene in each sample.…”