Genome-wide screen identifies novel genes required for Borrelia burgdorferi survival in its Ixodes tick vector

Abstract

Borrelia burgdorferi , the causative agent of Lyme disease in humans, is maintained in a complex biphasic life cycle, which alternates between tick and vertebrate hosts. To successfully survive and complete its enzootic cycle, B . burgdorferi adapts to diverse hosts by regulating genes required for survival in specific environments. Here we describe the first ever use of transposon insertion sequencing (Tn-seq) to identify genes required for B . burgdorferi survival in its tick host. We found that insertions into 46 genes resulted in a complete loss of recovery of mutants from larval Ixodes ticks. Insertions in an additional 56 genes resulted in a >90% decrease in fitness. The screen identified both previously known and new genes important for larval tick survival. Almost half of the genes required for survival in the tick encode proteins of unknown function, while a significant portion (over 20%) encode membrane-associated proteins or lipoproteins. We validated the results of the screen for five Tn mutants by performing individual competition assays using mutant and complemented strains. To better understand the role of one of these genes in tick survival, we conducted mechanistic studies of bb0017 , a gene previously shown to be required for resistance against oxidative stress. In this study we show that BB0017 affects the regulation of key borrelial virulence determinants. The application of Tn-seq to in vivo screening of B . burgdorferi in its natural vector is a powerful tool that can be used to address many different aspects of the host pathogen interaction.

Borrelia bavariensis: Vector Switch, Niche Invasion, and Geographical Spread of a Tick-Borne Bacterial Parasite

“…Some molecules that have been shown to have a function within the tick vector include the Outer surface protein A (OspA) which binds to the vector midgut molecule TROSPA (Pal et al, 2004); BBE31 which binds to the vector molecule Tre31, a protein secreted by tick midgut epithelial cells (Zhang et al, 2011); PdeB, a phosphodiesterase required for survival in, and transmission by, ticks; Lpm1, a surface molecule, depletion of which inhibits Borrelia in the vector (Koci et al, 2018); BB0365, BB0690, BptA, lp6.6, BBk32 are all required for persistence in the tick, while antigen P35 (BBA64) may play a role in tick-tohost transmission (Fikrig et al, 2000;Radolf et al, 2012;Brandt et al, 2014). In a recent study using transposon-based gene interruption approach, >100 genes were shown to be involved in Borrelia survival in larval ticks (Phelan et al, 2019). These included previously reported genes and novel genes important for tick survival of Borrelia.…”

Complement evasion strategies of Borrelia burgdorferi sensu lato

“…In order to survive within ticks, borreliae regulate their gene expression depending on the environmental conditions and various stimuli [10]. The spirochetes relocate from the animal host dermis to the tick gut lumen during a blood meal.…”

Interactions between Borrelia burgdorferi and its hosts across the enzootic cycle

“…7,27,28,[105][106][107] By studying a transposon library of Borrelia mutants, 108 Phelan et al were able to identify 46 genes that were essential to Borrelia survival in ticks after the blood meal. 109 Most of these genes were of unknown function and likely have a variety of functions critical for Borrelia survival and migration out of the gut. However, several of the genes appeared to be involved in protection against reactive oxygen species.…”

“…BB0017, a protein known to protect B. burgdorferi against reactive oxygen species, is required for tick survival through control of expression of other genes. 109 After establishing infection in the tick midgut, the next major event in the lifecycle is the nymphal blood meal. Spirochete gene expression changes in response to nymphal blood uptake are critical for B. burgdorferi survival and transmission to a new host.…”