Borrelia burgdorferi Requires Glycerol for Maximum Fitness During The Tick Phase of the Enzootic Cycle

Abstract

Borrelia burgdorferi, the spirochetal agent of Lyme disease, is a vector-borne pathogen that cycles between a mammalian host and tick vector. This complex life cycle requires that the spirochete modulate its gene expression program to facilitate growth and maintenance in these diverse milieus. B. burgdorferi contains an operon that is predicted to encode proteins that would mediate the uptake and conversion of glycerol to dihydroxyacetone phosphate. Previous studies indicated that expression of the operon is elevated at 23°C and is repressed in the presence of the alternative sigma factor RpoS, suggesting that glycerol utilization may play an important role during the tick phase. This possibility was further explored in the current study by expression analysis and mutagenesis of glpD, a gene predicted to encode glycerol 3-phosphate dehydrogenase. Transcript levels for glpD were significantly lower in mouse joints relative to their levels in ticks. Expression of GlpD protein was repressed in an RpoS-dependent manner during growth of spirochetes within dialysis membrane chambers implanted in rat peritoneal cavities. In medium supplemented with glycerol as the principal carbohydrate, wild-type B. burgdorferi grew to a significantly higher cell density than glpD mutant spirochetes during growth in vitro at 25°C. glpD mutant spirochetes were fully infectious in mice by either needle or tick inoculation. In contrast, glpD mutants grew to significantly lower densities than wild-type B. burgdorferi in nymphal ticks and displayed a replication defect in feeding nymphs. The findings suggest that B. burgdorferi undergoes a switch in carbohydrate utilization during the mammal to tick transition. Further, the results demonstrate that the ability to utilize glycerol as a carbohydrate source for glycolysis during the tick phase of the infectious cycle is critical for maximal B. burgdorferi fitness.

Borrelia burgdorferi bba66 Gene Inactivation Results in Attenuated Mouse Infection by Tick Transmission

“…Recent research investigating borrelia-vector interactions have focused on inactivation of global regulators, individual genes, and replicons to advance our understanding of B. burgdorferi tick colonization and persistence and vector transmission mechanisms (1,4,7,18,(37)(38)(39)(40)(41)(42)(43)(44)(45)(46)(47)(48)(49)(50)(51)(52)(53)(54). The loss of BBA66 activity did not completely abolish the ability of B. burgdorferi to invade the host by tick bite (at least when more than 4 ticks/mouse fed to repletion), but mouse infectivity was significantly impaired.…”

Study of the Response Regulator Rrp1 Reveals Its Regulatory Role in Chitobiose Utilization and Virulence of Borrelia burgdorferi

“…The necessity to utilize different carbohydrates is further supported by the presence of several carbon metabolism pathways and transporters in the genome of this spirochete (4). For instance, in addition to the glycolysis pathway utilizing glucose as the main carbon source, B. burgdorferi also encodes genes essential for metabolizing glycerol, chitobiose, and N-acetylglucosamine (GlcNAc) (4)(5)(6)(7)(8).…”

“…Glycerol is produced by the Ixodes tick as one of the cryoprotective agents, and chitin is the major component of cuticle of arthropod, including ticks (11)(12)(13). In vitro growth analysis has shown that B. burgdorferi is able to utilize glycerol as its carbon source in the absence of glucose (5,7,14). Also, mutants defective in glycerol metabolism are attenuated in overall survival within the tick vector.…”

“…Also, mutants defective in glycerol metabolism are attenuated in overall survival within the tick vector. These mutants exhibit delayed replication after a blood meal or are unable to persist effectively in feeding ticks, emphasizing the requirement of glycerol for maximal fitness of B. burgdorferi during the tick phase of the life cycle (5,14).…”

“…Among the three putative chitobiose transporter genes, chbA (BBB05), chbB (BBB06), and chbC (BBB04), only chbC is essential for chitobiose utilization in vitro (6,15). The expression of chbC was shown to be regulated by both RpoD and RpoS (16), and its expression is highly elevated in ticks (5). In vitro growth analysis showed that the chbC mutant is unable to utilize chitobiose as a carbon source when GlcNAc availability is limited.…”