Synthesis of Autoinducer 2 by the Lyme Disease Spirochete,Borrelia burgdorferi

Abstract

Defining the metabolic capabilities and regulatory mechanisms controlling gene expression is a valuable step in understanding the pathogenic properties of infectious agents such as Borrelia burgdorferi. The present studies demonstrated that B. burgdorferi encodes functional Pfs and LuxS enzymes for the breakdown of toxic products of methylation reactions. Consistent with those observations, B. burgdorferi was shown to synthesize the end product 4,5-dihydroxy-2,3-pentanedione (DPD) during laboratory cultivation. DPD undergoes spontaneous rearrangements to produce a class of pheromones collectively named autoinducer 2 (AI-2). Addition of in vitro-synthesized DPD to cultured B. burgdorferi resulted in differential expression of a distinct subset of proteins, including the outer surface lipoprotein VlsE. Although many bacteria can utilize the other LuxS product, homocysteine, for regeneration of methionine, B. burgdorferi was found to lack such ability. It is hypothesized that B. burgdorferi produces LuxS for the express purpose of synthesizing DPD and utilizes a form of that molecule as an AI-2 pheromone to control gene expression.

Genetic and physiological characterization of the Borrelia burgdorferi ORF BB0374-pfs-metK-luxS operon

“…luxS mutant B. burgdorferi are still able to infect mice and ticks, indicating that DPD synthesis is not absolutely essential for infection (Blevins et al, 2004; Hübner et al, 2003). Consistent with those results, luxS mutants can produce all of the proteins identified as being affected by DPD, although mutants produce different levels of those proteins than do wild-type B. burgdorferi (Babb et al, 2005;von Lackum et al, 2006von Lackum et al, , 2007. Taken together, these data suggest that B. burgdorferi uses DPD as a signal to fine tune gene expression levels, as opposed to a simple on/off switch.…”

“…Growth-phase-dependent expression of ORF BB0374, pfs, metK and luxS. Bacteria were harvested at densities of 6¾10 6 , 1¾10 8 , 1.5¾10 8 and 2¾10 8 bacteria ml "1 , corresponding to early exponential, mid-exponential, early stationary and late stationary phases, respectively (Babb et al, 2005). Three independently grown cultures were analysed for each time point, and each cDNA was analysed in quadruplicate.…”

“…Our previous studies demonstrated that B. burgdorferi pfs and luxS encode functional enzymes (Babb et al, 2005;Stevenson & Babb, 2002). The previously uncharacterized ORF BB0376 is located between pfs and luxS, with all three genes overlapping.…”

“…Some bacteria, such as the syphilis spirochaete Treponema pallidum, possess Pfs but lack LuxS, and therefore detoxify SAH only to the non-toxic S-ribosylhomocysteine (SRH) (Fraser et al, 1998;von Lackum et al, 2006). Other bacteria, B. burgdorferi included, further degrade SRH to DPD and homocysteine via the LuxS enzyme (Babb et al, 2005;Stevenson & Babb, 2002;Stevenson et al, 2003;Sun et al, 2004;Xavier & Bassler, 2003). The majority of bacteria salvage homocysteine for regeneration of methionine, for use in additional transmethylation reactions or protein synthesis (Winzer et al, 2002).…”

“…The majority of bacteria salvage homocysteine for regeneration of methionine, for use in additional transmethylation reactions or protein synthesis (Winzer et al, 2002). B. burgdorferi is among the minority of bacteria which lack methionine synthase, and are therefore unable to utilize the homocysteine produced by LuxS (Babb et al, 2005). Several lines of evidence indicate that B. burgdorferi instead uses the LuxS enzyme to Abbreviations: AI-2, autoinducer-2; DPD, 4,5-dihydroxy-2,3-pentanedione; SAH, S-adenosylhomocysteine; SAM, S-adenosylmethionine; SRH, S-ribosylhomocysteine; RTase, reverse transcriptase; Q-RT-PCR, quantitative reverse transcription-PCR.…”