Borrelia burgdorferiis an Adenine and Spermidine Auxotroph

Extensive diversity in RNA termination and regulation revealed by transcriptome mapping for the Lyme pathogen B. burgdorferi

Transcription termination is an essential and dynamic process that can tune gene expression in response to diverse molecular signals. Yet, the genomic positions, molecular mechanisms, and regulatory consequences of termination have only been studied thoroughly in model bacteria. We employed complementary RNA-seq approaches to map RNA ends for the transcriptome of the spirochete Borrelia burgdorferi - the etiological agent of Lyme disease. By systematically mapping B. burgdorferi RNA ends at single nucleotide resolution, we delineated complex gene arrangements and operons and mapped untranslated regions (UTRs) and small RNAs (sRNAs). We experimentally tested modes of B. burgdorferi transcription termination and compared our findings to observations in E. coli , P. aeruginosa , and B. subtilis . We discovered 63% of B. burgdorferi RNA 3' ends map upstream or internal to open reading frames (ORFs), suggesting novel mechanisms of regulation. Northern analysis confirmed the presence of stable 5' derived RNAs from mRNAs encoding gene products involved in the unique infectious cycle of B. burgdorferi . We suggest these RNAs resulted from premature termination and regulatory events, including forms of cis- acting regulation. For example, we documented that the polyamine spermidine globally influences the generation of truncated mRNAs. In one case, we showed that high spermidine concentrations increased levels of RNA fragments derived from an mRNA encoding a spermidine import system, with a concomitant decrease in levels of the full- length mRNA. Collectively, our findings revealed new insight into transcription termination and uncovered an abundance of potential RNA regulators.

Borrelia burgdorferi genes, bb0639-0642, encode a putative putrescine/spermidine transport system, PotABCD, that is spermidine specific and essential for cell survival

Polyamines are an essential class of metabolites found throughout all kingdoms in life. Borrelia burgdorferi harbors no enzymes to synthesize or degrade polyamines yet does contain a polyamine uptake system, potABCD. In this report, we describe the initial characterization of this putative transport system. After several unsuccessful attempts to inactivate potABCD, we placed the operon under the control of an inducible LacI promoter expression system. Analyses of this construct confirmed that potABCD was required for in vitro survival. Additionally, we demonstrated that the potABCD operon were upregulated in vitro by low osmolarity. Previously, we had shown that low osmolarity triggers the activation of the Rrp2/RpoN/RpoS regulatory cascade, which regulates genes essential for the transmission of spirochetes from ticks to mammalian hosts. Interestingly, induction of the pot operon was only affected in an rpoS mutant but not in a rpoN mutant, suggesting that the genes were RpoS dependent and RpoN independent. Furthermore, potABCD was upregulated during tick feeding concomitant with the initiation of spirochete replication. Finally, uptake experiments determined the specificity of B. burgdorferi's PotABCD for spermidine.

Stage-specific global alterations in the transcriptomes of Lyme disease spirochetes during tick feeding and following mammalian host adaptation

Borrelia burgdorferi, the agent of Lyme disease, is maintained in nature within an enzootic cycle involving a mammalian reservoir and an Ixodes sp. tick vector. The transmission, survival and pathogenic potential of B. burgdorferi depend on the bacterium's ability to modulate its transcriptome as it transits between vector and reservoir host. Herein, we employed an amplification-microarray approach to define the B. burgdorferi transcriptomes in fed larvae, fed nymphs and in mammalian host-adapted organisms cultivated in dialysis membrane chambers. The results show clearly that spirochetes exhibit unique expression profiles during each tick stage and during cultivation within the mammal; importantly, none of these profiles resembles that exhibited by in vitro grown organisms. Profound shifts in transcript levels were observed for genes encoding known or predicted lipoproteins as well as proteins involved in nutrient uptake, carbon utilization and lipid synthesis. Stage-specific expression patterns of chemotaxis-associated genes also were noted, suggesting that the composition and interactivities of the chemotaxis machinery components vary considerably in the feeding tick and mammal. The results as a whole make clear that environmental sensing by B. burgdorferi directly or indirectly drives an extensive and tightly integrated modulation of cell envelope constituents, chemotaxis/motility machinery, intermediary metabolism and cellular physiology. These findings provide the necessary transcriptional framework for delineating B. burgdorferi regulatory pathways throughout the enzootic cycle as well as defining the contribution(s) of individual genes to spirochete survival in nature and virulence in humans.

Functionality of Borrelia burgdorferi LuxS: the Lyme disease spirochete produces and responds to the pheromone autoinducer-2 and lacks a complete activated-methyl cycle

Borrelia burgdorferi produces Pfs and LuxS enzymes for breakdown of the toxic byproducts of methylation reactions, producing 4,5-dihydroxy-2,3-pentanedione (DPD), adenine, and homocysteine. DPD and its spontaneously rearranged derivatives constitute a class of bacterial pheromones named autoinducer-2 (AI-2). We describe that B. burgdorferi produces DPD during laboratory cultivation. Furthermore, addition of in vitro synthesized DPD to cultured B. burgdorferi resulted in altered expression levels of a specific set of bacterial proteins, among which is the outer surface lipoprotein VlsE. While a large number of bacteria utilize homocysteine, the other LuxS product, for synthesis of methionine as part of the activated-methyl cycle, B. burgdorferi was found to lack that ability. We propose that the main function of B. burgdorferi LuxS is to synthesize DPD and that the Lyme disease spirochete utilizes a form of DPD as a pheromone to control gene expression.

Carbohydrate utilization by the Lyme borreliosis spirochete, Borrelia burgdorferi

Growth kinetic analyses of Borrelia burgdorferi indicated that this bacterium can utilize a limited number of carbon sources for energy: the monosaccharides glucose, mannose, and N-acetylglucosamine, the disaccharides maltose and chitobiose, and glycerol. All of these carbohydrates are likely to be available to B. burgdorferi during infection of either vertebrate and arthropod hosts, enabling development of a model describing energy sources potentially used by the Lyme borreliosis spirochete during its natural infectious cycle.