Effects of Environmental Changes on Expression of the Oligopeptide Permease ( opp ) Genes of Borrelia burgdorferi

Abstract

We analyzed expression of a putative oligopeptide permease (Opp) of Borrelia burgdorferi. Unlike the opp operons of other bacteria for which there is a single substrate binding protein, B. burgdorferi codes for three substrate binding proteins (OppA-I to -III) in its opp operon and an additional two homologs on plasmids (OppA-IV and -V). Instead of a single promoter region regulating transcription of the entire operon, as seen in other bacterial opp operons, it appears that among oppA-I, -II, and -III, as well as oppA-IV and -V, each has a potential upstream promoter region. We tested the function of these putative promoter sequences by fusion to a promoterless ␤-galactosidase reporter gene in pCB182. Each of the promoter regions was found to be active. The level of activity in the reporter constructs closely paralleled the level of expression of each gene in in vitro-grown B. burgdorferi. Changes in carbon and nitrogen availability differentially affected individual promoters, but no changes in promoter activity were seen when Escherichia coli bacteria (with the promoter constructs) were grown in various concentrations of phosphate and leucine and changes in pH. Expression of specific oppA genes with B. burgdorferi varied significantly between its mouse and fed and unfed tick hosts. Differences in regulation of opp gene expression suggest a potential role in environmental response by the organism.

Oligopeptide Permease A5 Modulates Vertebrate Host-Specific Adaptation of Borrelia burgdorferi

“…Moreover, B. burgdorferi has limited metabolic capabilities with (i) few ORFs annotated as regulators of gene expression; (ii) no apparent biosynthetic pathways for synthesis of various amino acids, fatty acids, and nucleotides; and (iii) limited transport systems for acquiring key nutrients from the external environment. We therefore decided to investigate the role of one of the five paralogs of oligopeptide permease A proteins, BBA34, in vertebrate host-specific adaptation since it is (i) preferentially upregulated upon propagation of B. burgdorferi under conditions mimicking the mammalian host, (ii) incapable of binding oligopeptides, (iii) immunogenic, and (iv) comprised of a solute binding domain capable of binding/transporting key solutes (85). We undertook a genetic approach to assess the contribution of this lp54-encoded protein to vertebrate host-specific conditions by deleting bba34 in a noninfectious lp25-deficient strain ML23 (Fig.…”

“…However, unlike other bacteria, B. burgdorferi has 5 open reading frames (ORFs) annotated as homologs of OppA, suggesting that these proteins could play a significant role in acquiring select nutrients/solutes in specific microenvironments (11). Three of these OppA homologs (OppA1, -2, and -3) encoded on the chromosome bound heptapeptides with high affinities in a pH-dependent manner, while the other two homologs present on plasmids (OppA4 on cp26 and OppA5 or BBA34 on lp54) did not exhibit such binding characteristics (84,85). Additional studies also indicated that bba34 was upregulated when the culture conditions of B. burgdorferi were shifted from 25°C to 37°C and in spirochetes present in infected mouse tissues (52).…”

Analysis of Differences in the Functional Properties of the Substrate Binding Proteins of the Borrelia burgdorferi Oligopeptide Permease ( opp ) Operon

“…B. burgdorferi undergoes a complex natural life cycle in which it encounters vast changes in environmental conditions, such as nutrient availability, temperature, and pH, as it moves from tick to mammalian hosts. The individual promoters have been shown to respond differentially to various environmental conditions (29). For example, the expression of OppA-4 and OppA-5 is highly up-regulated by the bacteria in a mouse host, while the expression of OppA-1 is relatively constitutive regardless of whether the bacteria are grown in vitro or are present in tick or mouse hosts.…”

“…Wang et al found that each of the five B. burgdorferi OppA orthologues is under the control of a separate promoterwhich would allow for individual regulation of the expression of the proteins (29). B. burgdorferi undergoes a complex natural life cycle in which it encounters vast changes in environmental conditions, such as nutrient availability, temperature, and pH, as it moves from tick to mammalian hosts.…”

Alternate Sigma Factor RpoS Is Required for the In Vivo-Specific Repression ofBorrelia burgdorferiPlasmid lp54-BorneospAandlp6.6Genes

“…Not unexpectedly, the entry of a bloodmeal into a B. burgdorferi-infected tick is accompanied by extensive changes in the borrelial transcriptome and proteome, a process referred to as mammalian host adaptation (1,4,43). While a number of studies have demonstrated that the expression of many borrelial loci can be modulated by the manipulation of in vitro growth conditions (1,2,5,8,10,11,17,27,32,41,48,51,58,60,(63)(64)(65)68), we and others have shown that as-yet-undefined mammalian hostspecific cues are essential for triggering the genetic program(s) underlying host adaptation (1,2,8,18,27,32,46,49,51,52,63,64,66).…”