Identification and characterization of two differentially expressed Borrelia burgdorferi genes

Borrelia burgdorferi, the Lyme disease pathogen, has a complex life cycle in nature which involves a tick vector and diverse mammalian hosts. RpoS governs differential expression of various borrelial genes during its enzootic life cycle. Several microarray studies revealed bb0844 as an rpoS--regulated gene which had elevated expression under mammalian--like conditions. To elucidate the role of BB0844 in the spirochete life cycle, we constructed a bb0844 deletion mutant by replacing bb0844 with a borrelia--adapted spectinomycin resistance cassette by allelic exchange. Expression of bb0844 was induced in feeding nymphal ticks during spirochete transmission from ticks to mammals. The bb0844 mutant was fully infectious in mice both by needle inoculation and tick transmission. Moreover, bb0844 expression was not required for spirochete acquisition and transmission processes. The results demonstrate that BB0844 is not required for spirochete viability, pathogenicity or maintenance in the tick vector or the mammalian host. bb0844 is present at the right chromosomal telomere, but its presence is dependent on B. burgdorferi genotype. OspC type I has it on lp28--1 plasmid whereas OspC types A, D, G, H, K and U have it on the chromosome. On the contrary, OspC types E, J and M do not have bb0844 in their genomes.;Microarray--based analysis of B. burgdorferi gene expression in fed larvae and fed nymphs was performed to identify genes differentially expressed during these two tick stages. Among the genes detected in ticks, eight genes were encoding tetratricopeptide repeats (TPR) domain proteins. These structural motifs have been predicted to mediate protein--protein interactions. bb0236 is among these genes which was found to be expressed in both fed larvae and fed nymphs by microarray analysis. bb0236 transcript was detected during all tick stages by real--time RT--PCR and had significantly higher expression in joints as compared to hearts during murine infection. BB0236 was found to be expressed during mammalian infection. BB0236 is not surface exposed and present as either an integral membrane or a membrane--anchored protein. The consistent expression of bb0236 within ticks indicates that bb0236 might be important for B. burgdorferi survival in the tick vector.