Identification of 11 pH-regulated genes in Borrelia burgdorferi localizingto linear plasmids

When Borrelia burgdorferi is transmitted from the tick vector to the mammal ian host, the bacterium experiences alterations in its environment, such as changes in temperature and pH. Previously, we observed numerous alteration s in the membrane protein profile when B. burgdorferi B31 was grown at pH 7 .0 compared to pH 8.0, Here we identify 11 genes localizing to linear plasm ids that are up-regulated at pH 7.0 relative to pH 8.0 in vitro. Seven gene s (bba03, bba24, bba64, bba66, bbe31, bbj4l/bbi39 [encoding products that a re 99% identical], and bbk01) were indirectly identified by proteomic analy sis of membrane proteins. Another gene, bba36, was identified by screening a B. burgdorferi B31 genomic library with cross-adsorbed hyperimmune rabbit serum. Two additional genes, bba65 and bba73, were identified by Northern blot analysis. Genes bba64, bba65, bba66, bbj41/bbi39, and bba73 are member s of paralogous gene family 54, and bbe31 is a member of the closely relate d paralogous gene family 60. Gene bba24 is part of a bicistronic operon wit h bba25 that encodes the well-characterized decorin binding proteins A and B. All 11 genes were transcriptionally regulated, yet the degree of pH regu lation varied, with some genes more tightly regulated than others. The regi ons upstream of these pH-regulated genes appeared to be unrelated, yet many contained dyad repeats ranging from 12 to 25 nucleotides in length that ma y be involved in the regulation of these genes.