No abstract

Carbon storage regulator A (CsrA) is an RNA binding protein that has been characterized in many bacterial species to play a central regulatory role by modulating several metabolic processes. We recently showed that a homolog of CsrA in Borrelia burgdorferi (CsrA Bb , BB0184) was upregulated in response to propagation of B. burgdorferi under mammalian host-specific conditions. In order to further delineate the role of CsrA Bb , we generated a deletion mutant designated ES10 in a linear plasmid 25-negative isolate of B. burgdorferi strain B31 (ML23). The deletion mutant was screened by PCR and Southern blot hybridization, and a lack of synthesis of CsrA Bb in ES10 was confirmed by immunoblot analysis. Analysis of ES10 propagated at pH 6.8/37°C revealed a significant reduction in the levels of OspC, DbpA, BBK32, and BBA64 compared to those for the parental wild-type strain propagated under these conditions, while there were no significant changes in the levels of either OspA or P66. Moreover, the levels of two regulatory proteins, RpoS and BosR, were also found to be lower in ES10 than in the control strain. Quantitative real-time reverse transcription-PCR analysis of total RNA extracted from the parental strain and csrA Bb mutant revealed significant differences in gene expression consistent with the changes at the protein level. Neither the csrA Bb mutant nor the trans-complemented strain was capable of infection following intradermal needle inoculation in C3H/HeN mice at either 10 3 or 10 5 spirochetes per mouse. The further characterization of molecular basis of regulation mediated by CsrA Bb will provide significant insights into the pathophysiology of B. burgdorferi.

Borrelia burgdorferi, the causative agent of Lyme disease, undergoes rapid adaptive gene expression in response to environmental signals encountered during different stages of its life cycle in the arthropod vector or the mammalian host. Among all the plasmid-encoded genes of B. burgdorferi, several linear plasmid 54 (lp54)-encoded open reading frames (ORFs) exhibit the greatest differential expression in response to mammalian host-specific temperature, pH, and other uncharacterized signals. These ORFs include members of the paralogous gene family 54 (pgf 54), such as BBA64, BBA65, and BBA66, present on lp54. In an attempt to correlate transcriptional up-regulation of these pgf 54 members to their role in infectivity, we inactivated BBA64 and characterized the phenotype of this mutant both in vitro and in vivo. There were no major differences in the protein profiles between the BBA64 mutant and the control strains, while immunoblot analysis indicated that inactivation of BBA64 resulted in increased levels of BBA65. Moreover, there was no significant difference in the ability of the BBA64 mutant to infect C3H/HeN mice compared to that of its parental or complemented control strains as determined by culturing of viable spirochetes from infected tissues. However, enumeration of spirochetes using quantitative real-time PCR revealed tissue-specific differences, suggesting a minimal role for BBA64 in the survival of B. burgdorferi in select tissues. Infectivity analysis of the BBA64 mutant suggests that B. burgdorferi may utilize multiple determinants to establish infection in mammalian hosts.Lyme disease is the most prevalent arthropod-borne infection in the United States and remains a significant public health issue in certain geographic loci (3,46). It is a multiphasic disorder with clinical symptoms involving the cutaneous, musculoskeletal, cardiovascular, and nervous systems (62). Borrelia burgdorferi, the causative agent of Lyme disease, is transmitted to several vertebrate hosts, including humans, by the bite of infected Ixodes ticks. When ticks consume a blood meal from mammalian hosts, there is a rapid alteration of gene expression in B. burgdorferi, facilitating adaptation of the spirochetes to the highly disparate environmental conditions that exist between the tick vector and the vertebrate host (4, 9, 10, 15, 29, 30-32, 44, 53, 57-59, 63, 67). This adaptive gene expression may aid in the efficient trafficking of the spirochetes from the tick vector to the mammalian host and subsequently facilitate dissemination and colonization of various host tissues (16,22).Whole-genome transcriptional analyses using B. burgdorferi, propagated under in vitro growth conditions that mimic either the tick vector or mammalian host environment, have revealed preferential expression of plasmid-encoded genes (4,44,53,66). Among the several linear and circular plasmids present in B. burgdorferi, linear plasmid 54 (lp54) encodes the largest number of open reading frames (ORFs) that exhibit differential gene expression in respon...