Genetics and regulation of chitobiose utilization in Borrelia burgdorferi

Borrelia burgdorferi spends a significant proportion of its life cycle with in an ixodid tick, which has a cuticle containing chitin, a polymer of N-ac etylglucosamine (GlcNAc). The B. burgdorferi celA, celB, and celC genes enc ode products homologous to transporters for cellobiose and chitobiose (the dimer subunit of chitin) in other bacteria, which could be useful for bacte rial nutrient acquisition during growth within ticks. We found that chitobi ose efficiently substituted for GlcNAc during bacterial growth in culture m edium. We inactivated the celB gene, which encodes the putative membrane-sp anning component of the transporter, and compared growth of the mutant in v arious media to that of its isogenic parent. The mutant was no longer able to utilize chitobiose, while neither the mutant nor the wild type can utili ze cellobiose. We propose renaming the three genes chbA, chbB, and chbC, si nce they probably encode a chitobiose transporter. We also found that the c hbC gene was regulated in response to growth temperature and during growth in medium lacking GlcNAc.