ABSTRACTThe genome ofBorrelia burgdorferi, the Lyme disease spirochete, encodes a homolog (thebb0184gene product) of the carbon storage regulator A protein (CsrABb); recent studies reported that CsrABbis involved in the regulation of several infectivity factors ofB. burgdorferi. However, the mechanism involved remains unknown. In this report, acsrABbmutant was constructed and complemented in an infectious B31A3 strain. Subsequent animal studies showed that the mutant failed to establish an infection in mice, highlighting that CsrABbis required for the infectivity ofB. burgdorferi. Western blot analyses revealed that the virulence-associated factors OspC, DbpB, and DbpA were attenuated in thecsrABbmutant. The Rrp2-RpoN-RpoS pathway (σ54-σSsigma factor cascade) is a central regulon that governs the expression ofospC,dbpB, anddbpA. Further analyses found that the level of RpoS was significantly decreased in the mutant, while the level of Rrp2 remained unchanged. A recent study reported that the overexpression of BB0589, a phosphate acetyl-transferase (Pta) that converts acetyl-phosphate to acetyl-coenzyme A (CoA), led to the inhibition of RpoS and OspC expression, suggesting that acetyl-phosphate is an activator of Rrp2. Along with this report, we found that CsrABbbinds to the leader sequence of thebb0589transcript and that the intracellular level of acetyl-CoA in thecsrABbmutant was significantly increased compared to that of the wild type, suggesting that more acetyl-phosphate was being converted to acetyl-CoA in the mutant. Collectively, these results suggest that CsrABbmay influence the infectivity ofB. burgdorferivia regulation of acetate metabolism and subsequent activation of the Rrp2-RpoN-RpoS pathway.