Summary Borrelia burgdorferi (Bb) adapts to its arthropod and mammalian hosts by altering its transcriptional and antigenic profiles in response to

While numerous positively regulated loci have been characterized during the enzootic cycle of Borrelia burgdorferi, very little is known about the mechanism(s) involved in the repression of borrelial loci either during tick feeding or within the mammalian host. Here, we report that the alternative sigma factor RpoS is required for the in vivo-specific repression of at least two RpoD-dependent B. burgdorferi loci, ospA and lp6.6. The downregulation of ospA and Ip6.6 appears to require either a repressor molecule whose expression is RpoS dependent or an accessory factor which enables RpoS to directly interact with the ospA and Ip6.6 promoter elements, thereby blocking transcription by RpoD. The central role for RpoS during the earliest stages of host adaptation suggests that tick feeding imparts signals to spirochetes that trigger the RpoS-dependent repression, as well as expression, of in vivo-specific virulence factors critical for the tick-to-mammalian host transition.

The hypothesis that maternal generation from Mexico predicts infant receptive and expressive communication age at 22 months was investigated. Participants included 62 infants from Mexican American families who graduated from a neonatal intensive care unit (NICU) and 35 full-term infants also born to Mexican American parents. The results showed that infants born to mothers of recent generation from Mexico had lower language development scores than did infants born to mothers of later generation. Fathers'education levels were also significant predictors of infants'22-month language outcome, although maternal generation from Mexico remained a stronger predictor of outcome than did paternal education level for expressive language and for receptive language for the NICU graduates. The results support theories that emphasize the importance of environmental context on child development.