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.

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In this study, we aimed to analyze the global response to iron in the broad-range host pathogen Vibrio vulnificus under the hypothesis that iron is one of the main signals triggering survival mechanisms both inside and outside its hosts. To this end, we selected a strain from the main zoonotic clonal-complex, obtained a mutant in the ferric-uptake-regulator (Fur), and analyzed their transcriptomic profiles in both iron-excess and iron-poor conditions by using a strain-specific microarray platform. Among the genes differentially expressed, we identified around 250 as putatively involved in virulence and survival-related mechanisms. Then, we designed and performed a series of in vivo and in vitro tests to find out if the processes highlighted by the microarray experiments were in fact under iron and/or Fur control. Our results support the hypothesis that iron acts as a niche marker, not always through Fur, for V. vulnificus controlling its entire life cycle. This ranges from survival in the marine environment, including motility and chemotaxis, to survival in the blood of their hosts, including host-specific mechanisms of resistance to innate immunity. These mechanisms allow the bacterium to multiply and persist inside and between their hosts.