Effect of iron-limiting conditions on virulence gene expression in pathogenic Leptospira spp.

Abstract

Background: Leptospirosis is considered an important re-emerging disease of worldwide distribution, and aetiologically caused by pathogenic Leptospira species. Iron, with its wide redox potential, is inherently important for the growth of most living organisms. Consequently, attempts by hosts to limit unbound iron result in pathogens developing systems to overcome such conditions which invariably reflects in increased virulence. In this study, the effects of iron-limiting conditions on the expression of virulence-associated genes in Leptospira interrogans Portlandvere and Leptospira borgpetersenii Jules were examined. Methods & Materials: To assess the effect of iron-limitation, bacteria in EMJH were exposed to 10, 20 and 40 μM bipyridyl (metal chelator) at each of three temperature conditions, 30 °C, 37 °C, and 30 °C upshifted to 37 °C. Gene expression was analyzed by endpoint PCR and quantitative RT-PCR in biological replicates. Results: Endpoint RT-PCR indicated marginally higher transcription among Portlandvere compared to Jules grown under iron-limitation at upshift temperature and similar transcription rates between both species grown at 30 °C and 37 °C. Differential lenA, sph2, lipL41, lipL32 and loa22 expressions in iron-limited Jules and Portlandvere highlighted the integration of the pathogens’ response to temperature and iron-limiting conditions. In particular, changes in iron availability resulted in increased loa22 expression in both L. Portlandvere (p = 0.02) and L. Jules (p = 0.05). Further, reduced iron conditions resulted in concomitant increases in sph2 and lipL32 in Jules at 37 °C, and a decrease in lipL41 transcripts in both L. Jules and L. Portlandvere at 37 °C. Conclusion: These data suggest that there is tight co-regulation of virulence genes by iron and temperature, and that species differences could account for some differences in gene expression in L. Jules and L. Portlandvere in iron-limiting conditions.