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Effect of human fecal extracts on Campylobacter jejuni gene expression and pathogenesis Liu, Martha


Campylobacter jejuni (C. jejuni), a zoonotic commensal that is pathogenic in humans, is one of the most common bacterial causes of food borne illness worldwide. To assess how C. jejuni responds to the metabolome of a commensal host (chickens) versus a disease susceptible host (humans), differences in gene expression was evaluated after C. jejuni exposure to cell-free extracts prepared from chicken cecal and human fecal matter. RNA sequencing identified 12 genes with >2 fold difference in expression when C. jejuni was exposed to human fecal extracts in comparison to chicken cecal extract. 10 of these genes appear to be involved in iron uptake, of which 7 (CJJ81176_1649 to 1655) were part of one iron uptake system. This system likely acquires chelated iron not recognized by other iron uptake systems since measurement of total iron content showed that human fecal extracts contained ~4.5X more iron than chicken cecal extract. Homologs of the CJJ81176_1649 to 1655 proteins were identified in alpha, epsilon and gamma proteobacteria, and mapping of the homologous proteins to representative bacterial genomes showed that gene order and operon structure were well preserved for homologs of the entire CJJ81176_1649 to 1655 gene cluster. The widespread prevalence of the entire gene cluster putatively suggests that the proteins encoded by CJJ81176_1649 to 1655 represent a complete iron uptake system. The CJJ81176_1649 iron transporter and the p19 (CJJ81176_1650) periplasmic iron binding proteins have been previously characterized, but the downstream genes have not been directly studied and functions are predicted by homology. Deletion of CJJ81176_1651 to 1655 and the overlapping CJJ81176_1656 gene in this study rendered C. jejuni more sensitive to iron depletion than wild type, comparable to that of the p19 mutant. Furthermore, this iron uptake system appears to be involved in adaptation to low pH, but at the cost of increased sensitivity to hydrogen peroxide stress. This work demonstrates that the heretofore understudied, but widely conserved, CJJ81176_1649 to 1656 iron uptake system may be involved in host colonization by uptake of chelated iron more abundantly present in the human intestinal environment than that of the chicken cecum.

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