Understanding the Molecular Strategies of Campylobacter jejuni for Survival in Amoeba and Chicken.

Campylobacter jejuni endure to be major cause of gastroenteritis in humans worldwide. C. jejuni is fastidious in laboratory setup but can cause waterborne infection through contaminated water where none of these fastidious conditions are met. This dissertation presents an assortment of studies focused in reviewing three major factors which could present a helping hand to C. jejuni in its environmental survival viz. i) association with free-living amoebae (FLA) ii) horizontal gene transfer (HGT) contributing towards its genetic diversity iii). Viable but non-culturable (VBNC) state. Acanthamoeba is a FLA linked to environmental survival of many intracellular pathogens, including C. jejuni. In Chapter-2, we studied role of 10 important C. jejuni genes in C. jejuni-Acanthamoeba interactions. Deletion mutants of these C. jejuni genes were constructed and used in internalization and 24-hrs survival assay with A. castellanii and A. polyphaga. We found that these genes are important in C. jejuni-Acanthamoeba interactions. C. jejuni benefits in transition in changing ecology by its genetic diversity largely attributed by HGT. In Chapter-3, we presented evidence of extensive HGT through homologous recombination between two C. jejuni marker strains distinguished by their chromosomally encoded antibiotic markers. We found that naked extrachromosomal DNA is an important player in contributing genetic diversity in C. jejuni. Chicken cecal supernatant was found a better recombination medium for HGT for C. jejuni. In chapter-4, whole-proteome of C. jejuni from C. jejuni-Acanthamoeba interaction was analyzed using differentially expressed proteins. Relative abundance of 404 C. jejuni proteins help us understand that in 3hrs interaction C. jejuni shifts its metabolism towards fumarate in its intracellular survival in A. castellanii. Results from chapter-2 and 4, indicate that C. jejuni has conserved mechanisms while interacting with both human and amoeba host. Inability to culture using conventional culture techniques present a major hurdle in studying C. jejuni in its VBNC state. C. jejuni transition from physiologically active to VBNC, whole-proteome comparison between samples collected at time-points between 1day and 30days was made in chapter-5. After clustering analysis by using 575 identified C. jejuni proteins, 7 clusters of proteins were identified which share a similar trend in this transition period