Reversible Germline Dynamics of Caenorhabditis elegans During Exposure to Pathogenic Bacteria

Abstract

Little is known of how pathogen infection affects reproductive fitness and fecundity in metazoa. Caenorhabditis elegans is a free-living nematode and well-characterized animal model that encounters pathogenic microbes in its natural environment. How these pathogens affect the reproductive capacity of C. elegans is not well understood. In this thesis, I examine the effect that exposure to the Gram-negative pathogenic bacteria Pseudomonas aeruginosa has on the reproductive system of C. elegans hermaphrodites. In Chapter One, I discuss the literature surrounding host-pathogen interactions as well as stress responses as they relate to the C. elegans germline.

In Chapter Two, I identify several processes that arise in the C. elegans gonad upon exposure to pathogenic Pseudomonas aeruginosa. I show there is a marked reduction in brood size with concomitant reduction in gonad size and the number of nuclei in the germline. I define two processes that are induced that contribute to the decrease in the number of germ cell nuclei. First, I observe that infection with P. aeruginosa leads to the induction of programmed germ cell death. Second, I observe that this exposure induces mitotic quiescence in the proliferative zone of the C. elegans gonad. Importantly, these processes appear to be reversible; when animals are removed from the presence of P. aeruginosa, germ cell death is abated, germ cell nuclei numbers increase, and brood sizes recover.

In Chapter Three, I discuss the possible implications of these findings and their potential evolutionary value to the host , as well as avenues for further study. The reversible germline effects during exposure to P. aeruginosa may represent an adaptive response to improve survival of progeny and may serve to facilitate resource allocation that promotes survival during pathogen infection.