Investigating the genes responsible for Paramecium caudatum’s response to Holospora undulata bacterial infection

Abstract

Holospora undulata is a bacterial endosymbiont of the freshwater unicellular protist, Paramecium caudatum. It has been found that different strains of P. caudatum exhibit varying rates of resistance to the bacterial infection (Weiler et al., 2020). In this experiment, six genes that were found to be upregulated during H. undulata infection, were chosen to be observed among several different strains of P. caudatum that evolved from a common ancestral line. In this paper, only genes CC3 and UK3 will be discussed. A multiple sequence alignment was performed to observe the differences in nucleotide and amino acid changes across each strain for each respective gene. To better understand the evolutionary selection that these genes undergo, Z-Tests (pairwise and overall averages) were performed for each gene in respect to each type of selection (neutral, positive, or purifying). Additionally, phylogenies were created to provide a visual of relatedness of the gene within each of the strains. As a result, gene CC3 was found to undergo purifying selection and UK3 undergoes neutral selection. This information allows for more insight on the genetic and coevolutionary behavior within Paramecium caudatum as a response to Holospora undulata infection. Keywords: Biology, Holospora undulata, Paramecium caudatum, genetics, evolution, bacteria, endosymbiosis, coevolution