Draft Genome of Entamoeba marina Provides Insights Into the Attenuation of Pathogenicity and Adaptation to the Marine Environment

Entamoeba is the amoebozoan parasite commonly found in the intestines of animals. E. marina is the first exception isolated from marine sediments, possibly adapting from animal intestines to the sea. However, the evolutionary process of E. marina remains uncertain due to the lack of a genome sequence. Here, we present the de novo genome and transcriptome of E. marina using Oxford Nanopore MinION and Illumina HiSeq/MiSeq. The genome of E. marina is approximately 37.5 Mbp in length and consists of 202 contigs, which is the second longest, next to E. invadens. E. marina showed a significant reduction in the major virulence-associated gene families, including cysteine proteases, lysosomal enzyme transporters, and surface galactose/N-acetylglucosamine-specific lectins, suggesting diversification, more specifically, reduction of pathogenicity-related genes. Genome and RNA-seq analyses also indicated genes either conserved throughout eukaryotes or laterally transferred from prokaryotes, and potentially responsible for salt tolerance. Our study provides insights into the mechanisms underlying the lifestyle changes in the evolution of parasitic eukaryotes.