A Small Genome Amidst the Giants: Evidence of Genome Reduction in a Small Tubulinid Free-Living Amoeba

Abstract

This study investigates the genomic characteristics ofEchinamoeba silvestris, a small-sized amoeba within the Tubulinea clade of the Amoebozoa supergroup. Despite Tubulinea’s significance in various fields, genomic data for this clade have been scarce. E. silvestrispresents the smallest free-living amoeba genome within Tubulinea and Amoebozoa to date. Comparative analysis reveals intriguing parallels with parasitic lineages in terms of genome size and predicted gene numbers, emphasizing the need to understand the consequences of reduced genomes in free-living amoebae. Functional categorization of predicted genes inE. silvestrisshows similar percentages of ortholog groups to other amoebae in various categories, but a distinctive feature is the extensive gene contraction in orphan (ORFan) genes and those involved in biological processes. Notably, among the few genes that underwent expansion, none are related to cellular components, suggesting adaptive processes that streamline biological processes and cellular components for efficiency and energy conservation. The investigation delves into genomic structural evidence, including gene content and repetitive elements, illuminating the distinctive genomic traits ofE. silvestrisand providing reinforcement for its compact genome size. Overall, this research underscores the diversity within Tubulinea, highlights knowledge gaps in Amoebozoa genomics, and positionsE. silvestrisas a valuable addition to genomic datasets, prompting further exploration of complexities in Amoebozoa diversity and genome evolution.