Exploring the biology and evolution of Blastocystis and its role in the microbiome

Blastocystis is a microbial eukaryote, considered to be the most prevalent microbe colonizing the human gut, colonising approximately one billion individuals worldwide. Although Blastocystis presence has been linked to intestinal disorders, its pathogenicity still remains controversial due to its high prevalence in asymptomatic carriers. Having 17 genetic subtypes, Blastocystis is extremely diverse and can withstand fluctuations of oxygen in the gut. Blastocystis harbors peculiar mitochondrion-related organelles (MROs), which are considered to be an intermediate form between a typical aerobic mitochondrion and an obligate anaerobic hydrogenosome. Another interesting fact about Blastocystis concerns its mixed genome: 2.5% of the Blastocystis proteins have been laterally acquired from eukaryotes and prokaryotes. These acquired genes are associated with carbohydrate scavenging and metabolism, anaerobic amino acid and nitrogen metabolism, oxygen-stress resistance, and pH homeostasis. In addition, Blastocystis has proteins associated with secretion that are potentially involved in infection, escaping host defense and even affect composition of the prokaryotic microbiome and inflammation of the gut. In this chapter, we will challenge the state-of-the-art on Blastocystis knowledge, and we will present published data that can be used to understand the genomic adaptations of this microbial organism and its role within the microbiome of the hosts.