The Genome of Blastocystis sp. Isolated from the Oriental cockroach

Abstract

Blastocystis spp. are unicellular anaerobic stramenopiles that inhabit the colons of a wide range of animals. Previous genome studies of Blastocystis were restricted to mammalian and avian-colonizing subtypes. To investigate a deeper-branching subtype, I used next generation sequencing technologies to characterize the genome of a Blastocystis species from the Oriental cockroach. The ≈40kb mitochondrion-related organelle (MRO) genome was larger than other Blastocystis subtypes but had mostly conserved gene content and order. The nuclear genome was 17.1 Mbp in length, 19.9% GC and differed from other Blastocystis subtypes in gene content by 15-27%. Amongst the encoded proteins are key enzymes of anaerobic ATP generation. Laterally-acquired genes previously described in Blastocystis sp. ST1 were also identified. Unexpectedly, 40% of the nuclear genes possessed homopolymer trinucleotide insertions encoding polyasaparagines. If these mutations are slightly deleterious, they were possibly fixed in the population by genetic drift due to a small effective population size.