AUTHOR=Mukhtar Irum , Wu Siyi , Wei Shurong , Chen Ruanni , Cheng Yunying , Liang Chen , Chen Jianming 

TITLE=Transcriptome Profiling Revealed Multiple rquA Genes in the Species of Spirostomum (Protozoa: Ciliophora: Heterotrichea)

JOURNAL=Frontiers in Microbiology

VOLUME=11

YEAR=2021

URL=https://www.frontiersin.org/journals/microbiology/articles/10.3389/fmicb.2020.574285

DOI=10.3389/fmicb.2020.574285

ISSN=1664-302X

ABSTRACT=<p>Adaptation to life at different oxygen tensions plays a role in protozoan ecology and controls the distribution of different species in anoxic habitats. The ciliate genus <italic>Spirostomum</italic> inhabiting fresh or low salinity water globally where these species are considered as bioindicators. Under anaerobic or low oxygen conditions, the rhodoquinol-dependent pathway has been reported in the species from the class Heterotrichea. With the help of RNA sequencing (RNAseq) data, <italic>Spirostomum</italic> spp., are suitable for deep molecular investigations on <italic>rquA</italic> for rhodoquinone (RQ) biosynthesis. In this study, <italic>Spirostomum ambiguum</italic>, <italic>Spirostomum subtilis</italic>, and <italic>Spirostomum teres</italic> collected from densely vegetated freshwater habitat in Fuzhou, China, explored the evidence of <italic>rquA</italic>. Based on transcriptome analysis, two to three RquA proteins were identified in <italic>S. ambiguum</italic>, <italic>S. teres</italic>, and <italic>S. subtilis</italic>, respectively. The presence of a key Motif-I of RquA and mitochondrial targeting signals (MTS), also confirmed the identity of these as RquA. Furthermore, <italic>Spirostomum</italic> RquA proteins could be sorted into two groups based on their conserved amino acid (CAA) residues. Phylogenetic analysis also exhibited RquA division into two subclades contained RquA1 and RquA2/RquA3 and supports two to three paralogs of <italic>rquA</italic> genes in the genomes <italic>Spirostomum</italic> spp. Additional transcriptomes and genomes analysis of <italic>Blepharisma</italic> spp., and <italic>Stentor</italic> spp., respectively, also revealed at least two paralogs of <italic>rquA</italic> in members of the class Heterotrichea. The present study provides evidence for the presence of RquA and rhodoquinol dependent fumarate reduction pathway in <italic>Spirostomum</italic> species potentially use to respire in the oxygen-depleted habitats and two to three diverse <italic>rquA</italic> genes.</p>