Phylogenomic analyses reveal subclass Scuticociliatia as the sister group of subclass Hymenostomatia within class Oligohymenophorea

Scuticociliates and hymenostomes are two groups of the ciliate class Oligohymenophorea, a diverse clade that includes two model genera, Tetrahymena and Paramecium, which have been intensively studied due to their ease of culture and their amenability to a wide range of biochemical and genetic investigations. However, phylogenetic relationships among the subclasses of the Oligohymenophorea, and especially between the Scuticociliatia and Hymenostomatia, are not clearly resolved. Here, we investigate the phylogenetic relationship between the subclasses Scuticociliatia and Hymenostomatia based on omics data. The transcriptomes of five species, comprising four oligohymenophoreans and one colpodean, were sequenced. A supermatrix was constructed for phylogenomic analyses based on 113 genes encoding 43,528 amino acid residues from 26 taxa, including ten representatives of the class Oligohymenophorea. Our phylogenomic analyses revealed that the monophyletic Scuticociliatia is sister to the monophyletic Hymenostomatia, which together form the terminal branch within the monophyletic class Oligohymenophorea. Competing hypotheses for this relationship were rejected by topological tests. Our results provide corroborative evidence for the close relationship between the subclasses Scuticociliatia and Hymenostomatia, justifying the possible use of the model hymenostome T. thermophila as an effective experimental system to study the molecular and cellular biology of the scuticociliates. (C) 2015 Elsevier Inc. All rights reserved

Identification and characterization of the arsenite methyltransferase from a protozoan, Tetrahyrnena pyriformis

Arsenic (As) methylation in aquatic microbes plays a major role in the biogeochemistry of As. Protozoa, especially the free-living freshwater species, are important players in aquatic ecological health. In this study, an arsenite (As(III)) methyltransferase, TpyArsM, was identified and characterized in a free-living protozoan, Tetrahymena pyriformis. In order to confirm its function, TpyarsM gene was knocked-out in Tetrahymena and was also heterologously expressed in hypersensitive E. coil; these events resulted in expected decreases in As tolerance and methylation ability, respectively. In-vitro tests revealed that purified TpyArsM protein methylated inorganic As to mono- and di- methylarsenate, and also had the novel property of producing trimethylarsenite (TMA(III)) and dimethylarsine (Me2AsH) gases. This new methyltransferase gene, identified in a species near the base of the food web, has enriched our knowledge of As methyltransferases and has great potential for bioremediation of As-contaminated environments. (C) 2014 Elsevier B.V. All rights reserved.Arsenic (As) methylation in aquatic microbes plays a major role in the biogeochemistry of As. Protozoa, especially the free-living freshwater species, are important players in aquatic ecological health. In this study, an arsenite (As(III)) methyltransferase, TpyArsM, was identified and characterized in a free-living protozoan, Tetrahymena pyriformis. In order to confirm its function, TpyarsM gene was knocked-out in Tetrahymena and was also heterologously expressed in hypersensitive E. coli; these events resulted in expected decreases in As tolerance and methylation ability, respectively. In-vitro tests revealed that purified TpyArsM protein methylated inorganic As to mono- and di- methylarsenate, and also had the novel property of producing trimethylarsenite (TMA(III)) and dimethylarsine (Me2AsH) gases. This new methyltransferase gene, identified in a species near the base of the food web, has enriched our knowledge of As methyltransferases and has great potential for bioremediation of As-contaminated environments. (C) 2014 Elsevier B.V. All rights reserved