title: Trends in amino acid usage across the class Mollicutes.
abstract: Many studies have explored the mechanisms involved in relative amino acid usage (RAAU) in a variety of prokaryotes and eukaryotes. A strong bias was observed in highly expressed genes (HEGs) of endosymbiotic bacteria. By means of correspondence analysis, we studied the major trends affecting internal variability of RAAU in Mollicutes. The principal trend is related to the usage of smaller, less aromatic, and GC-rich coded amino acids in HEGs. Given the nature of the genetic code, these properties are linked among them. Expectedly, we found a slow evolutionary rate of HEGs, which is likely driven by purifying selection. On the other hand, the rest of the genes accumulate rapid changes as a result of the extreme mutational bias toward A + T of the genomes and genetic drift, increasing internal variability. Amino acid changes across the phylogeny of the group were traced in order to estimate the mean molecular weight and aromaticity trends in each branch. Finally, we compared amino acid usage bias within and between Mollicutes and the free-living Firmicutes.
authors.affiliation: a Laboratorio de Organización y Evolución del Genoma, Facultad de Ciencias , UDELAR. Iguá 4225, Montevideo , 11400 Uruguay.
authors.forename: Andrés
authors.initials: A
authors.lastname: Iriarte
authors.forename: Juan Diego
authors.initials: JD
authors.lastname: Baraibar
authors.forename: Leticia
authors.initials: L
authors.lastname: Diana
authors.forename: Susana
authors.initials: S
authors.lastname: Castro-Sowinski
authors.forename: Héctor
authors.initials: H
authors.lastname: Romero
authors.forename: Héctor
authors.initials: H
authors.lastname: Musto
mesh_terms: D000596:Amino Acids / Q000378:metabolism*; D001426:Bacterial Proteins / Q000235:genetics / Q000378:metabolism; D015870:Gene Expression; D005798:Genes, Bacterial; D040961:Genetic Drift; D009154:Mutation; D010802:Phylogeny; D012641:Selection, Genetic; D008973:Tenericutes / Q000235:genetics / Q000378:metabolism*
chemical_list: D000596:Amino Acids; D001426:Bacterial Proteins