title: An intact plastid genome is essential for the survival of colorless Euglena longa but not Euglena gracilis.
abstract: Euglena gracilis growth with antibacterial agents leads to bleaching, permanent plastid gene loss. Colorless Euglena (Astasia) longa resembles a bleached E. gracilis. To evaluate the role of bleaching in E. longa evolution, the effect of streptomycin, a plastid protein synthesis inhibitor, and ofloxacin, a plastid DNA gyrase inhibitor, on E. gracilis and E. longa growth and plastid DNA content were compared. E. gracilis growth was unaffected by streptomycin and ofloxacin. Quantitative PCR analyses revealed a time dependent loss of plastid genes in E. gracilis demonstrating that bleaching agents produce plastid gene deletions without affecting cell growth. Streptomycin and ofloxacin inhibited E. longa growth indicating that it requires plastid genes to survive. This suggests that evolutionary divergence of E. longa from E. gracilis was triggered by the loss of a cytoplasmic metabolic activity also occurring in the plastid. Plastid metabolism has become obligatory for E. longa cell growth. A process termed "intermittent bleaching", short term exposure to subsaturating concentrations of reversible bleaching agents followed by growth in the absence of a bleaching agent, is proposed as the molecular mechanism for E. longa plastid genome reduction. Various non-photosynthetic lineages could have independently arisen from their photosynthetic ancestors via a similar process.
authors.affiliation: Department of Genetics, Faculty of Natural Sciences, Comenius University, Mlynská dolina G-1, 842 15, Bratislava, Slovak Republic.
authors.forename: Lucia
authors.initials: L
authors.lastname: Hadariová
authors.affiliation: Department of Biology and Ecology, Faculty of Natural Sciences, Matej Bel University, 974 01, Banská Bystrica, Slovakia.
authors.forename: Matej
authors.initials: M
authors.lastname: Vesteg
authors.affiliation: Department of Genetics, Faculty of Natural Sciences, Comenius University, Mlynská dolina G-1, 842 15, Bratislava, Slovak Republic.
authors.forename: Erik
authors.initials: E
authors.lastname: Birčák
authors.affiliation: Department of Biology, University of Memphis, Memphis, TN, 38152-3560, USA.
authors.forename: Steven D
authors.initials: SD
authors.lastname: Schwartzbach
authors.affiliation: Department of Genetics, Faculty of Natural Sciences, Comenius University, Mlynská dolina G-1, 842 15, Bratislava, Slovak Republic. krajcovic@fns.uniba.sk.|Department of Biology, Faculty of Natural Sciences, University of ss. Cyril and Methodius, 917 01, Trnava, Slovakia. krajcovic@fns.uniba.sk.
authors.forename: Juraj
authors.initials: J
authors.lastname: Krajčovič
mesh_terms: D000595:Amino Acid Sequence; D000900:Anti-Bacterial Agents / Q000494:pharmacology; D060365:Chloroplast Proteins / Q000235:genetics; D018742:DNA, Chloroplast / Q000235:genetics; D005056:Euglena gracilis / Q000235:genetics* / Q000254:growth & development; D044802:Euglena longa / Q000235:genetics* / Q000254:growth & development; D017353:Gene Deletion; D018628:Gene Dosage; D061125:Genes, Chloroplast / Q000235:genetics; D054627:Genome, Plastid / Q000235:genetics*; D016296:Mutagenesis / Q000187:drug effects; D015242:Ofloxacin / Q000494:pharmacology; D018087:Plastids / Q000235:genetics*; D017386:Sequence Homology, Amino Acid; D013045:Species Specificity; D013307:Streptomycin / Q000494:pharmacology; D013997:Time Factors
chemical_list: D000900:Anti-Bacterial Agents; D060365:Chloroplast Proteins; D018742:DNA, Chloroplast; D015242:Ofloxacin; D013307:Streptomycin
keywords: Antibiotics; Astasia; Bleaching; Euglenids; Plastid loss; Plastome degradation