title: Adaptation of a cyanobacterium to a biochemically rich environment in experimental evolution as an initial step toward a chloroplast-like state.
abstract: Chloroplasts originated from cyanobacteria through endosymbiosis. The original cyanobacterial endosymbiont evolved to adapt to the biochemically rich intracellular environment of the host cell while maintaining its photosynthetic function; however, no such process has been experimentally demonstrated. Here, we show the adaptation of a model cyanobacterium, Synechocystis sp. PCC 6803, to a biochemically rich environment by experimental evolution. Synechocystis sp. PCC 6803 does not grow in a biochemically rich, chemically defined medium because several amino acids are toxic to the cells at approximately 1 mM. We cultured the cyanobacteria in media with the toxic amino acids at 0.1 mM, then serially transferred the culture, gradually increasing the concentration of the toxic amino acids. The cells evolved to show approximately the same specific growth rate in media with 0 and 1 mM of the toxic amino acid in approximately 84 generations and evolved to grow faster in the media with 1 mM than in the media with 0 mM in approximately 181 generations. We did not detect a statistically significant decrease in the autotrophic growth of the evolved strain in an inorganic medium, indicating the maintenance of the photosynthetic function. Whole-genome resequencing revealed changes in the genes related to the cell membrane and the carboxysome. Moreover, we quantitatively analyzed the evolutionary changes by using simple mathematical models, which evaluated the evolution as an increase in the half-maximal inhibitory concentration (IC50) and estimated quantitative characteristics of the evolutionary process. Our results clearly demonstrate not only the potential of a model cyanobacterium to adapt to a biochemically rich environment without a significant decrease in photosynthetic function but also the properties of its evolutionary process, which sheds light of the evolution of chloroplasts at the initial stage.
authors.affiliation: Institute for Academic Initiatives, Osaka University, Suita, Osaka, Japan.
authors.forename: Kazufumi
authors.initials: K
authors.lastname: Hosoda
authors.affiliation: Department of Frontier Biosciences, Graduate School of Frontier Biosciences, Osaka University, Suita, Osaka, Japan.
authors.forename: Masumi
authors.initials: M
authors.lastname: Habuchi
authors.affiliation: Quantitative Biology Center, RIKEN, Suita, Osaka, Japan.
authors.forename: Shingo
authors.initials: S
authors.lastname: Suzuki
authors.affiliation: Department of Biotechnology, Graduate School of Engineering, Osaka University, Suita, Osaka, Japan.
authors.forename: Mikako
authors.initials: M
authors.lastname: Miyazaki
authors.affiliation: Department of Bioinformatic Engineering, Graduate School of Information Science and Technology, Osaka University, Suita, Osaka, Japan.
authors.forename: Go
authors.initials: G
authors.lastname: Takikawa
authors.affiliation: Department of Bioinformatic Engineering, Graduate School of Information Science and Technology, Osaka University, Suita, Osaka, Japan.
authors.forename: Takahiro
authors.initials: T
authors.lastname: Sakurai
authors.affiliation: Faculty of Agriculture and Life Science, Hirosaki University, Hirosaki, Aomori, Japan.
authors.forename: Akiko
authors.initials: A
authors.lastname: Kashiwagi
authors.affiliation: Department of Bioinformatic Engineering, Graduate School of Information Science and Technology, Osaka University, Suita, Osaka, Japan.
authors.forename: Makoto
authors.initials: M
authors.lastname: Sueyoshi
authors.affiliation: Department of Bioinformatic Engineering, Graduate School of Information Science and Technology, Osaka University, Suita, Osaka, Japan.
authors.forename: Yusuke
authors.initials: Y
authors.lastname: Matsumoto
authors.affiliation: Department of Biotechnology, Graduate School of Engineering, Osaka University, Suita, Osaka, Japan.
authors.forename: Ayako
authors.initials: A
authors.lastname: Kiuchi
authors.affiliation: Department of Frontier Biosciences, Graduate School of Frontier Biosciences, Osaka University, Suita, Osaka, Japan.
authors.forename: Kotaro
authors.initials: K
authors.lastname: Mori
authors.affiliation: Department of Frontier Biosciences, Graduate School of Frontier Biosciences, Osaka University, Suita, Osaka, Japan; Department of Bioinformatic Engineering, Graduate School of Information Science and Technology, Osaka University, Suita, Osaka, Japan; Exploratory Research for Advanced Technology (ERATO), Japan Science and Technology Agency, Suita, Osaka, Japan.
authors.forename: Tetsuya
authors.initials: T
authors.lastname: Yomo
mesh_terms: D000220:Adaptation, Biological; D000465:Algorithms; D052818:Autotrophic Processes; D005075:Biological Evolution; D002736:Chloroplasts / Q000378:metabolism*; D000458:Cyanobacteria / Q000502:physiology*; D004777:Environment; D016680:Genome, Bacterial; D059014:High-Throughput Nucleotide Sequencing; D008962:Models, Theoretical