1. Adaptation of a Cyanobacterium to a Biochemically Rich Environment in Experimental Evolution as an Initial Step toward a Chloroplast-Like State
- Author
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Go Takikawa, Tetsuya Yomo, Makoto Sueyoshi, Mikako Miyazaki, Akiko Kashiwagi, Kotaro Mori, Yusuke Matsumoto, Shingo Suzuki, Masumi Habuchi, Kazufumi Hosoda, Takahiro Sakurai, and Ayako Kiuchi
- Subjects
Cyanobacteria ,Artificial Ecosystems ,Chloroplasts ,Cell Membranes ,Adaptation, Biological ,lcsh:Medicine ,Biochemistry ,Genome Sequencing ,Amino Acids ,lcsh:Science ,chemistry.chemical_classification ,Experimental evolution ,Autotrophic Processes ,Multidisciplinary ,biology ,Endosymbiosis ,Ecology ,Synechocystis ,High-Throughput Nucleotide Sequencing ,Genomics ,Biological Evolution ,Amino acid ,Chloroplast ,Carboxysome ,Prokaryotic Models ,Cellular Structures and Organelles ,Algorithms ,Research Article ,Environment ,Photosynthesis ,Research and Analysis Methods ,Microbiology ,Ecosystems ,Microbial Ecosystems ,Model Organisms ,Plant and Algal Models ,Botany ,Genetics ,Molecular Biology Techniques ,Sequencing Techniques ,Molecular Biology ,Evolutionary Biology ,Bacterial Evolution ,lcsh:R ,Ecology and Environmental Sciences ,Biology and Life Sciences ,Proteins ,Bacteriology ,Cell Biology ,Models, Theoretical ,biology.organism_classification ,Organismal Evolution ,chemistry ,Microbial Evolution ,lcsh:Q ,Genome, Bacterial - 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.
- Published
- 2014