Isolation and Characterization of Temperature-Sensitive, High-CO_2 Requiring Mutant of Anacystis nidulans R2

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Temperature-sensitive (ts), high-CO_2 requiring mutants of Anacystis nidulans R2 were isolated by N-methyl-N'-nitro-N-nitrosoguanidine (MNNG) mutagenesis and ampicillin enrichment. One of these mutants was able to grow under ordinary air enriched with 5% CO_2, but not under ordinary air at 40℃. At 40℃, the concentration of CO_2 at which the rate of oxygen evolution reached half the maximum velocity (apparent K_m(CO_2) in photosynthesis) was 1,000 times higher in mutant cells than in wild type cells, whereas there was no significant difference in the maximum rate of photosynthesis. When wild type and mutant cells were incubated with 55 μM NaHCO_3 under illumination at 40℃, the initial rate of inorganic carbon (IC) transport from the medium into the cells and the maximum internal IC accumulation were significantly higher in wild type cells than in mutant cells. These results indicate that the isolated high-CO_2 requiring mutant lacks the ability in transporting IC into the cells at 40℃. Furthermore, the finding that the mutant cells which are defective in IC transport cannot grow under ordinary air suggests the importance of IC concentrating system(s) in photosynthesis of cyanobacteria.
日本植物生理学会の論文