Poster: Photosynthesis

Abs # 321: Expression of foreign RuBisCO in carboxysomeless mutant of a cyanobacterium, Synechococcus PCC 7942

Presenter:	Wadano, Akira , wadano@biochem.osakafu-u.ac.jp
Authors	Wadano, Akira  (A)   Tukamoto, Manabu  (A)   Iwaki, Toshio  (A)
Affiliations:	(A): Dept. Applied Biochem. Osaka Prefecture University

Cyanobacterium, Synechococcus PCC 7942, has carboxysomes as a component of inorganic carbon concentrating mechanism. The component contains ribulose 1,5-bisphosphate carboxylase/oxygenase (RuBisCO) and carbonic anhydrase. The existence of the organelle makes complicate the relationship between the content of RuBisCO and photosynthetic ability of the cyanobacterium. In order to simplify the relationship, carboxysomeless mutant was established with deletion of CCM gene. Then a foreign RuBisCO from Chromatium vinosum was expressed in the mutant using a promoter of PsbAII from Synechocystis PCC 6803. The C. vinosum RuBisCO has 30 M of KmCO₂ and 70 of specific factor, while KmCO₂ and specific factor of the cyanobacterium RuBisCO are about 250 M and 70. The highest activity of the enzyme in crude extract from the mutant was ca. 5 times of that from the control strain with the empty plasmid pUC303. The growth rates of these mutants were checked under enough light for the growth of wild strain. Under 5% CO2 concentration in air, the growth rate of the highest RuBisCO strain was about the same of that of the control strain. Under the 5% CO₂ and 2% O₂ condition, however, the former grew faster than it did under the condition mentioned above, while the growth rate of the control strain was not changed. These facts show that the photosynthesis of the cyanobacterium mutant is limited by the RuBisCO activity under the low O₂ condition. Unlike the case of the higher plant, the photosynthesis of the mutant is limited by the activity of RuBisCO instead of photosystem.