An inducible CO2 concentrating mechanism in cyanobacterium Anabaena sp strain PCC7120

In order to define its characteristics of the photosynthetic utilization of CO2 and HCO3- when the ambient inorganic carbon changed, HCG (High-CO2-Gro wing Cells) of cyanobacterium Anabaena sp. strain PCC7120 were prepared. Th e growth rate of HCG was higher than that of LCG (low-CO2-growing cells, i. e. air-growing cells). When the HCG cells were transferred from 5% CO2 to a ir levels of CO2 , a series of changes took place: its carbonic anhydrase a ctivity as well as its photosynthetic affinity to the external inorganic ca rbon significantly increased; the number of the carboxysomes, which is one of the most important components of CCM in cyanobacteria also increased. Th ese facts indicated that the CCM activity of Anabaena PCC 7120 was induced. When the pH in the medium increased from 6 to 9, the photosynthetic affini ty to external inorganic carbon of both HCG and LCG declined, while the app arent photosynthetic affinity to external CO2 increased. In the light of th ese findings, this inducible CCM in cyanobacteria provided a good model for the study of the photosynthetic Ci utilization in the phototrophic microog anisms.