Mechanism of Inorganic Carbon Uptake inChlorella saccharophila: The Lack of Involvement of Carbonic Anhydrase

A New Screening Method for Algal Photosynthetic Mutants (CO2-Insensitive Mutants of the Green Alga Chlorella ellipsoidea)

“…Three kinds of wild-type cells used for evaluation of the C-screening method have previously been shown to be different in photosynthetic affinity for DIC, and these differences are due to either the occurrence of externa1 CA or active DIC transport (Gehl et al, 1990;Matsuda and Colman 1995a;Williams and Colman, 1995). Visible differences on autoradiographs of 14C-labeled alga1 plaques among these wild-type cells reflected their photosynthetic affinities for DIC (data not shown).…”

“…Furthermore, the lower K,,,[DIC] value observed in airgrown C. saccharopkila as compared to that of air-grown C. ellipsoidea (Fig. 1) has been shown to be due to the occurrence of externa1 CA in C. sacchavopkiln (Gehl et al, 1990;Williams and Colman, 1995). Cells of air-and high-C0,-grown C. ellipsoidea showed maximal 14C incorporations of about 55 and 15%, respectively, of that in air-grown C. sacckarophila (Fig.…”

“…Chlorella ellipsoidea (UTEX 20) and Chlorella saccharophila (UTEX 2496) were grown axenically in batch culture as described previously (Gehl et al, 1990). High-C0,-grown cells of C. ellipsoidea were obtained by aerating cultures with 6% (v/v) CO,, harvested at mid-logarithmic phase (about 4 X 106 cells mL-'), and mutagenized with x-ray irradiation of 2, 5, or 10 krad.…”

Induction of CO2 and Bicarbonate Transport in the Green Alga Chlorella ellipsoidea (II. Evidence for Induction in Response to External CO2 Concentration)

“…The intracellular DIC concentration in 5-h-adapted cells was also measured at various concentrations of externa1 DIC with added CA. Inner cell volumes were measured as described by Gehl et al (1990). The average inner cell volume was 83.8 FL mg-' Chl (SE 5.54, n = 13) for high C0,-grown cells or 77.1 pL mg-' Chl (SE 2.53, n = 33) for adapting cells.…”

Identification of Distinct Internal and External Isozymes of Carbonic Anhydrase in Chlorella saccharophila

“…Since the DIC-concentrating mechanism in these algae is also repressed by COz, it has been suggested that extemal CA is required at alkaline pH to facilitate the supply of COZ to a transporter from a large HC03-pool at alkaline pH (Aizawa and Miyachi, 1986). Other evidence suggests that, under some conditions, the ability to transport inorganic carbon is not affected by the remova1 of extemal CA (Williams and Turpin, 1987;Gehl et al, 1990). The sequences of some forms of CA from spinach (Fawcett et al, 1990), pea (Majeau and Coleman, 1991), and C. reinhardtii as well as E. coli (Guilloton et al, 1992) have been established.…”