Evidence That an Internal Carbonic Anhydrase Is Present in 5% CO₂-Grown and Air-Grown Chlamydomonas

Abstract

Inorganic carbon (Ci) When Chlamydomonas reinhardtii is grown photoautotrophically with low levels ofC02, it becomes very efficient in utilizing external inorganic carbon for photosynthesis. Under these conditions, cells require only low concentrations of CO2 for growth (3), and CO2 fixation is not inhibited significantly by 02. Badger et al. (1) proposed that Chlamydomonas has the ability to raise the level of CO2 internally by a C.4 accumulation system. Accumulation of Ci would increase CO2 fixation and decrease photorespiration (17,19,26). However, the mechanism of this Ci uptake is unclear.

Thylakoid Lumen Carbonic Anhydrase (CAH3) Mutation Suppresses Air-Dier Phenotype of LCIB Mutant in Chlamydomonas reinhardtii

“…The requirement of a thylakoidal CA and an acidic compartment in a functional CCM was first suggested by Pronina and colleagues, and later CAH3 was identified and proposed to catalyze the rapid conversion of HCO 3 2 to CO 2 in the acidic thylakoid lumen, with the CO 2 then diffusing to the pyrenoid to supply elevated substrate CO 2 concentrations for Rubisco (Pronina et al, 1981;Pronina and Semenenko, 1990;Funke et al, 1997;Raven, 1997;Karlsson et al, 1998;Hanson et al, 2003;Moroney and Ynalvez, 2007). Consistent with previous reports (Spalding et al, 1983a;Moroney et al, 1987), the L-CO 2 -acclimated CAH3 single mutant wtsu6, generated in a cross between the suppressed line and wild type, accumulated a very high internal Ci concentration but was unable to use Ci efficiently for photosynthesis. However, the photosynthetic Ci affinity of this CAH3 single gene mutant wt-su6 still is significantly higher than that of the L-CO 2 -acclimated LCIB mutant ad1, which accumulates only very low internal Ci levels and cannot grow at all in L-CO 2 , both traits agreeing with prior reports of the characteristics of the allelic LCIB mutant pmp1 and various CAH3 single mutants (Spalding et al, 1983a(Spalding et al, , 1983bMoroney et al, 1987;Suzuki and Spalding, 1989).…”

Isolation and Characterization of a Mutant of Chlamydomonas reinhardtii Deficient in the CO2 Concentrating Mechanism

“…3). In wild-type, EZ caused an increased accumulation of Ci presumably by inhibiting an internal carbonic anhydrase (17,21). In the experiments with EZ, the periplasmic carbonic anhydrase was also inhibited.…”

“…It is presently thought to involve a C, transporter (14,20) and one or more isozymes of carbonic anhydrase (10,14,21). A carbonic anhydrase located in the periplasmic space of the alga has been identified as part of the CO2 concentrating system (6, 1 1, 31).…”

“…This protein is made only when the cells are grown in the light with low concentrations of CO2 (8, 27,29,30). The existence of other components of the CO2 concentrating system has been inferred from studies of C. reinhardtii mutants (23)(24)(25), Ci uptake measurements (21), and from 35S-labeling studies of cells that are adapting to low CO2 conditions (13).…”

Potassium Fluxes in Chlamydomonas reinhardtii (I.Kinetics and Electrical Potentials)

“…Cultures were stirred and aerated during their subsequent growth. Samples were withdrawn axenically from the flasks at hourly intervals and 1-mL samples (four replicates for each period) were layered on top of a small volume (200 pL) of silicone oil (1:l AR 20/AR 200; Wacker Chemie, Miinich, Germany) in a 1.5-mL microcentrifuge tube (Moroney et al, 1987). These subsamples were centrifuged (Eppendorf centrifuge 5415, Brinkmann) through the silicone oil for 20 s at 10,000 rpm.…”