Inorganic carbon acquisition in some synurophyte algae.

Area of Science:

• Photosynthesis research
• Algal physiology
• Carbon fixation mechanisms

Background:

• Synurophyte algae play a role in aquatic ecosystems.
• Understanding inorganic carbon (Ci) uptake mechanisms is crucial for algal photosynthesis.
• Previous studies on Ci uptake in algae have shown diverse strategies.

Purpose of the Study:

• To investigate the inorganic carbon (Ci) uptake mechanisms in three synurophyte algae species: Synura petersenii, Synura uvella, and Tessellaria volvocina.
• To determine if these algae utilize a CO2-concentrating mechanism.
• To elucidate the role of carbonic anhydrase and bicarbonate transport in their photosynthetic processes.

Main Methods:

• Measurement of internal pH using radiolabeled compounds.
• Mass spectrometry to monitor O2 evolution and CO2 uptake.
• Enzyme kinetic analysis of ribulose-1,5-bisphosphate carboxylase/oxygenase (Rubisco).

Main Results:

• All three species lack external carbonic anhydrase and direct bicarbonate uptake.
• Synura petersenii maintains an internal pH of 7.0-7.5, facilitating CO2 diffusion.
• Low whole-cell affinity for Ci was observed, with CO2 compensation points around 24 microM.
• Rubisco's high CO2 affinity (low K(m) values) appears to be the primary driver for Ci acquisition.

Conclusions:

• Synurophyte algae studied do not possess a typical CO2-concentrating mechanism.
• Inorganic carbon uptake is primarily driven by CO2 diffusion, supported by a significant pH gradient.
• The high CO2 affinity of Rubisco is a key adaptation for carbon acquisition in these species.