Architectural and biochemical advances in understanding microbial CO₂ concentrating mechanisms

CO₂ concentrating mechanisms (CCMs) are ubiquitous in phototrophs. They are found in the micro as well as the macro world. Different domains of life have developed strikingly different approaches to concentrate inorganic carbon around Rubisco, the most prevalent enzyme on earth. While prokaryotes have developed carboxysomes, icosahedral shell protein cages, microbial eukaryotic phototrophs such as green algae, on the other hand, have developed pyrenoids, liquid-liquid phase separated organelles. In contrast to carboxysomes and pyrenoids, which represent biophysical CCMs, some vascular plants (C4 & CAM plants) have developed biochemical ways of concentrating CO₂ around Rubisco. In this review, we discuss advances in structural, biochemical, and mechanistic understanding of microbial CCMs in the last 5-10 years.