Thread by @CellfOrganized

#Carboxysome positioning is not just for #Cyanobacteria!
New preprint from our lab.

The McdAB system positions α-carboxysomes in proteobacteria

biorxiv.org/content/10.110…

Thread!

Carboxysomes are protein-based organelles essential for carbon fixation in cyanobacteria and proteobacteria, and are responsible for almost half of global CO2 fixation.

We previously identified the McdAB system responsible for carboxysome positioning in S. elongatus. McdA is a ParA-like ATPase that uses the nucleoid as a matrix to distribute carboxysomes down the cell length using McdB as its carboxysome adaptor.

We also recently found that McdAB systems are widespread in beta-cyanobacteria, but absent in alphas!

Since α-carboxysomes are thought to have arisen in proteobacteria and then horizontally transferred into α-cyanobacteria, this raised the question of whether α-carboxysome-containing proteobacteria possess a McdAB system for positioning α-carboxysomes.

We identified the McdAB α-carboxysome positioning system in the model chemoautotrophic proteobacterium H. neapolitanus. Without McdA or McdB, carboxysomes for a massive nucleoid-excluded polar aggregate.

Bioformatic analysis finds that >90% of α-carboxysome-containing proteobacterial genomes encode for an McdAB system.

Our bioinformatics provide an explanation as to why α-carboxysome-containing proteobacteria encode an McdAB system, while α-cyanobacteria do not.

Cyanobacterial α-carboxysomes likely originated from a proteobacterium lacking the mcdAB system within their α-carboxysome operon!

Finally, the presence of McdAB for both carboxysome types begged the question, what about other Bacterial MicroComparments (BMCs) involved in a myriad of metabolic reactions?

We find McdAB sequences neighboring BMC components across diverse microbes.

...we gonna be busy...

This paper was a team effort!

Bioinformatics and Writing by Josh MacCready
Microscopy by Lisa Tran
Biochem by @JoeBasalla
B2H by @puspannehakim

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