[VIDEO] How bacteria organize their factories, and what it means for a bioeconomy

  • Dec 6, 2018
  • Ducat lab, fundamental research
  • Feature News Story
  • By Igor Houwat, Danny Ducat

Deep in the bowels of the Arctic Ocean, or floating at the edges of scalding hot springs at Yellowstone National Park, cyanobacteria thrive in conditions that kill most other life forms. One out of three breaths we take is thanks to the oxygen they create through the process of expand iconphotosynthesis.

expand iconCyanos – as they are called for short - are tiny, each 25 times smaller than the width of a human hair. But they are great at photosynthesis because each cyano cell contains special factories, called expand iconcarboxysomes. The carboxysome increases the efficiency of capture of carbon dioxide from the air. That carbon dioxide is then used to make energy molecules that the cyanos live on.

The factories are so productive that scientists want to use them to make stuff they don't naturally create. New products could include biofuels, industrial materials, or medical tools. And these green production methods wouldn’t require fossil fuels to work.

But first, we are learning how the factories are built and how they work.

New research from the labs of Danny Ducat and Katherine Osteryoung, from Michigan State University, and Anthony Vecchiarelli, from the University of Michigan, shows how the factories ‘get in an orderly line’ inside their hosts, to maximize their impact. The knowledge gives us the potential to someday control their movement inside cyanos (see video). The study is published in eLife.

The Science: Skating across DNA

“Each cyanobacterium has 4 to 8 factories that are aligned in the cell through a mechanism that separates them from one another, and spaces them evenly apart. But that mechanism has eluded us so far,” says Daniel Ducat, Assistant Professor at the MSU-DOE Plant Research Laboratory.

Joshua MacCready, a graduate student in the Ducat and Osteryoung labs, found that factories get in line in their spots in a system that works like Velcro.

Animation of factory skating across DNA
McdB (red) interacts with McdA (green), causing the carboxysome to skate across the DNA.

A expand iconprotein, called McdB, coats the outside of the factories and acts like Velcro hooks. Another protein, called McdA, analogous to tiny loops, binds to the DNA that floats inside the entire cyano.

As a factory moves in the cell, the “hooks” on its surface find a “loop” on the DNA. The two connect, and the factory is pulled in the direction of that connection.

Unlike Velcro however, the hooks (McdB) can pull the loop (McdA) off of the DNA. That leaves the factories free to look for another partner, using DNA as a surface to ‘skate' across. This continual search for new binding partners pulls the carboxysome factory in a certain direction (see gif above).

The system also keeps factories spaced away from each other inside a cyano cell (see figure below).

Figures of the McdB-A system's alignment
A) Heat map of the McdB/McdA interaction localizing on a cyanobacterium cell's central axis; B) The system stays on that axis as it moves inside the cell; C) Differing numbers of carboxysome per cell impacts their linear arrangement, but they remain centrally aligned and equally spaced from each other.
By Joshua MacCready, 2018

The team thinks this mechanism serves two purposes:

  • Cell division. By controlling where it places factories, a parent cyano makes sure its daughter cells each get the same number of factories and starts its life on an equal footing.
  • Resource usage. By staying apart, carboxysome factories don’t compete for their surrounding resources.

“The beauty of this system is that it is self-organized. There is no master regulator directing it. It is all based on local chemical attractions,” Danny says.

So what applications does this knowledge tease?

To repurpose these factories to make biofuels and other products, scientists will need to control their placement inside cells, so they can do their most efficient work

“If we can make this work, making products like biofuels from sunlight and some carbon dioxide might be even more efficient. The result is a much friendlier environmental output,” Danny says.

“There is evidence this system is universal across different types of factories found in various bacterial species. That means we have a lot of options to test out different end products.”

This work was primarily funded by the National Science Foundation. Equipment support was provided by the US Department of Energy, Office of Basic Energy Sciences.