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Survival of the fattest: Understanding the role of polyesters in root nodule bacteria

Tuesday, September 19, 2017

S. meliloti bacteriaEven Sinorhizobium meliloti suffers from a weight gain once in a while.

Except that what this bacteria species produces as “fat” is actually a very useful form of biodegradable polyester called polyhydroxybutyrate (PHB). In order to understand how PHB is involved in S. meliloti’s transition from soil inhabitant to an agriculturally important nitrogen fixing symbiont, however, researchers need to understand how this carbon storage mechanism is controlled at the genetic level.

This week, a team of biologists at the University of Waterloo published their transcriptional analysis – a first step toward identifying which genes influence production of PHB – in S. meliloti under the extreme conditions of feast and famine in its environment. It’s under feast conditions that S. meliloti starts overproducing PHB for later use as a food source during leaner times.

Their study appears in the journal mSystems.

The researchers removed key genes in the PHB pathway and studied how the cells responded in the feast and famine conditions. RNA sequencing results showed the bacteria’s carbon storage pathway is somehow linked to its ability to metabolize nitrogen. Additional bioinformatics analysis also predicts which protein may be involved in this regulatory response. They plan to use these results to design their next series of experiments.

Thumbnail of an alfalfa nodule housing the symbiotic bacteria S. meliloti bacteria.S. meliloti, a bacterium that fixes nitrogen in alfalfa roots, has often been used as a model organism to study microbe–plant symbiosis. Agricultural scientists have studied its important role in chemically transforming nitrogen from a gas in the atmosphere into a form that plants can use as fertilizer while the bacteria live in the plant’s roots (image left).

Ultimately, this research could lead to a process for production of PHB and other members of this class of compounds called polyhydroxyalkanoates using related bacteria called methanotrophs, with landfill methane as feedstock. Potential products from polyhydroxyalkanoates include biodegradable food packaging and other products currently based on the petroleum-sourced polypropylene, and they are already used in the production of some plastics and medical products.

Authors on the paper include PhD candidate Maya D’Alessio, former student Ricardo Nordeste, Professor Andrew C. Doxey, and Professor Trevor C. Charles.

The project was funded by a Strategic Projects Grant and a Discovery Grant from the Natural Sciences and Engineering Research Council of Canada and by Genome Canada. Maya D’Alessio was supported by an Ontario Graduate Scholarship.

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