Multitasking Microbes Could Improve Biofuel Economics

The Science

Newswise — Lignin is a major part of plant cells that makes them strong and rigid. It is made of compounds known as aromatics strung together in chains. Scientists have engineered microbes that can funnel these aromatics into single chemicals used to make plastics and other valuable materials. New research shows that one bacterium can be modified to simultaneously produce two valuable compounds from pretreated sorghum biomass: carotenoids and an acid called PDC. Carotenoids are a group of organic pigments used in nutritional supplements, drugs, and cosmetics. PDC can be used to make plastics. The bacteria accumulate carotenoids within their cells, and they secrete PDC from the cells, providing two valuable products that can be easily separated in a single batch.

The Impact

Lignin is the world’s largest renewable source of aromatic carbon. However, its complex and irregular structure makes it hard to break apart into useful components. Most industrial microbes cannot process the mix of aromatics in lignin that has been treated with chemicals to separate the lignin from plant sugars. Converting this abundant raw material into valuable products is one of the keys to making plant-based products a cost-competitive alternative to fossil fuels and petrochemicals. Using microbes to produce multiple products in a single batch could make biorefineries more sustainable and economically viable. This would help make bioproducts more useful in efforts to respond to climate change.

Summary

Scientists with the Great Lakes Bioenergy Research Center showed that a strain of Novosphingobium aromaticivorans naturally produces the carotenoid nostoxanthin. By deleting or adding selected genes, they engineered strains that produced the valuable carotenoids beta-carotene, lycopene, zeaxanthin, and astaxanthin. They showed that these engineered strains produced carotenoids at comparable levels when grown either in laboratory media or in alkaline-pretreated sorghum biomass, which contains a mixture of aromatics.

Finally, they engineered strains that when grown on sorghum liquor produced zeaxanthin, beta-carotene, or astaxanthin concurrently with 2-pyrone-4,6-dicarboxylic acid (PDC), a potential building block for biodegradable polymers. Combined, the results show that N. aromaticivorans can simultaneously produce valuable intracellular and extracellular commodities when grown in the presence of either pure aromatics or pretreated lignocellulosic biomass.

Funding

This material is based on work supported by the Great Lakes Bioenergy Research Center of the Department of Energy Office of Science, Office of Biological and Environmental Research, and by a National Institutes of Health NIH Training Grant.