09/17/2020

Novel Bacterium Uses Iron and Lignin to Grow Without Oxygen

Scientists explored ways to modify or decompose lignin for industrial applications to produce renewable fuels and chemical feedstocks.

The Science

Lignin is a network of rigid molecules that makes plant stems woody. It is the largest renewable source of phenolics, molecules for biofuels, and renewable chemical feedstocks. However, it is a largely untapped resource because lignin is difficult to chemically break down into useful components. Now a team of scientists has studied how a novel bacterium uses lignin to support its growth under oxygen-free conditions. The scientists identified a protein from this bacterium that interacts with iron bound to lignin and potentially generates reactive molecules that could break down lignin.

The Impact

Aerobic fungi and bacteria that live in oxygen-rich environments are the most common microbes studied for lignin destruction. However, these growing conditions result in costly processes for industrial biotechnology because they require constant aeration and mixing. Thirty years ago, anaerobic bacteria that live in oxygen-free conditions were thought not to have a role in the degradation of lignin. However, more recent findings have confirmed they do have these capabilities. Continued research into the biochemistry of their lignin degradation abilities could make these anaerobic bacteria a suitable alternative to aerobic microorganisms for industrial applications.

Summary

Tolumonas lignolytica BRL6-1 is a novel soil bacterium isolated from forest soils in Puerto Rico growing on lignin as the sole carbon source under oxygen-free conditions. To determine how lignin is involved in the anaerobic metabolism and growth of this bacterium, scientists compared the protein abundance in cultures that were either amended or unamended with lignin.

The team isolated a protein from the lignin-amended cultures that had structural similarity to a family of proteins, called radical S-adenosylmethionine (SAM) proteins, which are known to be abundant in anaerobic bacteria and support a diverse range of metabolic processes. Based on further studies of this protein, and other efforts on carbon metabolism and iron availability, the team believes that this bacterium uses a protein in the radical SAM superfamily to interact with iron [Fe(III)] bound to lignin. This interaction reduces iron to Fe(II) for cellular use and increases bacterial growth under lignin-amended conditions. The process potentially generates organic free radicals and causes a radical cascade which that could separate lignin into its components. Further research should clarify the extent to which this mechanism is similar to that of lignin-destroying enzymes under oxygen-rich conditions.

This work was performed as part of the Plant and Ecosystem Phenotyping Integrated Research Platform at EMSL, the Environmental Molecular Sciences Laboratory (EMSL), a U.S. Department of Energy Office of Science user facility. At EMSL, the scientists used a Velos Orbitrap mass spectrometer.

Principal Investigator(s)

Kristen DeAngelis
University of Massachusetts
deangelis@microbio.umass.edu

Josh Adkins
Pacific Northwest National Laboratory
joshua.adkins@pnnl.gov

Funding

Office of Biological and Environmental Research, within the U.S. Department of Energy (DOE) Office of Science, for the DOE Joint BioEnergy Institute and the Environmental Molecular Sciences Laboratory; and the U.S. Environmental Protection Agency.

References

G. Chaput, et al., “Lignin induced iron reduction by novel sp., Tolumonas lignolytic BRL6-1.” PLOS ONE 15, e0233823 (2020). [DOI:10.1371/journal.pone.0233823]