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bioRxiv · 10.1101/2020.05.14.095802

Iron Chelator-Mediated Anoxic Biotransformation of Lignin by Novel sp., Tolumonas lignolytica BRL6-1

Chaput, G.·Billings, A. F.·DeDiego, L.·Orellana, R.·Adkins, J. N.·Chu, R.·Simmons, B.·DeAngelis, K. M.
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Abstract

Lignin is the second most abundant carbon polymer on earth and despite having more fuel value than cellulose, it currently is considered a waste byproduct in many industrial lignocellulose applications. Valorization of lignin relies on effective and green methods of delignification, with a growing interest in the use of microbes. Here we investigate the physiology and lignin biotransformation mechanisms of the novel facultative anaerobic bacterium, Tolumonas lignolytica BRL6-1, under anoxic conditions. Physiological and biochemical changes were compared between cells grown anaerobically in either lignin-amended or unamended conditions. In the presence of lignin, BRL6-1 had a higher biomass and shorter lag phase compared to unamended conditions, and 14% of the proteins determined to be significantly higher in abundance by log2 fold-change of 2 or greater were related to Fe(II) transport in early exponential phase. Ferrozine assays of the supernatant (<10 kDa fraction) confirmed that Fe(III) was bound to lignin and reduced to Fe(II) only in the presence of BRL6-1, suggesting redox activity by the cells. LC-MS/MS analysis of the secretome showed an extra band at 20 kDa in lignin-amended conditions. Protein sequencing of this band identified a protein of unknown function with homology to enzymes in the radical SAM superfamily. Expression of this protein in lignin-amended conditions suggests its role in radical formation. From our findings, we suggest that BRL6-1 is using a protein in the radical SAM superfamily to interact with the Fe(III) bound to lignin and reducing it to Fe(II) for cellular use, increasing BRL6-1 yield under lignin-amended conditions. This interaction potentially generates organic free radicals and causes a radical cascade which could modify and depolymerize lignin. Further research should clarify the extent to which this mechanism is similar to previously described aerobic chelator-mediated Fenton chemistry or radical producing lignolytic enzymes, such as lignin peroxidases, but under anoxic conditions.

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Chaput, G., Billings, A. F., DeDiego, L., Orellana, R., Adkins, J. N., Chu, R., Simmons, B., DeAngelis, K. M.. 2020-05-14. Iron Chelator-Mediated Anoxic Biotransformation of Lignin by Novel sp., Tolumonas lignolytica BRL6-1. https://doi.org/10.1101/2020.05.14.095802

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