P51: Isolation of lignin- and cellulose- degrading bacteria from tropical soils for biofuel feedstock deconstruction

Plant biomass deconstruction poses a large challenge to the biofuels industry, creating a need to find better methods that will more easily breakdown the plant’s two main structural components-- cellulose and lignin. The goal of this project was to identify cellulose- and lignin-degrading microorganisms from Puerto Rican tropical forest soils, where high plant litter decomposition rates have been observed in previous studies. Our efforts focused on bacterial cultivation since there are few bacterial taxa known to degrade lignin. Microbes were selectively cultivated using minimal media agar with lignin or cellulose as a sole carbon source. Cellulose and lignin degradation rates of our isolates were measured in vitro using 2 assays: 4-methylumbelliferone (MUB)-linked substrate and L-3,4-dihydroxyphenylalanine (L-DOPA) assay. We cultivated over one hundred isolates that were able to utilize cellulose or lignin as a sole carbon source.  The most cellulolytic isolates ranged from 5 to 9 µmol of MUB released per hour per OD of microbial cells.  The most lignolytic isolates produced over 1 OD of L-DOPA per hour per OD of microbial cells.  Based on 16S rRNA gene sequencing, our top performing isolates were members of the Proteobacteria phylum -- Burkholderia, Massilia, Klebsiella, and included several previously uncultured bacteria clones. These taxa merit further investigation in order to discover their possible application in the biofuel industry. Their enzymes may aid the plant deconstruction process, consequently making future biofuels less costly and more energy efficient.