(325d) Isolation and Characterization of Lignin-Modifying Activity of Bacteria From Rainforest Soils

The commercialization of cellulosic biofuels requires the cost-effective release of fermentable sugars from plant biomass. Since cellulose in plant cell walls is intricately interlinked with hemicellulose and lignin, access to the fermentable sugars can only be achieved by the removal of lignin. Current physicochemical pretreatment technologies involve high energy consumption and operating costs. Enzymatic ?loosening? of the lignin matrix may be an environmentally benign and less expensive pretreatment alternative due to its potential for the production of value-added compounds from lignin. While wood-decaying fungi abound, their enzymes are often less robust in terms of thermal and pH stability and are more difficult to optimize by protein engineering than are bacterial enzymes. The Peruvian Rainforest of Tambopata supports a rich diversity of vegetation that grows in relatively nutrient poor soils. It is believed that the soil microbes in that region have developed fast turnover rates of organic matter which is credited as one of the main factors that supports plant mega diversity. In this study, 72 bacterial strains were isolated from Rainforest soils that had been incubated with biomass residues from corn, soybean and pine for 16 weeks. An assay based on the temporal decolorization of polymeric dye Remazol Brilliant Blue R (RBBR) was used to select for strains secreting oxidizing enzymes such as peroxidases and laccases. Positive strains that were found to completely decolorize RBBR over a period of 5 days were then incubated with milled corn stover in submerged fermentation systems. A method was developed, using liquid chromatography/mass spectrometry (LC/MS), to detect monomers released from corn stover lignin during the growth of these strains. Twelve aromatic compounds, derived from p-hydroxyphenyl, guaiacyl and syringyl units of lignin, were selected as standards. Relative peak areas of five compounds namely ferulic acid, p-coumaric acid, p-hydroxybenzaldehyde, p-hydroxyacetophenone and vanillin were found to be different when obtained from corn stover incubated with positive strains compared to those obtained from uninoculated corn stover. These results confirmed the ability of the selected strains to modify lignin structure. This is the first instance that a method using LC/MS has been reported for the detection of microbial lignin modification.