S157: Anaerobic feedstock-adapted consortia and isolates from Puerto Rico tropical forest soils

The breakdown of lignocellulosic plant biomass is a key first step in the conversion of plant sugars to biofuels, and this process has posed a great challenge to the economically viability of biofuels. The microbial communities in wet tropical soils of the Puerto Rican forest are capable of fast and near total mineralization of leaf plant litter, making them our focus in overcoming this challenge. This study characterizes microbial communities and isolates microorganisms with lignocellulosic enzyme activity from soil from four forest types ranging in redox states form oxic to anoxic. Soils were incubated anaerobically and amended with switchgrass. Each soil type was anaerobically passed through a succession of transfers in minimal media with switchgrass as the sole carbon source. Methane and carbon dioxide production rates were monitored throughout transfers and community profiling was performed using the high-density 16S ribosomal RNA microarray PhyloChip. Switchgrass mineralization peaked at 2.20 g CO₂ h^-1 g^-1 and was sustained for 6 days. Microbial communities analysis revealed Actinobacteria and Gammaproteobacteria as dominant organisms. Media amended with iron had higher richness than media containing switchgrass only, with 324 distinct taxa compared to 81 taxa without iron amendment. From these incubations twenty-five anaerobic isolates utilizing switchgrass or lignin as sole carbon sources have been obtained. These isolates were comprised of  Klebsiella, Tolumonas, Clostridium, Enterobacter, and Pseudomonas species. The diversity of anaerobic lignin degraders found in these soils reiterates the importance of anaerobic decomposition in these environments and highlights the potential for discovery.