Screening for novel bacteria from the bioenergy feedstock switchgrass (Panicum virgatum L.)

Abstract

Switchgrass is considered as a good candidate for biofuel, especially ethanol production due to its huge biomass output and high cellulose content. In a search for novel microorganisms capable of using and degrading switchgrass to produce sugars and ethanol, enrichment experiments were established to screen for microorganisms from soil samples obtained at the University of Tennessee Agricultural Research Station, Jackson, Tennessee. Three enrichments were prepared and incubated at different pH and temperatures: (1) 30°C, pH 5, (2) 30°C, pH 8 and (3) 60°C, pH5. Bulk community DNA was directly extracted from the enrichments. Microbial community structures were determined by phylogenetic analysis of 16S rRNA gene sequences retrieved from the enrichment cultures containing switchgrass as the carbon source. The mesophilic enrichments were dominated by Sarcina, Anaerobacter, and Clostrium, which were not found in the thermophilic enrichment. The thermophilic enrichment selected for two types of bacteria belonging to the class Bacilli (Geobacillus and Saccharococcus). The thermophilic enrichments were dominated by the Geobacillus spp. (Firmicutes, class Bacilli), and Saccharococcus (Firmicutes, class Bacilli); both containing thermophilic microorganisms with some cellulolytic members. Enzymatic assays detected the presence of enzymes involved in cellulose (β-glucosidase and cellobiohydrolase) and hemicellulose degradations (β-xylosidase); and the activity tends to be higher in the enrichments incubated at 30°C.

Keywords:

• switchgrass
• cellulose
• Geobacillus
• Saccharococcus
• soil enrichment

Acknowledgements

This work was supported by the Laboratory Directed Research and Development Program of Oak Ridge National Laboratory – US Department of Energy under Contract No. DE-AC05-00OR22725. Partial funding was also provided by the US-DOE Faculty and Student Teams (FaST) Program and the Office for the Vice President for Research (OVPR) grant of the University of Michigan. The authors thank Chris Schadt for providing the lab space at Oak Ridge National Laboratory.