DNA Half-Life Measurements for Fermentation Biomass Applied to Farm Fields as a Fertilizer for Corn and Fescue Crops

Industrial fermentation processes produce large amounts of microbial biomass that are removed from high-value products and often discarded in landfills or incinerators.  Previous studies have documented the value of fermentation biomass as a fuel for production of electricity or steam, or as a fertilizer for specialty or row crops.  Since the composition of fermentation biomass varies for individual fermentation processes, and this composition influences phytotoxicity, availability of nutrients, plant yield, and related factors, field trials are necessary to determine value of the bioresidual stream as a fertilizer.  In this study, we compared synthetic fertilizers to heat-inactivated fermentation biomass that was generated during the production of 1,3-propanediol.  The fertilizer impact was compared for fescue and yellow dent corn crops on agricultural fields in Tennessee during the 2015 growing season.  Of particular interest was the fate, persistence, and horizontal transfer of strain-specific deoxyribonucleic acid (DNA) signatures found in the heat-inactivated biomass.  The half-life of DNA in soil is well documented in literature; however, these studies are often conducted under laboratory conditions that attempt to simulate field conditions and model DNA.  In order to confirm fate and persistence under field conditions, we conducted a 120-day field trial in which total DNA was extracted from soils, and PCR was performed to determine the presence of strain-specific DNA.  Results indicate that the half-life for genetic material associated with 1,3-propanediol fermentation biomass is significantly shorter (approximately 18-20 hours) than reported in literature.  Degradation rates appeared to be driven primarily by ultraviolet light and secondarily, through secondary fermentation by environmental microorganisms inhabiting the biomass.