Isolation and Evaluation of Purple Nonsulfur Bacteria From Beef Cattle Feedlot Playas for the Production of Hydrogen.

The Southern High Plains of Texas are home to large open beef cattle feedlot operations with an animal capacity of 40,000 to 70,000 animals per feedlot. This area has also seen the recent influx of large dairy operations. These operations produce significant amounts of animal waste stream. Historically, wastewater cleanup has significant energy requirements (~25% of the operational cost of a modern municipal sewage treatment facility) and thus attempts at water recovery or reuse at animal feeding operations (AFOs) have been limited to irrigation of nearby crops and dust abatement procedures or evaporation to concentrate biosolids. Increasing recoverable water from beef and dairy AFOs and associated milk and cheese processing plants could result in significant conservation of a valuable resource. Wastewater thus represents a potential biofuel feedstock for the coproduction of hydrogen gas or the generation of electricity. In research to be described here, we focus on the isolation and identification of hydrogen producing bacteria that are capable of utilizing this waste stream. Purple non-sulfur bacteria (PNSB) are found widely disseminated in nature (both aquatic and terrestrial environments) and in waste streams where sufficient light and anaerobic conditions prevail.  PNSB can utilize solar energy to drive energetically unfavorable metabolic reactions and can potentially divert 100% of the electrons from an electron-donating substrate (organic fractions within manure) to hydrogen production. A diverse collection of approximately 300 plus PNSB isolates were obtained from two AFOs. These isolates comprised 20 distinct 16S rDNA profiles as determined by ARDRA; whereas ITS analysis revealed a slightly higher level of genetic diversity. Hydrogen gas production was determined using an Agilent GC instrument. A defined microbiological media was used to perform a comparative assessment of hydrogen production rates (µmoles H₂ gas/mg dry weight of cells) for each genotype of strains.