Termite Hindgut Bacteria TAV5: Key to Lignocellulose Waste Decomposition

Abstract Description: Bioenergy from lignocellulose biomass in landfills is one of the promising candidates to help move towards a fossil fuel free future (Zhang et al., 2021). More than 50% of the 149 million metric tons of MSW landfilled in the U.S. annually are derived from lignocellulosic materials (De la Cruz, 2014). Unfortunately, lignin is resistant to microbial attack under low oxygen conditions which normally occur in landfills, and it often shields lignocellulose components (cellulose and hemicellulose) from decomposition as well. Without an effective method of decomposing lignin, at least 10–35% of lignocellulose will likely remain undegraded in landfills, taking up valuable landfill space and lowering the potential for producing renewable energy such as methane (De la Cruz, 2014). Traditional physical/chemical methods for destroying lignin are typically costly due to energy and chemical requirements and can create toxic intermediates (Rahimi et al., 2020).
Termites are commonly known for their ability to degrade wood, which contains high levels of lignin; microorganisms present in the hindgut of termites are responsible decomposition of lignin in wood. TAV5 (Termite Associated Verrucomicrobia) is the fastest-growing microorganism isolated from the hindgut of Reticulitermes flavipes termite, the most widespread subterranean termite in North America. Its genome contains genes associated with methylotrophic competency which code for enzymes that structurally modify lignin (Kotak et al., 2015). The overall goal of our research is to use TAV5 to modify lignin and boost methane production from MSW. Unlike other microorganisms able to degrade lignin (including the popular white rot fungi), TAV5 can grow in low levels of oxygen present in landfills.
Lab tests have been conducted in batch-scale reactors (125 mL) with various kinds of waste (paper, yard, wood, and agricultural wastes including rice straw, corn stover, rice husk and wheat straw) to determine the optimal ratios of TAV5 to anaerobic digester (AD) microorganisms (representing landfill anaerobic microorganisms) to decompose waste and produce methane. Based on batch tests, optimal ratios of TAV5 to AD microorganisms were used to seed wastes (mixed, yard, and wood) in 6-gallon reactors. Field-scale tests with agricultural wastes will commence soon.
Addition of TAV5 increased methane production from mixed waste, yard waste, and wood, by 49%, 34%, and 297%, respectively. TAV5 decreased acid soluble lignin by 7–39%, depending on waste type. TAV5 grown under aerobic conditions and room temperature (not requiring a heated anaerobic chamber) was found to remain viable and increase methane production under low-level oxygen conditions (1–2%). This finding will lessen costs for growing large volumes of it for seeding landfills.