Wetland tyrosinases: global contributors to climate change!

Wetlands are globally distributed ecosystems that combine plant growth with water-logged soils. Wetlands cover roughly five percent of the total land surface but, in contrast, store one- third of the overall soil carbon stock. This is equivalent to 70 percent of the carbon stored in the atmosphere in the form of CO2. These vast carbon stores have been accumulated by wetlands over the last millennia as the wetland vegetation utilizes carbon (in the form of CO2) from the atmosphere to form biomass during photosynthesis. Carbon remains stored in wetlands until the biomass is broken down by microbial enzymes. Wetlands differ from other ecosystems: they slow down the degradation of biomass. Thus, wetlands have been acting as carbon sinks for thousands of years. Responsible for the slow degradation of biomass in wetlands are phenols. Phenols are a chemical group of molecules naturally produced by plants and released into their environment, where they inhibit the activities of a broad spectrum of microbial enzymes. They, therefore, also inhibit the decomposition of biomass. In the presence of oxygen, tyrosinases are among the few enzymes capable of degrading phenolic compounds. Due to water-logging, oxygen from the air cannot enter wetland soils. This renders tyrosinases inactive and allows phenols to accumulate. Consequently, the absence of oxygen in wetland soils has stabilized carbon stores over the past millennia. However, due to climate change, reduced rainfall, and increased summer drought, wetlands are at risk of drying out. This will allow oxygen from the air to enter wetland soils. In turn, this will increase the breakdown of phenolic compounds by tyrosinases. Eventually, this leads to increased decomposition rates of biomass and an increased release of carbon currently stored in wetlands back into the atmosphere as CO2. Thus, tyrosinases are key enzymes controlling the release of vast amounts of CO2 from wetlands an important process in times of climate change. This project aims at studying the diversity and activity of tyrosinases and tyrosinase-producing bacteria in wetlands on a global scale. For the first time, tyrosinases from wetlands will be recombinantly expressed and investigated biochemically. Furthermore, the project will analyze the production of tyrosinases by bacteria in wetlands, focusing on the influence of changing environmental conditions, caused by climate change. In addition, the proliferation and diversity of TYR-producing bacteria under changing environmental conditions will be investigated. These results will increase our understanding of the effects of climate change on TYRs in wetlands and will aid in developing strategies to reduce CO2 emissions from wetlands.