Microbial activity and metamitron degrading microbial communities differ between soil and water-sediment systems

Area of Science:

• Environmental microbiology
• Biogeochemistry
• Soil science

Background:

• Metamitron, a widely used herbicide, is frequently detected in various environmental compartments.
• Understanding its environmental fate, particularly degradation pathways and microbial involvement, is crucial for risk assessment.
• Degradation rates and microbial communities differ significantly between terrestrial (soil) and aquatic (water-sediment) systems.

Purpose of the Study:

• To investigate and compare microbial activity, metamitron mineralization rates, and the composition of metamitron-degrading microbial communities in soil versus water-sediment systems.
• To elucidate the role of different microbial groups, including primary and necromass degraders, in metamitron turnover.
• To utilize stable isotope probing with ¹³C₆-metamitron to track microbial assimilation and identify active degraders.

Main Methods:

• Application of ¹³C₆-metamitron to controlled soil and water-sediment microcosms.
• Measurement of soil respiration to assess microbial activity.
• Quantification of metamitron mineralization and incorporation of ¹³C into microbial biomass via Phospholipid Fatty Acids (PLFAs).

Main Results:

• Metamitron increased respiration in soil but suppressed it in water-sediment systems.
• Metamitron mineralization was approximately two-fold faster in soil compared to the water-sediment system.
• ¹³C incorporation into PLFAs was higher in soil, indicating greater activity of metamitron degraders. Specific microbial groups (Gram-negative, Gram-positive bacteria, actinobacteria in soil; Gram-negative bacteria in sediment) were identified as primary degraders, with actinobacteria and fungi involved in necromass consumption.

Conclusions:

• Microbial communities responsible for metamitron degradation are system-dependent (soil vs. water-sediment) and change over time.
• The turnover of metamitron in complex environments is driven by synergistic interactions among different microbial groups (primary and necromass degraders).
• Environmental conditions significantly influence herbicide degradation efficiency and the structure of the involved microbial consortia.