Biosurfactant slows down n-hexadecane biodegradation: ¹³C-labeled rhamnolipid tracing

Area of Science:

• Environmental Microbiology
• Bioremediation
• Biogeochemistry

Background:

• Rhamnolipids are widely used in bioremediation, but their metabolic fate and regulatory roles are not fully understood.
• Understanding how rhamnolipids interact with target contaminants and microbial communities is crucial for optimizing their application.

Purpose of the Study:

• To trace the metabolic fate of ¹³C-labeled rhamnolipids in environmental matrices.
• To evaluate the impact of rhamnolipids on n-hexadecane mineralization and identify underlying mechanisms.
• To assess the overall carbon fate and bioremediation efficiency.

Main Methods:

• Production of ¹³C-labeled rhamnolipid using *Pseudomonas aeruginosa* ATCC 27853.
• Stable isotope tracing to quantify rhamnolipid partitioning and mineralization.
• Scanning Electron Microscopy (SEM) to visualize bacterial surface encapsulation.
• Analysis of pH, fatty acid secretion, and enzyme activity.
• Structural Equation Modeling (SEM) to determine contributing factors to the observed effects.

Main Results:

• Rhamnolipid addition reduced n-hexadecane degradation by 18% due to bacterial encapsulation and altered membrane permeability.
• Despite reduced degradation, complete mineralization of n-hexadecane to CO₂ increased by 20% (priming effect).
• ¹³C tracing showed 84% of rhamnolipid was mineralized to CO₂, with only 5.5% assimilated into biomass.
• Increased oxidase activity was identified as a key factor contributing to the priming effect.

Conclusions:

• Rhamnolipids exhibit a complex role in bioremediation, initially inhibiting contaminant degradation but ultimately enhancing overall mineralization via a priming effect.
• The developed ¹³C tracing methodology accurately tracks carbon-based additive fate.
• Optimizing bioremediation requires evaluating the total carbon fate of additives to enhance efficiency and minimize environmental risks.