Competitive interfacial adsorption of surfactants suppresses alkane biodegradation in yeast-stabilized Pickering...

The application of chemical dispersants in marine oil spill bioremediation remains controversial due to uncertain effects on microbial activity. This study investigated how four diverse surfactants impact n-tetradecane biodegradation by the marine hydrocarbonoclastic yeast Yarrowia lipolytica. The tested agents encompassed hydrophilic Tween 80, lipophilic Span 80, the commercial dispersant GH-2, and a biological rhamnolipid. Elevated surfactant concentrations severely suppressed biodegradation, whereas low concentrations exhibited negligible effects. Systematic characterization of macroscopic phase behaviors and microscopic interfacial dynamics elucidated the underlying mechanisms. This severe suppression is fundamentally driven by intense competitive interfacial adsorption. Surface tension, infrared spectroscopy, and zeta potential analyses confirmed a sequential displacement mechanism. Exogenous surfactants preferentially bound to the yeast cells. This initial binding altered cellular surface chemistry and amplified electrostatic repulsion. Concurrently, these molecules outcompeted the cells for interfacial sites. Confocal laser scanning microscopy and an in situ emulsion polymerization technique provided direct visual evidence. These high-resolution techniques captured extensive cellular desorption and the emergence of cell-free interfacial domains. Ultimately, physical displacement via competitive adsorption functions as a primary mechanism stalling interfacial biodegradation. However, its specific macroscopic manifestation heavily depends on inherent surfactant properties. Hydrophilic agents induce simple cellular desorption, whereas highly lipophilic surfactants trigger catastrophic phase inversion. Regardless of these macroscopic differences, this competitive behavior hinders interfacial biocatalysis by physically isolating cells from hydrophobic substrates. These findings provide critical mechanistic insights for optimizing marine dispersant application strategies.