The effects of a synthetic and biological surfactant on the community composition and metabolic activity of a freshwater biofilm

Abstract

SummarySurfactants are used to control microbial biofilms in industrial and medical settings. Their known toxicity on aquatic biota and their longevity in the environment has encouraged research on biodegradable alternatives such as rhamnolipids. While previous research has investigated the effects of biological surfactants on single species biofilms, there remains a lack of information regarding the effects of synthetic and biological surfactants in freshwater ecosystems. We conducted a mesocosm experiment to test how the surfactant sodium dodecyl sulphate (SDS) and the biological surfactant rhamnolipid altered community composition and metabolic activity of freshwater biofilms. Biofilms were cultured in the flumes using lake water from Lake Lunz in Austria, under high (300 ppm) and low (150 ppm) concentrations of either surfactant over a four week period. Our results show that both surfactants significantly affected microbial diversity. Up to 36% of microbial OTUs were lost after surfactant exposure. Rhamnolipid exposure also increased the production of the extracellular enzymes leucine aminopeptidase and glucosidase, while SDS exposure reduced leucine aminopeptidase and glucosidase. This study demonstrates that exposure of freshwater biofilms to chemical and biological surfactants caused a reduction of microbial diversity and changes in biofilm metabolism, exemplified by shifts in extracellular enzyme activities.Originality-Significance StatementTo our knowledge this is the first study that examines the effects of the chemical surfactant sodium dodecyl sulphate and the biological surfactant rhamnolipid on a mixed species freshwater biofilm. Research typically focuses on single species biofilms in medical or industrial settings. Therefore, we are also the first study that examines the community composition and metabolic activity of a mixed freshwater biofilm exposed to these surfactants, and are the only study that has examined the carbon and nitrogen content of an exposed aquatic biofilm. Our results will help to shape policy surrounding the input of contaminants of emerging concern such as surfactants into waterways, and potentially to help manage the use of these chemicals within industrial settings as a means to control biofilms.