Ecological impacts of biological and chemical surfactants on aquatic biofilm growth, metabolism, and carbon cycling

  • Stephanie Gill

Student thesis: Doctoral Thesis


Surfactants are researched for their ability to reduce biofouling and biofilm build up in medical and industrial environments. Constant usage of these chemicals both as anti-biofilm agents and within personal care products has led to an increase in their presence environmentally. This thesis studied the effects of surfactants on marine and freshwater biofilms which are important to local aquatic biogeochemical cycling.

Exposure of biofilms to the synthetic surfactant, sodium dodecyl sulphate, and biological surfactant, rhamnolipid, led to alterations in community composition, significant decreases in biodiversity, and increases in antimicrobial resistance gene retention. Overall, more sensitive taxa such as Arenimonas, decreased in favor of more resistant, and potentially pathogenic taxa, including Brevundimonas. Rhamnolipid exposed biofilms retained eight of the nine identified antimicrobial resistance genes while SDS retained five and the control retained four.

Surfactant exposure also altered biofilm metabolic activity. Increases in activity of the extracellular enzymes beta glucosidase and leucine aminopeptidase occurred after rhamnolipid exposure while decreases occurred after exposure to SDS. Carbon: Nitrogen also decreased significantly when rhamnolipid and grazer exposure occurred together, disrupting a previously beneficial holobiont relationship between grazers and biofilm.

Overall, both biological and synthetic surfactant exposure have direct effects on freshwater and marine biofilm structure and metabolic activity. This could lead to future biofilm loss and compositional changes, with implications for decreases in local biogeochemical cycling, and human and environmental health hazards.
Date of AwardDec 2022
Original languageEnglish
SponsorsVice Chancellors Research Scholarship
SupervisorIbrahim Banat (Supervisor), Joerg Arnscheidt (Supervisor), William Ross Hunter (Supervisor) & Jakob Schelker (Supervisor)


  • Aquatic toxicology
  • Rhamnolipid
  • Sodium dodecyl sulphate
  • Marine
  • Freshwater
  • Metagenomics

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