Predicting the minimum liquid surface tension activity of pseudomonads expressing biosurfactants

I. U. Mohammed, Yusuf Y. Deeni, Simona M. Hapca, Kimberley McLaughlin, Andrew J. Spiers

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    Bacteria produce a variety of biosurfactants capable of significantly reducing liquid (aqueous) surface tension (γ) with a range of biological roles and biotechnological uses. In order to determine the lowest achievable surface tension (γMin), we tested a diverse collection of Pseudomonas-like isolates from contaminated soil and activated sludge, and identified those expressing biosurfactants by drop-collapse assay. Liquid surface tension reducing ability was quantitatively determined by tensiometry, with 57 isolates found to significantly lower culture supernatant surface tensions to 24.5 – 49.1 mN m−1. Differences in biosurfactant behaviour determined by foaming, emulsion and oil-displacement assays, was also observed amongst isolates producing surface tensions of 25 – 27 mN m−1, suggesting that a range of structurally-diverse biosurfactants were being expressed. Individual distribution identification (IDI) analysis was used to identify the theoretical probability distribution that best fitted the surface tension data, which predicted a γMin of 24.24 mN m−1. This was in agreement with predictions based on earlier work of published mixed–bacterial spp. data, suggesting a fundamental limit to the ability of bacterial biosurfactants to reduce surface tensions in aqueous systems. This implies a biological restriction on the synthesis and export of these agents or a physical-chemical restriction on their functioning once produced.
    Original languageEnglish
    Pages (from-to)37–43
    Number of pages7
    JournalLetters in Applied Microbiology
    Issue number1
    Early online date24 Sep 2014
    Publication statusPublished - Jan 2015


    • Biosurfactant
    • Liquid surface tension
    • Pseudomonas
    • Surfactant
    • Statistical prediction


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