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Predicting the minimum liquid surface tension activity of pseudomonads expressing biosurfactants
Author(s) -
Mohammed I.U.,
Deeni Y.,
Hapca S.M.,
McLaughlin K.,
Spiers A.J.
Publication year - 2015
Publication title -
letters in applied microbiology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.698
H-Index - 110
eISSN - 1472-765X
pISSN - 0266-8254
DOI - 10.1111/lam.12331
Subject(s) - library science , sociology , computer science
Bacteria produce a variety of biosurfactants capable of significantly reducing liquid (aqueous) surface tension ( γ ) with a range of biological roles and biotechnological uses. To determine the lowest achievable surface tension ( γ Min ), 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 were 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 γ Min 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. Significance and Impact of the Study Numerous surveys of biosurfactant‐producing bacteria have been conducted, but only recently has an attempt been made to predict the minimum liquid surface tension these surface‐active agents can achieve. Here, we determine a theoretical minimum of 24 mN m −1 by statistical analysis of tensiometry data, suggesting a fundamental limit for biosurfactant activity in bacterial cultures incubated under standard growth conditions. This raises a challenge to our understanding of biosurfactant expression, secretion and function, as well as being of interest to biotechnology where they are used in an increasingly wide range of applications.