Mohammed I U, Deeni Y, Hapca S M, McLaughlin K, Spiers A J
SIMBIOS Centre & School of Science, Engineering and Technology, Abertay University, Dundee, UK.
Lett Appl Microbiol. 2015 Jan;60(1):37-43. doi: 10.1111/lam.12331. Epub 2014 Oct 29.
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 (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 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 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.
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.
细菌可产生多种生物表面活性剂，这些生物表面活性剂能够显著降低液体（水相）表面张力（γ），具有一系列生物学作用和生物技术用途。为了确定可达到的最低表面张力（γMin），我们测试了从受污染土壤和活性污泥中分离出的多种假单胞菌属样菌株，并通过液滴塌陷试验鉴定出那些表达生物表面活性剂的菌株。通过张力测定法定量测定液体表面张力降低能力，发现57株菌株可将培养上清液表面张力显著降低至24.5 - 49.1 mN m-1。在产生表面张力为25 - 27 mN m-1的菌株中，还观察到通过泡沫、乳化和油置换试验确定的生物表面活性剂行为差异，这表明表达了一系列结构多样的生物表面活性剂。使用个体分布识别（IDI）分析来识别最适合表面张力数据的理论概率分布，预测γMin为24.24 mN m-1。这与基于已发表的混合细菌菌株早期工作数据的预测一致，表明细菌生物表面活性剂降低水相系统表面张力的能力存在基本限制。这意味着对这些物质的合成和输出存在生物学限制，或者在其产生后对其功能存在物理化学限制。
已经对产生生物表面活性剂的细菌进行了大量调查，但直到最近才有人尝试预测这些表面活性剂能够达到的最低液体表面张力。在这里，我们通过对张力测定数据的统计分析确定理论最小值为24 mN m-1，这表明在标准生长条件下培养的细菌培养物中生物表面活性剂活性存在基本限制。这对我们理解生物表面活性剂的表达、分泌和功能提出了挑战，同时也引起了生物技术领域的兴趣，因为它们在越来越广泛的应用中得到使用。
