Abstract
This study evaluated the effects of a trehalolipid biosurfactant produced by Rhodococcus ruber IEGM 231 on the bacterial adhesion and biofilm formation on the surface of polystyrene microplates. The adhesion of Gram-positive (Arthrobacter simplex, Bacillus subtilis, Brevibacterium linens, Corynebacterium glutamicum, Micrococcus luteus) and Gram-negative (Escherichia coli, Pseudomonas fluorescencens) bacteria correlated differently with the cell hydrophobicity and surface charge. In particular, exponentially growing bacterial cells with increased hydrophobicities adhered stronger to polystyrene compared to more hydrophilic stationary phase cells. Also, a moderate correlation (0.56) was found between zeta potential and adhesion values of actively growing bacteria, suggesting that less negatively charged cells adhered stronger to polystyrene. Efficient biosurfactant concentrations (10–100 mg/L) were determined, which selectively inhibited (up to 76 %) the adhesion of tested bacterial cultures, however without inhibiting their growth. The biosurfactant was more active against growing bacteria rather than resting cells, thus showing high biofilm-preventing properties. Contact angle measurements revealed more hydrophilic surface of the biosurfactant-covered polystyrene compared to bare polystyrene, which allowed less adhesion of hydrophobic bacteria. Furthermore, surface free-energy calculations showed a decrease in the Wan der Waals (γLW) component and an increase in the acid-based (γAB) component caused by the biosurfactant coating of polysterene. However, our results suggested that the biosurfactant inhibited the adhesion of bacteria independently on their surface charges. AFM scanning revealed three-type biosurfactant structures (micelles, cord-like assemblies and large vesicles) formed on glass, depending on concentrations used, that could lead to diverse anti-adhesive effects against different bacterial species.
Highlights
Prevention and control of microbial biofilms are becoming of increasing importance in medical and industrial sectors since biofilms cause many recalcitrant patient infections in the clinical environment, spreading air- and foodborne pathogens and the fouling of industrial surfaces (Zezzi do Valle Gomes and Nitschke 2012; BannatBiosurfactants, surface-active compounds produced by certain microorganisms were found to inhibit bacterial adhesion through the bioconditioning of surfaces or by interacting with bacterial cells and modifying theirKuyukina et al AMB Expr (2016) 6:14 properties (Busscher et al 1997; Meylheuc et al 2001; Monteiro et al 2011)
Greater anti-adhesive effects of the biosurfactant were observed against actively growing B. subtilis, C. glutamicum, E. coli, M. luteus and P. fluorescence cells (Table 2), which allowed estimating the biosurfactant concentrations effectively inhibiting the biofilm formation by bacteria on polystyrene (Fig. 2)
Greater anti-adhesive effects of the biosurfactant were observed against actively growing B. subtilis, C. glutamicum, E. coli, M. luteus and P. fluorescence cells (Table 2), whereas resting cells of these strains were poorly inhibited or even stimulated by the biosurfactant
Summary
Prevention and control of microbial biofilms are becoming of increasing importance in medical and industrial sectors since biofilms cause many recalcitrant patient infections in the clinical environment, spreading air- and foodborne pathogens and the fouling of industrial surfaces (Zezzi do Valle Gomes and Nitschke 2012; BannatBiosurfactants, surface-active compounds produced by certain microorganisms were found to inhibit bacterial adhesion through the bioconditioning of surfaces or by interacting with bacterial cells and modifying theirKuyukina et al AMB Expr (2016) 6:14 properties (Busscher et al 1997; Meylheuc et al 2001; Monteiro et al 2011). Non-toxic trehalolipid biosurfactants produced by non-pathogenic actinobacteria of the genus Rhodococcus have many industrially important properties summarized in several recent reviews (Kuyukina and Ivshina 2010; Franzetti et al 2010; Kuyukina et al 2015). We previously showed that a biosurfactant from Rhodococcus ruber IEGM 231 prevented the adhesion of human monocites to polystyrene, inhibiting their cytokine production, without any cytotoxic effects (Gein et al 2011). This biosurfactant was shown to stimulate the adhesion of the producing strain to solid surfaces (Ivshina et al 2013). We intended to study anti-adhesive and inhibitory effects of the biosurfactant against several strains of Gram-positive and Gram-negative bacteria
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