Abstract
Interfering with the quorum sensing bacterial communication systems has been proposed as a promising strategy to control bacterial biofilm formation, a key process in biofouling development. Appropriate in vitro biofilm-forming bacteria models are needed to establish screening methods for innovative anti-biofilm and anti-microfouling compounds. Four marine strains, two Pseudoalteromonas spp. and two Vibrio spp., were selected and studied with regard to their biofilm-forming capacity and sensitivity to quorum sensing (QS) inhibitors. Biofilm experiments were performed using two biofilm cultivation and quantification methods: the xCELLigence® system, which allows online monitoring of biofilm formation, and the active attachment model, which allows refreshment of the culture medium to obtain a strong biofilm that can be quantified with standard staining methods. Although all selected strains produced acyl-homoserine-lactone (AHL) QS signals, only the P. flavipulchra biofilm, measured with both quantification systems, was significantly reduced with the addition of the AHL-lactonase Aii20J without a significant effect on planktonic growth. Two-species biofilms containing P. flavipulchra were also affected by the addition of Aii20J, indicating an influence on the target bacterial strain as well as an indirect effect on the co-cultured bacterium. The use of xCELLigence® is proposed as a time-saving method to quantify biofilm formation and search for eco-friendly anti-microfouling compounds based on quorum sensing inhibition (QSI) strategies. The results obtained from these two in vitro biofilm formation methods revealed important differences in the response of biosensor bacteria to culture medium and conditions, indicating that several strains should be used simultaneously for screening purposes and the cultivation conditions should be carefully optimized for each specific purpose.
Highlights
Biofilms are made of microbial sessile communities characterized by cells that are attached to a substratum or other surfaces, are embedded in a self-produced matrix of extracellular polymeric substances, and exhibit an altered phenotype compared to planktonic cells [1]
Since biofilm formation is the first step in the biofouling process, numerous reports have evaluated the inhibition of bacterial biofilms for the identification of anti-biofouling compounds [25,36,53,54,55]
An understanding of the mechanisms that can be used as targets to interfere with the bacterial adhesion process and biofilm growth and maturation is essential to develop new non-toxic strategies for the control of microfouling
Summary
Biofilms are made of microbial sessile communities characterized by cells that are attached to a substratum or other surfaces, are embedded in a self-produced matrix of extracellular polymeric substances, and exhibit an altered phenotype compared to planktonic cells [1]. Besides their consequences for human health, bacterial biofilms are based on important processes such as biocorrosion and constitute the initial step in the biofouling process of submerged surfaces, serving as the substratum on which other micro- and macro-organisms settle and grow. Compounds targeting the inhibition of bacterial biofilm without affecting bacterial growth are of special interest
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