Quorum-sensing inhibitor (QSI) is one of the most promising and environmentally friendly agents for marine antifouling. In this study, the activities of three kinds of QSIs 3,4-dibromo-2(5)Hfuranone, 4-nitropyridine-N-oxide and indole were evaluated on the growth of two marine diatoms Cylinthrotheca sp. and Nitzschia closterium. At the same time, the effects of QSIs on the formation of the diatom-biofilm were also discussed. All the results showed that QSIs significantly inhibited the growth, and the effects depended on the dose and diatom species. The extracellular polymeric substance contents in the diatom-biofilm were significantly reduced by QSIs. However, the contents of polysaccharide in culture mediums were increased, which might result in the destruction of diatom cells. Combined with the results of crystal violet staining-biofilm and images of scanning electron microscopy, it was further demonstrated that QSIs inhibited the biofilm formation of Cylindrotheca sp., and the inhibitory effect of 4-nitropyridine-N-oxide was superior to that of 3,4-dibromo-2(5)H-furanone and indole.ARTICLE HISTORY
Diatoms contribute to carbon fixation in the oceans by photosynthesis and always form biofouling organized by extracellular polymeric substances (EPS) in the marine environment. Bacteria-produced quorum-sensing signal molecules N-acyl homoserine lactones (AHLs) were found to play an important role in the development of Cylindrotheca sp. in previous studies, but the EPS composition change was unclear. This study used the technology of alcian blue staining and scanning electron microscopy (SEM), confocal laser scanning microscopy (CLSM), and time-of-flight secondary ion mass spectrometry (ToF-SIMS) to directly observe the biofilm formation process. The results showed that AHLs promote the growth rates of diatoms and the EPS secretion of biofilm components. AHLs facilitated the diatom-biofilm formation by a forming process dependent on the length of carbon chains. AHLs increased the biofilm thickness and the fluorescence intensity and then altered the three-dimensional (3D) structures of the diatom-biofilm. In addition, the enhanced EPS content in the diatom-biofilm testified that AHLs aided biofilm formation. This study provides a collection of new experimental evidence of the interaction between bacteria and microalgae in fouling biofilms.
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