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This study investigated the physicochemical interactions between a rhamnolipid biosurfactant and a biofilm layer. A concentration of 300 μg mL(-1) of rhamnolipids, which is around the critical micelle concentration value (240 μg mL(-1)), showed great potential for reducing biofilm. The surface free energy between the rhamnolipids and biofilm layer decreased, as did the negative surface charge, due to the removal of negatively charged humic-like, protein-like, and fulvic acid-like substances. The carbohydrate and protein concentrations composed of extracellular polymeric substances decreased by 31.6% and 79.6%, respectively, at a rhamnolipid concentration of 300 μg mL(-1). In particular, rhamnolipids can interact with proteins, leading to a reduction of the N source and amide groups on the membrane. For carbohydrates, the component ratio of glucosamine was decreased, but the levels of glucose and mannose that form the majority of the carbohydrates remained unchanged. To our knowledge, the present study is the first attempt at studying the interactions of the two phases of rhamnolipids and the biofilm layer, and as such is expected to clarify the mechanism by which rhamnolipids lead to a reduction in biofilm.

This study evaluated the effects of salinity on the physiological characteristics of Vibrio sp. B2 and biofilm formation on nanofiltration (NF) membrane coupons used in the high recovery seawater desalination process. The test conditions were at 0.6, 1.2, and 2.4 M sodium chloride (NaCl), equivalent to salinity of seawater, brine at 50% and 75% water recovery, respectively. High salinity inhibited the cell growth rate but increased the viability and bacterial membrane integrity. In addition, protein and eDNA concentrations of salinity-stressed bacteria were increased at 1.2 and 2.4 M NaCl. In particular, protein concentration was linearly correlated with the NaCl concentration. Similarly, less biofilm formation on the NF membrane coupon (without permeation flux) was observed by the salinity-stressed bacteria; however, the production of extracellular polymeric substances (EPS) was significantly increased as compared to control, and protein was an influential factor for biofilm formation. This study shows that salinity-stressed bacteria have a high potential to cause biofouling on membrane surface as the bacteria still maintain the cell activity and overproduce EPS. The potential of biofilm formation by the salinity-stressed bacteria has not been reported. Therefore, the findings are important to understand the mechanisms of membrane biofouling in a high salinity environment.

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Due to the increased occurrence of cyanobacterial blooms and their toxins in drinking water sources, effective management based on a sensitive and rapid analytical method is in high demand for security of safe water sources and environmental human health. Here, a competitive fluorescence immunoassay of microcystin-LR (MCYST-LR) is developed in an attempt to improve the sensitivity, analysis time, and ease-of-manipulation of analysis. To serve this aim, a bead-based suspension assay was introduced based on two major sensing elements: an antibody-conjugated quantum dot (QD) detection probe and an antigen-immobilized magnetic bead (MB) competitor. The assay was composed of three steps: the competitive immunological reaction of QD detection probes against analytes and MB competitors, magnetic separation and washing, and the optical signal generation of QDs. The fluorescence intensity was found to be inversely proportional to the MCYST-LR concentration. Under optimized conditions, the proposed assay performed well for the identification and quantitative analysis of MCYST-LR (within 30 min in the range of 0.42-25 μg/L, with a limit of detection of 0.03 μg/L). It is thus expected that this enhanced assay can contribute both to the sensitive and rapid diagnosis of cyanotoxin risk in drinking water and effective management procedures.

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