The flocculation behaviors of B. licheniformis CGMCC 2876 under different culture conditions were studied in this paper. In the non-bioflocculant producing process, the flocculability of B. licheniformis was enhanced with an increase of ionic strength from 0.001 to 0.3 M, and similar results were observed with the decrease of pH from 7 to 4. The interfacial free energy between cells was 38.8 mJ m−2, suggesting the cells with hydrophilic surfaces repelled each other. In the bioflocculant producing process, extended DLVO theory was adopted to describe the flocculation behavior. The changes in the flocculation behavior of bacterial cells were primarily attributed to the hydrophobic attraction energy interaction between cells with the lowest value of −104.1 mJ m−2. Combined with scanning electron microscopy (SEM), transmission electron microscopy (TEM) and X-ray photoelectron spectroscopy analysis, the cell auto-flocculation of B. licheniformis was finally attributed to the hydrophobic polysaccharide secreted as a cell capsule, which led to an increased surface hydrophobicity, thus increasing the flocculation potential.

In this work, the effects of different factors on the flocculating activity and flocculation mechanism of bioflocculant XMMBF from Bacillus licheniformis are investigated. The results show that the optimum concentration of bioflocculant for kaolin clay sedimentation is 4 mg/L. Both monovalent and bivalent cations increase the flocculating activity, whereas trivalent cations inhibit it. The optimum pH and concentration of kaolin clay suspension are 5–11 and 2–10 g/L, respectively. The adsorption of XMMBF on kaolin clay is described using the Langmuir adsorption model. Infrared spectrum shows the carboxyl groups, amino groups, and hydrogen bonds in XMMBF prefer the flocculation process. The zeta potential of kaolin clay can be changed from −26.26 to −1.08 mV by both Ca2+ and XMMBF. The formation of ionic bonds in the floc can be related to its sensitivity to HCl. Finally, through the help of SEM pictures, the flocculation mechanism of XMMBF is proposed.

•Alkaline sodium phosphate buffer was used to extract phenolic compounds.•Phenolic-rich precipitate formed during the acidification of the extracts.•Proteins and carbohydrates contented in the precipitates were determined.•The simple preparation process indicated prospective industrial potential.The alkaline extraction and acid precipitation of longan seed phenolic compounds were investigated to develop a more practical process than currently exists to isolate these chemicals. By using an alkaline buffer as the extraction solvent, the yield of total phenols reached 46.86±0.43 mg/g after conventional solid–liquid extraction. Because of the benefit achieved from the preconcentration process, an acid precipitation efficiency of 65.29 ± 0.38% was obtained, and the separation yield of phenols reached 22.04 ± 1.95 mg/g. However, the purity of the phenolic extract was influenced by the presence in the precipitate of proteins and carbohydrates, which both moved together in all four precipitation fractions at different pH values. The FRAP assay and the assay of the radical-scavenging activity revealed the strong antioxidant activity possessed by the phenolic compounds in the precipitate extracts. This preparation process for phenolic compounds has obvious advantages, such as easy operation, safe products and low production cost, which indicated its prospective industrial potential.

Bioflocculants are special high-molecular weight polymers produced by microorganisms. Despite the fact that several types of bioflocculants from different species of bacteria have been reported, there is a large gap in our knowledge regarding the molecular machine responsible for the production of bioflocculants. To investigate genes involved in bioflocculant synthesis, a fosmid library was generated from Bacillus licheniformis genomic DNA and screened for the production of bioflocculant. Four positive clones with distinct flocculation were isolated by a two-pooling scheme. The clone with 662 U ml−1 flocculating activity was sequenced. As a result, a 30-kb fragment with 26 hypothetical genes was identified in the bioflocculant-producing clone. Most of the predicted proteins encoded by the inserted genes showed significant homology with enzymes involved in the biosynthesis of polysaccharide. Based on these homologies, a biosynthesis pathway and two gene clusters involved in the production of the polysaccharide bioflocculant were proposed with the integration of functional descriptions of individual genes by metabolic databases, and a glucose-sensitive glycosidases was predicted. This research supplied significant data for potential application of bioflocculant-producing strains in wastewater refining and industrial downstream treatments.

A bioflocculant produced by B. licheniformis was investigated with regard to a low-cost culture medium and its industrial application. Molasses replaced sucrose as the sole carbon source in bioflocculant fermentation. The optimum low-cost culture medium was determined to be composed of 20 g/L molasses, 0.4 g/L urea, 0.4 g/L NaCl, 0.2 g/L KH2PO4, 1.6 g/L K2HPO4, and 0.2 g/L MgSO4. The bioflocculant from B. licheniformis was then applied to treat sugarcane-neutralizing juice to remove colloids, suspended particles, and coloring matters in a sugar refinery factory. The optimal operation conditions were a bioflocculant dosage of 21 U/mL, pH 7.3 and a heating temperature of 100°C. The color and turbidity of the sugarcane juice reached IU 1267 and IU 206, respectively, after clarification with the bioflocculant; these values were almost the same as those acquired following treatment with polyacrylamide (PAM), the most widely applied flocculant in sugar industries. These results suggest the great potential for use of bioflocculants in the sugar refinery process.

A novel type of waist cross-linked micelle (WCM) was developed as an intelligent drug carrier via the self-assembly guiding free radical polymerization of an amphiphilic oligomer: octadecyl, polyethylene glycol butenedioates (O–B–EGs). By changing the concentration of O–B–EG reaction solution, WCMs with monolayer, compound and vesicle-like morphologies were obtained. These WCMs showed controllable temperature responsive properties. DLS and UV-vis analyses indicate that the critical temperatures at which WCMs show an abrupt change in particle size evidently increases with the increase in the molecular weight of the PEG chains. Direct switching of the release of pyrene in WCMs is also realized by a slight change of temperature. Pyrene is released rapidly at the temperatures around the critical temperature of the WCMs, but a further increase in temperature shuts down the release of pyrene. More importantly, these WCMs exhibit reversible and rapid pyrene releasing-absorbing behavior. We suggest that these excellent properties endow WCMs with great potential in drug encapsulation and controlled release

The constant-rate fed-batch production of the polygalacturonic acid bioflocculant REA-11 was studied. A controlled sucrose-feeding strategy resulted in a slight improvement in biomass and a 7% reduction in flocculating activity compared with the batch process. When fed with a 3 g l−1 urea solution, the flocculating activity was enhanced to 720 U ml−1 in 36 h. High cell density (2.12 g l−1) and flocculating activity (820 U ml−1) were obtained in a 10-l fermentor by feeding with a sucrose-urea solution, with values of nearly two times and 50% higher than those of the batch process, respectively. Moreover, the residual sucrose declined to 2.4 g l−1, and residual urea decreased to 0.03 g l−1. Even higher flocculating activity of 920 U ml−1 and biomass of 3.26 g l−1 were obtained by feeding with a sucrose-urea solution in a pilot scale fermentation process, indicating the potential industrial utility of this constant-rate feeding strategy in bioflocculant production by Corynebacterium glutamicum.

Fermentation of bioflocculant with Corynebacterium glutamicum was studied by way of kinetic modeling. Lorentzian modified Logistic model, time-corrected Luedeking–Piret and Luedeking–Piret type models were proposed and applied to describe the cell growth, bioflocculant synthesis and consumption of substrates, with the correlation of initial biomass concentration and initial glucose concentration, respectively. The results showed that these models could well characterize the batch culture process of C. glutamicum at various initial glucose concentrations from 10.0 to 17.5 g·L− 1. The initial biomass concentration could shorten the lag time of cell growth, while the maximum biomass concentration was achieved only at the optimal initial glucose concentration of 16.22 g·L− 1. A novel three-stage fed-batch strategy for bioflocculant production was developed based on the model prediction, in which the lag phase, quick biomass growth and bioflocculant production stages were sequentially proceeded with the adjustment of glucose concentration and dissolved oxygen. Biomass of 2.23 g·L− 1 was obtained and bioflocculant concentration was enhanced to 176.32 mg·L− 1, 18.62% and 403.63% higher than those in the batch process, respectively, indicating an efficient fed-batch culture strategy for bioflocculant production.A three-stage fed-batch strategy was proposed for bioflocculant production by C. glutamicum. In the three stages, i.e. the lag phase, the quick biomass growth and the bioflocculant production stages, the glucose concentration and dissolved oxygen were adjusted according to the prediction results from the modified kinetic models presented in this study. Results show that the biomass and bioflocculant production are largely improved in this three-stage fermentation over the conventional fed-batch fermentation.Download full-size image

A novel type of waist cross-linked micelle (WCM) was developed as an intelligent drug carrier via the self-assembly guiding free radical polymerization of an amphiphilic oligomer: octadecyl, polyethylene glycol butenedioates (O–B–EGs). By changing the concentration of O–B–EG reaction solution, WCMs with monolayer, compound and vesicle-like morphologies were obtained. These WCMs showed controllable temperature responsive properties. DLS and UV-vis analyses indicate that the critical temperatures at which WCMs show an abrupt change in particle size evidently increases with the increase in the molecular weight of the PEG chains. Direct switching of the release of pyrene in WCMs is also realized by a slight change of temperature. Pyrene is released rapidly at the temperatures around the critical temperature of the WCMs, but a further increase in temperature shuts down the release of pyrene. More importantly, these WCMs exhibit reversible and rapid pyrene releasing-absorbing behavior. We suggest that these excellent properties endow WCMs with great potential in drug encapsulation and controlled release