Long-term preservation at low temperature of Escherichia coli cells embedded in egg white glass formed by slow drying at room temperature.

Sterile homogeneous egg white (EW) is obtained through a three-step process, high-speed homogenization, centrifugation, and ultraviolet radiation. After incorporating 1.056 × 1010 CFU/g of Escherichia coli, the EW mixture was dehydrated by slow drying to form a brittle, water-soluble, and transparent bacteria-embedded egg white glass (BE-EWG). The BE-EWG stored at -20 °C for 4 months maintains almost all the cell growth functions and proliferation activities of the labeled E. coli, and most of the cell functions and 60 % of the proliferation activities are maintained for up to one year. The BE-EWG exhibits a porous hydrogel membrane structure after heat treatment, and many E. coli cells are accommodated in a grid with a pore size of 2-10 mm. The loss of bacteria-carrying viability after storage at room temperature may be related to the Maillard reaction between protein and glucose in EW, which results in the structural changes caused by protein cross-linking, darkened color and water insolubility of the BE-EWG. Therefore, the method of embedding E. coli cells in EWG as solid form at room temperature to avoid ice crystal formation during cryopreservation is more beneficial for storage, packaging and shipping at -20 °C.

Green immobilization and efficient proliferation of Escherichia coli cells in polyvinyl alcohol hydrogel membranes by unidirectional nanopore dehydration.

BACKGROUND: The immobilized technology for microbial or cells has the advantages of high microbial activity, high microbial density per unit space, good tolerance, strong shock, load resistance, high processing efficiency, and high reuse rate. It is now widely used in environmental remediation, water quality treatment, biodegradation, food industry, chemical analysis, energy development, medicine and pharmaceuticals, and other fields. RESULTS: A novel Escherichia coli cell-immobilizing polyvinyl alcohol hydrogel membrane (ECI-PVAHM) was prepared by unidirectional nanopore dehydration (UND) from a 10% polyvinyl alcohol (PVA) aqueous solution containing enhanced green fluorescent protein-labeled E. coli. This bacteria-loaded film has high water stability, flexibility, transparency, and mechanical robustness. Its tensile strength, elongation rate, and swelling rate are in the ranges 0.66-0.90 MPa, 300-390%, and 330-800%, respectively. The effective bacterial load of ECI-PVAHM is 2.375 × 109-1010 CFU/g (dry weight), which does not affect the original crystal structure of the PVAHM. This biofilm has a porous network structure with pore sizes between 0.2 and 1.0 µm, and these cells are embedded in the PVAHM network. When the immobilized cells were continuously cultured for 20 days, and the medium was renewed twice daily, their relative proliferation efficiency after 40 cycles could still be maintained at ~ 91%. CONCLUSION: The above results show that the cell division, proliferation ability, and metabolic activity of immobilized E. coli were not affected by the physical barrier of the porous network structure of the hydrogel. This UND-based ECI-PVAHM has potential applications in molecular biology, biopharmaceutical expression and production, bioreactors, and fuel cells.

Degraded Sericin Significantly Regulates Blood Glucose Levels and Improves Impaired Liver Function in T2D Rats by Reducing Oxidative Stress.

Sericin could be degraded well into low-molecular-weight sericin (SS) through a novel and environmentally friendly recycling process using an ultrasonically degumming method in Ca(OH)2 aqueous solution. The oral administration of the SS has an evidently hypoglycemic effect on STZ-induced T2D rats. At oral doses of 2.5 and 5% SS for four weeks, the fasting blood glucose decreased by over 60% compared with that in the untreated model group. Oral glucose tolerance and insulin tolerance were ameliorated by the peptide treatment. The serum insulin level was reduced by approximately 35%, the insulin resistance index was reduced by more than 66%. The 8-hydroxy-2 deoxyguanosine level showed a large reduction of 20%, and the total antioxidant activities significantly increased. Hematoxylin-eosin staining and fluorescent immunostaining sections showed that liver and pancreas damage was partly recovered in T2D rats. In summary, oral SS demonstrated evidently hypoglycemic effects mainly related to reducing oxidative stress in the damaged liver and pancreas of T2D rats. Therefore, these results have suggested that the degraded sericin has a potential use in SS-based healthy functional food or hypoglycemic drugs as a waste recovered from sericulture resources.