Water-soluble carboxymethyl chitosan was prepared from dried shrimp shells. The intrinsic viscosities of its samples were measured to evaluate the stability of carboxymethyl chitosan. The influential factors of stability, such as heat, pH, ionic strength, ultraviolet radiation, and sterilization were studied. The results demonstrate that the intrinsic viscosities of water-soluble chitosan will be influenced, to a certain extent, by the change of pH and ionic strength. Ultraviolet radiation and sterilized processes not only exept influence on the degradation of chitosan, but also have prominent effects on the molecular structure of it. Besides, temperature will also affect the speed of degradation, and chitosan can be stored at a temperature as low as 2 degrees C-8 degrees C.
Chitosan ; chemical synthesis ; chemistry ; Drug Stability ; Hydrogen-Ion Concentration ; Solubility ; Temperature

In order to overcome the challenges of insufficient restriction enzyme sites, and construct a fusion-expression vector with flexible fusion direction, we designed an LB cloning system based on the type IIS and type IIT restriction enzymes LguⅠ and BbvCⅠ. The LB cloning system is constructed by inserting the LB fragment (GCTCTTCCTCAGC) into the multiple cloning site region of the broad-host plasmid pBBR1MCS-3 using PCR. The LB fragment contains partially overlapped recognition sites of LguⅠ and BbvCⅠ. Therefore, the same non-palindromic sequence will be generated by these two restriction endonucleases digestion. This feature can be used to quickly and flexibly insert multiple genes into the expression vector in a stepwise and directed way. In order to verify the efficacy of the cloning system, two glycosyltransferase genes welB and welK of Sphingomonas sp. WG were consecutively fused to the LB cloning vector, and the recombinant plasmid was transferred into Sphingomonas sp. WG by triparental mating. The results showed that gene fusion expression has little effect on sphingan titer, but enhanced the viscosity of sphingan. The viscosity of the sphingan produced by recombinant strain Sphingomonas sp. WG/pBBR1MCS-3-LB-welKB was 24.7% higher than that of the wild strain after fermentation for 84 h, which would be beneficial for its application. In conclusion, the application of LB cloning system were verified using Sphingomonas sp. WG. The LB cloning system may provide an efficient tool for fusion expression of target genes.
Base Sequence ; Cloning, Molecular ; Fermentation ; Plasmids/genetics* ; Sphingomonas/metabolism*