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In order to increase yield,take the Bacillus subtilis Asr as the expreession strain, the fermentation process of Bacillus subtilis Asr was optimized by orthogonal test and response surface method. The results show that three main factors affecting bacterial yield are leaching yeast powder, MgSO4 and CaCl2. The best fermentation medium formulation is as following: sucrose 20 g/L, peptone 10 g/L, leaching yeast powder 8.65 g/L, K2HPO4 3.0 g/L, MgSO4 0.27 g/L and CaCl2 0.53 g/L. The optimal culture conditions are as following: 37 ℃, initial pH 7.0, inoculum of 10% and stirring speed of 250 r/min. After the optimization, the highest yield of Bacillus subtilis Asr reaches 7.30×108 cfu/mL, which is 3.95 times higher than that before optimization. The study provides a technical reference for the subsequent bacterial scale-up culture in fermentor and the optimization of fermentation medium from other Bacillus subtilis.

Collagen of type Ⅱ is the major component of hyaline cartilage in animals. Based on its biocompatibility, biodegradability and many other biological properties, for example promoting cell growth and differentiation, collagen of type Ⅱ has been widely applied in various fields, such as tissue engineering material, food, cosmetic, packaging, etc.. In recent years, using genetic engineering to produce recombinant collagen of type Ⅱ is popular. The structure, function and application of collagen of type Ⅱ are described, the latest research progress for producing recombinant collagen of type Ⅱ by genetic engineering is put forward, and the large-scale production of hydroxylated collagen in E.coli in the future is previewed, which would be helpful for the further development and study of collagen of type Ⅱ.

As a kind of green and healthy microecologics, Bacillus subtilis could balance the intestinal flora, promote the nutrient absorption and enhance immunity. Microecologics is one of the ideal antibiotics alternative, which are effective in preventing and treating animal disease and promoting the growth and development of the animal. Because of its advantages, such as no toxin side effect and no residual or drug-resistant, microecologics has been used in livestock breeding widely. Here, we concluded the characteristics and mechanism of Bacillus subtilis,elaborated application of microecologics on livestock breeding, discussed its problems and suggested its solved methods. In the end, the future of microecologics was expected in order to provide a reference for subsequent livestock breeding.

Once damaged, articular cartilage should be repaired or replaced owing to its limited self-repair capacity. But traditional methods for treating cartilage defect are not satisfying. In contrast, tissue engineering offers promising hope for cartilage disease. In the three main factors of tissue engineering, such as seed cells, scallfold materials and signal molecules, scallfold materials play a fundamental role. The paper reviews cartilage scallfold materials, introduces collagen type Ⅱ, hyaluronic acid and chondroitin sulfate which naturally exist in cartilage, and dicusses the current problems and the future directions of tissue engineering scallfold.