Engineering yeast cell factories to produce biodegradable plastics and their monomers: Current status and prospects.

Traditional plastic products have caused serious environmental pollution due to difficulty to be degraded in the natural environment. In the recent years, biodegradable plastics are receiving increasing attention due to advantages in natural degradability and environmental friendliness. Biodegradable plastics have potential to be used in food, agriculture, industry, medicine and other fields. However, the high production cost of such plastics is the bottleneck that limits their commercialization and application. Yeasts, including budding yeast and non-conventional yeasts, are widely studied to produce biodegradable plastics and their organic acid monomers. Compared to bacteria, yeast strains are more tolerable to multiple stress conditions including low pH and high temperature, and also have other advantages such as generally regarded as safe, and no phage infection. In addition, synthetic biology and metabolic engineering of yeast have enabled its rapid and efficient engineering for bioproduction using various renewable feedstocks, especially lignocellulosic biomass. This review focuses on the recent progress in biosynthesis technology and strategies of monomeric organic acids for biodegradable polymers, including polylactic acid (PLA), polyhydroxyalkanoate (PHA), polybutylene succinate (PBS), and polybutylene adipate terephthalate (PBAT) using yeast cell factories. Improving the performance of yeast as a cell factory and strategies to improve yeast acid stress tolerance are also discussed. In addition, the critical challenges and future prospects for the production of biodegradable plastic monomer using yeast are also discussed.

[Effects of gender and age on protein secretion in saliva of transgenic mice expressing human nerve growth factor].

Nerve growth factor (NGF) can promote the development, differentiation and regeneration of neurons. Recently, in order to efficiently produce human NGF (hNGF) drugs with better efficacy, we created transgenic mice expressing hNGF specifically in their salivary glands, and purified highly active hNGF protein from their saliva. Some studies reported that the NGF secretion in mouse saliva is affected by gender and age. Here, in order to select hNGF transgenic mice with high NGF secretion for saliva collection and hNGF purification, we divided transgenic mice into 4 groups, including 28-day-old young males and females, 63-day-old adult males and females. We compared their saliva volume, total salivary protein amount, salivary mNGF protein amount and salivary hNGF protein amount. The results showed that the saliva volume as well as amounts of total salivary protein, salivary mNGF protein and salivary hNGF protein secreted by 63-day-old transgenic mice were significantly higher than those secreted by sex-match 28-day-old transgenic mice, and the salivary hNGF protein amount secreted by male transgenic mice at the age of 63 days was significantly higher than that of female transgenic mice at the same age; Among 4 groups of mice, 63-day-old male transgenic mice secreted the highest salivary hNGF content, which was about 46 times higher than that secreted by the 28-day-old female transgenic mice. Therefore, 63-day-old male transgenic mice should be selected for saliva collection and hNGF purification.