Production of high protein straw feed by recombinant Saccharomyces cerevisiae
1. Inspiration
Hubei Province is a major breeding and planting province. A large number of straws produced by plantation are inefficient, resulting in resource waste and environmental pollution. At the same time, feed materials such as corn and soybeans cannot meet the breeding needs of this province, resulting in a contradiction between humans and animals competing for food.
Therefore, the project plans to use crop straws as raw material to develop non-grain feed by means of synthetic biology, so as to realize the linkage between plantation and breeding, which is of great significance to reduce breeding costs and alleviate the food crisis.
2. Background
Non-grain feed — the most direct and efficient way to reduce costs in the animal husbandry
High proportion
In the livestock breeding, feed costs account for 50% or even the highest of the total breeding costs. Currently, the raw materials for feed mainly rely on grain, but there is a shortage of supply and a lack of price advantage in grain.
High demand
Taking corn as an example, the consumption of corn in 2022 reached 295 million tons. Compared to the corn production and consumption in the past five years, the average annual corn supply gap in China exceeds 30 million tons.
High price
Due to the rapid growth of feed and industrial corn consumption, corn prices have increased. Since 2016, both domestic corn prices and corn import prices have experienced significant increases. The domestic corn market price has increased from 1518 yuan/ton at the end of 2016 to 2823 yuan/ton at the end of 2022, and the corn import price has increased from 1681 yuan/ton at the end of 2016 to 2824 yuan/ton at the end of 2022, with an increase of 86% and 68%, respectively.
Therefore, developing non-grain feed raw materials is the most direct way to reduce costs in the animal husbandry, which is of great significance for solving food security.
3. Advantages and problems
Significant advantage
Crop straw is the most important non-grain feed material, and the yield of crop straw is huge. Fully utilizing crop straw as feed can effectively decrease the grain used for forage and alleviate the food crisis.
Cellulose, hemicellulose and lignin in straw are closely combined and intertwined to form coarse fiber, which makes straw as direct feed with low nutritional value, low protein content, poor taste, high crude fiber content and low digestibility.
Microbial fermentation can transform some straw into bacterial bodies rich in protein and fat, and microorganisms have relatively low nutritional requirements and can utilize complex organic compounds that cannot be utilized by livestock and poultry.
The large amount of bacteria in straw is conducive to the formation of gut microbiota in livestock and poultry, improving their disease resistance and reducing the use of antibiotics. Straw will have a special aroma after microbial fermentation, and after fermentation, it will make the straw softer, more palatable, and have a larger intake.
Existing problems
The cellulose in straw can be degraded into glucose by microorganisms in ruminants and then utilized, but the main source of meat in China is mainly pigs and poultry, which cannot effectively utilize cellulose.
In addition to the main cellulose, straw also contains about 30% of hemicellulose, which can be degraded into five carbon sugars, such as xylose. Hemicellulose cannot be effectively used by various livestock and poultry, including ruminants, resulting in a huge waste of biomass resources.
The protein content of yeast single cell protein (SCP) is similar to that of fish meal, and it is rich in various essential amino acids, making it a very promising feed protein. The wild type Saccharomyces cerevisiae can only ferment glucose, and cannot use xylose, which causes a very serious waste of resources.
Therefore, developing an efficient microbial platform to co convert glucose and xylose from lignocellulosic biomass hydrolysates into single-cell proteins is of great significance for improving the utilization rate of lignocellulosic biomass.
4. Solutions
This project is divided into three modules.
One is the cellulose degradation module, which uses cellulase to degrade cellulose in straw into glucose.
The second is xylan degradation module, which degrades xylan in straw into xylose through xylanase.
The third is the xylose utilization module, which is recombined into Saccharomyces cerevisiae through xylose isomerase to realize the utilization of xylose.
Further optimize the cellulose degradation module and randomly mutate the β-glucosidase in cellulose degradation using error prone PCR method to improve the enzyme activity.
A recombinant Saccharomyces cerevisiae strain capable of degrading and utilizing cellulose and hemicellulose in straw is constructed to produce high protein straw feed by fermentation.