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Source: Science and Technology Daily

Science and Technology Daily, Beijing, August 13 (Reporter Zhang Mengran) According to the official website of the Swiss Federal Institute of Technology in Zurich, the school team has proposed a new method for producing cellulose using bacteria. This method follows the evolutionary mechanism of natural selection, allowing scientists to quickly cultivate tens of thousands of bacterial variants and select the strains that can produce the most cellulose.

Scientists have been trying to turn microorganisms into living "production factories" so that they can produce large quantities of desired products more quickly. This requires targeted modification of bacterial genomes or cultivation of the most suitable bacterial strains.

The acetic acid bacteria K. sucrofermentans can produce high-purity cellulose. Cellulose materials help heal wounds and prevent infection, and are in high demand for biomedical applications, packaging materials, and textiles. However, the wild type of this bacterium grows slowly and produces limited amounts of cellulose, so a way had to be found to increase production.

Using the new method, the research team successfully cultivated several acetic acid bacteria variants that produced 70% more cellulose than the original strain.

The team first irradiated the bacterial cells with ultraviolet light to randomly damage sites in the bacterial DNA. Then, they placed the bacteria in a dark room to prevent DNA damage repair, thereby inducing mutations. They used a micro-instrument to encapsulate each bacterial cell in a small drop of nutrient solution and allowed the cells to produce cellulose for a specific period of time. After the incubation period, they used fluorescence microscopy to analyze which bacterial cells produced the most cellulose and which produced none or very little cellulose.

With the help of a newly developed sorting system, the team automatically sorted out bacterial cells that have evolved to produce large amounts of cellulose. The sorting system is fully automated and very fast. It only takes a few minutes to scan 500,000 droplets with a laser and sort out the droplets with the highest cellulose content. Finally, four strains were selected, whose cellulose production is 50%-70% higher than that of the wild type.

The evolved acetic acid bacteria cells grew at the interface of air and water in the glass bottle and produced a cellulose mat. The natural weight of this mat is between 2 and 3 milligrams and the thickness is about 1.5 millimeters. The cellulose mat produced by the evolved variant is almost twice as heavy and thick as the wild type.

The team's next step will be to test the new microorganism under actual industrial conditions.

Cellulose is the most widely distributed and abundant polysaccharide in nature. Some strains of acetic acid bacteria can synthesize cellulose, but the synthesis rate under natural conditions is too slow to meet human needs. This time, the team imitated the "natural selection method", leaving cells that can produce a large amount of cellulose and eliminating "lazy and slippery" cells to help acetic acid bacteria cells "evolve". The newly developed sorting system played an important role. It can "recognize" who is the "excellent employee" who produces cellulose at a glance. Next, researchers will further verify whether this evolved acetic acid bacteria can play a role in increasing production and income in industrial production.