Team:SDU CHINA/Description

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      In nature, the microorganisms don't exist in isolation but interact and cooperate to achieve complex activities in the ecosystem. The microbial co-culture is to cultivate two or more different populations of cells steadily in a system by an artificial way. In the co-culture system, the natural microbial ecosystem can be intimated to stablish the full potential of microbes. It is promising in the areas of technology, energy, environment and so on.

Energy

      As the world's population is growing, people demand more and more amounts of energy to supply their lifestyle. People exploit fossil resources, but at the same time, it also destroys the original ecological environment of the earth.So it is a good idea to transfer the useless lignocellulose into bioenergy. Using bacteria to deconstruct lignocellulose can lower the costs of production significantly, but the problem is that there are few bacteria which can deconstruct lignocellulose in quantity. However, the researchers find that co-culture of bacteria and/or fungi in consolidated bioprocessing(CBP) is an efficient way of breakdown of complex biopolymers.[1]

Research

      Archaea bacteria have been recognized as a major domain of life since 1970s and play an important role in the tree of life. Therefore, the research of Archaea is very urgent. Traditional culture methods often lead to slow growth or even no growth, so this fact forces the scientists to find a new cultivation method to improve archaeal cultivation. A large number of studies show that in the artificially-built co-culture system, the cooperation between the bacteria in the intimated natural environment can greatly promote the growth of archaea. However, this theory has not been put into practice because the proportion of the bacteria in the system cannot be controlled.[2]

Environment

      Anaerobic digestion, an economic and energy-efficient biological technology, is widely applied in the treatment of a variety of wastewater streams. However, due to the influence of many factors, it can not be used in the anaerobic treatment of chemical organic wastewater. To solve this issue, the scientists suggest combining the bacteria co-culture and the anaerobic digestion of DROW as a way to achieve the complete degradation of certain organics.[3]

Food

      In the field of food, co-culture has been long used to make alcohol products, lactic acid products and so on. In the previous studies, the stable co-culture system is built on the basis of natural antagonism in the different strains of bacteria. In the recent years, the researchers start to develop new lactic acid bacteria drink by establishing stable co-culture system.[4]

Medicine

      A large number of naturally occurring secondary metabolites from plants and microbes have been explored for their pharmacological properties and used as drugs. They can effectively help people cambat infectious dieases. Unfortunately, antibiotic resistance is growing faster than the discovery of new antibiotics, which might threaten human health. Many studies confirm that most secondary metabolite gene clusters I microorganisms are silent under laboratory growth conditions and the relative gene can be induced only by interacting with certain bacteria. Therefore, the cotrolled co-cultivation represents an important method to stimulate microorganisms to produce certain secondary metabolite.[5]

Industry

      The microbial production has traditionally relied on a single engineered microbe and it faces many limitations, including high metabolic burden, inactive enzyme expression and numerous byproduct formation. Co-culture can address these problems well by distracting the metabolic burden.[6]

      There are many ways to build co-culture systems, but they are not widely used because they cannot meet their needs. In order to gain a deeper look into the needs of co-cultivation systems, we paid a visit to the companies, hospitals, and SKLMT in related fields and learned the iGEM projects in previous years. At present, the methods that people construct a co-culture system include directly inoculating different bacteria in a certain proportion and using specific auxotrophic bacteria. However, these techniques are neither robust nor portable across different organisms.
      Besides, in these solutions, the ratio of the bacteria is fixed and can not be regulated dynamically. But in practical application, the demand for the number of the bacteria with different labours and functions changes in a specific time. There is a need for a stable and portable co-culture system that allows people to regulate the ratio dynamically by simple procedures.

      We have set out to engineer a genetic circuit that allows ratiometric control of populations in a co-culture by different lights. Our genetic circuit employs three modules： the light control part, the quorum sensing (QS) part and the toxin/antitoxin part. The light control part receives light of a specific wavelength and activates the quorum sensing part. The quorum sensing module releases a specific HSL, producing toxins in specific bacteria, and producing antitoxins in another, thereby controlling the number and proportion of the bacteria.

Reference

[1] Jones, J. A. , & Wang, X. . (2017). Use of bacterial co-cultures for the efficient production of chemicals. Curr Opin Biotechnol, 53, 33-38.
[2]Sun, Y., Liu, Y., Pan, J. et al. Microb Ecol (2019).Perspectives on Cultivation Strategies of Archaea.Microbial Ecology pp 1–15。
[3]Sperandio, G. B., & Filho, E. X. (2019). Fungal co-cultures in the lignocellulosic biorefinery context: A review. International Biodeterioration & Biodegradation,, 109-123.
[4]Garcia, C., Rendueles, M., & Diaz, M. (2019). Liquid-phase food fermentations with microbial consortia involving lactic acid bacteria: A review. Food Research International,, 207-220.
[5]Kong, Z., Li, L., Xue, Y., Yang, M., & Li, Y. (2019). Challenges and prospects for the anaerobic treatment of chemical-industrial organic wastewater: A review. Journal of Cleaner Production,, 913-927.
[6]Plass, J. L., Homer, B. D., & Kinzer, C. K. (2015). Foundations of Game-Based Learning.. Educational Psychologist, 50(4), 258-283.
[7] https://2018.igem.org/Team:UCAS-China
[8] https://2016.igem.org/Team:Imperial_College

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