Sayak Banerjee, Amity University Kolkata
Adaptive laboratory evolution has become a substantial tool for the development of microbial strains with enhanced genetically modified features. The long-term Escherichia coli evolution experiment is a good example. It has emphasized how evolution under adequate conditions can be utilized to understand adaptive processes. These experiments have helped to determine the possible evolutionary outcomes. They have also unveiled the divergence between the fitness trajectories and mutation rates of clonal asexual populations. Additionally, the adaptive laboratory evolution of co-cultures has facilitated the study of the emergence of interspecies interactions and metabolite exchange. The main objective of these studies is the development of microbial models of cross-feeding. Since amino acid cross-feeding is common in natural communities, cross-feeding involving other nutrients must be studied more.
Adaptive laboratory evolution can be applied to any organism not amenable to genetic engineering. For its success, the basic requirement is that, under selected conditions, the trait of interest is correlated to fitness. This minimal requirement underlines the restricted applicability to the traits which implement a toll on the cell fitness, like metabolite secretion. The core faculties of the European Molecular Biology Laboratory have employed mutualistic cross-feeding to impose selection pressure for increased production of the target compound. The aim was to enhance the fitness-costly metabolite secretion while keeping the advantages provided by adaptive laboratory evolution.
Adaptive laboratory evolution of a mutualistic community:
They tested this in a mutualistic microbial community consisting of lactic acid bacteria (LAB), Lactobacillus plantarum, and engineered Saccharomyces cerevisiae strains. The LAB used can naturally produce B-group vitamins (riboflavin or folate), and the yeast is auxotrophic for one of those vitamins. When the community is grown under excess nitrogen, the yeast secretes amino acids for which the LAB strains are naturally auxotrophic. Therefore, the requirement for obligate mutualism is satisfied by the yeast-LAB community. The co-evolution not only exhibited improvement in growth, but also the increased secretion of riboflavin. It resulted in positive selection for an increase in vitamin biosynthesis with more efficient consumption of the amino acids secreted by the yeast.
The results showed that natural selection can be employed to increase the production of the desired compound. It was achieved by coupling it with community fitness via cross-feeding. The researchers observed that monoculture evolution experiments displayed a lack of improvement. This change ensured a link between the phenotype showing improved secretion and the selection pressure imposed by the cross-feeding. They also observed that the selection pressure is connected to the presence of the mutualistic partner rather than the absence of the compound in the surroundings.
Moreover, bacterial cells with limited secretion capacity could be considered cheaters that can result in the collapse of the whole community. Although a majority of isolates that are evolved show enhanced secretion, the poor secretors lack the sufficient fitness advantage over high riboflavin secretors. They stated spatial segregation to be a common mechanism for cheater suppression and stabilization of mutualistic interaction.
Implementation of the Co-evolution approach:
Therefore, the scientists concluded that co-evolution is potent against the emergence of the phenotypes which are non-cooperating. The high secretors prevail by balancing the fitness burden of improved vitamin secretion with the evolution of better nutrient utilization. This approach allows the targeted improvement of fitness-costly metabolites by natural selection in adaptive laboratory evolution. This method can be used in organisms in which genetic engineering is restricted. It could also be applied to organisms in which the genetic basis of the trait of interest is unknown. Besides, biotechnological, the co-evolution approach could answer many ecological questions on the emergence of cross-feeding and mutualism in microbial communities.
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Reference:
- Konstantinidis, D., Pereira, F., Geissen, E., Grkovska, K., Kafkia, E., Jouhten, P., Kim, Y., Devendran, S., Zimmermann, M., & Patil, K. R. (2021). Adaptive laboratory evolution of microbial co‐cultures for improved metabolite secretion. Molecular Systems Biology, 17(8). https://doi.org/10.15252/msb.202010189
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Author info:
Sayak Banerjee is a 3rd year Biotechnology Engineering Student with great interest in Immunology and Molecular genetics. He is a creative scientific writer in Bioxone with an inclination towards gaining knowledge regarding vast sections of Biotechnology and emphasizing himself in various wet lab skills.
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