Microorganisms select or modify their metabolism, especially energy metabolism, according to their environment to optimize their energy efficiency. I wonder. The following projects related to such propositions have been and are currently being implemented.
The genes required by microorganisms at high temperatures are thought to differ depending on the growth conditions, but the number of genes required for E. coli to grow at high temperatures has been estimated to be 72 (Murata et al., 2019). These genes were grouped into eight categories: genes for energy metabolism, outer membrane organization, DNA double-strand break repair, tRNA modification, protein quality control, translation control, cell division and transporters. Of these, 21 genes are classified as energy metabolism, accounting for 30% of all heat-stable genes, suggesting that deletion of genes involved in metabolism causes loss of heat-tolerance in Escherichia coli. However, since LB medium is used for screening these genes, it is difficult to clarify how metabolism differs between medium temperature (37°C) and high temperature (45°C). Therefore, we are studying how E. coli metabolizes glucose at medium and high temperatures, and whether there are important factors in high-temperature metabolism.
Two different approaches have been tried to understand the thermotolerance of microorganisms and the mechanism of thermostabilization. One is to clarify the genes necessary for growth at high temperatures, that is, heat-tolerant genes, by comprehensively destroying the genes of microorganisms, and to clarify the functional classification of the heat-tolerant genes discovered by this. It is a comparison between microorganisms. This analysis revealed that there is a variety of thermostable genes and that there is commonality between strains (Murata et al., 2019; Charoensuk et al., 2017). In another approach, mutations are introduced into genes that allow cells to survive in a high-temperature environment, the growth limit of the microorganism of interest. Therefore, we analyzed what kinds of mutations occur in what kind of genes when the cells of microorganisms that have been bred by adapting to high temperatures become heat resistant. Mutations occurred mainly in genes related to cell membranes and genes involved in transcription and translation, and similarity was observed in these mutated genes among different microorganisms, suggesting the possibility of generalization of thermostability. (Kosaka et al., 2021). These analyzes left several questions open. It is the bias of heat-resistant genes in strains and the difference between heat-tolerance and heat-tolerance.