Charoensuk Kannikar, Sakurada Tomoko, Tokiyama Amina, Murata Masayuki, Kosaka Tomoyuki, Thanonkeo Pornthap, Yamada Mamoru
Division of Product Development and Management Technology, Faculty of Agro-Industrial Technology, Rajamangala University of Technology Tawan-ok, Chanthaburi Campus, Chanthaburi, 22100 Thailand.
Life Science, Graduate School of Science and Technology for Innovation, Yamaguchi University, Ube, 755-8505 Japan.
Biotechnol Biofuels. 2017 Aug 24;10:204. doi: 10.1186/s13068-017-0891-0. eCollection 2017.
High-temperature fermentation (HTF) technology is expected to reduce the cost of bioconversion of biomass to fuels or chemicals. For stable HTF, the development of a thermotolerant microbe is indispensable. Elucidation of the molecular mechanism of thermotolerance would enable the thermal stability of microbes to be improved.
Thermotolerant genes that are essential for survival at a critical high temperature (CHT) were identified via transposon mutagenesis in ethanologenic, thermotolerant TISTR 548. Surprisingly, no genes for general heat shock proteins except for were included. Cells with transposon insertion in these genes showed a defect in growth at around 39 °C but grew normally at 30 °C. Of those, more than 60% were found to be sensitive to ethanol at 30 °C, indicating that the mechanism of thermotolerance partially overlaps with that of ethanol tolerance in the organism. Products of these genes were classified into nine categories of metabolism, membrane stabilization, transporter, DNA repair, tRNA modification, protein quality control, translation control, cell division, and transcriptional regulation.
The thermotolerant genes of and that had been identified can be functionally classified into 9 categories according to the classification of those of , and the ratio of thermotolerant genes to total genomic genes in is nearly the same as that in though the ratio in is relatively low. There are 7 conserved thermotolerant genes that are shared by these three or two microbes. These findings suggest that possesses molecular mechanisms for its survival at a CHT that are similar to those in and . The mechanisms may mainly contribute to membrane stabilization, protection and repair of damage of macromolecules and maintenance of cellular metabolism at a CHT. Notably, the contribution of heat shock proteins to such survival seems to be very low.
高温发酵（HTF）技术有望降低生物质转化为燃料或化学品的生物转化成本。对于稳定的高温发酵而言，开发耐热微生物必不可少。阐明耐热性的分子机制将有助于提高微生物的热稳定性。
通过转座子诱变，在产乙醇的耐热菌株TISTR 548中鉴定出了在临界高温（CHT）下生存所必需的耐热基因。令人惊讶的是，除了 外，未包含一般热休克蛋白的基因。这些基因中发生转座子插入的细胞在约39°C时生长存在缺陷，但在30°C时正常生长。其中，超过60%的细胞在30°C时对乙醇敏感，这表明该生物体的耐热机制与乙醇耐受机制部分重叠。这些基因的产物可分为九类代谢、膜稳定、转运、DNA修复、tRNA修饰、蛋白质质量控制、翻译控制、细胞分裂和转录调控。
已鉴定出的 和 的耐热基因可根据 的分类在功能上分为9类，尽管 中的耐热基因比例相对较低，但其耐热基因与总基因组基因的比例与 中的几乎相同。这三种或两种微生物共有7个保守的耐热基因。这些发现表明， 具有与 和 类似的在临界高温下生存的分子机制。这些机制可能主要有助于膜稳定、大分子损伤的保护和修复以及在临界高温下维持细胞代谢。值得注意的是，热休克蛋白对这种生存的贡献似乎非常低。
