Functional Genomics of Extremophiles, Faculty of Agriculture, Graduate School, Kyushu University, 6-10-1 Hakozaki, Higashi-Ku, Fukuoka, 812-8581, Japan.
Department of Chemistry and Biotechnology, Graduate School of Engineering, Tottori University, 4-101 Koyama-Minami, Tottori, 680-8550, Japan.
J Antibiot (Tokyo). 2018 Mar;71(3):382-389. doi: 10.1038/s41429-017-0003-1. Epub 2018 Jan 18.
Stress-induced mutagenesis can assist pathogens in generating drug-resistant cells during antibiotic therapy; however, if and how antibiotics induce mutagenesis in microbes remains poorly understood. A non-pathogenic thermophile, Geobacillus kaustophilus HTA426, efficiently produces derivative cells resistant to rifampicin and streptomycin via rpoB and rpsL mutations, respectively. Here, we examined this phenomenon to suggest a novel mutagenic mode induced by antibiotics. Fluctuation analysis indicated that mutations occurred via spontaneous mutations during culture. However, mutations were much more frequent in growing cells than stationary cells, and mutation sites were varied through cell growth. These observations suggested that growing cells induced mutagenesis in response to antibiotics. An in-frame deletion of mfd, which governs transcription-coupled repair to correct DNA lesions on the transcribed strand, caused mutations that were comparable between growing and stationary cells; therefore, the mutagenic mechanism was attributable to DNA repair defects where growing cells depressed mfd function. Mutations occurred more frequently at optimal growth temperatures for G. kaustophilus than at a higher growth temperature, suggesting that the mutagenesis relies on active cellular activities rather than high temperature-associated DNA damage. In addition, the mutagenesis may involve a mutagenic factor targeting these sites, in addition to mfd depression, because rpoB and rpsL mutations were dominant at thymine and guanine sites on the transcribed strand. A similar mutagenic profile was observed for other Geobacillus and thermophilic Bacillus species. This suggests that Bacillus-related thermophiles commonly induce mutagenesis in response to rifampicin and streptomycin to produce resistant cells.
应激诱导的突变可以帮助病原体在抗生素治疗过程中产生耐药细胞；然而，抗生素如何诱导微生物发生突变仍知之甚少。一种非致病性嗜热菌，Geobacillus kaustophilus HTA426，能够通过 rpoB 和 rpsL 突变分别有效地产生对利福平（rifampicin）和链霉素（streptomycin）耐药的衍生细胞。在这里，我们研究了这一现象，提出了一种抗生素诱导的新突变模式。波动分析表明，突变是在培养过程中通过自发突变发生的。然而，在生长细胞中突变的频率比在静止细胞中高得多，并且突变位点随着细胞生长而变化。这些观察结果表明，生长细胞对抗生素诱导了突变。mfd 的缺失会导致转录偶联修复功能丧失，从而引起突变，在生长细胞和静止细胞中，突变的频率相当；因此，这种突变机制归因于 DNA 修复缺陷，生长细胞抑制了 mfd 的功能。在 Geobacillus kaustophilus 的最佳生长温度下，突变发生的频率高于在较高生长温度下，这表明突变依赖于活跃的细胞活动，而不是与高温相关的 DNA 损伤。此外，除了 mfd 抑制之外，突变还可能涉及靶向这些位点的诱变因子，因为 rpoB 和 rpsL 突变在转录链上的胸腺嘧啶和鸟嘌呤位点更为常见。在其他 Geobacillus 和嗜热芽孢杆菌物种中也观察到类似的突变特征。这表明，芽孢杆菌相关的嗜热菌通常会在受到利福平（rifampicin）和链霉素（streptomycin）的刺激时，诱导突变以产生耐药细胞。
