Uchijima Tomoki, Kato Shingo, Tanimoto Kazuya, Shiraishi Fumito, Hamamura Natsuko, Tokunaga Kohei, Makita Hiroko, Kondo Momoko, Ohkuma Moriya, Mitsunobu Satoshi
Department of Science and Technology for Biological Resources and Environment, Graduate School of Agriculture, Ehime University, 3-5-7 Tarumi, Matsuyama, Ehime 790-8566, Japan.
Japan Collection of Microorganisms, RIKEN BioResource Research Center, 3-1-1 Koyadai, Tsukuba, Ibaraki 305-0074, Japan.
FEMS Microbiol Ecol. 2025 May 20;101(6). doi: 10.1093/femsec/fiaf051.
Chemolithotrophic neutrophilic iron (Fe)-oxidizing bacteria, which mainly belong to the family Gallionellaceae, universally prevail in terrestrial environments changing Fe cycling. However, they are typically recognized as difficult-to-culture microbes. Despite efforts, there are few Fe(II)-oxidizing lithotroph isolates; hence, their physiological and ecological knowledge remains limited. This limitation is largely owing to difficulties in their cultivation, and we hypothesize that the difficulty exists because substrate and mineral concentrations in the cultivation medium are not tuned to a specific environmental condition under which these organisms live. To address this hypothesis, this study proposes a novel custom-made medium approach for chemolithotrophic Fe(II)-oxidizing bacteria; a method that manipulates medium components through diligent analysis of field environment. A new custom-made medium simulating energy substrates and nutrients under the field condition was prepared by modifying both chemical composition and physical setup in the glass-tube medium. In particular, the modification of the physical setup in the tube had a significant effect on adjusting dissolved Fe(II) and O2 concentrations to the field environment. Using the medium, Gallionellaceae members were successfully enriched and a new Gallionellaceae species was isolated from a natural hot spring site. Compared with conventional medium, the custom-made medium has significantly higher ability in enriching Gallionellaceae members.
化能自养嗜中性铁（Fe）氧化细菌主要属于嘉利翁菌科，普遍存在于改变铁循环的陆地环境中。然而，它们通常被认为是难以培养的微生物。尽管人们做出了努力，但铁（II）氧化化能自养菌的分离株却很少；因此，我们对它们的生理和生态知识仍然有限。这种局限性很大程度上是由于它们培养困难，我们推测存在这种困难是因为培养基中的底物和矿物质浓度没有根据这些生物生存的特定环境条件进行调整。为了验证这一假设，本研究提出了一种针对化能自养铁（II）氧化细菌的新型定制培养基方法；一种通过对野外环境进行细致分析来操控培养基成分的方法。通过改变玻璃管培养基中的化学成分和物理设置，制备了一种模拟野外条件下能量底物和营养物质的新型定制培养基。特别是，管内物理设置的改变对将溶解的铁（II）和氧气浓度调整到野外环境有显著影响。使用这种培养基，成功富集了嘉利翁菌科成员，并从一个天然温泉地点分离出了一种新的嘉利翁菌科物种。与传统培养基相比，定制培养基在富集嘉利翁菌科成员方面具有显著更高的能力。
