Growth and formaldehyde degradation of photoheterotrophic Methylobacterium within radiation fogs
mBio Volume 17, Issue 6, 27 April 2026
The atmosphere contains thousands to millions of bacterial cells per cubic meter. However, it remains unclear if microbes are at all active or growing in situ or whether they are merely being transported in an inactive state. Based on the analyses of 32 overland radiation fog events over a 2-year period, we show that fog waters, with bacterial concentrations similar to those in continental or marine bodies of water, contain microbiomes well differentiated in composition from those in the dry aerosol microbiomes that occur locally before, during, or after fog events. They are consistently and strongly enriched in photoheterotrophic Methylobacterium species, suggesting that fog populations may be metabolizing volatile C1 compounds in situ, although phototrophy seems much less important. Indeed, metabolically active bacteria in the fog, and representative isolates of the main field populations, can degrade formaldehyde at unprecedently high rates; most of this activity seems to play a detoxification role. The increase in bacterial aerobiome counts upon intervening fog events, the dependence of microbial concentration on ambient temperature, the increases in cell size and frequency of dividing cells in fog water with respect to cells in interstitial aerosols of fogs, in addition to their metabolic capacity, all suggest that the fog water microbiome is actually growing. Consequently, droplets of atmospheric water should be considered a potential aquatic microhabitat. Our results highlight the fog microbiome’s role in atmospheric chemistry and have implications for fog harvesting as a source of fresh water for human use.
- 大気中には大量の細菌が存在するが、実際に活動・増殖しているかは不明だった
- 2年間にわたり32回の放射霧イベントを解析し、霧水中の微生物群集を調査
- 霧水中の細菌濃度は湖沼や海洋と同程度
- 霧の微生物群集は、周辺の乾燥エアロゾル中の群集とは明確に異なる
- 霧中では Methylobacterium が一貫して優占
- 揮発性C1化合物を利用している可能性が示唆された
- 霧由来細菌および分離株は、ホルムアルデヒドを極めて高い速度で分解
- この活性の主な役割は炭素獲得よりも解毒と考えられた
- 霧発生時に細菌数が増加
- 微生物濃度は気温と相関
- 霧中の細胞は周囲エアロゾル中の細胞より大型で、分裂中の細胞も多い
- 霧中の微生物は単に輸送されているのではなく、その場で増殖している可能性が高い
- 大気中の水滴は微生物にとって一時的な水圏環境として機能することを提唱
- 霧を単なる「微生物の運搬媒体」ではなく、「増殖可能な生息環境」として示した
- Methylobacterium が大気中でも活発に活動する可能性を示唆
- 大気化学や霧水利用（フォグハーベスティング）への影響を考える上で重要な知見