Hydrogen-dependent autotrophic growth in phototrophic and chemolithotrophic cultures of thermophilic bacteria, Chloroflexus aggregans and Chloroflexus aurantiacus, isolated from Nakabusa hot springs.

The genus Chloroflexus is a deeply branching group of thermophilic filamentous anoxygenic phototrophic bacteria. The bacteria in this genus have been shown to grow well heterotrophically under anaerobic photosynthetic and aerobic respiratory conditions. We examined autotrophic growth in new isolates of Chloroflexus strains from hot springs in Nakabusa, Japan. The isolates belonging to Chloroflexus aggregans (98.7% identity of 16S rRNA gene sequence to the respective type strain) and Chloroflexus aurantiacus (99.9% identity to the respective type strain) grew photoautotrophically under a 24% H2 atmosphere. We also observed chemolithotrophic growth of these isolates under 80% H2 and 5% O2 conditions in the dark. This is the first report showing that Chloroflexus grew under both photoautotrophic and chemolithotrophic conditions in addition to photoheterotrophic and aerobic chemoheterotrophic conditions. © FEMS 2019.