Isolation of Chloroflexus aurantiacus and related thermophilic phototrophic bacteria from Japanese hot springs using an improved isolation procedure.

Abstract

The multicellular filamentous green bacteria, Chloroflexus species, inhabit natural hot springs. For the isolation of these bacteria, a new isolation method was developed using an organic medium and culture under alternating aerobic and anaerobic conditions. The improved method reliably provided a high rate of isolation of the thermophilic photoheterotrophs. Ten strains that may belong to this genus were isolated from Japanese hot springs in various areas. All these new isolates were thermophilic photosynthetic bacteria that were morphologically similar to Chloroflexus aurantiacus. The isolates were also similar to C. aurantiacus in photosynthetic pigments and guanine plus cytosine (G+C) contents. The results of DNA-DNA hybridization and quinone composition analysis indicated that eight of the new strains belong to C. aurantiacus, while two strains (MD-66 and YI-9) which have the ability to form bacterial mat-like dense aggregates, were significantly different from C. aurantiacus.