Microorganisms live in a wide variety of environments differing in the presence or absence of oxygen. A filamentous bacterium, Chloroflexus aggregans grows by both aerobic respiration and anoxygenic photosynthesis. Habitat of C.aggregans is microbial mats where many species of bacteria co-exist to make densely packed aggregates. C.aggregans is widely distributed within the mats, but the population at aerobic surface of the mats was limited. In this study, we tried to clarify how C.aggregans distributes within the microecosystem.

C.aggregans cells were suspended into a soft agar medium which was free in organic compounds. The agar medium was solidified in glass test tubes and incubated in the dark at 60˚C.

When incubated under air as a gas phase of the tubes, cell density of lower parts of the medium decreased during the incubation and thin layer containing high cell density appeared at the depth of 1cm from the agar surface. The thin layer was developed at deeper part when higher oxygen concentration of the gas phase was applied. In either case, colors of an oxidation-reduction indicator showed the upper part from the thin layer was oxidative and the lower part was anaerobic.

These results suggested the density of C.aggregans cells is high around the border between anaerobic and microaerobic as a result of their motility in vitro, possibly in nature too.