This is a view of an anaerobic roll tube in which a mixed culture of methane producing bacteria have been suspended and grown in an agar base medium containing 2.5 g/l sodium formate, 2.5 g/l sodium acetate, 2.0 ml/l (60%) sodium lactate, 2.0 ml/l methanol, and 2.0 ml/l ethanol. It was incubated for 28 days at 35 oC. Gray light-colored colonies of approximately 0.5 - 1 mm can be seen here in room light, and some black-dark brown colonies are also visible (38, 70, 124, 137, 229, 231).
The ability of methane producing bacteria to fluoresce under UV light has been used by other groups as a means of isolation, identification, and enumeration of methanogenic bacteria. We did find that methane-producing colonies do fluoresce under low-frequency ultraviolet light, however this mechanism was not clearly understood. The black-dark brown colonies (Desulfovibrio) did not exhibit fluorescence.
This is a view of the above tube under low-frequency ultraviolet light. Colonies larger than 0.5 mm can be seen to fluoresce in this 30 second time exposure. Although, this is an interesting phenomenon, it was not considered practical for methanogen enumeration in our situation because colonies <0.5 mm did not emit enough light for detection (38, 124, 137, 229, 231).
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