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Abstract

Fluorescent-dye-conjugated oligonucleotides were used as "phylogenetic" probes
to identify sulfate reducing bacteria (SRB) in a photosynthetic biofilm. Two samples
of biofilm from a trickling filter in a waste-water treatment plant were incubated for
48 hr's; one in darkness, the other in daylight. Chemical gradients of (02, S2-, and
pH) in the biofiIn1s were then measured with microelectrodes prior to rapid freezing
and slicing on a cryo-microtome. The vertical slices were stained with three different
probes: a sulfate reducing bacterial (inclusive for most species of the 8-group of
purple bacteria), a Desulfobacter, and a non-hybridising control probe. A good
correlation between the vertical distribution of SRB and the measured 02-profile was
found, with the SRB being restricted to the deeper anaerobic layers.