Evaluation of Biolog MT plates for aromatic and chloroaromatic substrate utilization tests

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Abstract
Biolog MT microplates are miniaturized substrate utilization test plates that exploit the colorimetric change in tetrazolium dyes as they are reduced in the presence of respiring bacteria. The test plates are attractive for the rapid screening of culture collections for unusual degradative activities. We evaluated these plates for the screening for the use of aromatic and chloroaromatic compounds by a culture collection of bacteria isolated from the waste water treatment system of a pulp and paper mill. We found that cell densities between 106 and 109 colony-forming units/mL could be used with the kits. However, the substrate concentration required to allow utilization detection lay between 0.25 and 2.5 mM, a level not significantly different from that required for more classical tests. Bacterial utilization of aromatic substrates such as phenol, vanillin, and benzoate could not be detected when the manufacturer's instructions were followed, because all proved to be toxic to test strains at the recommended test concentrations. We assessed the toxicity of monochlorophenols, 5-chlorovanillin, and 3-chlorobenzoate to representative species from our collection and found that only the latter two were sufficiently nontoxic to be tested with these microplates. The value of the tetrazolium dye reduction assay used in these kits to screen for bacterial utilization of more toxic substrates is limited by the high substrate concentrations required.Key words: substrate utilization, bacteria, aromatic, chloroaromatic, test kit.

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