A rapid screening method for micro-organisms degrading polycyclic aromatic hydrocarbons in microplates

A method for enumerating micro-organisms degrading polycyclic aromatic hydrocarbons (PAHs) was developed. The micro-organisms present in water samples are incubated in 96-well microplates, in which the desired PAHs are available as sole carbon source in a liquid mineral-salts medium (MSM). Walls and bottoms of the wells in the microplates are covered with PAHs by dissolving them in a non-polar solvent and pipetting this solution into the wells. After solvent elimination under vacuum, the PAHs remain on the surface of the wells. The formation of coloured products during microbial degradation of PAHs causes colouring of the MSM, thus allowing evaluation of the cell titre by determining the most probable number. Usage of an electronic multichannel pipette makes the work faster and more effective. This allows the inoculation of several microplates pre-treated with different PAHs out of one serial dilution. On the one hand, this method is very effective in screening the usability spectrum of different PAHs microorganisms; on the other hand it allows the additional employment of other sources of hydrocarbons.