RAPID SCREENING FOR BACTERIAL PHENOTYPES CAPABLE OF BIODEGRADING ANIONIC SURFACTANTS - DEVELOPMENT AND VALIDATION OF A MICROTITRE PLATE METHOD

The Biolog microtitre plate assay, which is based on tetrazolium dye r eduction as an indicator of sole-carbon-source utilization, has been e valuated as a rapid method to investigate the biodegradation of five c lasses of anionic surfactant by pure and mixed cultures of bacteria, T he assay gave reproducible results over a fourfold range of inoculum o ptical density, and the surfactant concentration was selected to provi de a compromise between the length of the lag period prior to colour p roduction and the maximum colour produced, A kinetic model was develop ed and used to analyse the appearance of colour in the assay and was f ound to give rise to three biologically significant parameters describ ing the processes underlying the assay. No false-positives were obtain ed with environmental isolates, The small number of false-negatives ob tained (< 8% of the total) could be explained by the methodology used to prepare the bacterial inoculum, All isolates which were positive in the Biolog assay were shown to be both primary and ultimate degraders of the test surfactant, These results show that the method provides a useful means of studying the biodegradation of anionic surfactants by both pure and mixed cultures of bacteria and will find use in the rap id analysis of biodegradation kinetics and specificities of larger num bers of individual isolates than hitherto possible. In addition, an im portant benefit of the methodology is that it can be used for direct a nalysis of the biodegradation potential of whole bacterial communities without having to make an artificial selection during laboratory grow th.