Dissolved organic matter as a confounding factor in the determination of pollution-induced community tolerance (PICT) of bacterial communities to heavy metals using the leucine incorporation method

Abstract

PICT methodology using the leucine incorporation method (Leu-PICT) is useful for assessing heavy metal contamination in soils. First, bacterial community is exposed to metal in the soil (selection phase), developing tolerance if metal exerts toxicity. Secondly, in detection phase, bacterial suspensions are obtained, and tolerance is quantified by a second exposition of bacterial community to the metal using Leu-PICT methodology. However, during detection phase when Leu-PICT is performed, some characteristics of bacterial suspensions may change metal bioavailability. We assess the influence of dissolved organic matter (DOM) in bacterial suspensions, as humic acids (HA), on Leu-PICT determination to Cr, Cu, Ni, Pb and Zn. Results showed that the presence of HA in bacterial suspensions causes underestimations of bacterial community tolerance to Cr (increasing Cr toxicity), and overestimations of bacterial community tolerance to Cu, Ni, Pb, and Zn (reducing metal toxicity). In addition, the magnitude of these overestimations was different depending on the metal.