The kinetics of polycyclic aromatic hydrocarbon (PAH) biodegradation assessed by isothermal titration calorimetry (ITC)

Interest in the biodegradation mechanisms and environmental fate of hydrophobic organic compounds (HOC) such as polycyclic aromatic hydrocarbons (PAHs) is motivated by their ubiquity in the environment, their persistence and their potentially deleterious effect on human health. Due to their high hydrophobicity, PAH tend to interact with non-aqueous phases and natural organic matter and, as a consequence, are poorly bioavailable for microbial degradation. Here, a novel calorimetric approach was developed and successfully tested in order to gain real time information on the kinetics and the physiology of PAH bioconversion in aqueous systems. Anthracene-degrading soil bacterium Mycobacterium frederiksbergense LB501T was exposed to a pulsed titration of dissolved anthracene and the resulting thermal reaction monitored. The heat flux signals of the biodegradation of 180 ng anthracene were interpreted in terms of the Michaelis-Menten kinetics and the parameters KA and image of anthracene degradation were derived. The comparison with a conventional method shows the suitability of isothermal titration calorimetry (ITC) to extract kinetic degradation parameters of organic trace pollutants from simple ITC experiments.