Mixed pollutant degradation by Methylosinus trichosporium OB3b expressing either soluble or particulate methane monooxygenase: can the tortoise beat the hare?

Methanotrophs have been widely investigated for in situ bioremediation due to their ubiquity and their ability to degrade halogenated hydrocarbons through the activity of methane monooxygenase (MMO). It has been speculated that cells expressing the soluble form of MMO (sMMO) are more efficient in cleaning up sites polluted with halogenated hydrocarbons due to its broader substrate range and relatively fast degradation rates compared cells expressing the other form of MMO, the particulate MMO (pMMO). To examine this issue, the biodegradation of mixtures of chlorinated solvents, i.e., trichloroethylene (TCE), trans-dichloroethylene (t-DCE), and vinyl chloride (VC), by Methylosinus trichosporium OB3b in the presence of methane using either form of MMO was investigated over longer time frames than those commonly used, i.e., days instead of hours. Growth of M. trichosporium OB3b along with pollutant degradation were monitored and analyzed using a simple comparative model developed from the Omega model created for analysis of the competitive binding of oxygen and carbon dioxide by ribulose bisphosphate carboxylase. From these findings, it appears that at concentrations of VC, t-DCE, and TCE greater than 10 microM each, methanotrophs expressing pMMO have a competitive advantage over cells expressing sMMO due to higher growth rates. Despite such an apparent growth advantage, pMMO-expressing cells degraded less of these substrates at these concentrations than sMMO-expressing cells during active growth. If the concentrations were increased to 100 muM, however, not only did pMMO-expressing cells grow faster, they degraded more of these pollutants and did so in a shorter amount of time. These findings suggest that the relative rates of growth substrate and pollutant degradation are important factors in determining which form of MMO should be considered for pollutant degradation.