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 ⍀ 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 M 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 M, 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.Chlorinated hydrocarbons are used for a variety of uses, including degreasing of metal parts, scouring of textiles, and the production of organic chemicals and pharmaceuticals. Due to their extensive uses coupled with both accidental and purposeful releases, these compounds are commonly found in subsurface soils and groundwater (38,45). Although these compounds are refractory, they have been shown to be degraded through a variety of microbially mediated processes. Specifically, under anaerobic conditions, many of these compounds have been shown to be reductively dechlorinated (6,15,25,33,34,42). Under aerobic conditions, some of these compounds can be utilized as growth substrates (12, 24) or more commonly cooxidized in conjunction with a growth substrate such as methane, ammonia, toluene, or phenol (3, 4, 17-21, 30, 32, 36, 37, 41, 43, 44). Of the cells capable of growth on these substrates, methanotrophs are often used for the degradation of chlorinated hydrocarbons due to their ubiquity (23).In methanotrophs, the enzyme responsible for chlorinated solvent degradation, methane monooxygenase (MMO), is also responsible for the initial oxidation of the sole gro...