The utilization of the fuel oxygenate Me tert-Bu ether (MTBE) and related compds. by microorganisms was investigated in a mainly theor. study based on the YATP concept. Expts. were conducted to derive realistic maintenance coeffs. and Ks values needed to calc. substrate fluxes available for biomass prodn. Aerobic substrate conversion and biomass synthesis were calcd. for different putative pathways. The results suggest that MTBE is an effective heterotrophic substrate that can sustain growth yields of up to 0.87 g g-1, which contradicts previous calcn. results. Sufficient energy equiv. were generated in several of the potential assimilatory routes to incorporate carbon into biomass without the necessity to dissimilate addnl. substrate, efficient energy transduction provided. However, when a growth-related kinetic model was included, the limits of productive degrdn. became obvious. Depending on the maintenance coeff. ms and its assocd. biomass decay term b, growth-assocd. carbon conversion became strongly dependent on substrate fluxes. Due to slow degrdn. kinetics, the calcns. predicted relatively high threshold concns., Smin, below which growth would not further be supported. Smin strongly depended on the max. growth rate mmax, and b and was directly correlated with the half max. rate-assocd. substrate concn. Ks, meaning that any effect impacting this parameter would also change Smin. The primary metabolic step, catalyzing the cleavage of the ether bond in MTBE, is likely to control the substrate flux in various strains. In addn., deficits in oxygen as an external factor and in redn. equiv. as a cellular variable in this reaction should further increase Ks and Smin for MTBE.