Growth of Ralstonia eutropha on inhibitory concentrations of phenol: diminished growth can be attributed to hydrophobic perturbation of phenol hydroxylase activity

The effect of phenol concentration on growth and biodegradative capacity of Ralstonia eutropha regarding phenol was examined. Kinetic analysis indicat ed that phenol had a strong inhibitory effect on phenol metabolism and grow th rate, although biomass yields remained constant, indicating that this ph enomena was not caused by increased maintenance requirements. Measurements of specific enzyme activities involved specifically in the catabolic pathwa y of meta fission of phenol indicated that gene expression cannot explain t he diminished metabolic rates at inhibitory phenol concentrations. This phe nomenon is due to in vivo inhibition of enzyme activities and notably to ph enol hydroxylase activity. Furthermore, other nonmetabolizable organic alco hols provoked a similar effect on both specific growth rate and phenol hydr oxylase activity, indicating that inhibition was probably associated with m odified membrane fluidity, partially offset by a change in the fatty acid c omposition of cellular lipids. (C) 1999 Elsevier Science Inc. All rights re served.