Growth temperature dependence of channel size of the major outer-membrane protein (OprF) in psychrotrophic Pseudomonas fluorescens strains

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Abstract
The outer-membrane (OM) permeability of the psychrotrophic bacteriumPseudomonas fluorescensstrain MFO for the -lactam mezlocillin is increased at the optimum growth temperature (28 C) compared to low growth temperatures (8 C). In an attempt to explain this phenomenon, OM protein content was studied in cultures grown at both temperatures. No significant difference in proportion or composition was found, suggesting that a change in the structure and function of porins could be responsible for the differential permeability. The major OM protein OprF of two psychrotrophicP. fluorescensstrains, MFO and OE 28.3, was purified from cultures grown at 8 C and 28 C in order to reincorporate them in solvent-free lipid bilayers. From cultures grown at the same temperature, OprF displayed very similar channel-forming properties for both strains. Decreasing the growth temperature induced a threefold reduction of the major conductance values (250270 pS in 1 M NaCl for 28 C cultures and 8090 pS in 1 M NaCl for 8 C cultures). The trypsin digestion kinetics showed a very different reactivity for these porins between cultures grown at 8 C and 28 C. This may indicate that the pore structure of OprF is modified depending on the growth temperature, as suggested by its functional behaviour.