GROWTH TEMPERATURE-DEPENDENCE OF CHANNEL SIZE OF THE MAJOR OUTER-MEMBRANE PROTEIN (OPRF) IN PSYCHROTROPHIC PSEUDOMONAS-FLUORESCENS STRAINS

The outer-membrane (OM) permeability of the psychrotrophic bacterium P seudomonas fluorescens strain MFO for the beta-lactam mezlocillin is i ncreased at the optimum growth temperature (28 degrees C) compared to low growth temperatures (8 degrees C). In an attempt to explain this p henomenon, OM protein content was studied in cultures grown at both te mperatures. No significant difference in proportion or composition was found, suggesting that a change in the structure and function of pori ns could be responsible for the differential permeability. The major O M protein OprF of two psychrotrophic P. fluorescens strains, MFO and O E 28.3, was purified from cultures grown at 8 degrees C and 28 degrees C in order to reincorporate them in solvent-free lipid bilayers. From cultures grown at the same temperature, OprF displayed very similar c hannel-forming properties for both strains. Decreasing the growth temp erature induced a threefold reduction of the major conductance values (250-270 pS in 1 WI NaCl for 28 degrees C cultures and 80-90 pS in 1 M NaCl for 8 degrees C cultures). The trypsin digestion kinetics showed a very different reactivity for these porins between cultures grown a t 8 degrees C and 28 degrees C. This may indicate that the pore struct ure of OprF is modified depending on the growth temperature, as sugges ted by its functional behaviour.