Pore size dependence on growth temperature is a common characteristic of the major outer membrane protein OprF in psychrotrophic and mesophilic Pseudomonas species.

Pseudomonas species adapt well to hostile environments, which are often subjected to rapid variations. In these bacteria, the outer membrane plays an important role in the sensing of environmental conditions such as temperature. In previous studies, it has been shown that in the psychrotrophic strain P. fluorescens MF0, the major porin OprF changes its channel size according to the growth conditions and could affect outer membrane permeability. Studies of the channel-forming properties of OprFs from P. putida 01G3 and P. aeruginosa PAO1 in planar lipid bilayers generated similar results. The presence of a cysteine- or proline-rich cluster in the central linker region is not essential for channel size modulations. These findings suggest that OprF could adopt two alternative conformations in the outer membrane and that folding is thermoregulated. In contrast, no difference according to growth temperature was observed for structurally different outer membrane proteins, such as OprE3 from the Pseudomonas OprD family of specific porins. Our results are consistent with the fact that the decrease in channel size observed at low growth temperature is a particular feature of the OprF porin in various psychrotrophic and mesophilic Pseudomonas species isolated from diverse ecological niches. The ability to reduce outer membrane permeability at low growth temperature could provide these bacteria with adaptive advantages.