Effect of growth temperatures on the protein levels in a psychrotrophic bacterium, Pseudomonas fragi

Pseudomonas fragi has the ability to grow between 0 and 35 degrees C and grows optimally at 30 degrees C. Cellular proteins from mid-log-phase cells growing from 4 to 34 degrees C were labeled with L-[35S]methionine during 1 generation time and analyzed by two-dimensional gel electrophoresis. The electrophoretic patterns revealed differences in the patterns of protein synthesis over this temperature span. A qualitative comparison of cellular proteins led to their separation into five thermal classes. The first class contained proteins whose relative rates of synthesis were unaffected by the growth temperature. Three other classes included proteins with optimal expression at 4 to 10, 15 to 20, and 25 to 30 degrees C. A fifth class contained proteins which were more specifically synthesized at a supraoptimal growth temperature (34 degrees C). Two low-molecular-mass proteins, designated C7.0 and C8.0, were highly concentrated at 4 to 10 degrees C, and their relative rates of synthesis steadily increased with decreasing temperature. Polyclonal antibodies were separately raised against these two proteins. Immunological analyses revealed cross-reaction between these two proteins and between two additional low-molecular-mass proteins which were maximally produced at elevated temperatures. Antisera directed against C8.0 recognized the major cold shock protein of Escherichia coli, CspA, indicating the presence of similarities between these proteins.