We have compared the protein expression of gel-entrapped Escherichia coli cells submitted to a cold shock at 4 degreesC with those of exponential- and stationary-phase free-floating counterparts. Autoradiograms of two-dimensional gel electrophoresis patterns of proteins radiolabeled with L-[S-35]methionine were compared using computing scanning densitometry. The levels of 203 proteins synthesized during the temperature shift were significantly and reproducibly higher than those corresponding to synthesis at 37 degreesC. A principal component analysis (PCA) was performed on the synthesis levels of these 203 proteins in the different incubation conditions tested. This study showed that the protein response of immobilized cells after the cold shock was significantly different from those of exponential- and stationary-phase free-floating organisms. For instance, protein SSB was specifically overexpressed by shocked immobilized organisms. Such induction of specific molecular mechanisms in immobilized bacteria might explain the high resistance of sessile-like organisms to stresses.