All these considerations underline the importance of studying bacterial protein profiles in different experimental conditions. Comparative proteomic analysis is among the most suitable tools to evaluate the phenotypic responses of a food starter or a probiotic strain to a certain environment. For instance, lactose starvation stress and the effect of the surfactant Tween-80 as a protective agent, have been evaluated in Lactobacillus casei GCRL163 by a comparative study based on nanoLC-MS/MS [Al Naseri 22]. A gel-free proteomic approach was used to elucidate the acidic stress response in Lactobacillus plantarum 423 [Heunis 23]. As far as proteomics is concerned, 2DE in-gel techniques proved to be of particular interest allowing us also to detect enzyme isoforms. For instance, it is possible to discriminate a differential biosynthesis of isoenzymes involved in either glycolytic or gluconeogenetic direction of Embden-Meyerhof-Parnas route [24]. Since the beginning of the proteomic era, several protocols have been set up to recover proteins from different cell districts allowing to separately analyze different subproteomes expressed by microorganisms (Fig. 1). The analysis of subproteomes represents a valuable tool to obtain additional information on specific problems: membrane protein patterns can reveal induction of transporters [24] and, since the first adaptive modifications to hostile environments occur at envelope level, stress tolerance pathways [25]. On the other hand, surface and extracellular proteomes help typing probiotic bacteria by elucidating what happens in the bacterium-host interface. In this context, a very recent cutting-edge paper [Le Marechal 26] describes three methods to recover key surface proteins involved in immune-modulation in Propionibacterium freudenreichii.