In this project, the metaproteome of the marine bacterioplankton was analyzed to assess its respone towards an algal bloom in the southern North Sea in spring 2010. Proteins were extracted applying two different methods: (i) applying chemical cell lysis using trifluoroethanol in combination with in-solution digest and (ii) mechanical cell lysis applying bead beating, SDS-PAGE prefractionation and in-gel digest. Both samples were analyzed by nanoLC and ESI-iontrap MS. In case of the TFE lysis samples, also nanoLC-MALDI-TOF MS was applied.