The ability of two strains of bacteria to cooperate in the synthesis of an enzyme complex (a minicellulosome) was examined. Three strains of Bacillus subtilis were constructed to express Clostridium cellulovorans genes engB, xynB, and minicbpA. MiniCbpA, EngB, and XynB were synthesized and secreted into the medium by B. subtilis. When the strains with the minicbpA and engB genes or with xynB were cocultured, minicellulosomes were synthesized, consisting in one case of miniCbpA and EngB and in the second case of miniCbpA and XynB. Both minicellulosomes showed their respective enzymatic activities. We call this phenomenon "intercellular complementation." Interesting implications concerning bacterial cooperation are suggested from these results.