Bacterial microcompartments: breakthroughs in fundamental biology increase application potential

Bacterial microcompartments (BMCs) are polyhedral structures formed by many prokaryotic lineages to enhance fitness in adverse environments.  In particular, Salmonella enterica has the capability to form BMCs designed for the utilization of both ethanolamine and 1,2-propanediol (Eut and Pdu BMCs, respectively) and in the native host, numerous BMCs are formed per cell and are mobile, moving rapidly throughout the cell.  In a recent breakthrough, our group successfully produced recombinant Eut BMC in Escherichia coli by expressing Eut shell proteins isolated from S. enterica.  Furthermore, a Eut BMC-specific targeting sequence was identified which reliably directed eGFP to the BMC interior.  However, the coexpression of all five Eut BMC structural elements only lead to a single, immobile BMC per cell, indicating that additional factors are required for the formation of multiple BMCs per cell, and also for their mobility.  There is an obvious need to address the limitations of our current recombinant systems to increase the efficiency of designer pathways targeted to BMCs in the future.  To that end, we have characterized the function of two proteins, whose function has yet to be determined.  We hypothesized that these ancillary elements might be necessary for organizing how many compartments form per cell, and how these compartments achieve mobility.  Our results indicate that these newly-characterized open-reading frames not only contribute to BMC biogenesis, but also control the dynamic nature of Eut BMCs in vivo.  These results lay the groundwork for more sophisticated engineering of BMCs and greatly increase their application potential for biocatalysis.