Biotechnological applications of type 1 secretion systems.

Bacteria have evolved a diverse range of secretion systems to export different substrates across their cell envelope. Although secretion of proteins into the extracellular space could offer advantages for recombinant protein production, the low secretion titers of the secretion systems for some heterologous proteins remain a clear drawback of their utility at commercial scales. Therefore, a potential use of most of secretion systems as production platforms at large scales are still limited. To overcome this limitation, remarkable efforts have been made toward improving the secretion efficiency of different bacterial secretion systems in recent years. Here, we review the progress with respect to biotechnological applications of type I secretion system (T1SS) of Gram-negative bacteria. We will also focus on the applicability of T1SS for the secretion of heterologous proteins as well as vaccine development. Last but not least, we explore the employed engineering strategies that have enhanced the secretion efficiencies of T1SS. Attention is also paid to directed evolution approaches that may offer a more versatile approach to optimize secretion efficiency of T1SS.