Figure 1

Schematic drawing of a bacterial cell showing the localization of recombinantly expressed cellulases and cellulosomes. Recombinant cellulases are expressed and stored in the cytoplasm or targeted to the periplasm through specific protein transporters (such as Tat- and Sec-pathways). Gram-negative bacteria (right) possess a thick outer membrane that restricts extracellular protein transport, thus protein secretion occurs via a specific protein transporter or membrane permeabilization (occurring, for example, due to damage of the cell envelope). Gram-positive bacteria (left) lack the outer membrane leading to a more efficient secretion. Secreted cellulases are either free in solution, either as single cellulases or as cellulosomes, or are displayed on the cell surface via an anchor protein such as Blc or PgsA as single cellulases or as mini-cellulosomes. GH: glycosyl hydrolase; Sec: secretion protein; Tat: twin-arginine-transporter.