초록
<P><B>Background</B></P><P>Cellulose is highly recalcitrant and thus requires a specialized suite of enzymes to solubilize it into fermentable sugars. In <I>C</I>. <I>thermocellum</I>, these extracellular enzymes are present as a highly active multi-component system known as the cellulosome. This study explores the expression of a critical <I>C</I>. <I>thermocellum</I> cellulosomal component in <I>T</I>. <I>saccharolyticum</I> as a step toward creating a thermophilic bacterium capable of consolidated bioprocessing by employing heterologously expressed cellulosomes.</P><P><B>Results</B></P><P>We developed an inducible promoter system based on the native <I>T</I>. <I>saccharolyticum xynA</I> promoter, which was shown to be induced by xylan and xylose. The promoter was used to express the cellulosomal component <I>cipA</I>*, an engineered form of the wild-type <I>cipA</I> from <I>C</I>. <I>thermocellum</I>. Expression and localization to the supernatant were both verified for CipA*. When a Δ<I>cipA</I> mutant <I>C</I>. <I>thermocellum</I> strain was cultured with a CipA*-expressing <I>T</I>. <I>saccharolyticum</I> strain, hydrolysis and fermentation of 10 grams per liter SigmaCell 101, a highly crystalline cellulose, were observed. This trans-species complementation of a <I>cipA</I> deletion demonstrated the ability for CipA* to assemble a functional cellulosome.</P><P><B>Conclusion</B></P><P>This study is the first example of an engineered thermophile heterologously expressing a structural component of a cellulosome. To achieve this goal we developed and tested an inducible promoter for controlled expression in <I>T</I>. <I>saccharolyticum</I> as well as a synthetic <I>cipA</I>. In addition, we demonstrate a high degree of hydrolysis (up to 93%) on microcrystalline cellulose.</P>