טכניון מכון טכנולוגי לישראל
הטכניון מכון טכנולוגי לישראל - בית הספר ללימודי מוסמכים  
Ph.D Thesis
Ph.D StudentDror Tali
SubjectRegulation of the Cellulosomal Genes in Clostridium
thermocellum
DepartmentDepartment of Biotechnology and Food Engineering
Supervisor Professor Yuval Shoham


Abstract

Closridium thermocellum is a celluloloytic anaerobic thermopile that produces a unique enzymatic complex capable of efficient degradation of cellulose. The complex, termed cellulosome, is made of a large non-catalytic unit, the scaffoldin, and 9 catalytic units of various glycoside-hydrolase families. The interaction between the catalytic units and the scaffoldin is mediated by specific domains, cohesins on the scaffoldin and dockerins on the catalytic units. The scaffoldin also contains domains that allow its attachment to cellulose and to the cell surface, via anchoring proteins. To date very little is known on the regulation of the cellulosomal genes. In this study, using RNase protection assays, the transcriptional levels of selected cellulosomal genes were determined in batch and continuous cultures. Under carbon limitation, the expression of celS (exo-glucanase) and the anchoring genes olpB and orf2 increase with decrease in the growth rate. Under nitrogen limitation (cellobiose in access) the expression of these genes is lower compare to that of carbon limitation, suggesting that these genes are repressed by cellobiose. In addition, the expression of olpB, celS and cipA is regulated by cell density as demonstrated in chemostat cultures operated at various cell densities. The expression levels of the endo-glucanases celG, celB and celD, are not effected by the mentioned growth conditions. Taken together, the results of this work indicate that the composition of the cellulosme and its ability to bind the cell surface is regulated at the transcriptional level by several key genes. Some cellulosomal genes appear to be constitutive and their expression is not influenced by the growth conditions.