2-22: Construction of a signal peptide library to screen for optimal secretion in Geobacillus thermoglucosidasius

To extend the catabolic range of industrially useful organisms to polymeric substrates such as cellulose and hemicellulose requires efficient secretion of relevant enzymes into the extracellular milieu. This potentially rate limiting step is, in part, mediated by N-terminal signal peptides of varying length and amino acid sequence.

The facultatively-anaerobic, Gram-positive thermophile Geobacillus thermoglucosidasius can ferment a range of pentose and hexose monomers and oligomers and has been metabolically engineered to produce bioethanol in high yield. However, it has limited ability to degrade lignocellulose derived carbohydrate polymers.  Nevertheless, genome sequence analysis has identified a number of potentially secreted proteins containing signal peptides. Here we describe the construction of a G. thermoglucosidasius signal peptide library to serve as a tool for the optimisation of heterologous protein secretion in this organism.

Evidence from the Bacillus genus suggests that no “one-size-fits-all” signal peptide exists for the optimal secretion of different proteins. Therefore, predicted signal peptide sequences from G. thermoglucosidasiushave been introduced upstream of three reporter genes, alpha-amylase, pectate lyase and levansucrase. These reporters can be assessed semi- and fully quantitatively with metachromatic colony agar assays and simple spectrophotomeric assays, respectively. Results from analysis of the matrix combining signal peptides with reporters will be presented.

The creation of this library paves the way for optimising the secretion of extracellular enzymes to improve the industrial utility of G. thermoglucosidasius.