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Background  Consolidated bioprocessing (CBP) is a cost-effective approach for the conversion of lignocellulosic biomass to biofuels and biochemicals. The enzymatic conversion of cellulose to glucose requires the synergistic action of three types of enzymes: exoglucanases, endoglucanases and β-glucosidases. The thermophilic, hemicellulolytic  Geobacillus thermodenitrificans  T12 was shown to harbor desired features for CBP, although it lacks the desired endo and exoglucanases required for the conversion of cellulose. Here, we report the expression of both endoglucanase and exoglucanase encoding genes by  G. thermodenitrificans  T12, in an initial attempt to express cellulolytic enzymes that complement the enzymatic machinery of this strain.    Results  A metagenome screen was performed on 73  G. thermodenitrificans  strains using HMM profiles of all known CAZy families that contain endo and/or exoglucanases. Two putative endoglucanases, GE39 and GE40, belonging to glucoside hydrolase family 5 (GH5) were isolated and expressed in both  E. coli  and  G. thermodenitrificans  T12. Structure modeling of GE39 revealed a folding similar to a GH5 exo-1,3-β-glucanase from  S. cerevisiae . However, we determined GE39 to be a β-xylosidase having pronounced activity towards  p -nitrophenyl-β- d -xylopyranoside. Structure modelling of GE40 revealed its protein architecture to be similar to a GH5 endoglucanase from  B. halodurans , and its endoglucanase activity was confirmed by enzymatic activity against 2-hydroxyethylcellulose, carboxymethylcellulose and barley β-glucan. Additionally, we introduced expression constructs into T12 containing  Geobacillus  sp. 70PC53 endoglucanase gene  celA  and both endoglucanase genes ( M1  and  M2 ) from  Geobacillus  sp. WSUCF1. Finally, we introduced expression constructs into T12 containing the  C. thermocellum  exoglucanases  celK  and  celS  genes and the endoglucanase  celC  gene.    Conclusions  We identified a novel  G. thermodenitrificans  β-xylosidase (GE39) and a novel endoglucanase (GE40) using a metagenome screen based on multiple HMM profiles. We successfully expressed both genes in  E. coli  and functionally expressed the GE40 endoglucanase in  G. thermodenitrificans  T12. Additionally, the heterologous production of active CelK, a  C. thermocellum  derived exoglucanase, and CelA, a  Geobacillus  derived endoglucanase, was demonstrated with strain T12. The native hemicellulolytic activity and the heterologous cellulolytic activity described in this research provide a good basis for the further development of  G. thermodenitrificans  T12 as a host for consolidated bioprocessing.    Electronic supplementary material  The online version of this article (10.1186/s12896-018-0453-y) contains supplementary material, which is available to authorized users.

Engineering Geobacillus thermodenitrificans to introduce cellulolytic activity; expression of native and heterologous cellulase genes