In recent years a number of hyperthermophilic micro-organisms of Sulfolobales have been found to produce trehalose from starch and dextrins. In our laboratory genes encoding the trehalosyl dextrin forming enzyme (TDFE) and the trehalose forming enzyme (TFE) of S. solfataricus MT4 have been cloned and expressed in E. coli (Rb791). Here we report the construction of a new protein obtained by fusion of TFE and TDFE coding sequences which is able to produce trehalose from dextrins at high temperature by sequential enzymatic steps. We demonstrate that the bifunctional fusion enzyme is able to produce trehalose starting from malto-oligosaccharides at 75 degrees C. Furthermore we partially purified the recombinant fusion protein from bacterial cell free extracts and from insoluble fractions in which the fusion protein was also found as aggregate in inclusion bodies.