Short communication: technological and genotypic comparison between Streptococcus macedonicus and Streptococcus thermophilus strains coming from the same dairy environment.

The species Streptococcus thermophilus is widely used for the preparation of several dairy products, and its technological contribution is clear. On the other hand, although Streptococcus macedonicus was first described more than 10 yr ago and, despite the scientific interest around this issue, the exact role of Strep. macedonicus in cheese making has yet to be clarified. In this study, 121 strains belonging to both species and isolated from the same dairy environment were genetically characterized by random amplification of polymorphic DNA (RAPD)-PCR and compared for the main biochemical features of technological interest, such as acid production, galactose utilization, citrate metabolism, exopolysaccharide production, and lipolytic, ureolytic, exocellular proteolytic, and decarboxylasic activities. Analysis by RAPD-PCR highlighted a remarkable genotypic heterogeneity among strains in both species, and, at a similarity level of 78%, all the isolates and reference strains of Strep. thermophilus grouped together and were well separated from the strains of Strep. macedonicus, confirming that these 2 species are different microbial entities. Comparison between genetic and phenotypic or biotechnological data did not reveal any relationships.

Enzymes from Sulfolobus shibatae for the production of trehalose and glucose from starch.

Enzymes that convert starch and dextrins to alpha,alpha-trehalose and glucose were found in cell homogenates of the hyperthermophilic acidophilic archaeon Sulfolobus shibatae DMS 5389. Three enzymes were purified and characterized. The first, the S. shibatae trehalosyl dextrin-forming enzyme (SsTDFE), transformed starch and dextrins to the corresponding trehalosyl derivatives with an intramolecular transglycosylation process that converted the glucosidic linkage at the reducing end from alpha-1,4 to alpha-1,1. The second, the S. shibatae trehalose-forming enzyme (SsTFE), hydrolyzed the alpha-1,4 linkage adjacent to the alpha-1,1 bond of trehalosyl dextrins, forming trehalose and lower molecular weight dextrins. These two enzymes had molecular masses of 80 kDa and 65 kDa, respectively, and showed the highest activities at pH 4.5. The apparent optimal temperature for activity was 70 degrees C for SsTDFE and 85 degrees C for SsTFE. The third enzyme identified was an alpha-glycosidase (Ss alpha Gly), which catalyzed the hydrolysis of the alpha-1,4 glucosidic linkages in starch and dextrins, releasing glucose in a stepwise manner from the nonreducing end of the polysaccharide chain. The enzyme had a molecular mass of 313 kDa and showed the highest activity at pH 5.5 and at 85 degrees C.

Industrial-scale production and rapid purification of an archaeal beta-glycosidase expressed in Saccharomyces cerevisiae.

The application of enzymes isolated from extreme thermophiles in biotechnological processes is hampered by their unconventional fermentation conditions. The expression, in mesophilic hosts, of genes encoding for thermophilic proteins enables these difficulties to be overcome and permits the production of enzymes in high yield by using conventional fermentation plants and an efficient enzyme purification utilizing heat precipitation of host proteins. The beta-glycosidase gene from Sulfolobus solfataricus, a thermoacidophilic archaeon growing at 87 degrees C and pH 3.5, has been cloned and expressed in Saccharomyces cerevisiae (baker's yeast). The fermentation of a S. cerevisiae strain on a 100-litre scale and the two-step purification of the expressed beta-glycosidase by cell autolysis and extracts thermal precipitation is described. This procedure, after 72 h of autolysis, gave a yield 56-fold higher with respect to that obtained with the beta-glycosidase from S. solfataricus.