Five strains of the extreme thermophilic Rhodothermus marinus were screened for the production of amylolytic and pullulytic activities. The culture medium for the selected strain, R. marinus ITI 990, was optimized using central composite designs for enhanced enzyme production. The optimized medium containing 1.5 g l(-1) of maltose and 8.3 g l(-1) of yeast extract yielded amylase, pullulanase and a-glucosidase activities of 45, 33 and 2.1 nkat ml(-1), respectively. Among the various carbon sources tested, maltose was most effective for the formation of these enzymes, followed by soluble maize starch, glycogen and pullulan. The crude amylase and pullulanase showed maximum activities at pH 6.5-7.0, and 85 and 80 degreesC, respectively. At 85 C amylase and pullulanase had half lives of 3 h and 30 min, respectively. (C) 2003 Elsevier Ltd. All rights reserved.