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The saccharolytic anaerobic bacteria Halonatronum saccharophilum, Amphibacillus fermentum, and Amphibacillus tropicus produce formate, the main fermentation product. In the alkaliphilic community, formate is used as the preferential substrate for sulfate reduction. To reveal the pathways of carbohydrate fermentation by these bacteria, the activity of the key enzymes of carbohydrate metabolism and their pH dependence was studied. It was established that H. saccharophilum utilized glucose by the fructose bisphosphate and hexose monophosphate pathways, and A. tropicus, by the fructose bisphosphate and Entner–Doudoroff pathways. The activity of the key enzymes of all three pathways of glucose metabolism was detected in Amphibacillus fermentum. According to the data obtained, the glucose catabolism in H. saccharophilum, A. fermentum, and A. tropicus mainly proceeds via the fructose bisphosphate pathway. The pH optima of the key enzymes of the glucose metabolism of the alkaliphiles are shifted to alkaline values. In A. tropicus, formate is formed from pyruvate under the action of pyruvate formate-lyase; and in the haloanaerobe H. saccharophilum, formate dehydrogenase is involved in formate metabolism. [ABSTRACT FROM AUTHOR]