Lake Averno sediment was used to isolate the facultative anaerobic bacteria having the potential for H(2) production. Twenty-five out of 35 isolates recovered from the sediment sample produced hydrogen under anaerobic conditions from glucose with yields ranging from 0.1 to 0.49 mol H(2)/mol glucose. Identification based on 16S rRNA gene sequence analysis revealed that most of them belong to the Firmicutes group, with a prevalence of the Paenibacillus polymyxa species. Seven distinct genomic fingerprints among the 11 P. polymyxa isolates were obtained using the random amplified polymorphic DNA (RAPD) technique. Glucose fermentation by P. polymyxa isolates was investigated. Glucose was totally consumed after 3 days of fermentation. The fermentation products were hydrogen (0.18-0.47 mol H(2)/mol glucose), ethanol (0.1-0.5 mol ethanol/mol glucose), and 2,3-butanediol (0.1 mol 2,3-butanediol/mol glucose). Lower amounts of acetic, butyric, formic, lactic, and propionic acids were detected. All metabolic data concerning P. polymyxa isolates were analyzed by cluster analysis to reveal similarities and/or differences with clustering based on RAPD profiles. Despite the high metabolic similarity among almost all P. paenibacillus isolates, results of cluster analyses of metabolic and genetic data do not match completely.