Keywords: فرهنگ مخلوط بی هوازی; Metabolic heterogeneity; Anaerobic mixed culture; Fermentative hydrogen production; Adaptive laboratory evolutionALE, adaptive laboratory evolution; POR, pyruvate-ferredoxin oxidoreductase; FNO, ferredoxin-NAD+ oxidoreductase; Fdred2−, reduced ferredoxin;