Significant hydrogen production by Enterococcus faecium IITGEN1 and Proteus mirabilis IITGEN2 newly isolated from local waste sources

In the present study, significant hydrogen producing bacteria Enterococcus faecium IITGEN1 and Proteus mirabilis IITGEN2 were newly isolated from local waste sources via dark fermentation. The effects of process parameters like pH (3–10), temperature (32–40 °C), carbohydrate (sucrose, dextrose, cellulose, xylose, lactose and fructose), carbohydrate concentration (1–5 g/L), and stirring speed (125–200 rpm) were studied. The highest hydrogen yield was observed for 1 g sucrose/L concentration at pH 7, 38 °C and stirring speed of 175 rpm. The maximum hydrogen yields at the most favorable process parameters were 4.4 and 4.25 mol H₂/mol sucrose in presence of E. faecium IITGEN1 and P. mirabilis IITGEN2, respectively. Among liquid products, E. faecium IITGEN1 produced butyric acid (3600 mg/L) and propionic acid (1600 mg/L), while P. mirabilis IITGEN2 produced mainly butanol (4000 mg/L) followed by butyric acid (3400 mg/L) after 48 h. The lower yield of hydrogen for P. mirabilis IITGEN2 might be due to consumption of hydrogen in intermediate steps producing significant amount of butanol. Both the bacteria followed Pyruvate: Ferredoxin Oxidoreductase pathway while only E. faecium IITGEN1 followed Pyruvate: Formate lyase pathway. Degradation of sucrose followed first order kinetics in presence of both the strains. The higher value of rate constant for P. mirabilis IITGEN2 (k = 0.027 h⁻¹) compared to that of E. faecium IITGEN1 (k = 0.023 h⁻¹) suggested faster degradation kinetics of the former. The study gives a comprehensive insight into isolation and characterization of hydrogen producing strains, assessing their performance under broad range of process values.