Identification and enhanced hydrogen evolution in two alginate-immobilized strains of Brevundimonas diminuta isolated from sludge and waterlogged soil

As hydrogen gas is a clean energy carrier, finding out strains of higher hydrogen evolving capacity than those recorded in the literature is the target of this work. Two bacteria were isolated from sludge and water logged soil samples at Arab Elmadabegh (Assiut) and Sohag (Upper Egypt). Phenotypic, genotypic as well as electron microscopic characterization revealed that they are two strains of Brevundimonas diminuta (B1 and B2). They both are motile short rods, Gram negative, acid and hydrogen producers. However, growth (O.D. 660 nm) in control cultures of B1 was relatively higher than B2, and protein contents were markedly the opposite while hydrogen yield of B1 was almost double that of B2. The hydrogen yield of control cultures occurred at the first 72 h giving 570 and 300 ml/culture of B1 and B2, respectively. Alginate immobilization supplemented with CaCO3 greatly elevated the efficacy of hydrogen production to 1200 ml/culture for B1 and 1300 ml for B2. Variation in the enhanced level of hydrogen evolution by CaCO3 may indicate variation in the amount of acid produced. The hydrogen produced is exclusively a hydrogenase enzyme activity since both strains did not exhibit any nitrogenase activity. Hydrogenases (Hox and Hup) of the two strains exhibited their maximum activity rates at 72 h that is similar to their growth and hydrogen yield.