LAUSR

Abstract This study was designed to identify the most potent N2-fixing and biofuel producing Bacillus species. Four isolates were selected as the most efficient N2-fixing organisms which confirmed by nifH gene expression. These isolates were identified genetically by 16S rRNA as Bacillus thuringensis, Bacillus subtilis, Bacillus pumilus and Bacillus licheniformis. The highest biohydrogen production was 2450 and 2300 ml/L from 6% sugarcane molasses by B. thuringensis and B. subtilis respectively. Nitrogenase activity of B. thuringensis and B. subtilis were 1.4 and 1.3 μmol C2H4 min−1 mg protein −1 at 6% molasses. Ethanol production was 1.55 and 1.03 g/L, while butyric acid was 10.39 and 5.9 g/L at 6% molasses by B. thuringensis and B. subtilis at 6% molasses, respectively. Acetic acid formation was 1.1 and 0.55, lactic acid was 0.07 and 0.05, while butyric acid was 10.39 and 5.9 g/L at 6% molasses by B. thuringensis and B. subtilis, respectively. Spent bacterial biomass of the two Bacillus species were reused as a biofertilizer for enhancing the growth of sunflower and corn plants. Inoculation of sunflower and corn seeds with B thuringensis and B subtilis significantly increased dry weight, total protein, total carbohydrates and pigment contents over control plants. This enhancement could be attributed to the efficiency of biological N2-fixation due to nitrogenase activity of the tested Bacillus species. These results suggest that the possibility of interlinking biofuel technology with biofertilizer production by reusing N2-fixing spent bacterial biomass of Bacillus could be increase the economic feasibility of the bioenergy production from molasses.