Metagenomic analysis of autochthonous microbial biomass from banana waste: Screening design of factors that affect hydrogen production

In this study, Plackett–Burman designs were applied to evaluate the effects of independent variables (pH 5.5–7.7, temperature 30-44 °C, headspace volume 40–60%, percentage of inoculum 5–15% and carbohydrates concentration 3–15 g L−1) on fermentative hydrogen production by autochthonous bacteria from banana waste. The screening experiments showed only pH, temperature and headspace were significant variables affecting hydrogen production (PH2), in which the highest PH2 of 38.08 mL was obtained at pH 7.5, 44 °C, 40% headspace, 15% inoculum and 15 g L−1 carbohydrates concentration. Clostridium and Lactobacillus were the most abundant autochthonous acidogenic bacteria and were associated with the production of acetic acid (0.02–0.72 g L−1), butyric acid (0.03–2.66 g L−1), lactic acid (0.26–5.14 g L−1) and ethanol (0.08–0.64 g L−1) in the assays. Genes related to carbohydrate metabolism, acidogenesis and H2 production enzymes were identified, such as fructokinase, glucose 6-phosphate dehydrogenase, lactate dehydrogenase and pyruvate ferredoxin oxidoreductase.