Hydrogen Production Of Alternanthera Philoxeroides Utilization With Enterobacter Aerogenes Mutated By Nuclear Irradiation

Hydrogen as a renewable energy resource has received considerable attention because of the depletion of fossil fuels.Biological hydrogen production using micro-organisms has a prospect of application since it is an environmental friendly and less energy intensive process.Enterobacter aerogenes as facultative anaerobes with fast growth rates and high hydrogen production rates has a potential in industrial application.In this study,E.aerogenes strains were mutated with nuclear irradiation and positive mutants were screened by color-circle method to increase hydrogen producing capacity through enhancing hydrogenase activity and optimizing metabolic pathways;fermentative hydrogen production of E.aerogenes mutant strains were enhanced using steam-heated acid pretreated and high-efficient hydrolysed cellulosic biomass as substrate.E.aerogenes were mutated for the first time by 60Co γ-rays,and efficient mutants of hydrogen-producing bacteria were screened with colour circles of fermentative acid by-products.The size of the colour circle shows the quantity of fermentative acid by-products;the larger colour circle means the more metabolic acid production,and it’s probable that the hydrogen yield will be enhanced.The screened E.aerogenes ZJU1 mutant with larger colour circles enhanced the hydrogenase activity from 89.8 mL H2/(g DW·h)of the wild strain to 157.4 mL H2/(g DW·h).Formate hydrogenlyase and hydrogenase activities of the mutant with enhanced glycolysis and pyruvate metabolism was improved;thus,hydrogen production via FHL pathway and NADH pathway was promoted.The hydrogen yield of 301 mL H2/g glucose with the mutant was higher by 81.8%than that of the wild strain(166 mL/g glucose).The peak hydrogen production rate of 27.2 mL/(L·h)with the mutant was higher by 40.9%compared with that of the wild strain(19.3 mL/(L·h)).The mutant produced more acetate and butyrate but less ethanol compared with the wild strain during hydrogen fermentation,which were concordant with improved hydrogen productivity.The hereditary stability of the hydrogen producing capacity with E.aerogenes ZJU1 mutant was certified after iterative cultivation.E.aerogenes ZJU1 mutant improved fermentative hydrogen production using alternanthera philoxeroides,which was pretreated and high-efficiently hydrolized.Microcosmic analyses demonstrated that steam-heated acid pretreatment resulted in serious damage to the cellulose structure of alternanthera philoxeroides,many fragments were degradated with a large amount of cracks;crystal cellulose decreased,amorphous cellulose increased and crystallinity index decreased from 17.6 to 10.8.Reducing sugar yield of steam-heated acid pretreated alternanthera philoxeroides was 0.354 g/g biomass with H2SO4 1%,steam temperature 135 ℃ and heated time 15 min;and it could be increased to 0.575 g/g biomass after enzyme hydrolysis.The hydrogen yield of 62.2 mL H2/g-TVS with E.aerogenes ZJU1 using pretreated and high-efficiently hydrolized alternanthera philoxeroides,which was higher by 31.8%than that with the wild strain(47.2 mL H2/g-TVS).The peak hydrogen production rate increased from 1.42 mL H2/g-TVS/h to 4.64 mL H2/g-TVS/h by optimising fermentative bacterial quantity;meanwhile,hydrogen yield of 89,8 ± 5.4 mL H2/g-TVS was improved by 42.8%.