Fermentative Hydrogen-producing Bacteria And Aerobic Bacteria Coculture Enhances Biological Hydrogen Production Under Aerobic Condition

Biotechnology,which produces a promising alternate fuel — hydrogen by microorganisms and mainly contains photosynthetic organisms in the light or fermentation metabolism of anaerobic bacteria,standing out as an environmentally friendly process,has drawn increasing attention.Although various enhancement of hydrogen production has been studied,there are still many problems remain unsolved for hydrogen production industrialization.Ethanol-type fermentation is favorable for hydrogen production and its metabolites are H2,CO2,acetate and neutral ethanol that could be further utilized.Like all the other Ethanoligenens,E.harbinense YUAN-3 is strict anaerobe which obtain the electrons from pyruvate oxidation,and an auto-aggregative bacterium which was favorable for industrial purpose.In the laboratory,the medium of strict anaerobes were usually boiled then flushed with argon or nitrogen gas for at least 10 min to maintain the anaerobic condition,but an anaerobic treatment method like that has the weakness of uneconomical or become hard to conduct in a pilot-scale.For those cells cannot easily be monocultured like E.harbinense YUAN-3,establishing synthetic interactions between populations may improve the culturing success or cell behavior.The presence of another cell population,in another word,mixed cultures,have been widely used for industrial applications to product bioenergy,such as synthetic industrial consortia,synthetic ecologies or ot her complex interactions.Co-culture of anaerobe and aerobe to scavenge oxygen is one of the strategies used to create the anaerobic habitat,known as biological oxygen consumption apart from chemical methods and physical methods,offering the advantages of simple,reliable,and lower outlay.To support hydrogen production in pilot scale,effective synthetic microbial consortia of anaerobe and aerobe is required to enhancing the overall uptake of nutrients and resist to environmental conditions oscillations.Culture conditions can obvious affect cell growth and hydrogen production.It is attractive for fermentative hydrogen production to operate at high substrate concentrations,but it would always suffer from product and substrate inhibition.Although lots of investigates have been conducted about optimal culture parameters,different species or strains prefer various conditions.In particular,L-cysteine was a low-cost reducing agent which was could reduce the oxidation–reduction potential(ORP)values of the nutrient solution and promote the growth rate of some bacteria.In our study,we picked facultative anaerobic strain P.aeruginosa PAO1 as joint inoculum with strain E.harbinense YUAN-3 to realize hydrogen production under limited aerobic conditions.The optimized operational conditions such as L-cysteine concentration and glucose concentration are also confirmed in batch test to achieve maximum hydrogen yield.With the readily formation of aggregates,stable artificial communities composed of a facultative anaerobic strain and a strict anaerobic strain has been obtained.Furthermore,continuous culture was carried out for 2 generations by employing the suggested optimized medium c omposition,applying the conventional anaerobic treatment as control group to test the stability of our synthetic microbial consortia and determine the compromise of abandoning the conventional anaerobic method.In this process,two crucial operation parameters — L-cysteine and glucose concentrations — were analyzed and optimized to 5 ~ 10 mmol/L and 15 g/L,respectively.A significant enhancement of hydrogen yield of 1.11 mol-H2/mol-glucose was realized and quiet stable for 2 generations with the formed globate microbial consortia by initially joint inoculate of PAO1 and YUAN-3.