Isolation And Characteristics Of A Novel Mesophilic Hydrogen-producing Bacterium With Straw Hydrolysates Including Xylose And Glucose

Fermentative biological hydrogen production technology has now become a hot research field, in view of its ability to combine effectively waste treatment with energy recovery. In order to realize the industrialization of biohydrogen production and reduce the cost of hydrogen production, the researchers extensively conduct biohydrogen research, and one of the major research directions is dedicated to find low-cost substrates of hydrogen production, and expand the scope of available substrates. There are a lot of cheap and microorganisms rarely directly degrade renewable lignocelluloses; however, which mainly composed of cellulose, hemicellulose and lignin. Usually it needs to be pretreated and enzymatic hydrolyzed to liquid product-based pentose and hexose, and then is decided to be used. Currently, the attention of biohydrogen production, however, is generally dominated to research the utilization of single hexose substrate. Pentose, a component part of hemicellulose, for biohydrogen production has been no breakthrough. Therefore, in order to improve lignocellulose utilization of hemicellulose, it is necessity to isolate hydrogen-producing bacterium that is ability to use efficiently pentose and hexose to produce hydrogen. Which can increase the efficiency of lignocellulose and reduce the cost for fermentative biohydrogen production, to achieve bio-hydrogen fermentation industrialization has important practical significance.Based on the above issues, this study carried through finding hydrogen-producing bacterium simultaneous using xylose and glucose. Firstly, samples, came from cow dung compost, are be enriched and cultured in xylose, glucose and both mixed substrates, and highly efficient hydrogen producing communities were given, followed by DGGE technique to analyze the structure of their communities. The results showed that the different hydrogen producing communities from different substrates were obtained to have only differences in structure, and similar in type of communities. The novel hydrogen-producing bacteria were isolated from hydrogen producing communities with mixed sugar substrates using Hungate anaerobic technique. According to the phylogenetic relationships and physiological and biochemical characteristics, the isolated strain T2 was verified as a new species under Clostridium, whose category name is called Clostridium hydrogeniproducens sp. nov.. Clostridium hydrogeniproducens was its type species, strain T2^T (= NBRC 105657T = CCTCC AB 209026T) as a model strain.When initial pH was 6.5 and the substrate concentration was under 60 mmol/l, the average yeild of hydrogen production of strain T2 using xylose and glucose was 2.32 mol-H₂/mol-xylose and 2.76 mol-H₂/mol-glucose, and the specific hydrogen production rate was 10.07 mmol-H₂/g-cdw/h and 9.47 mmol-H₂/g-cdw/h, respectively. Hydrogen production capacity of strain T2 is front rank.The characteristics and differences of hydrogen production bacteria T2, how to use xylose and glucose to produce hydrogen, were revealed by researching the dynamics of hydrogen production using xylose and glucose. When the substrate concentration is the 2-10 mmol/l, the hydrogen-producing bacteria T2 obtained parameters, such as the maximum biomass, the potential growth rate, substrate consumption rate and hydrogen production rate, which appeared a linear growth by using xylose and glucose. In comparison, the obtained parameters from glucose as substrate were larger than other ones. The potential growth rate equation is constructed and described characteristics of hydrogen-producing bacteria T2 in logarithmic growth phase. The synchronization of hydrogen index equation is constructed and described relationship of growth and hydrogen production of strain T2. It is speculated that xylose by hydrogen-producing bacteria T2 uptake through the xylose isomerized xylulose by xylose isomerase and then enter the pentose phosphate pathway to be used.Hydrogen production characteristics of the hydrogen producing bacteria T2 using the mixed substates of both xylose and glucose, were studied based on batch, continuous and fed-batch fermentation. The results show that strain T2 can metabolize simultaneously effectively xylose and glucose to produce hydrogen, although the increases of the proportion of glucose in the mixed sugar, to a certain extent, inhibited the xylose utilized to produce hydrogen by T2. This problem was be solved very well by fed-batch fermentation strategy, making xylose utilized in mixed sugar equivalent to the utilization of pure xylose.Liquid and solid products were be acquired by steam explosion of corn straws acidified by acetic acid. The hydrogen-producing study on xylose and glucose from steam explosion liquid acidated utilized by T2 through the expansion of substrate concentration. The maximum yeild of hydrogen production was 1.37 mol-H₂/mol-xylose and 2.17 mol-H₂/mol-glucose, respectively, for 60% and 79% under normal conditions, indicating that T2 had strong adaptation and resilience. The maximum yeild of hydrogen production of T2 with the solid substances of corn straws to produce hydrogen by the methods of SHF and SSF, were 71ml/g-CS and 110ml /g-CS, respectively, which was the highest hydrogen yield of available straw used by pure strains. Therefore, it was be demonstrated adequately that the hydrogen-producing bacteria T2 could utilize pentose and hexose hydrolysates of corn straw to produce efficiently hydrogen.