| Cellulose is the most abundant renewable natural resource and a promising renewable energy source that could be potential alternative to the unsustainable fossil fuel energy.Biofuels and bioenergy production could be performed by bacterium.The strain that degrades celluloseat the fastest known rate is the anaerobic thermophile Clostridium thermocellum,which forms a highly organized extracellular multi-enzyme complex,the cellulosome,for efficient cellulose degradation.C.thermocellum is difficult to separate,because co-existence with other accompanying non-cellulolytic bacteria.We found that the use of co-culture of Clostridium thermocellum JN4 and Thermoanaerobacterium thermosaccharolyticum GD17 significantly improves overall cellulosic biofuel productivity.In the Chapter ?,we investigated the interactions and discovered underlying mechanism of improving the efficiency.In contrary to a mutualisitic relationship that was previously reported,it was found that there is an amensal relationship,although T.thermosaccharolyticum relieves carbon catabolite repression of C.thermocellum for obtaining more cellobiose released from lignocelluloses,T.thermosaccharolyticum significantly obstructs the growth of C.thermocellum in the co-culture system.The improvement in the endproducts formation is due to the strong competitive metabolic advantage of T.thermosaccharolyticumover C.thermocellum in the conversion of glucose or cellulobiose into final products.The possibility of controlling and rebalancing these microbial consortia for modulating cellulose degradation has achieved by adding stimulants of T.thermosaccharolyticum in the co-culture.In the Chapter ?,previous research has proven that hydrogen is profoundly produced by co-culture of C.Thermocellum JN4 and co-culture of non-cellulolytic strain T.thermosaccharolyticum GD17 than mono-culture of the C.thermocellum JN4,but the reasons of this improvement are still unknown.So,we worked out to find that co-relationship between C.thermocellum JN4 and T.thermosaccharolyticum GD17,the phylogenetic analysis of both species were analyzed at genetic level of the hydrogenase-coding genes,penta and tetra multimeric[FeFe]hydrogenases were present in both species and interestingly each of them contained Ech-type[NiFe]hydrogenase complex in cell.We carried out the comparative studied through transcriptional analysis.Our findings proven that hydrogenase-coding genes in C.thermocellum are arranged by glucose and cellobiose carbohydrates,while hydrogenase-coding genes in T.thermosaccharolyticum werestopped.However,the presences of hydrogenase-coding genes in mono-and co-cultures shown co-culture surroundings enhanced the transcriptional changes of hydrogenase-coding genes in T.thermosaccharolyticum whether C.thermocellum did not produced such changes in genes.The metabolic analysis shown T.thermosaccharolyticum produces H2 at the rate of 4-12 fold higher than C.thermocellum.These results lead to the conclusion that the improvement of H2 production in the co-culture over mono-culture should be attributed to changes in T.thermosaccharolyticum but not C.thermocellum.Further suggestions can be made that C.thermocellum and T.thermosaccharolyticum perform highly specific tasks in the co-culture,and optimization of the co-culture for more lignocellulosic biohydrogen production should be focused on the improvement of the non-cellulolytic bacterium.In conclusion,these investigations reveal a novel amensal relationship between C.thermocellum and a non-cellulolytic companion,in contrast to the previously hypothesised mutualistic relationship.Suggestion canbe made that T.thermosaccharolyticum is primarily responsible for the improved hydrogen production in a C.thermocellum/T.thermosaccharolyticum co-culture.These discoveries serve as a basis for designing and optimizing microbial consortia between cellulolytic and non-cellulolytic bacteriatomodulate cellulose conversion. |
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