Biohydrogen Production From Sugarcane Bagasse By T. Aotearoense SCUT27/Δldh And Thetranscription Analysis Of The Improved Tolerance Strain To High Concentration Substrate

Hydrogen is regarded as an attractive future energy for its high energy content and zeroCO2emissions. Currently, the majority of hydrogen is generated from fossil fuels. Howeverfrom an environmental perspective, sustainable hydrogen production from low cost oflignocellulosic biomass should be considered. Thermophilic hydrogen production is attractivesince it can potentially convert a variety of biomass-based substrates into hydrogen at highyields. In this research, hydrogen production from sugarcane bagasse acid hydrolysates byThermoanaerobacterium aotearoenseSCUT27/Δldh was studied. A mutant strain withimproved tolerance to high concentration sugars was isolated. We analyzed the transcriptomesequencing data to reveal the gene expression differences and to better understand themolecular mechanism.Influences of components from sugarcane bagasse hydrolysates on hydrogen productionby T. aotearoense SCUT27/Δldh were evulated. SCUT/Δldh could utilize single or mixturecarbon source as substrate to produce hydrogen efficiently. It is worth noting that SCUT/Δldhhas the strong capability to utilize benchwood xylan and dextran as the single carbon sourceto support cell growth and hydrogen release without any cellulase or xylanase addition. Itshowed the inhibition phenomena of cell growth became very apparent at the phenolconcentration of2g/L. However, there was no real distinction among final cell densities after12h fermentation in the observational concentrations of2-furaldehyde (furfural) and5-hydroxymethyl furfural (HMF). Unfortunately, high concentration of carbon source (higherthan80g/L) could result in extended lag phaseand decreased hydrogen and ethanol yields.Sugarcane bagasse (SCB) was used as substrate for hydrogen production by T.aotearoense SCUT27/Δldh. Key parameters of acid hydrolysis were studied through theresponse surface methodology. Maximum hydrogen productivity was achieved under theconditions of2.3%of H2SO4for114.2min at115oC. Using these conditions, the besthydrogen yield of1.86mol H2/mol total sugar and the hydrogen production rate (HPR) of0.52L/L·h were obtained from2L SCB hydrolysates in5L fermentor, which showed afavorable comparison with the literature reported.Additionally, no obvious carbon cataboliterepression (CCR)was observed during the fermentation using the multi-sugars assubstrates.Considering these advantages and impressive hydrogen production rate, the potential ofhydrogen production by T. aotearoense SCUT27/Δldh is intriguing. And thethermophilic, anaerobic fermentation using SCB hydrolysates as mediumby this strain wouldbea more practice and eco-friendly process.A mutant with improvedtolerance to higher carbon source, designated as SCUTG3#4,was evolved and isolated. Using120g/L sugar mixture as carbon source, the fermentation lagphase was shortened to24h from100h, with the final hydrogen volume arrived at3.09L.The highest ethanol yield was increased to1.22mol/mol sugar. A total of35and24geneswere significantly upregulated and downregulated in the presence of120g/L sugar mixturecompared with50g/L sugar mixture, respectively.Further analysis showed that accumulationof UDP-Gal (UDP-α-D-galactose) and CAIR were increased. Downregulated mtGDP in theglycerol phospholipid metabolism pathway led to the promotion of glycerol. Down regulationof DNA replication and the enhancement of ABC transportter were the stress response ofmicroorganisms to the hyperosmotic solution.