Recent advances in second generation ethanol production by thermophilic bacteria

There is an increased interest in using thermophilic bacteria for the production of bioethanol from complex lignocellulosic biomass due to their higher operating temperatures and broad substrate range. This review focuses upon the main genera of thermophilic anaerobes known to produce ethanol, their physiology, and the relevance of various environmental factors on ethanol yields including the partial pressure of hydrogen, ethanol tolerance, pH and substrate inhibition. Additionally, recent development in evolutionary adaptation and genetic engineering of thermophilic bacteria is highlighted. Recent developments in advanced process techniques used for ethanol production are reviewed with an emphasis on the advantages of using thermophilic bacteria in process strategies including separate saccharification and fermentation, simultaneous saccharification and fermentation (SSF), and consolidated bioprocessing (CBP).Peer Reviewe

Production of ethanol from sugars and lignocellulosic biomass by Thermoanaerobacter J1 Isolated from a hot spring in Iceland

Thermophilic bacteria have gained increased attention as candidates for bioethanol production from lignocellulosic biomass. This study investigated ethanol production by Thermoanaerobacter strain J1 from hydrolysates made from lignocellulosic biomass in batch cultures. The effect of increased initial glucose concentration and the partial pressure of hydrogen on end product formation were examined. The strain showed a broad substrate spectrum, and high ethanol yields were observed on glucose (1.70 mol/mol) and xylose (1.25 mol/mol). Ethanol yields were, however, dramatically lowered by adding thiosulfate or by cocultivating strain J1 with a hydrogenotrophic methanogen with acetate becoming the major end product. Ethanol production from 4.5 g/L of lignocellulosic biomass hydrolysates (grass, hemp stem, wheat straw, newspaper, and cellulose) pretreated with acid or alkali and the enzymes Celluclast and Novozymes 188 was investigated. The highest ethanol yields were obtained on cellulose (7.5 mM·g−1) but the lowest on straw (0.8 mM·g−1). Chemical pretreatment increased ethanol yields substantially from lignocellulosic biomass but not from cellulose. The largest increase was on straw hydrolysates where ethanol production increased from 0.8 mM·g−1 to 3.3 mM·g−1 using alkali-pretreated biomass. The highest ethanol yields on lignocellulosic hydrolysates were observed with hemp hydrolysates pretreated with acid, 4.2 mM·g−1.This work was sponsored by RANNÍS, Technology Development Fund, projects 081303408 (BioEthanol) and RAN091016-2376 (BioFuel), and the Research Fund of the University of AkureyriRitrýnt tímaritPeer reviewe

Progress in Second Generation Ethanol Production with Thermophilic Bacteria

Thermophilic bacteria have gained increased attention as prospective organisms for bioethanol production from lignocellulosic biomass due to their broad substrate spectra including many of the hexoses pentoses, and disaccharides found in biomass and biomass hydrolysates, fast growth rates, and high tolerance for extreme cultivation conditions. Apart from optimizing the ethanol production by varying physiological parameters, genetic engineering methods have been applied. This review focuses upon those thermophilic anaerobes recognized as being highly ethanologenic, their metabolism, and the importance of various culture parameters affecting ethanol yields, such as the partial pressure of hydrogen, pH, substrate inhibition, and ethanol tolerance. Also, recent developments in evolutionary adaptation and genetic engineering of thermophilic anaerobes are addressed

Dataset describing the amino acid catabolism of Thermoanaerobacter strain AK85: The influence of culture conditions on end product formation

The dataset describes the catabolism of the 20 proteogenics amino acids and their end products by Thermoanaerobacter strain AK85 under different electron scavenging conditions with an emphasis on the branched-chain amino acids as reported in Scully and Orlygsson, 2019.Landsvirkjun, Reykjavik, Iceland. NYR-08 - 2015Peer Reviewe

Ethanol production by a Paenibacillus species isolated from an Icelandic hot spring: Production yields from complex biomass

Ethanol production using Paenibacillus strain J2 was studied on carbohydrates and lignocellulosic biomass hydrolysates including grass (Phleum pratense) and barley straw (Hordeum vulgare). The strain has a broad substrate spectrum; fermentation of glucose yielded ethanol (major product), acetate, butyrate (minor), hydrogen, and carbon dioxide. At glucose concentrations below 30 mM fermentation was not inhibited. Higher substrate loadings resulted in decreased glucose utilization and a shift of end products towards butyrate. The maximum yields of ethanol were 1.45 mol ethanol mol glucose-1. The end products from lignocellulosic (4.5 g L-1 dw) biomass hydrolysates pretreated with 0.5% HCl or NaOH (control was unpretreated) prior to cellulase treatment were investigated. Ethanol production from cellulose hydrolysates without chemical pre-treatment yielded 5.5 mM ethanol g-1 with lower yields from paper and lignocellulosic biomasses (1.2-1.7 mM g-1). Ethanol production was enhanced by dilute acid or base pre-treatment combined with enzymatic treatment with the highest yields from grass (3.2 mM ethanol g-1).RANNIS, (Technology Development Fund) (BioFuel), grant number RAN091016-2376 Research Fund of the University of AkureyriRitrýnt tímaritPeer reviewe

Fermentation of mannitol extracts from brown macro algae by Thermophilic Clostridia

Publisher's version (útgefin grein)Mannitol-containing macro algae biomass, such as Ascophyllum nodosum and Laminaria digitata, are a potential feedstock for the production of biofuels such as bioethanol. The purpose of this work was to evaluate the ability of thermophilic anaerobes within Class Clostridia to ferment mannitol and mannitol-containing algal extracts. Screening of the type strains of six genera, Caldanaerobius, Caldanaerobacter, Caldicellulosiruptor, Thermoanaerobacter, Thermobrachium, and Thermoanaerobacterium) was conducted on 20 mM mannitol and revealed that 11 of 41 strains could utilize mannitol with ethanol being the dominant end-product. Mannitol utilization seems to be most common within the genus of Thermoanaerobacter (7 of 16 strains) with yields up to 88% of the theoretical yield in the case of Thermoanaerobacter pseudoethanolicus. Six selected mannitol-degrading strains (all Thermoanaerobacter species) were grown on mannitol extracts prepared from A. nodosum and L. digitata. Five of the strains produced similar amounts of ethanol as compared with ethanol yields from mannitol only. Finally, T. pseudoethanolicus was kinetically monitored using mannitol and mannitol extracts made from two macro algae species, A. nodosum and L. digitata for end-product formation.AVS research fund, grant R15065-15.Peer reviewe

Influence of Inhibitory Compounds on Biofuel Production from Oxalate-Rich Rhubarb Leaf Hydrolysates Using Thermoanaerobacter thermohydrosulfuricus Strain AK91

The present investigation is on bioethanol and biohydrogen production from oxalate-rich rhubarb leaves which are an underutilized residue of rhubarb cultivation. Rhubarb leaves can be the feedstock for bioethanol and biohydrogen production using thermophilic, anaerobic bacteria. The fermentation of second-generation biomass to biofuels by Thermoanaerobacter has already been reported as well as their high ethanol and hydrogen yields although rhubarb biomass has not been examined for this purpose. Thermoanaerobacter thermohydrosulfuricus strain AK91 was characterized (temperature and pH optima, substrate utilization spectrum) which demonstrates that the strain can utilize most carbohydrates found in lignocellulosic biomass. Additionally, the influence of specific culture conditions, namely the partial pressure of hydrogen and initial glucose concentration, were investigated in batch culture and reveals that the strain is inhibited. Additionally, batch experiments containing common inhibitory compounds, namely carboxylic acids and aldehydes, some of which are present in high concentrations in rhubarb. Strain AK91 is not affected by alkanoic carboxylic acids and oxalate up to at least 100 mM although the strain was inhibited by 40 mM of malate. Interestingly, strain AK91 demonstrated the ability to reduce alkanoic carboxylic acids to their primary alcohols; more detailed studies with propionate as a model compound demonstrated that AK91’s growth is not severally impacted by high propionate loadings although 1-propanol titers did not exceed 8.5 mM. Additionally, ethanol and hydrogen production from grass and rhubarb leaf hydrolysates was investigated in batch culture for which AK91 produced 7.0 and 6.3 mM g−1, respectively

Dataset describing the amino acid catabolism of Thermoanaerobacter pseudethanolicus

The dataset depicts the catabolism of branched-chain amino acids by Thermoanaerobacter pseudethanolicus in the presence of thiosulfate under different culture conditions. The results reveal that the strain can degrade all three branched-chain amino acids resulting in the production of their corresponding branched-chain fatty acids and branched-chain alcohols with the fatty acids always being the dominant product. The highest amounts of 2-methyl-1-butanol from isoleucine were at pH 6.5, liquid-gas ratio of 0.98, and at 20 mM thiosulfate concentration. A kinetic experiment of the branched-chain amino acids was done in the presence of thiosulfate as are data on selected enzyme activities related to alcohols and aldehydes. Finally, an NMR study using 13C1 methyl-1-butyrate during the degradation of leucine in the presence of thiosulfate was done to prove that the 13C1-methyl-1-butanol was indeed from its corresponding fatty acid