Production of Ethanol from Sugars and Lignocellulosic Biomass byThermoanaerobacterJ1 Isolated from a Hot Spring in Iceland

Abstract

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.

Recent Advances in Second Generation Ethanol Production by Thermophilic Bacteria

“…Highest yield observed were 1.5 mol ethanol/mol glucose by Thermonaaerobacterium AK17 at low glucose concentrations but lowered to less than 1.0 mol ethanol/mol glucose at increased initial substrate loadings [42]. [18] g-glucose; gal-galactose; man-mannose; x-xylose; a-arabinose; cel-cellobiose; suc-sucrose; X-xylan; ND-not determined; E-ethanol; A-acetate; L-lactate; P-pectin; H-hydrogen; *-ability varies depending upon strain; C-cellulose; F-formate; S-starch; FF-furfuraldehyde; HMF-5-hydroxymethyl-furfuraldehyde; I-inositol; and ArC-aromatic compounds.…”

“…Their habitats include geothermal areas [16][17][18], deep sea vents [19], river bank sediments [20], and artificial habitats such as self-heated compost piles [21], municipal solid waste or sewage sludge [22], oil wells [23], and thermally treated foods [24]. This suggests that thermophilic anaerobes are somewhat ubiquitous in nature.…”

“…Thus, hydrogen accumulation does not occur allowing for a complete catabolism of glucose to end products. Conversely, batch fermentation with monocultures allows hydrogen to accumulate leading to a change in end production profile in some Thermoanaerobacter species [18,58,77]. This is well known for sugars and some amino acids.…”

“…Although this inhibiton may also be caused by accumulated hydrogen or by low pH, it could also be an intriquing factor for thermophiles. One strain of Thermoanaerobacter, strain J1, has though been shown to be very tolerant towards high sugar concentrations [18]. This high ethanol producing thermophile produces up to 1.7 mol ethanol/mol glucose up to initial glucose concentrations of 100 mM.…”

“…Recent investigations on two Thermoanaerobacter strains, AK5 and J1 showed promising results from various types of hydrolysates made from chemically and enzymatically pretreated lignocellulosic biomass (Table 2) [18,58]. Recent investigaton on a co-culture of C. thermocellum and C. thermolactimum showed 75% and 90% ethanol yields on crystaline cellulose and xylose, respectively [96].…”