Cellulase Production from Spent Lignocellulose Hydrolysates by Recombinant Aspergillus niger

Abstract

A recombinant Aspergillus niger strain expressing the Hypocrea jecorina endoglucanase Cel7B was grown on spent hydrolysates (stillage) from sugarcane bagasse and spruce wood. The spent hydrolysates served as excellent growth media for the Cel7B-producing strain, A. niger D15[egI], which displayed higher endoglucanase activities in the spent hydrolysates than in standard medium with a comparable monosaccharide content (e.g., 2,100 nkat/ml in spent bagasse hydrolysate compared to 480 nkat/ml in standard glucose-based medium). In addition, A. niger D15[egI] was also able to consume or convert other lignocellulose-derived compounds, such as acetic acid, furan aldehydes, and phenolic compounds, which are recognized as inhibitors of yeast during ethanolic fermentation. The results indicate that enzymes can be produced from the stillage stream as a high-value coproduct in secondgeneration bioethanol plants in a way that also facilitates recirculation of process water.Energy security, petroleum depletion, and global warming have been the main driving forces for the development of renewable fuels that can replace petroleum-derived fuels, such as gasoline and diesel. Bioethanol is currently the most commonly used renewable automobile fuel. It is largely produced by fermentation of sugar-or starch-containing feedstocks, such as cane sugar, corn, and wheat. However, the supply of these crops is relatively limited and many of them can be considered human food resources. Lignocellulose is a more-abundant and less-expensive raw material with the potential to give a high net energy gain (11,17).In the production of bioethanol from lignocellulosic materials, hydrolytic enzymes, such as cellulases and cellobiases, can be used to convert the lignocellulosic polysaccharides to monosaccharides. Microorganisms can be used to ferment the monosaccharides to ethanol. The yeast Saccharomyces cerevisiae is one of the most suitable microorganisms for ethanol production and is favored in industrial processes. However, S. cerevisiae only metabolizes hexose sugars. Many lignocellulosic materials consist of a significant proportion of xylan and arabinan, which give rise to pentose sugars. The cost of enzymes for the hydrolysis of polysaccharides and the inability of S. cerevisiae to utilize pentose sugars have been pointed out as two bottlenecks for commercialization of cellulosic ethanol production (9, 25). Considerable research efforts have therefore been focused on reducing the enzyme cost by producing more-efficient enzymes from cheaper growth media (25). Other efforts have been focused on different approaches to convert pentose sugars to ethanol by using recombinant microorganisms (3, 10).A novel approach to reduce the enzyme cost and to optimally utilize all sugars generated from lignocellulose would be to produce hydrolytic enzymes, such as cellulases, from the pentose fraction remaining after consumption of hexoses by S. cerevisiae (Fig. 1). The cellulases produced can then be used on site in the next round of hydrolysis of the lignoce...

Side by Side Comparison of Chemical Compounds Generated by Aqueous Pretreatments of Maize Stover, Miscanthus and Sugarcane Bagasse

“…In general, the pretreatment liquor is more enriched in pentose sugars (and the remaining cell wall material enriched in hexoses) when NaOH is used as compared to H 2 SO 4 . This might be favourable as these sugars could be used in fermentation with yeasts optimised to use pentose sugars [42] or pentose-fermenting organisms such as Geobacillus [43] or by filamentous fungi for enzyme production [44] or used in anaerobic digesters to produce methane for bioenergy applications. In addition to sugars, other potentially useful chemical building blocks present in the alkaline pretreatment liquors were characterised.…”

Hyper-Productivity, Characterization, and Exploitation of a Cellulase Complex from a Novel Isolate of Aspergillus tubingenesis S2 using Lignocellulose-based Material

“…Microorganisms including fungi and bacteria convert these waste products into useful products (biofuel) by producing various enzymes (Anwar et al 2012;Imran et al 2016). Filamentous fungi produce a variety of cellulases by consuming cheaper carbon sources such as cellulosic waste biomass or lignocellulosic biomass, which will minimize the cost of the industrial fermentation process (Alriksson et al 2009). Fungal species such as Aspergillus, Penicillium, Humicola, Trichoderma, and other microbial strains have been reported with enzyme secretion potentialities including cellulases, hemicellulases, and many other cell wall-degrading enzymes.…”

Fruit waste streams in South Africa and their potential role in developing a bio-economy

“…93 Furthermore, studies showed the production of cellulase and xylanase by A. niger strains cultured on the waste lignocellulosic streams remaining after fermentation of sugarcane bagasse and northern spruce. 94,95 In principle, it should be possible to grow A. niger strains on spent fruit waste streams after ethanolic fermentation, and on olive mill waste streams, with the simultaneous production of high-valued enzymes.…”