Progress and challenges in the engineering of non-cellulolytic microorganisms for consolidated bioprocessing

Haan, Riaan den; Rensburg, Eugéne van; Rose, Shaunita H.; Görgens, Johann F.; Zyl, Willem H. van

doi:10.1016/j.copbio.2014.10.003

Cited by 132 publications

(72 citation statements)

References 35 publications

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“…Ideally, some or all of these steps would be performed in a singlepot consolidated bioprocess (5), provided that suitable microorganisms can be developed for such an approach. Strategies to engineer microorganisms for carbohydrate-active enzyme (CAZyme) (http://www.cazy.org/) (6) production include, e.g., optimizing and boosting the production of homologous enzymes, as well as the introduction of novel or complementary heterologous enzymes and pathways into a promising host (7)(8)(9).…”

mentioning

confidence: 99%

Activating Intrinsic Carbohydrate-Active Enzymes of the Smut Fungus Ustilago maydis for the Degradation of Plant Cell Wall Components

Geiser

Reindl

Blank

et al. 2016

Appl Environ Microbiol

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The microbial conversion of plant biomass to valuable products in a consolidated bioprocess could greatly increase the ecologic and economic impact of a biorefinery. Current strategies for hydrolyzing plant material mostly rely on the external application of carbohydrate-active enzymes (CAZymes). Alternatively, production organisms can be engineered to secrete CAZymes to reduce the reliance on externally added enzymes. Plant-pathogenic fungi have a vast repertoire of hydrolytic enzymes to sustain their lifestyle, but expression of the corresponding genes is usually highly regulated and restricted to the pathogenic phase. Here, we present a new strategy in using the biotrophic smut fungus Ustilago maydis for the degradation of plant cell wall components by activating its intrinsic enzyme potential during axenic growth. This fungal model organism is fully equipped with hydrolytic enzymes, and moreover, it naturally produces value-added substances, such as organic acids and biosurfactants. To achieve the deregulated expression of hydrolytic enzymes during the industrially relevant yeast-like growth in axenic culture, the native promoters of the respective genes were replaced by constitutively active synthetic promoters. This led to an enhanced conversion of xylan, cellobiose, and carboxymethyl cellulose to fermentable sugars. Moreover, a combination of strains with activated endoglucanase and ␤-glucanase increased the release of glucose from carboxymethyl cellulose and regenerated amorphous cellulose, suggesting that mixed cultivations could be a means for degrading more complex substrates in the future. In summary, this proof of principle demonstrates the potential applicability of activating the expression of native CAZymes from phytopathogens in a biocatalytic process. IMPORTANCEThis study describes basic experiments that aim at the degradation of plant cell wall components by the smut fungus Ustilago maydis. As a plant pathogen, this fungus contains a set of lignocellulose-degrading enzymes that may be suited for biomass degradation. However, its hydrolytic enzymes are specifically expressed only during plant infection. Here, we provide the proof of principle that these intrinsic enzymes can be synthetically activated during the industrially relevant yeast-like growth. The fungus is known to naturally synthesize valuable compounds, such as itaconate or glycolipids. Therefore, it could be suited for use in a consolidated bioprocess in which more complex and natural substrates are simultaneously converted to fermentable sugars and to value-added compounds in the future. O ne central aim of a sustainable bioeconomy is the switch from fossil-to bio-based production of platform chemicals and other valuable substances. To date, the most promising feedstock for biorefineries is lignocellulosic nonfood plant biomass (1). Lignocellulose is a complex composite mainly consisting of cellulose, hemicelluloses, pectin, and lignin (2). The selective conversion of lignocellulosic biomass comprises different steps: pret...

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confidence: 99%

Activating Intrinsic Carbohydrate-Active Enzymes of the Smut Fungus Ustilago maydis for the Degradation of Plant Cell Wall Components

Geiser

Reindl

Blank

et al. 2016

Appl Environ Microbiol

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“…In the case of (ligno)cellulosic feedstocks, substantial cost reductions can be realized when cellulose hydrolysis and product formation are integrated into a single organism (a concept known as 'consolidated bioprocessing'). In ''Progress and challenges in the engineering of non-cellulolytic microorganisms for consolidated bioprocessing'' Den Haan et al [9] give an inspiring overview of the current status in this highly relevant domain of biofuels research. While clearly specifying the challenges involved in functional expression of multi-component cellulolytic systems in heterologous hosts and under harsh industrial conditions, the authors are optimistic that these challenges will prove to be surmountable.…”

Section: Synthetic Biology To Enable Novel Substrate Capabilitiesmentioning

confidence: 99%

Editorial overview: Energy biotechnology

Papoutsakis

Pronk

2015

Current Opinion in Biotechnology

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“…Recombinant cellulolytic yeast can utilize diverse synthetic substrates such as carboxymethyl cellulose, phosphoric acid swollen cellulose (PASC), and Avicel microcrystalline cellulose via secreted cellulases [14]. Fungal cellulases can be secreted by yeast using the original secretion signal peptide.…”

Section: Enhancing Secretion Of Cellulolytic Enzymes By Yeastmentioning

confidence: 99%

“…To overcome these limitations, many researchers have attempted to develop recombinant microbial strains capable of hydrolyzing lignocellulose to glucose [8,14,15]. Heterologous expression of genes encoding cellulases and hemicellulases in recombinant strains can promote biomass utilization, which simplifies the biorefinery process by integrating biological processes (enzyme production, saccharification, and fermentation).…”

Section: Introductionmentioning

confidence: 99%

Rational design and evolutional fine tuning of Saccharomyces cerevisiae for biomass breakdown

Hasunuma

Ishii

Kondo

2015

Current Opinion in Chemical Biology

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Progress and challenges in the engineering of non-cellulolytic microorganisms for consolidated bioprocessing

Cited by 132 publications

References 35 publications

Activating Intrinsic Carbohydrate-Active Enzymes of the Smut Fungus Ustilago maydis for the Degradation of Plant Cell Wall Components

Activating Intrinsic Carbohydrate-Active Enzymes of the Smut Fungus Ustilago maydis for the Degradation of Plant Cell Wall Components

Editorial overview: Energy biotechnology

Rational design and evolutional fine tuning of Saccharomyces cerevisiae for biomass breakdown

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