Phytopathogenic Fungi: Useful Tools to Degrade Plant Biomass for Bioethanol Production (original) (raw)
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Plant Cell Wall–Degrading Enzymes and Their Secretion in Plant-Pathogenic Fungi
Approximately a tenth of all described fungal species can cause diseases in plants. A common feature of this process is the necessity to pass through the plant cell wall, an important barrier against pathogen attack. To this end, fungi possess a diverse array of secreted enzymes to depolymerize the main structural polysaccharide components of the plant cell wall, i.e., cellulose, hemicellulose, and pectin. Recent advances in genomic and systemslevel studies have begun to unravel this diversity and have pinpointed cell wall-degrading enzyme (CWDE) families that are specifically present or enhanced in plant-pathogenic fungi. In this review, we discuss differences between the CWDE arsenal of plant-pathogenic and non-plant-pathogenic fungi, highlight the importance of individual enzyme families for pathogenesis, illustrate the secretory pathway that transports CWDEs out of the fungal cell, and report the transcriptional regulation of expression of CWDE genes in both saprophytic and phytopathogenic fungi.
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Background The discovery and development of novel plant cell wall degrading enzymes is a key step towards more efficient depolymerization of polysaccharides to fermentable sugars for the production of liquid transportation biofuels and other bioproducts. The industrial fungus Trichoderma reesei is known to be highly cellulolytic and is a major industrial microbial source for commercial cellulases, xylanases and other cell wall degrading enzymes. However, enzyme-prospecting research continues to identify opportunities to enhance the activity of T. reesei enzyme preparations by supplementing with enzymatic diversity from other microbes. The goal of this study was to evaluate the enzymatic potential of a broad range of plant pathogenic and non-pathogenic fungi for their ability to degrade plant biomass and isolated polysaccharides. Results Large-scale screening identified a range of hydrolytic activities among 348 unique isolates representing 156 species of plant pathogenic and non-pat...
Closely related fungi employ diverse enzymatic strategies to degrade plant biomass
Biotechnology for Biofuels, 2015
Background: Plant biomass is the major substrate for the production of biofuels and biochemicals, as well as food, textiles and other products. It is also the major carbon source for many fungi and enzymes of these fungi are essential for the depolymerization of plant polysaccharides in industrial processes. This is a highly complex process that involves a large number of extracellular enzymes as well as non-hydrolytic proteins, whose production in fungi is controlled by a set of transcriptional regulators. Aspergillus species form one of the best studied fungal genera in this field, and several species are used for the production of commercial enzyme cocktails. Results: It is often assumed that related fungi use similar enzymatic approaches to degrade plant polysaccharides. In this study we have compared the genomic content and the enzymes produced by eight Aspergilli for the degradation of plant biomass. All tested Aspergilli have a similar genomic potential to degrade plant biomass, with the exception of A. clavatus that has a strongly reduced pectinolytic ability. Despite this similar genomic potential their approaches to degrade plant biomass differ markedly in the overall activities as well as the specific enzymes they employ. While many of the genes have orthologs in (nearly) all tested species, only very few of the corresponding enzymes are produced by all species during growth on wheat bran or sugar beet pulp. In addition, significant differences were observed between the enzyme sets produced on these feedstocks, largely correlating with their polysaccharide composition. Conclusions: These data demonstrate that Aspergillus species and possibly also other related fungi employ significantly different approaches to degrade plant biomass. This makes sense from an ecological perspective where mixed populations of fungi together degrade plant biomass. The results of this study indicate that combining the approaches from different species could result in improved enzyme mixtures for industrial applications, in particular saccharification of plant biomass for biofuel production. Such an approach may result in a much better improvement
Sugars and pH : A clue to the regulation of fungal cell wall-degrading enzymes in plants
Physiological and Molecular Plant Pathology, 2004
In recent years, substantial progress has been made in understanding the role of cell wall-degrading enzymes in virulence of fungal pathogens using genetic tools. A homologous recombination-mediated targeted gene disruption of a single pectolytic gene decreased virulence in multiple fungal pathogens. Furthermore, differential regulation of a gene that encodes a cell wall-degrading enzyme during infection under different host environments has recently been examined, and host pH and sugars are involved in the regulation of the polygalacturonase gene. We will provide a brief overview of the biology of the macerating diseases caused by phytopathogenic Alternaria pathogens in particular hosts, followed by a description of possible mechanisms controlling the differential expression of genes encoding cell wall-degrading enzymes in the infected host. q
Destructuring plant biomass: Focus on fungal and extremophilic cell wall hydrolases.
The use of plant biomass as feedstock for biomaterial and biofuel production is relevant in the current bio-based economy scenario of valorizing renewable resources. Fungi, which degrade complex and recalcitrant plant polymers, secrete different enzymes that hydrolyze plant cell wall polysaccharides. The present review discusses the current research trends on fungal, as well as extremophilic cell wall hydrolases that can withstand extreme physico-chemical conditions required in efficient industrial processes. Secretomes of fungi from the phyla Ascomycota, Basidiomycota, Zygomycota and Neocallimastigomycota are presented along with metabolic cues (nutrient sensing, coordination of carbon and nitrogen metabolism) affecting their composition. We conclude the review by suggesting further research avenues focused on the one hand on a comprehensive analysis of the physiology and epigenetics underlying cell wall degrading enzyme production in fungi and on the other hand on the analysis of proteins with unknown function and metagenomics of extremophilic consortia. The current advances in consolidated bioprocessing, altered secretory pathways and creation of designer plants are also examined. Furthermore, recent developments in enhancing the activity, stability and reusability of enzymes based on synergistic, proximity and entropic effects, fusion enzymes, structure-guided recombination between homologous enzymes and magnetic enzymes are considered with a view to improving saccharification.
Bmc Genomics, 2013
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Fungal enzyme sets for plant polysaccharide degradation
Applied Microbiology and Biotechnology, 2011
Enzymatic degradation of plant polysaccharides has many industrial applications, such as within the paper, food, and feed industry and for sustainable production of fuels and chemicals. Cellulose, hemicelluloses, and pectins are the main components of plant cell wall polysaccharides. These polysaccharides are often tightly packed, contain many different sugar residues, and are branched with a diversity of structures. To enable efficient degradation of these polysaccharides, fungi produce an extensive set of carbohydrate-active enzymes. The variety of the enzyme set differs between fungi and often corresponds to the requirements of its habitat. Carbohydrate-active enzymes can be organized in different families based on the amino acid sequence of the structurally related catalytic modules. Fungal enzymes involved in plant polysaccharide degradation are assigned to at least 35 glycoside hydrolase families, three carbohydrate esterase families and six polysaccharide lyase families. This mini-review will discuss the enzymes needed for complete degradation of plant polysaccharides and will give an overview of the latest developments concerning fungal carbohydrate-active enzymes and their corresponding families.
Fungal biology and agriculture: revisiting the field
2003
Plant pathology has made significant progress over the years, a process that involved overcoming a variety of conceptual and technological hurdles. Descriptive mycology and the advent of chemical plant-disease management have been followed by biochemical and physiological studies of fungi and their hosts. The later establishment of biochemical genetics along with the introduction of DNA-mediated transformation have set the stage for dissection of gene function and advances in our understanding of fungal cell biology and plant-fungus interactions. Currently, with the advent of high-throughput technologies, we have the capacity to acquire vast data sets that have direct relevance to the numerous subdisciplines within fungal biology and pathology. These data provide unique opportunities for basic research and for engineering solutions to important agricultural problems. However, we also are faced with the challenge of data organization and mining to analyze the relationships between fungal and plant genomes and to elucidate the physiological function of pertinent DNA sequences. We present our perspective of fungal biology and agriculture, including administrative and political challenges to plant protection research.
This excerpt∗ is taken from the author’s biography that describes the period (1977-1979) the author spent in South Africa at the University of Natal in Pietermaritzburg, and documents the research program he developed, as well as travel and life in that country. The author arrived in South Africa by ship in late November 1976 en-route from West Germany to take up a 3-year contract as Lecturer (Assistant Professor) in Biochemistry. In settling into an academic environment, the author wrote and presented lectures in his teaching courses, and proposed themes for a program of research. A new line of research was initiated on the Bioconversion (now called Biorefining) of Plant Biomass (lignocellulosic materials), viz., the enzymes associated with the degradation of the components of the plant cell wall, and chiefly cellulose. This research theme would be continued after the author left South Africa, and would occupy the author’s interest throughout his entire career of some 47 years. A research theme of this nature was of strategic importance in developed nations of the world, and stemmed from the crisis affecting the supply of liquid motor fuels as a consequence of OPEC’s control over crude petroleum prices during the mid-1970’s. The author was awarded generous grant funding from the university and other organizations in South Africa to develop his research programs. The author supervised 2 Masters and 1 PhD student during his tenure, who developed research projects on enzymes derived from fungal isolates, Monilia sp., Sclerotium rolfsii, Trichoderma reesei, degrading cellulose and hemicellulose. An Honours student investigated the in-vitro biosynthesis of xanthan. Several invitations were received during the author’s tenure at the university that included: Visiting Professor to France (Grenoble, Nantes, Paris); presentation of Plenary Lectures on xylanases at conferences in the United Kingdom, Portugal and France; delivering research seminars on xylanases in Switzerland, Germany and Sweden; and to write two book chapters. Highlights arising from the research projects on Monilia sp., a highly cellulolytic ascomyceteous fungus, included two discoveries: a new enzyme activity (cellobiose dehydrogenase), and short-fibre forming activity (macerase) responsible for deconstructing filter paper into short cellulose fibres without concomitant hydrolysis of cellulose. The Monilia species produced a suite of enzymes to degrade lignocellulosic materials: 5 cellulases (2 exo- and 3 endo- enzyme types), one hemicellulase (xylanase), and three β-glucosidases (1 intracellular, 2 extracellular). The β-glucosidases were selected for further studies on their localization, regulation of synthesis by induction-repression mechanisms, and purification to homogeneity of one of the extracellular enzymes. Other research developments included: the isolation and characterization of several xylanases from Trichoderma reesei QM-9414; and significant headway was made on the in-vitro biosynthesis of the exopolysaccharide xanthan using membrane enzyme preparations from Xanthomonas campestris. The author’s time in South Africa presented opportunities to travel widely throughout the southern African continent (South Africa, Kalahari, Namibia, Zimbabwe), and especially to wild game parks (Kruger, Umfolozi, Kalahari, Hwange, Etosha) and Victoria Falls, where animals congregated in their native habitats: elephant, rhinoceros, giraffe, crocodile, various antelope species, cape buffalo, and the big feline species (lion, leopard, cheetah) among others, and countless species of birds ranging from ostrich, vultures and eagles to smaller birds. Due to the worsening racial events arising from the South African government’s policy of apartheid, and the war on terrorism with black factions, the author left South Africa in December 1979.