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- Herausgeber: Bentham Science Publishers
- Kategorie: Wissenschaft und neue Technologien
- Serie: Mycology: Current and Future Developments
- Sprache: Englisch
Sustainable Utilization of Fungi in Agriculture and Industry covers current knowledge about different fungal microorganisms, including economically important filamentous fungi and yeasts. 22 chapters summarize information about scientific investigations and the application of fungi in the production of industrial enzymes, organic acids (citric acid, lactic acid, etc.), biofuel (ethanol and hydrogen) and bioactive compounds for sustainable processes in agriculture, bioremediation, and the industrial production of pharmaceuticals.
Each chapter gives an updated and detailed account on fungal microbes and their sustainable utilization in agriculture, white biotechnology, and other valuable industrial applications. Contributions are written by experts in mycology and industrial biotechnology, presenting a broad perspective of the field in a simple, yet engaging style.
Sustainable Utilization of Fungi in Agriculture and Industry is an informative reference for general readers, trainees, interested in sustainability measures in agriculture and industry. The book also serves as a resource for scholars, students and teachers involved in botany, microbiology, biotechnology and life sciences courses.
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Veröffentlichungsjahr: 2002
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FOREWORD
The discipline of biology that is devoted to studying fungi is termed mycology. These organisms are classified in a kingdom, characterized by heterotrophy meaning absorption of nutrients typically by secreting digesting enzymes into their environment. Fungi are abundant worldwide, and the diversity has been estimated at 5.1 to 12 million species by mycologists; among them, a minor fraction of about 1,40,000 species have been characterized and identified. A major part of the extant fungi on Earth is yet to be characterized. Non-culturable fungi in the environmental samples are characterized by constructing their genomes from metagenomes and sequencing internal transcribed spacers.
Fungi occur in normal as well as extreme environments. They perform an essential role in the decomposition of organic matter and have fundamental roles in nutrient cycling and exchange in the environment. Such functions are played by the consortia of fungi and other microbes which are referred to as microbiomes. They are free living or symbionts/parasites on plants and animals. The arrival of next-generation sequencing technology allows fungal genomes to be sequenced for phylogenetic studies up to the species level. Fungal and yeast genome sequencing projects have been launched to sequence 1000 fungal and budding yeast genomes.
Fungi have served a crucial role as model organisms for biological inquiry, such as brewer’s yeast, Saccharomyces cerevisiae; and pink bread mould, Neurosporacrassa. Major insights like the nature of the gene, autophagy, control of cell cycle, and how telomeres function have been made using morphologically simple organisms with complex cellular machinery similar to human cells. Because of their typically small genome sizes and life cycle stages with free-living haploid states, fungi have served as models for genome evolution and reconstruction of phylogenetic relationships using genome scale data.
Although fungi are relatively understudied, they are an essential, fascinating and biotechnologically useful group of organisms with an incredible biotechnological potential for industrial exploitation. Hyde and co-workers (Fungal Diversity, 2019, 97: 1-136) have recently detailed 50 ways in which fungi can be exploited. As compared to other biological systems (e.g. plants), fungi have the great advantage that they can be grown in large bioreactors on an industrial scale.
The laudable attempt of editing a book entitled ‘Sustainable Utilization of Fungi in Agriculture and industry’ is a welcome step by Dr. S. Ajmera and others. This book comprises 22 chapters, on various aspects of fungi, contributed by those engaged in teaching mycology/microbiology/biotechnology in various academic institutions. I wish to place on record my appreciation for the editors of the book. I sincerely hope and wish that graduate and post-graduate students, scholars and teachers in broad areas of botany, microbiology, biotechnology and Life Sciences will find this book useful.
PREFACE
Fungi and their application in Agricultural or Industrial Microbiology are being utilized for food security, providing a solution to produce bioenergy, chemicals, and other bioproducts from renewable resources. The fungi that are employed in sustainable agriculture and industrial microbiology are able to secrete compounds that are useful for plant growth promotion, thereby producing organic acids, hydrolytic enzymes, functional bioactive compounds and biocatalytic agents with promising applications in various economically important fields such as environment, agriculture, food and dietary, biotechnology, medicine, pharmaceuticals, and associated sectors.
The present book, “Sustainable Utilization of Fungi in Agriculture and Industry” covers the investigations of different fungal microorganisms (filamentous fungi and yeast) and their potential application in the production of industrial enzymes, organic acids (citric acid, lactic acid, etc), biofuel (ethanol, H2 gas) and bioactive compounds for diverse processes targeted at agriculture, bioremediation, industries, therapeutics, and diagnostics.
I strongly feel that the leading researchers with extensive, in-depth experience and expertise in fungal microbial biotechnology took the time and efforts to develop the outstanding book chapters. Each chapter is well written and explained so that the reader is given an up-to-date and detailed account of knowledge on fungal microbes and their sustainable utilization in agriculture, white biotechnology, and other innumerable industrial applications. I am very much sure that this book will be of great interest to the students, scientists, Ph.D. and postdoc researchers of life sciences especially, microbiologists, biochemists, microbial and fungal biotechnologists who are involved in investigations on fungal diversity and its sustainable utilization in agriculture and industry.
ACKNOWLEDGEMENT
I would like to express my earnest gratitude and appreciation to my colleagues for their valuable instruction, guidance, and positive appreciation in the successful completion of this book.
I am pleased to acknowledge Prof. Tulasi Satyanarayana, Professor Emeritus Netaji Subhas University of Technology, New Delhi, for his expert direction and foreword message for this book. I am extremely thankful for his incredible support.
I thank all authors for their great association and contribution that helped in this herculean task of bringing information in different aspects of mycology.
ACKNOWLEDGEMENT
Dr. Shanthipriya AjmeraI would like to express my earnest gratitude and appreciation to my colleagues for their valuable instruction, guidance, and positive appreciation in the successful completion of this book.
I am pleased to acknowledge Prof. Tulasi Satyanarayana, Professor Emeritus Netaji Subhas University of Technology, New Delhi, for his expert direction and foreword message for this book. I am extremely thankful for his incredible support.
I thank all authors for their great association and contribution that helped in this herculean task of bringing information in different aspects of mycology.
Sincere regards
Chief Editor
Shanthipriya AjmeraDEDICATION
We all have dreams, but making dreams a reality takes a lot of determination, commitment, self-discipline, and effort. This book is dedicated to my parents & family for always loving and supporting me.
List of Contributors
The Versatile Potential of Fungi in Human Life and Ecosystem
Divya Ajmeera1,Gokul Shankar Sabesan2,Shanthipriya Ajmera3,*Abstract
Fungi play a major role in the well-being of human life as they are involved in health and nutrition processes on a large scale and are a major component of the global economy. Furthermore, they are the natural nutrient recyclers in the environment and thus balance the ecosystem. Also, through mycorhizal relationships, the fungi help in enhancing soil fertility by increasing the surface area for absorption of nutrients such as phosphorous, nitrogen, sulfur, etc., and other minerals such as zinc and copper. As fungi interact with various plant pathogens affecting crop production, they can be used as Microbial biological control agents or biopesticides and can be replaced for the usage of hazardous chemical pesticides for controlling plant pathogens. Here, we tried to explain the fungal importance to mankind and the ecosystem by listing its various applications in human life.
INTRODUCTION
Fungi are either single-celled (yeast) or multi-cellular (hyphae) eukaryotic heterotrophs. They help in balancing the ecosystems by acting as decomposers in a wide variety of habitats. On the other hand, fungi are responsible for diseases as they directly interact with other organisms, mostly plants and bacteria [1].
Fungi frequently grow in a dark and damp environment rich in decaying debris from plants and animals. Fungi release elements such as nitrogen and phosphorus from decaying organic matter because of their mode of nutrition (i.e., produce enzymes to digest the matter and then after ingestion). Many habitats have these
elements in low amounts but are required in large amounts for other living organisms to live and are mostly supplied by the fungi [1, 2].
Fungi are known for their utilization in the production of various foods and beverages. Fungi are found to involve in many industrial fermentative processes such as the production of single-cell proteins (SCP), antibiotics, enzymes, vitamins, etc., and have a major impact on the global industry, mostly in the area of health and nutrition [3].
In this chapter, we tried to elucidate the importance of Fungi in Human Life by listing out the various applications of fungi.
IMPORTANCE OF FUNGI IN HUMAN LIFE
The fungi are in usage for food, preservation, or other purposes by humans in various ways and are listed below.
As a Food
Industries utilize fungi in various processes for manufacturing large varieties of food useful for mankind.
Fungi are involved in the fermentation of grains to produce beer and fruits to produce wine, where they ferment sugars into ethanol and produce carbon dioxide under anaerobic conditions. For example, Saccharomyces cerevisiae, a single-cell fungus also known as baker's yeast/brewer's yeast, is an important ingredient for the production of wine, beer, and bread along and other wheat-based products like pizza, along with many applications in medical research. Another example is Aspergillus oryzae, involved in the production of a Japanese beverage called “Sake” by the fermentation of rice. The fungal species like Aspergillus oryzae, Pediococcus soyae, Saccharomyces rouxii (Fig. 1) are used in soy sauce production [4].
Fig. (1)) i. Saccharomyces cerevisiae, ii. Aspergillus oryzae (Image source: en.wikipedia.org).Several species, such as the Agaricus bisporus and the Portobello, produce button mushrooms for consumption, and other species such as Pleurotus, Lentinus edodes, and Auricularia (Fig. 2) are produced dominantly. Many other mushroom species such as morels, chanterelles, truffles, Milk mushrooms, porcini mushrooms, and black trumpets all demand a high price on the market due to their high protein and low calorific value [5].
Fig. (2)) i. Agaricus bisporus, ii. Pleurotus ostreatus, iii. Lentinus edodes, iv. Auriculariaauricula-judae (Image source: en.wikipedia.org).For certain types of cheeses, fungal spores are added to impart a unique flavor and textures to the cheese, for example; the blue color in cheeses (Fig. 3) such as Stilton and Roquefort is imparted by Penicillium roquefortii. Other examples of colored cheese are Gorgonzola, Stilton, and Danish Blue cheese [6].
Fig. (3)) Bleu de Gex, a creamy, semi-soft blue cheese made in the Jura region of France (source: en.wikipedia.org https://en.wikipedia.org/wiki/Blue_cheese).As a Prominent Source of SCP
The SCP or microbial proteins are the biomass or protein extracts from pure or mixed cultures of microorganisms such as algae, yeasts, fungi, or bacteria that may be used as a substitute for protein-rich foods. These are edible unicellular microorganisms suitable for human consumption or as animal feeds [7].
In recent years fungi have been utilized as rich sources of SCP and are now available commercially as human food. The SCP produced from fungi are advantageous over other microorganisms due to their low nucleic acid content, cholesterol, and fat since it contains no animal ingredients. As the fungal mycelium can be processed to give an appearance and 'mouth-feel of meat, it has the advantage of being suitable for vegetarians and those on low-calorie diets. In addition, the edible fungi (e.g., mushrooms) and products with fungal content (e.g., Roqueforti cheeses) are well accepted. Examples of fungi involved in SCP production are Fusarium graminearum (Fig. 4). which is available in the European markets as Quorn TM mycoprotein, the filamentous fungus Trichoderma viride, the yeasts Saccharomycopsis fibuliger and Candida tropicalis, Aspergillus niger, Penicillium chrysogenum, Fusarium avenacum, Neurospora sitoplila, etc [8, 9].
Fig. (4)) i. Fusarium graminearum, ii. Aspergillus fumigates, iii. Filamentous fungi, iv. Aspergillus niger (Image source: http://biomaster2011.blogspot.com/2011/03/use-of-filamentous-fungus-as-single.html).As Pharmaceutical Importance
The secondary metabolites of fungi are of great pharmaceutical importance and can be isolated to be used as drugs. Most of the fungal metabolites were reported to have antitumor, antiviral, antibacterial, and immunosuppressants activities.
Antibiotics: In the natural environment, fungi compete with bacteria for food and existing, and in this process, they release antibiotics to kill or inhibit the growth of bacteria. This was invented by Alexander Fleming in 1928 that discovered the first antibiotic, penicillin, and was produced by Penicillium notatum (Fig. 5), used to treat bacterial and fungal infections. Other examples include Cephalosporin from species of Cephalosporium and Griseofulvin from Penicillium griseofulvum and Penicillium patulum [10, 11].
Fig. (5)) i. Penicillium notatum (http://quentinqsaccos.blogspot.com/2011/09/in-penicillium-simple.html), ii. Penicillium griseofulvum(http://www.schimmel-schimmelpilze.de/penicillium-griseofulvum.html).Statins: Fungal metabolic reactions can produce Statins are products of fungi. For example, Aspergillus terreus produces lovastatin, Aspergillus Phoma produces squale statin, and Penicillium citrinum produces mevastatin as its secondary metabolites (Fig. 6). Statins inhibit an enzyme responsible for the synthesis of cholesterol and are hence used in lowering low-density lipoproteins in human blood vessels. Statins are also found in stem cell technology in treating damaged tissues [12, 13].
Fig. (6)) i. Aspergillus terreus (en.wikipedia.org), ii. Penicillium citrinum (http://thunderhouse4-yuri. blogspot.com/2015/08/penicillium-citrinum.html).Ergot alkaloids: The precursors of steroid hormones and ergot alkaloids are used to stop bleeding. Alkaloids can be produced by using strains of Calviceps fusiformis and Calviceps paspalii (Fig. 7), which act on the sympathetic nervous system causing blood vessels’ dilation. They also cause smooth muscle contractions, particularly in the uterus, thus applied to induce abortion [14, 15].
Fig. (7)) i. Calviceps fusiformis (mycoportal.com), ii. Calviceps paspalii ( https://doi.org/10.1002/ jobm.3620300115).Immune suppressants: cyclosporine, an Immune suppressant drug produced by several fungal species like Tolypocladium inflatum (Fig. 8), Trichoderma polysporum, and Cylindrocarpon lucidum is an essential tool for patients who had organ transplantation where it can prevent organ rejection by inhibiting T cell activation in the human immune system [16-18].
Fig. (8)) i. Tolypocladium inflatum (Pasero, G & Piero, Marson. (2012). Short story of antirheumatic therapy.VIII. The immunodepressants. Reumatismo. 64. 44-54. 10.4081/reumatismo.2012.44.), ii. Cylindrocarpon species (source: Bruce Watt, University of Maine, Bugwood.org).Others: Fungi such as Psilocybe semilanceata and Gymnopilus junonius (Fig. 9) were found to have a compound called Psilocybin used for its hallucinogenic properties for thousands of years [19].
Fig. (9)) i. Psilocybe semilanceata, ii. Gymnopilus junonius (en.wikipedia.org).As a Source of Vitamins
Most of the fungi studied are a good source of vitamins and the yeast extract and yeast tablets are popular for B group vitamin supplements. Other species Nematospora gossypii and Eremothecium ashbyi (Fig. 10) are now used to produce B vitamins industrially [20].
Fig. (10))Eremothecium ashbyi (https://www.diark.org/diark/species_list/Eremothecium_gossypii_ ATCC_10895).As a Source of Enzymes
Fungi have been the organism of choice for enzyme isolation since their biology is well characterized and fall under generally regarded as safe (GRAS). The fungal genera Aspergillus and Penicillium are widely exploited for industrially important enzymes like fungal cellulases, gluconase and glycosidase [21]. Enzymes from fungal origin show many advantages over the other animal or plant cells as sources of enzyme, which include metabolic flexibility, they can be grown readily using simple growth media, stability can be achieved using mutagenesis, etc [22].
Several microbial enzymes are involved in various industrial processes. For example, different Aspergillus species produce amylases that are used for improving bread quality. Glucose oxidases from Penicillium notatum are used in the biochemical assays. Catalases isolated from Aspergillus niger are used in cold sterilization. Other enzymes include lipases, cellulases, invertases, and pectinases of great industrial importance [23].
As Model Research Organisms and Designing of Vectors
The usage of yeast as vectors is widely exploited in genetic engineering for desirable gene expression in both prokaryotic and eukaryotic systems. Examples for yeast vectors are YAC, YRP, YIP, YEP, etc [24]. Fungi serve as an important model for research as they are simple eukaryotic organisms that can produce and modify proteins as human cells do and help to discover human gene analogs. Yeasts can be grown as easily as bacteria using simple culture media, and with advances in modern genetics, yeast has become an important and much better organism that can be applied in recombinant DNA technology experiments. Examples include many genes that originated from Saccharomyces cerevisiae and Neurospora crassa (Fig. 11) [25, 26].
Fig. (11))Neurospora crassa (source: en.wikipedia.org).IMPORTANCE OF FUNGI IN AGRICULTURE AND ENVIRONMENT
As Plant Growth Promoters and Disease Suppressor
The root colonizing nonpathogenic fungi are generally called plant growth-promoting fungi. They are involved in both promoting growths of plants by producing high-value products like mycoprotein as well as plant protection as they can suppress the disease in a plant by triggering induced systemic resistance. These Fungal pathogens are capable of producing many root fibers and thus increase the maximum uptake of nutrients and water for high yield. For example, Trichoderma viridae (Fig. 12) and Fusarium were found to increase the number of root fibers in maize and tomato plants. Penicillium and Phoma are examples of other common plant growth-promoting fungi [27-29].
Fig. (12))Trichoderma viridae (https://www.sciencephoto.com/media/843835/view/trichoderma-viride-fungus-light-micrograph).As Biofertilizer
The symbiotic association between fungi and plants is called the mycorrhizal association (Fig. 13). The fungi help in the absorption of the inorganic nutrients such as phosphor, nitrogen, and sulfur from the soil which is then used by plants. Also, these fungal filaments increase the surface area for absorption of other mineral nutrients such as zinc and copper. Hence, mycorrhiza can be used as biofertilizers. For example, the fungi belonging to the genus Glomus form mycorrhiza with the roots of the plants [30].
Fig. (13)) Mycorrhizal relationship between fungi and plant roots (Image source: 1. https://fungi.com/blogs/articles/get-associated-with-mycorrhizae 2. https://fifthseasongardening.com/the-fungal-internet-mycorrhizal-fungi-more 3. Claroideoglomus etunicatum (W.N. Becker & Gerd) C. Walker & A. Schüßler 2010 (MUCL 47650) in vitro culture).The mycorrhizae show specificity in making mycorrhizal association with plants through which they help by providing nutrition (phosphate absorption) and protection (by forming the covering over the roots). The species Septagloeum gillis, Colletotrichum gloeosporiordes, and Wallrothiella arecuthobii target Mistletoes. Phyllosticta (Glycosmis), Leptosphaerulina trifolia (Passiflora), Puccinia chondrillina (Rush weed), Cercospora ageratinae (Pamakani weed) are some examples of the fungi and their specific target [31].
As Biopesticides
Some pathogenic fungi become parasites of pathogens such as bacteria or other fungi that compete for nutrients and space with and specifically attack the damaging pests leaving the animals or plants uninfected. They also act as a biological pesticide and help control the population of damaging pests. These fungi are known as Entomopathogenic fungi (Fig. 14) and are useful in eliminating harmful disease-causing pathogens such as insects, mites, weeds, nematodes, and other fungi without using the hazardous chemical pesticide. For example, Beauveria bassiana, a pathogenic fungus, was found to control the emerald ash borer that attacks ash trees whose wood is used for making furniture and flooring. Other fungi that are involved in the biological control of various pests are Verticillum lecanii, Metarhizium anisopliae, different species of Paecilomyces [32, 33].
As Agents in Bioconversion and Degradation
Fungi are excellent organisms with multiple natural capabilities that make them useful in a wide variety of industrial purposes. Fungi such as Trametes versicolor, Polyporus ance, Poria monticola, Lenzitis trabea (Fig. 15) are used in the degradation of lignin to useful low molecular weight Petroleum products and to soften wood in paper industries.
They are also involved in the biodegradation of pesticides and some of the toxic chemicals like benzopyrene, cyanides, azides, petroleum, and dioxin, etc [34, 35].
Fig. (14)) i. Green peach aphid, Myzus persicae, killed by the fungus Pandora neoaphidis (Image source: en.wikipedia.org), ii. Western tarnished plant bug (Lygus hesperus) killed by the entomopathogenic fungus, Beauveria bassiana (Photo by Surendra Dara) Image source: Sumanth S.R. Dara, Suchitra S. Dara, Alap Sahoo, Haripriya Bellam, and Surendra K. Dara (2014). Can entomopathogenic fungus Beauveria bassiana be used for pest management when fungicides are used for disease management? E-journal of entomology and biologicals. https://ucanr.edu/blogs/blogcore/postdetail.cfm?postnum=15671, iii. Ant infected by an entomopathogenic fungus (Image source: sciencesource.com). Fig. (15)) i. Trametes versicolor, ii. Polyporus tuberaster, iii. Polyporus varius, iv.Lenzitis trabea (source: en.wikipedia.org).Fungal cellulases derived from Fusarium, Penicillium, Trichoderma are involved in the degradation of agricultural residues, forest residues otherwise deposited in the soil. Peroxidase enzymes of Penicillium, Crysosporium, and Streptomyces species have the potential to biodegrade Amaranth dye and heterocyclic dyes. Pleurotus ostreatus (Fig. 16) is capable of degrading several hazardous nitro explosives, including Nitrobenzene, 4-Nitrophenol, 4-Nitroaniline, 1-Methoxy 4 nitrobenzene, 2-Methoxy 4-nitro phenol, 1, 2, di Methoxy 4 nitrobenzene, etc [35, 36].
Fig. (16)) i. Pleurotus ostreatus, ii. Crysosporium (source: en.wikipedia.org).Other Ecological Uses
The fungi are also involved in the Biomineralization of Heavy Metals from wastewater and industrial effluents. For example, the mycelial beads of Penicillium like mercury, copper, nickel, lead, and cadmium [37, 38].
CONCLUSION
Fungi have the diverse potential of great economic importance. They are well known for their usage in nutrition processes to improve poor diet on a large scale and are a major component of the global economy. They play the most important role in human health as the fungal products are capable of treating infections and serious diseases. The fungal enzymes have been exploited for their biochemical and catalytic properties. Further, fungi are extremely useful in the degradation of explosives and hydrocarbons in the environment. They are proved to be biofertilizers and biopesticides, thus help in maintaining the ecological balance in the environment and improve crop production in agriculture. Even more, the fungi find its tremendous usage in Recombinant DNA technology, thus increasing the market for microbial enzymes. Fungi, thus found to be amazing organisms provided by nature to mankind and the ecosystem due to their versatile usage in human life as well as to the environment.
CONSENT FOR PUBLICATION
Not applicable.
CONFLICT OF INTEREST
The author declares no conflict of interest, financial or otherwise.
ACKNOWLEDGEMENT
Declared none.
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S. Vanitha1,*,A. Sai Padma1Abstract
Soil health or soil quality is governed by a continuous, functional interplay between the soil and its microbiota, plants and animals. Soil quality is crucial for sustainable agriculture production and for nurturing the health of all living organisms. It is therefore in the best interest of society to prioritize sustainable soil management practices for future generations. Microbes play a vital role in maintaining ecosystems by coordinating with plants to facilitate nutrient and organic matter cycling. A consortium of fungi plays a critical role in degrading and transforming dead organic matter into suitable forms that can be reused by other organisms. As ecosystem regulators, fungi enhance the structure of soil formation and regulate physiological processes within the soil, making it a supportive habitat for other living organisms. They also help in controlling plant diseases and pest infestations by acting as biocontrol agents. Understanding the roles of fungi and soil enzymes in the earth’s biogeochemical cycles can facilitate improved agricultural productivity and sustainability. For example, increasing the diversity of beneficial fungi in a habitat improves soil fertility, supporting sustainable production of plant based products while mitigating the application of undesirable chemicals as pest control agents.
INTRODUCTION
Sustainable agriculture production is dependent on soil quality and health. Soil is fragile, finite and precious, which is why it is necessary to raise awareness with special attention for its protection, both by its users and consumers. Soil fertility is the ability of soil to assist plant growth with a fruitful outcome in terms of sustainable and measurable yields with improved quality [1].
Processes Contributing to Soil Fertility
Healthy soil supports healthy food production. The majority of diversified microbial species have the potential to cleave a variety of bonds in chemicals. This reflects their ability to govern the important soil properties and functions [2].
A sequence of processes involving continuous cycling between the organic and inorganic forms of nutrients helps in the development of sustainable, healthy, and fertile soil. This involves a network of processes including mineralization, immobilization and cation exchange:
Mineralization- Decomposition of plant debris and animal wastes by microbes liberates nutrients into the soil in its inorganic form by a process called mineralization.Immobilization- Microorganisms transform these available micronutrients like phosphorus, nitrogen or potassium by associating with the microbial biomass through a mechanism often referred to as immobilization.The existence of an equilibrium between the above two processes depends on the accessibility and balanced availability of the major nutrients along with the soil carbon in its organic form to the microorganisms [3, 4].Occurrence of natural unwelcomed phenomena like lightning strikes allows fixation of atmospheric nitrogen in its nitrite form. Sometimes, the presence of denitrifying bacteria under anaerobic conditions like flooding can reduce these nitrogen derivatives.Cation exchange- Micronutrients that are cations like potassium can form electrostatic bonds with the negatively charged components in the soil.Our planet is a diverse habitat for living organisms and is associated with an intricate food web, facilitated by healthy soil. Healthy soil is comprised of living and non-living matter. The living matter is characterized by rich and abundant microbiota, and the non- living counterparts consisting of organic nutrients. Healthy, fertile soils are resistant to outbreaks of soil-borne infestation [5]. For example fertile soil has reduced and prevented the damage caused by pests as observed in maize stem borers [6], and healthy soil enriched with organic matter can enhance crop productivity.
Healthy soil does not contaminate our environment; rather, it alleviates changes in climate. Growing plants on healthy soil can remove atmospheric carbon dioxide; that is, it reduces greenhouse gas emissions and keeps the carbon underground. Also, healthy soil absorbs and stores water underground that could prevent flooding. The development of healthy soil is dependent on soil structure. It regulates water holding capacity and root depth. Plants uptake nutrients in a water-soluble form and follow biological, chemical, and physical processes for nutrient modifications and exchange it with nature. Plants with the help of microbes like bacteria and fungi acquire their essential nutrients from the soil, like fixing atmospheric nitrogen through root nodules in leguminous plants and mycorrhizae, a symbiotic association between fungi and plant roots.
To keep the soil as a healthy living system and thereby enhancing crop production, factors like improved soil structure with better nutrient and water holding capacity, a symbiotic association of microbes with plant roots to recycle nutrients, the existence of various communities of microbiota to reduce soil-borne infections plays a vital role [7].
Soil Microbiota
About 2-4 billion years ago, ancient microorganisms must have developed within Earth’s oceans. They utilized atmospheric nitrogen, increased in number and slowly liberated oxygen [8, 9]. This new environment was a starting material for more diversified microorganisms to grow and develop [10, 11]. These principal investors are now the key contributors in the construction of soil structures, which make them a healthy and fertile resource for other living organisms. Soil is a reservoir of microorganisms like bacteria, actinomycetes, fungi, algae and protozoa and their functions have a direct effect on the properties and functions of soil [12].
Among all the microbes, fungi are also plentiful in soil. Some of them are beneficial as they have a symbiotic relation with plants and are helpful in soil health. Organic materials in soils are utilized by fungi for their nutrition and growth. Fungi can grow in extreme conditions like acidic regions, dry and arid soils and also places that are high in moisture [13].
Etymology
Fungi are a member of the eukaryotic organisms that include both microscopic yeast and molds and macroscopic structures like mushrooms [14]. A fungus or Eumycota in Greek (eu means true and mykes- fungus) [15] has been directly adopted from the Latin word meaning Mushroom [16]. A characteristic that differentiates fungi from other organisms is the presence of glucan and chitin in their cell wall [17, 18]. As heterotrophs, they have absorptive nutrition. They absorb dissolved nutrients by secreting extracellular digestive enzymes into the environment, and this is caused by the absence of chlorophyll. They are spore-forming organisms and have both sexual and asexual types of reproduction. They are of special interest as they are principal decomposers in different ecosystems. A scientist working on fungi is a mycologist and the discipline of biology involving fungi is called mycology. Study on fungal toxins and their effects is called mycotoxicology, and fungal diseases in animals are often referred to as mycoses.
Diversity
The distribution of fungi is worldwide growing in wide extreme habitats like deserts and places with high salinity [19], in the presence of powerful ionizing radiation [20], as well as in ocean depth sediments [21]. It has been studied that fungi exist in UV and cosmic ray exposure, especially during travel to space [22]. In terrestrial habitats, most of the fungi are able to grow and still, several species are able to thrive in aquatic habitats, even in oceans at hydrothermal vents [23].
Taxonomists proposed the existence of 120,000 fungal species, but complete worldwide distribution has not yet been elucidated [24]. However, a 2017 study estimated that there may be 2.2 to 3.8 million fungal species [25]. The key criteria to classify fungi were based on morphological [26], biochemical and physiological characteristics. With the latest tools and techniques like DNA sequencing and phylogenetic analysis, the classification of fungi based on their genetic diversity has given more clarity within taxa [27].
Fungi is an extensive group of microorganisms that are abundant, as unnoticeable small structures with their enigmatic behavior on soil and dead matter. They also take part in the organic material decomposition and its exchange and cycling of nutrients with the environment. Presently, few fungal species are investigated as potential biological control agents that act as pesticides to manage weeds to address the issues of diseases in plants and insect pests.
Fungal enzymes
Mycobiota and their adaptable characteristics play a vital role in soil health. When compared globally, one-third of the fungal population exists in India. Fungi can populate, proliferate and prolong their growth in different habitats like soil, air, water, waste, etc. this territory extends from the tropics to the poles and from the tops of mountains to the depths of oceans. The Fungal kingdom includes 1.5 million species, out of which 74,000 species are classified and named [28]. Major factors contributing to the global distribution of fungi include climatic conditions, geographic location, micro habitat, fauna and flora of an area, and availability of nutrients.
Intense new farming procedures and few human activities may contribute to the emergence of drawbacks like depletion of soil fertility, eroding of soil, contamination of groundwater which directly damage the soil health. So, it becomes essential to evaluate the quality of soil at regular time intervals to monitor the changes happening and identify possible solutions at the earliest to save and protect our soil for future generations.
One of the major parameters that can be used to evaluate the quality of soil health is the assessment of soil enzyme activities. Life processes on soil are dependent on biocatalysts, namely enzymes that are macromolecular in nature. Some of the notable soil enzymes are oxidoreductases, hydrolases, isomerases, lyases, and ligases. Together all these main classes of enzymes play a fundamental role in many biochemical and biological activities in soil in balancing and maintaining soil health at its optimum.
Lignocellulolytic enzymes are categorized as hydrolytic and oxidative enzymes. Hydrolytic enzymes include the cellulases that are of three types, namely endoglucanases (that acts on cellulose amorphous regions), exoglucanase (act on cellulose directly) and glucosidase (acts on cellobiose). Another group in hydrolytic enzymes are the hemicellulases that are xylanases (xylan substrate), mannase (mannan) and arabinase (Arabinan). Oxidative enzymes include the ligninases that are further divided into two types, namely phenol oxidase (Laccase acts on polyphenolic compounds) and peroxidase (lignin peroxidase, manganese peroxidase, versatile peroxidase, and dye decolourizing peroxidase) (Table 1).
