Fungal Bioremediation

Fundamentals and Applications

Araceli Tomasini Campocosio, Hector Hugo Leon Santiesteban, Araceli Tomasini Campocosio, Hector Hugo Leon Santiesteban

• Éditeur: CRC Press
• Année: 2019
• ISBN:
  9781351795654
• Édition: 1
• Sujet: Physical Sciences
• Sous-sujet: Chemistry

This book highlights the role fungi play in bioremediation, as well as the mechanisms and enzymes involved in this process. It covers the application of bioremediation with fungi in polluted sites and gives a wide overview of the main applications of remediation, such as degradation of xenobiotics, gaseous pollutants, and metal reduction. The book explains the degradation of emergent pollutants and radioactive compounds by fungi, which is relevant to the current pollution problems that have been studied over the last few decades. The book also describes the most advanced techniques and tools that are currently used in this field of study.

PART I

FUNDAMENTALS

CHAPTER-1

The Role of the Filamentous Fungi in Bioremediation

Araceli Tomasini^1,* and H. Hugo León-Santiesteban²

¹ Departamento de Biotecnología, Universidad Autónoma Metropolitana-Iztapalapa, C.P. 09340, Ciudad de Mexico, Mexico.

² Departamento de Energía, Universidad Autónoma Metropolitana-Azcapotzalco, C.P. 02200, Ciudad de Mexico, Mexico.

^* Corresponding author: [email protected]

Abstract

The accumulation of hazard compounds, mainly of the anthropogenic origin, into the environment has triggered multiple environmental damages, many of which have directly affected the quality of human life. Bioremediation, which are characterized to use living organisms and/or macromolecules produced by them, has proved to be a successful, an inexpensive, and an environmentally-friendly alternative to eliminate pollutants. Historically, fungi have been highlighted in the field of bioremediation due to the facts that 1) they are the chief microorganisms responsible for degrading the organic matter in the environment, 2) they own an unique ability to remove pollutants by uptake phenomena (biosorption or bioaccumulation), and 3) they produce non-specific intracellular and extracellular enzymes with high catalytic capacity to transform pollutants to either less toxic or innocuous compounds; although, sometimes more toxic compounds than the original may be formed.

In this chapter is presented an overview of the role of fungi in the bioremediation. It briefly describes the different mechanisms used by fungi to remove pollutants, and the potential of fungi to act as bioremediation agents is exemplified.

1. Introduction

Environmental pollutants are a serious problem worldwide. They damage the ecosystems and all forms of life. Examples abound, such as climate change, diseases, and in some cases, mutagenic alterations that can lead to the death of organisms, just to name a few.

Pollution problems are increasing due to the rising human population and their anthropogenic activities. Compounds that cause pollution of the environment are increasing in quantity and diversity because of the lifestyle of this century that constantly demands new products and evolving technology. There are many toxic compounds used as pesticides, biocides, or as energy sources. Others are not toxic, but their accumulation in the environment is so high, that they can also cause pollution.

Given this problem, many studies have aimed at diminishing the toxic compounds present in the environment, either in the soil, water, or air. Physical, chemical, and biological processes have been proposed to remove the toxic compounds. All of them present advantages and disadvantages and their application depends on the type and concentration of pollutants and the site where they are present: soil, water, or air.

Biological processes involve organisms or biological activity to degrade or remove the pollutants; this is known as bioremediation. This chapter will describe the fundaments of bioremediation by fungi, deal with how they can remove toxic compounds, and provide some examples.

2. Bioremediation

Many definitions are given for bioremediation. One of the most accepted is: “bioremediation is a process to clean a polluted site using organisms as plants, algae, bacteria, and fungi” (Vidali 2001). Another definition used by many authors is the following: “bioremediation is a biological process to degrade or remove environmental contaminants from a polluted site, water, soil, and air, using organisms or biological activity as plants, algae, bacteria, fungi, and enzymes”.

The principal advantage of bioremediation compared to physical and chemical processes is the cost. In general, it is lower than the physical and chemical processes, besides that it is a process that does not produce more contaminants. The disadvantages are that the bioremediation process takes more time than physical or chemical processes. The second one is that the site to be cleaned must have the right conditions for the growth and development of organisms that carry out the processes of removal or degradation of the contaminants.

Bioremediation includes two mechanisms to diminish the polluted compounds, through degradation involving the chemical modification of the molecules, and removal, which is a sorption process of the polluting molecules. Removal of toxic compounds is accomplished through a sorption process, the compounds are absorbed by a substrate; in this case, a biological substrate, biomass, or agriculture waste that can be used wet or dry. Biodegradation involves a chemical change of the molecule to produce other compounds, generally less toxic, and the live organisms or their enzymatic system are responsible for the compound’s degradation.

Bioremediation involves different organisms. When plants are responsible for the remediation it is called phytoremediation. This process is one of the most economic ones, but it takes more time to be accomplished.

Bacteria, fungi, and algae can also be responsible for bioremediation; the efficiency depends on the type of compounds, the initial concentration of the toxic compounds, the site to be cleaned, and the microorganism to be used. In many cases, high efficiency is obtained using a microbial consortium containing a wide diversity of microorganisms, including different types of bacteria, fungi, and microalgae.

This chapter is focused on studying the role of filamentous fungi in bioremediation processes; the role of other organisms, such as plants, bacteria, and algae are not discussed, but it is important to know that bioremediation could also be using some of these organisms.

3. Filamentous Fungi

Fungi are eukaryotic and heterotrophic organisms that include unicellular and pluricellular fungi. The unicellular are yeasts, and the pluricellular are represented by all types of filamentous fungi, called as such due to their way of growth. Yeast are anaerobes and aerobes, and filamentous fungi are exclusively aerobes. This chapter will deal only with filamentous fungi.

They develop a tubular structure named hypha, the hyphae form the mycelium, fungi can reproduce by sexual or asexual spores, and by vegetative means from a mycelium segment. There are many types of filamentous fungi; they exist in terrestrial and aquatic habitats.

These fungi can grow as saprotrophs, which obtain their nutrients from dead organisms. They can grow also in symbiosis, which means a common life between two organisms including parasitism and mutualism. Parasitism is when only one of the organisms benefits and mutualism when both organisms are benefited; for example, mycorrhizae (mutualism with roots of plants) or lichens (mutualisms with algae) (Carlile et al. 2001).

They can grow in soil producing many hyphae that spread profusely all over the ground; despite fungi being microscopic, hyphae of Armillaria ostoyae can reach a spread rate of 1 m year⁻¹ (Peet et al. 1996). Armillaria bulbosa, a filamentous fungus type, has been reported as one of the largest and oldest-living organisms (Smith et al. 1992).

Some fungi are pathogenic agents of plants and they are responsible for the loss of agricultural products, which are an important food source. However, many other filamentous fungi are used to produce secondary metabolites, such as antibiotics, immunosuppressors, anticholesterolemics, etc. (Barrios-Gonzalez et al. 2003). An important role to note is that fungi are the primary organisms responsible for degrading organic matter in nature.

Filamentous fungi grow in soil, and many of them degrade organic compounds present in dead organisms, both animal and vegetal. Organic matter is converted into small molecules that can be used by other organisms as a source of energy, carbon, and nitrogen. The ability of fungi to degrade organic compounds has been exceeded by the large number of organic compounds present in the soil due to the increase of human populations in our planet. This ability has also been affected by the presence of toxic compounds, such as xenobiotics. These last compounds are not present in nature, but they are produced by humans for specific uses, such as pesticides, biocides, or are the result of waste or byproducts from industrial processes.

Bioremediation by fungi is an alternative process to remove, degrade, or render harmless toxic compounds using natural biological activity. The fungi belonging to the basidiomycetes were the first assayed to degrade toxic compounds, as it was observed that this class of fungi grows on fragments of trees that are lying on the ground in forests, causing their rotting. Depending on the type of rotting that they cause on wood, fungi are called white-, brown-, or bland-rot fungi. These fungi have a common characteristic, the production of an enzymatic system able to degrad...