Fungal Ecology and Biotechnology

Fungal Ecology

Ecology

• Ecology is the study of organisms in relation to each other and their environment.
• Fungi play a crucial role in ecosystems as primary agents of decomposition in terrestrial and aquatic environments.
• They are essential for breaking down and recycling cellulose and hemicelluloses.
• Fungi decompose wood, degrade natural and man-made materials, and can cause diseases in plants, animals, and humans.

Coprophilous Fungi

• Coprophilous fungi, or dung-loving fungi, are saprobic fungi that grow on animal dung.
• Succession in fungal communities is best studied on cow dung as a substrate.
• Initially, lower subdivision fungi like Pilobolus (a zygomycete) colonize the dung.
• Later stages are dominated by climax species in Basidiomycetes, such as mushrooms.
• Dung is a valuable source of organic matter, providing a habitat for saprotrophs and a site for studying ecological succession.

Saprotrophic Fungi - Pioneers

• Several species of Mucor, Rhizopus, and other Zygomycota are commonly found in soils or fecal-enriched materials and in the rhizosphere (root zone) of plants.
• These fungi utilize sugars and other simple soluble nutrients.
• Pioneer fungi colonize a substrate first, followed by other fungi.
• Spores of pioneer fungi germinate and grow rapidly in response to soluble nutrients.
• Within a few days, they produce asexual dispersal spores or sexual resting spores.
• Pioneer fungi typically have a short exploitative phase but high competitive ability.
• They usually cannot degrade complex structural polymers like cellulose.

Saprotrophic Fungi and Polymer Degradation

• Sapstain fungi colonize newly felled trees and are typical pioneer saprotrophs; sapstain is a discoloration considered a fault in timber.
• Several fungi have an extended growth phase on major structural polymers like cellulose, hemicelluloses, or chitin.
• When cellulose-rich materials (e.g., cereal straw) are buried in soil, they are colonized by fungi such as Fusarium and Trichoderma spp.
• Chitinous materials are colonized by another group of fungi, such as Mortierella spp. (Zygomycota) in soil or Chytridium confervae (Chytridiomycota) in freshwater habitats.
• Cellophane material buried in soil is colonized by cellulolytic chytrids (e.g., Rhizophlyctis rosea).

Fungi that Degrade Recalcitrant Polymers

• Fungi that degrade more resistant polymers, such as lignocellulose (cellulose complexed with lignin), often predominate in the later stages of decomposition.
• Several of these are Basidiomycota, including Mycena galopus, a common small toadstool in woodland leaf litter, and fairy ring fungi.

Secondary (Opportunistic) Invaders

• At many stages in the decomposition of natural materials, there are opportunities for secondary invaders to grow and feed on the breakdown products released by enzyme action (e.g., Thermomyces lanuginosus).

The Fungal Community of Composts

• A mixture of weak parasites and pioneer saprotrophic fungi are found in the first few days. Many were present on the original material, including leaf-surface fungi (e.g., Cladosporium), with maximum growth at 57–60°C.
• A few thermophilic fungi also grow in the first few days.
• Cellulolytic species of Ascomycota and mitosporic fungi colonize after peak-heating and grow over the next 10–20 days (e.g., Aspergillus fumigatus with max growth at 55°C, or Thermomyces lanuginosus with max growth at 62°C).
• As the temperature falls below 35–40°C, the thermophilic fungi start to decline, though A. fumigatus remains active.
• The compost is then colonized progressively by mesophilic fungi (e.g., Fusarium and Basidiomycota such as Coprinus cinereus, with max. growth at 40°C).
• Coprinus spp. represent the degraders of recalcitrant polymers. They utilize lignocellulose and are highly antagonistic to many other fungi, damaging their hyphae on contact by a process termed hyphal interference.
• At this stage, spores of the commercial mushroom, Agaricus bisporus (edible mushroom), can be introduced into the compost once this has cooled to below 30°C.
• An adequate supply of mineral nutrients is essential for composting and for the decomposition of organic matter in general: carbon-to-nitrogen (C:N ratio of approximately 10 : 1).

Lignocellulose and Biotechnology of Wood-Decay Fungi

• Lignocellulose (cellulose complexed with lignin) is abundant as a byproduct of the wood-processing industries and also in crop residues, presenting potential as a cheap commercial substrate.
• Cellulose can be degraded to sugars, which could be used to produce fuel alcohol by microbial fermentation as an alternative to fossil fuels.
• Phanerochaete chrysosporium (white rot fungus) produces lignin peroxidase to degrade lignin, offering a potential solution to degrade lignin from cellulose.
• Cellulose can be further digested to sugars and used in industries.
• White-rot fungi and their enzyme systems also have potential for bioremediation of land contaminated by aromatic pollutants, and many other processes.