1ESC 590.Soil Biota.fungi

7/30/2019 1ESC 590.Soil Biota.fungi

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Soil Biota II

Reading Assignment

Soil Microbiology:An exploratory

ApproachChapter 4, 5,6 & 7


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Fungi-Charcteristics

Fungi are eukaryotes- organisms whosecells have a distinct nucleus containing thegenetic material.

Fungi may be unicellular or multicellular.

True fungi have cells walls composedprimarily of a substance called chitin.

Posses filamentous mycelium net work ofindividual hyphal strands


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Mycelium divided by cross-walls called septa,however many fungi species are non-septate.

The hypae of no-septate fungi arecontinuous and multinucleate andfilaments don't bear cross-walls

Hyphae in fungi is rather broad and has adiameter appreciably greater than that ofactionomycetes.


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Hyphae may be vegetative or fertile, fertilehyphae produce either sexual or asexualpores.

Asexual spores or conidia are widespread innature, the sexual spores are relativelyuncommon

They are differentiated into genera and species on

the basis of morphology. Majority are saprophytes in soil and water.


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Most of them are saprophytes

Vast majority decompose plant materials.

Plate counts not very important

Fungistatis- Inhibition of fungal spores, tend

to be inhibited in soils.


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Fungi-Survival

Conidia- Asexual spores produced at theend of hyphae.

Chlamydospores Thick-walled cells appearing insome genera from preexistingcells in hyphae or from conidia.

Sclerotia They are hard, often largeresting structures often packedwith mycelium.


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Fungi-Taxanomic Groups

Acellular creeping plsamodium, which is ananimal-like but produces fungal-likereproductive structures.

Group is widely distributed in soil,especially associated with decayingvegetation in cool moist sites.

Some develop on herbage and others onanimal dung.


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2. Flagellate Fungi (Mastigomycotina)

a. Oomycetes:Pythium, Plasmopara,Phytophtora.

Produce biflagellate motile cells knownas zoospores

Spores in sexual stage are oospores are

within a sporangium; reproduction bygametangy.

Now classified as chromista.


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3. Sugar Fungi (Zygomycotina)

a. Zygomycetes (Conjugation Fungi) e.g.

Mucor,Rhizopus (common bread mold)

One of the two classes normallyencountered in soils

Usually produce well-developed

mycelium. The sexual resting spores are zygospores.

Most found in water environmental


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Found in soil and decaying plant

Some are opportunistic pathogens

Important economically, individual species are

used for commercial production of alcohols andorganic acid, such as lactic acid, citric and oxalicacid.

Rhizopus nigricans is the common bread mold.

Sexual spores are zygopores which results fromfusion of the nuclei of two cells that aremorphologically similar.


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Function and Ecology

1. Organothrophs, obtain carbon for cellsynthesis from preformed organicmolecules.

Can utilize both simple and complex foodmaterials.

Among carbon sources utilized are

sugars, organic acids, dissacharides,starch, pectin, cellulose, fats and lignin.


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2. Some are predators.

Various protozoa are especially susceptible

to the active species. Nematodes are also entrapped and devoured

frequently by specialized appendages or

hyphal extensions. Potential promise forbiocontrol.


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Among the common nematophagousgenera areArthrobotrys, Dactylaria andHarposporium

No definite function has been establishedfor the predaceous species, however it isbelieved that they may participate in the

microbiological balance in soil, limitingthe size and activity of the protozoan andnematode fauna.


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3. Participate in decomposition of complexorganic matter.

The organic matter transformationsbrought about by filamentous fungi inwell aerated environments often may bemore prominent than the reactions

catalyzed by bacteria.


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4. They utilize proteinaceous substancesand are therefore active in the formationof ammonium and simple nitrogen.

Under certain conditions fungi maycompete with higher plants for nitrate and

ammonium and lead to a decrease insoluble nitrogen content of soil.


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5. They participate in the formation ofhumus from fresh organic matter.Species involved includeAlternaria,

Aspergillus.

6. Several soil borne fungi are pathogenic.Only very small portion of the fungi

growing or surviving in soil isconcerned with plant disease.


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Species involved are generally classifiedin the generaFusarium, Phytopthora,Pythium, Sclerotium etc.

7. They also form unique association withhigher plants in the structure known asmycorrhiza or fungus rot.

8. Fungi also form association with algaeknown as lichens.

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1ESC 590.Soil Biota.fungi