Soil BiotaSoil Biota

Reading AssignmentReading Assignment

Soil Microbiology: Soil Microbiology: An exploratoryAn exploratoryApproachApproach

Chapter 4, 5,6 & 7Chapter 4, 5,6 & 7

Actinomycetes: FeaturesActinomycetes: Features

Belong to the order Actinomycetales Single celled and produced slender,

branched filaments which develop into a mycelium in all soil genera except for the genus Actinomyces.

Actinomycetes: FeaturesActinomycetes: Features

Individual filaments or hyphae are similar to fungal filament but are less broad, usuallyy 0.5 to 1.0 mm in diameter.

Produce single ,pairs or chains of asexaul spores known as conidia on the hyphae .

Few of the soil inhabitants bear their spores in a specialized structure known as a sporangium

Actinomycetes: FeaturesActinomycetes: Features

Usually saprophytes Competitive advantage seems to be in dry

soil, high pH, warm Temperatures and high organic matter

environments. Like Bacillus tend to exist in spores. Have aerial mycelium

Actinomycetes: FeaturesActinomycetes: Features

Have extensive branching Growth in liquid culture merely results in

turbidity.

Common Actinomycetes in SoilCommon Actinomycetes in Soil

1. Streptomyces Long chains of spores formed on filaments

growing above the medium Species very numerous in soil and many

produce antibiotics. Streptomyces are G+ and are oxidative

organotrophs.

Common Actinomycetes in SoilCommon Actinomycetes in Soil

They make up about 90% of the actinomycete isolations from soil.

They produce well developed compact branched mycelium and compact colonies on agar plates.

Mycelium does not divide into segments but gives rise to conidia

Reproduction is by production of aerial spores and by mycelial fragmentation.

Common Actinomycetes in SoilCommon Actinomycetes in Soil

Colonies on agar media tend to be tough and have a leathery consistency, and resist destruction by mechanical force.

They are the causal organisms of of potato scab, S. scabies

Many streptomyces produce antibiotics, variously antibacterial, antifungal, anti-algal or anti-tumor.

Common Actinomycetes in SoilCommon Actinomycetes in Soil

The also produce geosmin which is responsible for the smell of freshly plowed soil.

Chitin hydrolysis is often frequently encountered among many species of Streptomyces

Common Actinomycetes in SoilCommon Actinomycetes in Soil

2. Nocardia Second most abundant, about 10 to 30% They are aerobic and gram-positive. Mesophilic actinomycetes Filaments unstable, fragmenting into

bacteria-like units; filaments do not usually grow above medium and spores are rarely produced.

Common Actinomycetes in SoilCommon Actinomycetes in Soil

The colonies of Nocardia and true bacteria bear a marked resemblance to one another in general features and in consistency.

Some species are well documented for the metabolism of paraffins, phenols, steriods and pyrimidines.

Common Actinomycetes in SoilCommon Actinomycetes in Soil

3. Micromonospora Third most frequently encountered, and

forms less than 1-15% of actinomycetes growing on solid media.

Filaments do not grow above medium; single spores produced in and on surface of medium

Colonies are slow growing in most media

Common Actinomycetes in SoilCommon Actinomycetes in Soil

Each hyphae is between 0.3-0.8 mm in diameter, while the spores are oval to round and are produced at the terminus of the specialized conidiophores.

Micromonospora strains decompose chitin, cellulose, glucoides and hemicelluloses

Common Actinomycetes in SoilCommon Actinomycetes in Soil

4. Thermoactinomyces Very similar to micromonospora Single spores formed on filaments above

and within medium. Spores resistant; all species thermophilic Very common in heating compost heaps

Common Actinomycetes in SoilCommon Actinomycetes in Soil

5. Streptosporangium

Spores formed in sporagia or in chains on the filament above the media

Colony appearance similar to Streptomyces

Activity and FunctionActivity and Function

The develop far more leisurely than most fungi and bacteria.

Not effective competitors and are not prominent when nutrient levels is high and the pressure of competition is great.

Actinomycetes are heterotrophic feeders, and their presence is therefore conditioned by the availability of organic substrates.

Activity and Function Activity and Activity and Function Activity and FunctionFunction

Utilization of carbon sources include simple and highly complex organic molecules from organic acids,and sugars to polysaccharides proteins, lipids and aliphatic hydrocarbons.

Cellulose is decomposed by many species in pure culture, but rate of decomposition is slow.

Many strains have the capacity to synthesize toxic metabolites.

Activity and FunctionActivity and Function

They participate in a number of processes which include

a. Decomposition of certain resistant components of plant and animal tissues. They

are usually effective competitors only when resistant compounds remain

b. Formation of humus through the conversion of plant remains and leaf litter into the types of

compounds native to the soil organic fraction.

Activity and FunctionActivity and Function

c. Transformation at high temperature particularly in the rotting and heating of green

manures, hay, compost piles, and animal manures.

d. Cause of certain soil-borne disease of plants ; for example, potato scab and sweet potato

pox, for which the causal agents are S.scabies and S. ipomoeae, respectively.

Activity and FunctionActivity and Function

e. Cause of infections of humans and animals ; for example, Nocardia asteroides and N otitidis-caviarum..

f. Possible importance in microbial antagonism and in regulating the composition of the soil community. - This role may be a result of the ability of many

actinomycetes to excrete antibiotics or their capacity to produce enzymes that are responsible for lysis of fungi and bacteria.