LU11 microbes in soil environment, roles of microbes in recycling Flashcards
5 Microbes in soil
Ba,Ac-G,Fu,Pr,Al-Cy
- Bacteria - most numerous.
- Actinomycetes – filamentous growth (produces antibiotics).
– Odour of soil – geosmin, a gaseous substance produced by actinomycetes. - Fungi – in smaller numbers.
- Protozoa – plentiful (become dormant as cysts).
- Algae and cyanobacteria – photosynthetic (mostly on soil surface).
The Nitrogen Cycle
- Molecular N2 makes up almost 80 % of earth atmosphere.
- N2 must be fixed (combined ) with other elements for it be in usable forms.
- The resulting compounds such as nitrate ion and ammonium ions are theused by autotrophic organisms.
- In general, nitrogen in the atmosphere goes through fixation, nitrification and denitrification.
Microbial pathogens in Soil
Some microbes are insect pathogens.
- Example: Bacillus thurengiensis- a soil
bacterium that is pathogenic to
larvae of insects.
– It produces intracellular crystals of toxic
glycoproteins when it sporulate.
– Commercial preparation – spray on
plants; when insect ingest toxin will
quickly cause paralysis of insect’s gut,
widely used in insect’s control. - Example: Bacillus thuringiensis
The diamond-shaped crystal
shown next to the endospore is
toxic to insects that ingest it.
The Carbon Cycles
* All organic compounds contain carbon.
- All organic compounds contain carbon.
- CO2 is fixed into organic compounds by photoautotrophs.
- These organic compound provides nutrients for chemoheterotrophs.
- Chemoheterotrophs release CO2 that is then used by photoautotrophs.
- Carbon atom transferred from one organism to another in food chain.
- When organism die, the organic compounds are decomposed by microbes.
Microorganisms and Biogeochemical Cycles
* In biogeochemical cycles, certain chemical elements are recycled.
Microbes are essential to continue geochemical cycles:
1. Sulphur Cycle – the bacteria Thiobacillus, Beggiatoa, Thiothrix are involved in sulphur oxidation, Desulfovibrio in sulphate reduction.
2. The Carbon Cycles.
3. The Nitrogen Cycle.
- Microbes are also involved in transformation of other elements including potassium, iron, manganese, mercury, zinc and selenium.
– make minerals avail in soluble forms for plants
4 Microbial pathogens in Soil
C.t-c.b,H,V,F
- Soil – not a reservoir for human pathogens except for some spore-forming bacteria and helminths.
–Clostridium tetani (causes tetanus) and C. botulinum (causes botulinum)
are all endospore-forming pathogens. - Hookworm –spend half of life in soil.
- Viruses – causes plant diseases; penetrate plant cell wall by sap-feeding insects
- Most plant pathogens (fungi) are found in soil.
The Nitrogen Cycle - Ammonification
microbes decompose dead cells and release..
- Microbes decompose dead cells and release amino acids. [microbial decomposition]
- The amino groups of the amino acids are removed and converted into Ammonia (NH3
) [microbial ammonification] - The release of ammonia is called ammonification.
The Nitrogen Cycle - Nitrification
ammonia is oxidized to…
- Ammonia is oxidized to nitrates for energy by nitrifying bacteria.
NH4 (Ammonium ion) –> NO2- (Nitrite Ion) [nitrosomonas]
NO2 (Nitrite Ion) –> NO3- (Nitrate ion) [nitrobacter]
The Nitrogen Cycle - Denitrification
reduce nitrates to…
- Denitrifying bacteria reduce nitrates to molecular nitrogen (N2) which is release to the atmosphere as nitrogen gas.
NO3- (Nitrate Ion) –> N2 (Nitrogen gas)
NO3-(Nitrate Ion) –> NO2- (Nitrite Ion) –> N2O (Nitrous oxide) –> N2 (Nitrogen gas)
The Nitrogen Cycle - Nitrogen Fixation
N2 converted into NH3 by nitrogen-fixing bacteria
- N2 converted into ammonia by nitrogen-fixing bacteria (Rhizobium, Frankia, Azotobacter).
Nitrogen gas (N2) –> Ammonia (NH3) [nitrogen fixation] - Ammonium and nitrate are used by bacteria and plants to synthesize amino acid, then to proteins.
- Symbiotic fungi mycorrhizae (ecto and endo) live in and on plant roots ; increase surface area and nutrient absorption.
– eg: Ectomycorrhiza: The mycelial mantle of a typical ectomycorrhiza fungus surrounding a eucalyptus tree root. - Mycorrhizae infection influences
the growth of many plants. The
pine seedling on the left was
inoculated with mycorrhizae; the
seedling on the right was not. - Truffles. An ectomycorrhiza,
usually of oak trees.
Degradation of synthetic chemicals in the soils
- Many synthetic chemicals such as pesticides and plastic are recalcitrant.
– DDT (insecticide) – accumulate and concentrate in parts of food chain.
– Eagles and other birds accumulated DDT, causing suffered impaired reproductive ability (soft shells and break during incubation). - These xenobiotics are resistant to degradation.
- Leaching of toxic chemicals is also a problem.
- However, organic matters are easily degraded by microbes that promotes degradation or removal of these toxic chemicals.
- Bioremediation - use of microbes to detoxify or degrade pollutants; enhanced by nitrogen and phosphorus fertilizer.
- Bioaugmentation - addition of specific microbes to degrade a pollutant.
- Composting - arranging organic waste to promote microbial degradation by thermophiles.
Microbes in the Environment - Introduction
,,
- Microorganisms live in a wide variety of habitats.
- Most microorganisms:
–do not cause disease.
– saprophytes: get their nutrient from dead organic matter. - Some parasites get their nutrients from other microbes: Bdellovibrio bacteria prey on other bacteria.
- Some microbes are found living in mutualism.
– Both partners benefit (i.e. lichen).
– Commensals benefit from each other without causing harm (i.e. cellulose degraders). - Co-metabolism – one organism can perform a biochemical process if provided with certain chemicals by another organism.
Soil Microbiology and Cycle of Elements
Components of soil:
- Soil consists of solid inorganic matter, water, air and living organisms and decay products.
- Weathering of rocks adds minerals to soil.
- Source of organic matters- microbes, plants, animals, waste products.
- Humus- partially decomposed organic matter.
- Microbial life depends on water and O2
- Soil microbes decompose organic matter and transform nitrogen and sulfur-compounds into usable forms.
- Typical garden soil – million of bacteria; highest I top few cm and declines
rapidly.
what bacteria involved in Sulphur Cycle
- Thiobacillus, Beggiatoa, Thiothrix - sulphur oxidation
- Desulfovibrio - sulphate reduction.
Bioremediation
Bioremediation - use of microbes to detoxify or degrade pollutants; enhanced by nitrogen and phosphorus fertilizer.
