soil enzyme, its mechanism in soil ,soil microbes,type of enzyme etc,microbial enzyme reaction,enzyme activities affected soil microbes etc

12. Soil Enzymes: 1. Introduction
• First enzyme isolated was urease in 1923 by
Sumner
• Now about 2,000 have been isolated and 25
have 3 dimensional structure determined.

14. V. Soil Enzymes
• Importance of Soil Enzymes
» 1. Release of nutrients to the environment
e.g. urease breaks down urea to NH3
which is a plant nutrient.
» 2. Identification of soils
» 3. Indication of microbial activity
» 4. Sensitive indicator of ecological changes.

15. D. State of Enzyme in Soil
• Soil enzymes are very persistent i.e. very stable. Has
been found to persist for 1000 yrs.
• e.g. Urease and Phosphatase have been
demonstrated to be 9,000 yrs old in permafrost in
Alaska. Phosphatase and Catalase between 4,000
and 10,000 yrs old have been observed in old lake
sediments in Romania.
• Very resistant to destruction

16. E. Theories of Enzyme Stability in Soils.
• Several theories have been suggested for the stability
of soil enzymes in soils. Several of the mechanisms
suggested involve the interaction of enzyme protein
with clay minerals, organic matter and clay organic-
matter complexes.
• 1. Role of Clays:
• a. Most activity associated with clay fraction of
soil.

17. D. Theories of Enzyme Stability in Soils
» b. Adsorption of proteins readily occurs.
» c. Are more resistant to proteolysis and
microbial attack
» d. Increases inactivation temperature by
10oC

18. D. Theories of Enzyme Stability in Soils
• 2. Role of Organic Matter:
• Much of the information dealing with this
hypothesis has been derived from studies with
synthetic polymer enzyme complexes. Traps
protein molecule in tertiary structure thus
stabilizing the protein.
» a. Humus material known to stabilized to
soil-N compounds e.g. protein.

19. D. Theories of Enzyme Stability in Soils
» b. Enzyme attached to insoluble organic
matrices exhibit resistance to pH and
temperature changes, specificity change, like
soil enzyme.
» c. Protected by globular humus complexes.
» d. Inability to purify soil enzymes free of soil
organic matter.

20. D. Theories of Enzyme Stability in Soils
• 3. Role of Organic Matter-Clay
Complexes:
» a. Lignin plus bentonite (clay) protect
enzyme against proteolytic attack but not
bentonite alone.
» b. Enzyme bound to organic matter which
is bound to clay.

21. G. Application of Soil Enzyme Assays
• 1. Correlation with soil fertility.
• Difficult to show correlation especially fertility
with enzyme activity.
• 2. Use to correlate microbial activity.
• Used as index of soil microbial population
• Enzyme which correlated best 3, amides,
peroxidase and alkaline phosphatase.

22. G. Application of Soil Enzyme Assays
• 3. Correlate with biochemical cycling of various
elements in soil (C, N , S ).
• has met with only limited success.
• 4. Degree of pollution
• Impact of numerous chemicals on the biological
cycling of elements in soil can also be easily and
sensitively assessed by determining their effect on
soil enzyme activity.
• Nitrification is one of the sensitive assay toward
pollution i.e. sensitive to acidity NH4
+, NO3
-

23. G. Application of Soil Enzyme Assays
• 5. Forensic Purposes
• Can determine where soil comes from by looking at
activity, Km value of sample size.
• 6. To Assess Ecological Succession
• As ecosystem changes the enzyme activity changes
and this is due to O.M. changes.
• 7. Degradation of Herbicides? e.g. Enhance
herbicide degradation.