1) Organic compounds can be divided into four groups based on their biodegradability by microorganisms: compounds that can be used immediately, those that require acclimation, those that are degraded slowly or not at all, and those subject to cometabolic degradation. 2) Compounds in the first group include simple sugars, amino acids, and fatty acids and can be immediately metabolized. Compounds in the second group require a lag period for acclimation and selection of specialized microorganism species and induction of degrading enzymes. 3) The lag period can last from hours to weeks depending on the compound, microorganism, and environment. Once acclimation occurs, degradation rates increase

1. Biodegradation Reactions
For any one microorganism, organic compounds can
be divided into three groups according to their
biodegradability
1) Usable immediately as energy and nutrient source
2) Usable following acclimation by m.o.
3) Degraded slowly or not at all
4) Some believe existence of another group of
compound that are subject to co metabolic
degradation.

2. • First group includes
– Simple sugars
– Amino acids
– Fatty acids
– Other compounds
Enzymes needed for the metabolism are
constitutive or immediately inducible requiring
minimum acclimation.

3. • Second group- requires acclimation.
– A lag period occurs during which little or no
degradation takes place.
– Lag period or delay occurs because of following
processes which are interrelated…
A) Selection of spp. : This causes lag in response to
the initial phase of exponential growth of the
favored org.
B) Adaptation of existing m.o. through induction
of enzymes that catalyze degradation.

4. • Lag period is variable (hrs/days/weeks) depending on
chemical, organism, environmental condition.
• eg pyrazon degradation in garden soil :
– lag of 50 days has been reported.
• Once acclimation is achieved….
- population(active) has increased
- orgs have got adapted
- degradation rates increase rapidly associated with
primary alteration of the compound.

5. • Intense activity is followed by slower activity
associated with digestion of intermediates
formed.
• Primary population increases at first, then
levels off, and then gradually declines.
(once the substrate disappears or converted to
non metabolizable products or mineralized)

6. Lag(acclimation)
Intense activity
% Residual
slower rates.
Time

7. • Disappearance curve of the parent compound
can follow one of the several curves
depending on the kinetics of the reaction.
• First order, Second order, Mixed order, exponential,
linear etc

8. • Third group of compounds include
Naturally occurring compounds like..
- Humus, Lignin
Anthropogenic compounds like..
- Pesticides, PAHs, PCBs, Dyes
Degradation of these compounds does not take
place or takes place extremely slowly.
Compounds are not degradable or not easily
accessible.

9. • Cometabolism :
– Certain degradation reactions are cometabolic.
– Compd. doesn't serve as C or E source.
– Compd. resembles structurally to the natural
substrate of enzyme(s).