The document discusses microbe-microbe interactions and classifies them into positive and negative interactions, emphasizing their significance in ecosystems. It details two types of positive interactions: commensalism, where one species benefits while the other is unaffected, and synergism, where both populations benefit and rely on each other for survival. Examples of these interactions highlight their role in nutrient cycling and metabolic cooperation among microorganisms.

1. DEPARTMENT OF MICROBIOLOGY
SUBJECT: ENVIRONMENTAL MICROBIOLOGY
VIVEKANANDHA ARTS AND SCIENCE
COLLEGE FOR WOMEN
Veerachipalayam-637 303, Sankagiri, Salem Dt.,Tamil Nadu India.
Affiliated to Periyar University, Salem; Recognised Under Section 2(f) & 12(B) of the UGC Act,1956)
SUBJECT INCHARGE: SUBMITTED BY:
Dr. R. Mythili, Kaviya .A.R
Assistant professor, III. B.Sc., Microbiology,
Department of Microbiology Department of Microbiology,
VIAAS, Sankagiri. VIAAS, Sankagiri

2. MICROBE –MICROBE
INTERACTIONS

3. TYPES OF INTERACTIONS:
• Organisms don not exist alone in nature but in
a matrix of organisms of many species.
• When one or more types of organisms
reciprocate each others effect, it is calles interaction.
• Interactions are broadly classified based on
their effects on each other as positive interaction and
negative interactions.

4. POSITIVE INTERACTIONS:
NAME OF INTERACTIONS EFFECT OF
INTERACTIONS
POPULATION I POPULATION II
 Neutralism
0 0
 Commensalism
0 +
 Synergism
+ +

5. NEGATIVE INTERACTIONS:
NAME OF INTERACTIONS EFFECTS
OF INTERACTIONS
POPULATION I POPULATIO II
 Amensalism
0/ + -
 Competition
+ -
 Parasitism
+ -

6. Lets we see the positive interactions commensalism and synergism

7. COMMENSALISM:
• Commensalism defines the interaction in which two or
more population benefits and the other one is unaffected.
• It is a unidirectional relationship between populations.
• These kinds of interactions are quite common and they
occur when the uaffected population modifies the habitat in such a way
that a second population benefits,
• e.g, the removal of oxygen from a habitat, as a result of the
metabolic activities of a population facultatibe anaerobes, creates an
environment that is favourable for the growth of obligately anaerobic
populations.

8. Commensalism is exhibited in a number of ways
Production of growth factor :
 flavobacterium brevis excretes cysteine which is taken
up by legionella pneumophila.
Transformation of insoluble compounds to soluble one and further
into gaseous componets:
 Methane from sediment benefits methane oxidising
population in the overlying water .
 Hydrogen sulphide production in buried sediments
which helps the photo-autotrophic sulphur bacteria on the
sediment surface.

9. Conversion of organic molecules :
o convert organic molecules which become substrates for
other population is also commonly seen.
o e.g fungi release extracellular enzyme which decomposes
lignin to form simple glucose moieties which benefit the other
microorganisms.
Metabolic needs:
o Mycobacterium vaccae, growing on propane as a source of
carbon and energy , that oxidise cyclohexane to cyclohexanone which is
readily used up by other microorganisms like pseudomonas.
Neutralisation of a toxic material :
o oxidation of hydrogen sulphide by Beggiatoa and
benefited by the hydrogen sulphide sensitive aerobic organism .

10. SYNERGISM:
 synergism between two population
indicates that both populations benefits from the
relationship but the association is obligatory.
 Both populations are capable of surviving
independently, although they both gain advantage from
the synergistic relationship.
 Supply each other’s nutritional needs.

11. Synergism exhibited in a number of ways:
Convert amino acids:
 Arginine is converted to putrescience by E.coli
and Enterococcus faecalis both working together. E.faecalis can
convert arginine into ornithine and e.coli further converts
ornithine to putrescience,
 A task which cannot be performed by either of
the organisms alone.
 Both organisms allow the completion of a
metabolic pathway that otherwise would not be completed.

12. Suppy of growth factors :
 Suppy of growth factors by one population to
another.
Example,
 Nocardia and pseudomonas together can
degrade cyclohexane wherein Nocardia acts on cyclohexane
and supplies metabolic products to pseudomonas and in turn
the bacterium supplies biotin to nocardia.
 Lactobacillus arabinosus and Streptococcus
faecalis based on the mutual exchange of required growth
factors. L.arabinosus requires phenylalanine for growth, which is
produced by S.faecalis which is turn requires folic acid
produced by L.arabinosus.

13. Enzyme produced in synergistic relationship:
• The enzyme produced by microorganism that
are not produced by either population alone.
• Pseudomonas strains produce lecithinase
when grown together but not alone.
Degradation of agricultural pesticides:
• Athrobacter and Streptomyces together
degrade organophosphate insecticide diazinon, a task which
they cannot perform alone.
• Penicillium piscarium and geotrichum candidum
which remove toxic factors and produce useful substrates
from insecticides . Both together detoxify the pesticide
propanil.

14. • Penicillium cleaves propanil into propionic acid and 3,4-
dichloroaniline (toxic) ,Which is further detoxified by geotrichum.
Methane production by microorganism:
 Archaeal population involved in methane production
(methanogens) have interestin synergistic relationships with bacterial genera
indicate their syntrophic relationships with hydrogen consuming methanogenic
archaea.
 Syntrophomonas species oxidise butyric acid and caproic acid to
acetate and H2. Syntrophobacter oxidises propionic acid to acetate,co2 and H2 .
The acetate and H2 produced by these bacteria are used by methanogic
archaea to produce methane.
 Thus the metabolism of the methanogens maintains very low
concentrations of H2 thus increasing the growth rates of Syntrophomonas and
Syntrophobacter species.

15. Thank you
KAVIYA .A.R
III.B.sc.,Microbiology
Department of microbiology,
VIAASS, Sankagiri.