2. CHEMOTAXIS:
It is a phenomenon in which bacteria & other
microbes moves towards or away from some
chemicals present in the environment
This is very essential for microbes to search the
food around them
There are two types of chemotaxis,
1. positive chemotaxis
2. Negative chemotaxis
3. POSITIVE CHEMOTAXIS:
The movement of microbes towards a chemical
is called positive chemotaxis.eg;food,nutrients
NEGATIVE CHEMOTAXIS:
The movement of microbes away from the
chemical is called negative chemotaxis.eg:toxins
4. RHIZOSPHERE EFFECT
In 1904, Lorenz Hiltner coined the word
rhizosphere.
Rhizosphere is the layer around the
Root which is of 1-2mm thickness having
Secretions ,
He described the rhizosphere effect in which he
explained the predominance of microbial
population in rhizosphere region
5. HISTORY OF CHEMOTAXIS:
The migration of microbes is observed after the
development of microscopy.
The first description is given by
T.W.Engelmann(1881),W.F.Pfeffer(1884) in
bacteria and H.S.Jennings in ciliates
Nobel laureate E.Metchnikoff also contributed
in this research
At this time definitions for this phenomenon are
also made
6.
7. In 1970,1960’s revolution in microbiology
created many techniques used to study this
phenomenon .
On November 2006,Dr.Dennis Bray of
Cambridge university got Microsoft European
science award for his work on chemotaxis
taking place in E.coli.
10. CHEMOTAXIS IN SOIL
Many bacteria is growing near to the roots of
some plants this is because of the exudates of
roots in the rhizosphere region
So during plant growth the bacteria in the soil
moved towards the roots exudates using the
chemotactic activity to get nutrient
The root exudates contain vitamins , sugars,
Organic acids , amino acids,etc which attracts the
bacteria in the soil
11. CONT’D
In rice fields, the chemotaxis cause movement
of beneficial microbes towards the roots which
are involving in nutrient cycle, protection to the
plants etc.
They may create symbiotic relationship with the
Plants
They may attract pathogens to the plant
For example isoflavin secreted by the root of
Soya bean attracts a mutualist (Bradyrhizhobium
japonicum)and also a pathogen(Phytopthora
sojae).
12. FACTORS AFFECTING CHEMOTAXIS
Chemical compounds present in the place
affects the movement of microbes. For
example, if the chemical is nutritive or useful to
the bacteria it cause positive chemotaxis. If it is
toxic or not useful to that then it cause negative
chemotaxis
Temperature also affects this. For example
p.florescence have good chemotactic activity at
30ºc
13. Other than these, chemotactic activity is
affected by pH,water potential etc.
The water potential affects bacterial flow and
the secretion of root exudates
15. USE OF CHEMOTAXIS IN RHIZOBIUM
The plants of leguminaceae release a
particular enzyme to attract the microbes .the
rhizobium bacteria is attracted using
chemotaxis and they produce signal of their
arrival to the plant and cause the formation of
root nodules
