rhizomicroflora provide an effective way to cleaner and greener environment.

1. RHIZOREMEDIATION- PLANT MICROBES
INTERACTIONS IN THE REMOVAL OF
POLLUTANTS
Credit seminar
Micro 591
By:
Mehak Oberai
L-2013-BS-12-IM

2. Table of contents
Introduction
Bioremediation
Why rhizoremediation?
Rhizoremediation
Plant –microbe synergistic
relationship
Factors affecting the process
Improvement of the process
Mechanisms involved
Case studies
Advantages and disadvantages
Future prospect

3. The word remediation originated from latin word –”remediare” meaning to heal or to cure.
Various conventional methods were used for remediation of pollutants :
Dig up and remove to a
landfill.
Cap and contain i.e. maintain
in the same land but isolate it.

4. Shortcomings of conventional approaches :
o Harmful end products
o Environment instability
Alternate approach
oComplete destruction of pollutant
or
o Conversion to harmless products

5. The
physicochemical
techniques as
incineration,
excavation, de-
chlorination -a
better approach
but are
expensive,
uneconomical
Technologically
complex
Not readily
accepted by the
society
especially
incineration
Release of toxic
products in
certain cases
Labor intensive

7. Bioremediation.
Bioremediation is
the use of
biological
organisms to
break down or
immobilize
environmental
contaminants.
Advantages
Safer than other
methods of
cleanup.
Less cost of labor
and equipments
major work is
done by micro-
organisms.
Less disruption of
environment.

9. Use of the plants for the
purpose of
bioremediation is known
as phytoremediation.
A subset of
phytoremediation i.e.
rhizoremediation is
trending these days.

11. Now the question
arises why we go
for
rhizoremediation?
• The plant’s rhizosphere as
a niche for the microbial
growth.
• It is economical.
• It is eco-friendly
technique.
• In this we utilize plants
and microbes: plants are
easy to grow and
microbes are easy to
manage.

12. The recent approach –
rhizoremediation an effective
cleanup technology.
What is rhizoremediation?
• It is the use of plant roots and associated microbial consortium to
degrade environmental pollutants from soil.
• It aims at restoring contaminated sites to a condition useable for
intended purpose.
It is a process where micro-organisms
degrade soil contaminants in the
rhizosphere. The microbes involved
may range from certain bacteria,
actinomycetes to fungi and so on.

13. Soil pollutants that are remediated by this method are generally organic
compounds that can’t enter the plant because of their hydrophobicity.
Plants are not considered the main mode of remediation in this
technique.
Rather plant creates a niche for the microorganisms to do degradation.

14. Rhizoremediation is a type of in-situ bioremediation that occurs at the site of contamination. However it
can further be of two types :
Engineered
rhizoremediation
 use genetically
engineered degrading
microorganisms.
 intentionally add
certain root exudates to
enhance microbial
growth.
Intrinsic
rhizoremediation
 the natural conditions
are not disturbed .
 the remediation
process is carried out
in the natural
environment
Rhizoremediation

15.  Rhizoremediation is a superior technique as :
it involves
Plants: easy
to grow
Microbes:
easy to
handle
 Among the microorganisms the bacteria are the most
preferred .

16. Rhizoremediation
– a synergistic
relationship
between plant
roots and
microorganisms.
Plants provide
niche for the
microbes to grow
at the expense of
root exudates:
Plant roots act as a substitute to tillage as
these help the
root associated
microorganisms
to spread through
the soil.
To penetrate
layers normally
inaccessible
To incorporate
nutrients
To provide oxygen
and better redox
conditions
To provide large
surface area for
microbial growth
and penetration.

17. Plants live in symbioses with
mycorrhizae.
Microbes act as the biocatalysts that
remove the pollutants.
• The microbes increase the availability of the
compounds and the plants help in the extraction
and removal of such compounds.

18. • The presence of contaminants has
negative impact on plant growth.
• Studies have reported number of
rhizospheric microorganisms possess
contaminant degrading ability.
• The contaminants remediated involve
various xenobiotic chemicals :
pesticides, herbicides, solvents and
other organic compounds.
• Disposing of these toxic chemicals.
Can the microbes involved
in this process be known
as plant growth promoting
microorganisms (PGPM)?

19. Role of plants in
rhizoremediation:
Act as the source of nutrients in rhizosphere –mucigel secreted by root
cells, lost root cap cells, the starvation of root cells or the decay of
complete roots.
Plants release various photosynthesis derived organic compounds.
stimulating and activating various microbes.
Reduction in leaching of contaminants.
Aeration of soil.

20. Plant -bacteria interactions in rhizoremediation
These interactions occurring at the soil-root interface involve:
Root colonization by
the bacteria
Selection and
maintenance of
degradation
genes
Inter-kingdom
communication
which shape
the community

21. Root
colonization:
• Origin of biodegradative bacteria.
• Spread through the soil during root emergence and
growth.
• Bacteria can actively colonize the roots by the
chemotactic movements.

23. Regulation of the
gene expression
by root exudates:
• Role played by root exudates is crucial
• Selection of microbial population.
• Role played by aromatic structures.
• Co-substrate

24. Communicationand
dynamics:
•Multiple signals sent and received by plants.
•Recognition of microorganisms, recruitment
of catalytic potential, mycorrhization,
resistance to stresses and quorum sensing.
•Changing factors

25. Factors affecting
rhizoremediation:
Soil
conditions
Temperature pH
Soil organic
matter
Plant species
involved
Microbes
involved
Microbial
bioavailability of
pollutants

26. Soil conditions :
Soil moisture, soil pH, temperature, nutrients, size of soil
particles, nature of soil particles and soil physical and
chemical properties.
Microbial mineralization of pesticides .
linear correlation between soil moisture and pesticide
mineralization.
Soil water.

27. Temperature
Major factor.
It effects :
I. various biochemical reactions.
II. microbial activities.
III. have an impact on cell physiology.

28. pH
The
biodegradation
of a compound is
dependent on
specific enzymes
secreted by
microorganisms.
These enzymes
are pH
dependent and
bacteria tend to
have optimum
range between
6.5 and 7.5.
The
rhizoremediation
rate was slower
in lower pH soils
in comparison
with neutral and
alkaline soils.
It has direct
effect on the
biochemical
reactions.
There is
significant
relation between
adsorption and
soil pH.

29. Organic matter
• effects biodegradation of xenobiotics in soil
• Source

30. Plants involved:
• Tolerate the
concentrations of
contaminants
present.
They must be
able to grow and
survive in local
environment.
The depth of the
contamination.
Plant age.

31.  Suitable plant-microbe pairs
 Kuiper et al (2004) described the pair of a grass species with a
naphthalene degrading microbe which protected the grass against
the toxic effects of naphthalene.
 These microbes used naphthalene as the nutrient source for their
growth and multiplication.

32. Amora-Lazccinoetal(2010)

33. Micro-organisms
involved:
Microbial
consortium
more effective.
Presence of
partners.
Increased
humification.

34. Strategies to
improve
rhizoremediation
(promotion of
rhizoremediation)
• Bio-stimulation
• Bio-augmentation
• Transgenic plants

36. MECHANISMS INVOLVED IN ECORESTORATION BY MICROBES:
BIOSURFACTANT
PRODUCTION
ORGANIC ACID
PRODUCTION
SIDEROPHORE
PRODUCTION
ACC DEAMINASE PRODUCTION
BIOFILM
FORMATION
INCREASED
HUMIFICATION
RELEASE OF ENZYMES

37. BIOSURFACTANT

38. Bioremediation
of polyaromatic
hydrocarbons
(PAHs) using
rhizosphere
technology:
The increasing
industrialization has
led to the elevated
increase in release
of anthropogenic
chemicals .
PAHs are one
among these.
Need for their
removal:
•Toxic
•Carcinogenic
•Mutagenic

39. oVarious bacteria involved in their degradation: Pseudomonas
aeruginosa, Pseudomonas fluorescens, Mycobacterium, Haemophilus,
Rhodococcus, Paenibacillus etc.
o PAHs concentration in soil: 1µg/kg to 300g/kg.

41. Biological
degradation
of
naphthalene:
•Various metabolic pathways and
enzymes are involved.
•The bacterial PAH catabolic genes often
occur as large plasmid along-with
regulatory genes
•Adaptation of the indigenous microbes
towards this degradation.
•These are hydrophobic -degradation is
brought about by bio surfactants.

42. Examples :
 Among PAHs, benzopyrene is considered quite toxic and carcinogenic. Studies show that bacteria are able
to degrade it. eg:- Pseudomonas, Agrobacterium, Bacillus, Burkholderia and Sphingomonas.

48. Role of rhizobacteria in remediating heavy metal contaminated soil
• Heavy metals as micronutrietns.
• Toxic in excess
• Biological destruction not possible
• Biotransformation possible

50. Advantages
:
Economic
Eco-
friendly
Less labor
intensive
Disadvantages :
Microbial ecology in
rhizosphere is not yet
fully understood.
Slow process

51. Technological
advances
Reduced cost
of next
generation
sequencing
techniques
Insight into
complex
interactions in
rhizosphere
Improvement
of the process
Promising
and fertile
research area
Future
aspects:

52. References:
• Amora-Lazccino E, Guerrero-Zuniga L A, Rodriguez-Tovar A, Rodriguez-Dorantes A and Vasquez-Murrieta M S (2010)
Rhizospheric plant-microbe interactions that enhance the remediation of contaminated soils. App Microbiol & Microbiol
Biotechnol 4: 251-56.
• Corgie S C, Joner E J and Leyval C (2003) Rhizospheric degradation of phenanthrene is a function of proximity to roots.
Plant & Soil 257: 143-50.
• Kuiper, I, Lagendigk E L, Bloemberg G U and Luternberg B J J (2004) Rhizoremediation: A beneficial plant-microbe
interaction. Mol plant-microbe interactions 17: 06-15.
• Segura A, Rodriguez-Conde S, Ramos C and Ramos J L (2009) Bacterial responses and interactions with plants during
rhizoremediation. Microbiol Biotechnol 2: 452-64.
• Thijis S and Vangronsveld J (2015) Rhizoremediation: Principles of plant microbe interactions. Springer International
Publishers, Switzerland.
• Vergani L, Mapelli F, Zonardini E, Terzaghi E, Guardo A, Morosini C, Raspa G and Boren S (2016) Phyto-
rhizoremediation of polychlorinated biphenyl contaminated soils: an outlook on plant-microbe beneficial interactions. Sci
Total Environ 1: 01-12.
• Yan-de J, Zhen-li H and Xiao Y (2007) Role of soil rhizobacteria in phytoremediation of heavy metal contaminated soils.
J Zhenjiang Uni Sci 8:192-207.