Nanotechnology

1. Master’s Seminar presentation
Course code – PL PATH -591
Topic : Pros and cons of silver nanoparticles against
agriculturally important microbes
Presented by : Surender Kumar
Roll no: M- 1595/22
Department of Plant Pathology
School of Agricultural Sciences
Date : 23 November,2023

2. INTRODUCTION
 Nanotechnology - Greek word 'nano' meaning 'dwarf '
 “nano” - one billionth of a meter or 10-9m
 Deals with structures in the size range of 1 to 100 nm .
Norio Taniguchi(1974)
Nanoparticles

3. APPLICATION
Nanoparticles in agriculture is focused on:
 Nanogenetic manipulation of agricultural crops.
 Agricultural diagnostics.
 Controlled release of nanofertilizers and nano-complexes
 Nano pesticides and Nanoherbicides

4. Pros of silver nanoparticles
Broad spectrum activity
Antimicrobial
Green Synthesis
Low concentration
Reduced resistance
Biocompatibilty with plants

5. Broad Spectrum Activity
 Effective against a wide range of agricultural microbes, making them
versatile in combating different types of plant diseases which may be
caused be fungi, bacteria or viruses.
Viruses
Fungi
Insects
Protozoa
Bacteria Broad
Spectrum
Activity of
AgNPs

6. Broad
Spectrum
Activity of
AgNPs
Table 1: Broad spectrum activity of silver nanoparticles against microbes

7. Mechanism of AgNPs against microbes
High Surface Area: Increased surface area allow for
more contact points, thus increasing the effectiveness of
antimicrobial action.

8.  Cell Membrane Disruption: Cellular damage and
leakage of cellular contents.
 ROS Generation: oxidative stress, microbial cell death.
 Enzyme inhibition: disrupts vital cellular processes,
survival and reproduction.
 DNA Binding: genetic mutation, cell death.

9. Characterization of Ag NPs Toxicity assessment of Ag NPs
No. TEM size SC Use Organisms Doses Effect References
1 20 nm Silica Ag Soluble Bacillus subtilis 100µg/ml Inhibition (Park et al.,
2006)
2 250-300nm TiO2 Ag Soluble Aspergillus niger 12.5µg/ml Inhibition (Gutierrez et al.,
2010)
3 20nm Silica Ag Soluble Magnaporthe grisea 10µg/ml Inhibition (Park et al.,
2006)
4 20nm Silica Ag Soluble Botrytis cinerea 10µg/ml Inhibition (Park et al.,
2006)
5. 20nm Silica Ag Soluble Rhizoctonia solani 10µg/ml Inhibition (Park et al.,
2006)
6. 20nm Silica Ag Soluble Pseudomonas
syringae
100µg/ml Inhibition (Park et al.,
2006)
7. 20nm Silica Ag Soluble Colletotrichum
gloeosporioides
10µg/ml Inhibition (Park et al.,
2006)
8. 250-300nm TiO2 Ag Soluble Candida albicans 6.4µg/ml Inhibition (Gutierrez et al.,
2010)
Table 2:Effects of AgNPs on microbial cells

10. Green synthesis
AgNPs can be synthesized by physical, chemical and biological method.
Chemical approaches are non-ecofriendly and expensive.
AgNPs can be biosynthesized by using a number of bacteria (Pseudomonas stutzeri,
Lactobacillus casei) and fungi (Aspergillus niger, Trichoderma viride, Fusarium
oxysporum and plants (Carica papaya, Citrus limon).

11. • This can be attributed to their high surface area to volume ratio, allowing
them to efficiently interact with microbial cells.
• Small size enables them to penetrate bacteria, fungi and viruses, disrupting
cellular processes and leading to microbial death.
• AgNPs induce oxidative stress within the microbial cell.
Low concentration

12. • AgNPs have a lower chance of causing resistance in microbe.
• This is due to their multiple modes of actions.
Reduced resistance
Biocompatibility with Plants
• AgNPs can be designed to be biocompatible with plants, minimizing potential
harmful effects on the plant host while effectively targeting plant pathogens.

13. Cons of silver nanoparticles
Harmful impact on beneficial
microbes
Environmental Impact
Toxicity of Plants
Resistance Development
Human Health Concern
Regulatory Concern

14. Harmful impact on beneficial microbes
•AgNPs may not discriminate between harmful and beneficial microorganisms.
•Oktarina and Singleton (2020) reported that Trichoderma harzianum colony was affected
by high levels of AgNPs.
Fig: Colony diameter of Trichoderma harzianum grow on CDA at
200 mgL-1. The colony diameter was measured every 24 hours for
four days.

15. Fig: Colony diameter of Trichoderma harzianum grow on CDA at
600 mgL-1.The colony diameter was measured every 24 hours for
four days.
Fig: Colony diameter of Trichoderma harzianum grow on CDA at
1000 mgL-1.The colony diameter was measured every 24 hours for
four days.

16. Environmental Impact
The diverse application of AgNPs has led to increase in production and their release into
the environment.
Can be released directly and indirectly into the environment throughout their life cycle.
Fig: AgNPs’ release pathways and associated impacts on the environment

17. Toxicity
to plants
Morphological
Level
Physiological
Level
Cellular and
Molecular
Level

18. Morphological Level
-Inhibition of seed germination and root growth, and reduction of biomass and leaf area.
-AgNPs significantly decreased plant biomass, inhibited shoot growth and caused root
abscission in Spirodela polyrrhiza (Jian et al., 2012).
-Exposure to higher concentrations (5-20 mgL-1) of AgNPs resulted in reduction of the
biomass in Arabidopsis thaliana (Kaveh et al., 2013).
Arabidopsis thaliana
Spirodela polyrrhiza

19. Physiological Level
-AgNPs can disrupt the synthesis of chlorophyll in leaves, nutrient uptake, reduce
transpiration and alter hormones.
-AgNPs accumulation in Arabidopsis thaliana leaves disrupted the thylakoid membrane
structure, and decreased chlorophyll content, leading to the inhibition of plant growth
(Qian et al., 2014).
Fig: Relative inhibition rate of root elongation of A.
thaliana plants after 1 and 2 weeks of exposure to AgNPs

20. Cellular and Molecular Level
-Inhibition of plant growth after AgNPs exposure is accompanied with alteration of cell
structure and cell division.
-AgNPs with a concentration of to 60 mgL-1 could penetrate the cell wall, and damage the
cell morphology and its structure in rice (Mirzajani et al., 2013).
-AgNPs could reduce the size of the vacuole and lead to the reduction of cell turgidity and
cell size in maize (Zea mays L.) and cabbage (Brassica oleracea var. capitata L.) (Pokhrel
and Dubey, 2013).
Fig: Schematic diagram representing uptake, translocation, and major phytotoxicity
of silver nanoparticles (AgNPs) in plant.

21. Resistance Development
Despite reduced microbial resistance development, there remains the possibility of
microbes to develop resistance towards AgNPs.
This possibility can be attributed to various factors:
Rapid evolution of microbial populations, allowing for adaptation.
Selective pressure exerted by the continuous application of AgNPs favors the survival and
proliferation of resistant strains.
Consequences
 Hinders the effectiveness of AgNPs as a sustainable solution for disease control in
agriculture.
 The emergence of resistant strains may lead to unintended ecological consequences, as
these microbes play vital roles in soil health and nutrient cycling.

22. Types of
nanoparticle
Resistant organism Resistance
developed
after how
many
generations
or days of
evolution
Genetic /cellular/ phenotypic changes
observed
Reference
Citrate-coated
Ag
nanoparticles
E.coli K-12 MG1655 225
generations
Mutation in cusS, purl, rpoB, ompR Graves et al.,
2015
Ag
nanoparticles
E.coli/BW25113/ΔyhaK - Overproduction of
exopolysaccharids
Joshi et al.,
2012
Ag
nanoparticles
E.coli 013, Pseudomonas
aeruginosa CCM 3955
and E. coli CCM 3954
- Production of adhesive flagellum
protein flagellin triggering nanoparticle
aggregation
Panáček et
al., 2018
ZnO
nanoparticles
E. coli 25
generations
Changes in cell shape-rod to oval
probably due to low expression of
membrane protein RodZ, porins
Zhang et
al., 2018
Ag
nanoparticles
Model microbiota of
environmental or clinical
setting: E.
coli and Bacillus sp.
- Modulation of Z-ring division septum,
upregulation of cytoprotective genes-
permease components, efflux proteins.
Gunawan et
al., 2013
Table 3: Examples of microbial resistance to antimicrobial nanoparticles.

23. Mechanisms of microbial resistance to nanoparticles:
(a) Biofilm — bacteria produce exopolysaccharides, biofilm to protect themselves or to
aggregate nanoparticles.
(b) Motility structures — hypermotile bacteria can evade nanoparticles and increase
nutrient availability.
(c) Shape change — bacteria switch shapes (rods to oval) by the isomerization of fatty acids,
membrane lipids, and proteins and filter out nanoparticles.
(d) Efflux systems — resistant microbes are known to overproduce efflux complex systems.
(e) Operons — activation specialized operons and genes make activate cytoprotective
mechanisms in bacteria.
(f) Cell division disruption — nanoparticle stress can disrupt cell cycle regulation contribute
to its resistance.

24. Human Health Concerns
 AgNPs are small enough to penetrate through body barriers.
 Human exposure to AgNPs mainly takes place through three different routes of
exposure, including skin, gastrointestinal and lung.
 AgNPs also affect the respiratory chain of mitchondria ,producing ROS and lead to
DNA damage (Jaswal and Gupta, 2023).
Fig: Possible consumption and cytotoxicity of silver nanoparticles in cell.

25. Regulatory concerns
Integration of AgNPs into agriculture has raised regulatory concerns for balancing the
potential benefits of these nanoparticles with their environmental and health implications.
In India, the regulation of nanotechnology-based agri-products falls under the purview of
various agencies and laws, including the Department of Biotechnology (DBT), the
Ministry of Environment, Forest and Climate Change (MoEFCC), the Food Safety and
Standards Authority of India (FSSAI), and the Indian Council of Agricultural Research
(Kumari et al., 2023).
.

26.  AgNPs in agriculture offers promising benefits as antimicrobials.
Despite their versatility and efficacy, concerns arise over potential harm to beneficial
microbes, plant toxicity, and the development of microbial resistance.
Standardized testing methods and clear frameworks are vital for responsible AgNP s
use.
Ongoing research is essential to address gaps in understanding long-term effects on
plant microbes, ecosystems, and human health.
Global regulatory bodies, play a crucial role in shaping guidelines for the safe
integration of silver nanoparticles in agriculture. A cautious and informed approach,
coupled with adaptive regulation, can ensure the sustainable and responsible utilization
of AgNPs in agricultural systems.
Conclusion

27. THANK YOU