This document discusses the role of microbial volatiles in improving plant growth and productivity. It notes that current agricultural practices rely heavily on pesticides and chemicals that harm the environment. Microbial volatile organic compounds produced by bacteria and fungi provide an alternative for protecting plants and enhancing growth. The document reviews evidence that specific volatile compounds from microbes like Bacillus and Trichoderma can modulate plant functions like defense, nutrient uptake, and stress tolerance. It also summarizes studies demonstrating that exposing plants to these microbial volatiles can increase plant growth, yield, and resistance to pathogens. The document concludes that understanding microbial volatile interactions is key to developing more sustainable agricultural strategies.

1. Microbial Volatiles: Their role
in improving plant growth &
productivity
KRASH KUMAR KUSHWAHA
MSc (Ag.) Microbiology, IARI,
New Delhi
1

2. BACTERICIDES
MVOCs
2
krashkushwaha24@gmail.com

3.  Current agricultural practice depends on a wide use of
pesticides, bactericides, and fungicides , but in the end,
they drastically affect human and environment health
 Increased demand for organic products indicates
consumer preference for reduced chemical use.
 Therefore, there is a need to develop novel sustainable
strategies for crop protection and enhancement that do
not rely on genetic modification and/or harmful
chemicals.
An increasing body of evidence indicates that bacterial
and fungal microbial volatile organic compounds (MVOCs)
might provide an alternative to the use of chemicals to
protect plants from pathogens and provide a setting for
better crop welfare. 3

4.  Low-molecular weight compounds
 Lipophilic in nature
 Low boiling point
 Products of primary and secondary metabolism
 Formed during the metabolism of fungi and bacteria4

5. 5

6. Modulation of crop growth
Defense
Nutrient uptake
Stress tolerance
Communication
Antagonists
Mutualistic symbionts 6

7. 7

8. 8
Bacteria Fungi

9. Bacterial volatiles play an important role in-
 Bacterial–plant interactions
 Bacterial– bacterial interactions
 Bacterial–fungal interactions
9

10. Some bacteria preferentially live in the soil closely associated with the plant roots,
exploiting the rich nutrient exudates that plants deliver into the soil. These bacteria are
called rhizobacteria
VOCs produced by rhizobacteria are involved in their interaction with plant-pathogenic
microorganisms and host plants and show antimicrobial and plant growth activities
10

11.  Two volatile compounds 3-hydroxy-2-butanone and 2,3-butanediol were released
consistently from strains B. subtilis GB03 and B. amyloliquefaciens IN937a whereas these
compounds were not released from other strain
 These volatile were found to significantly enhance total leaf surface area of A. thaliana

12.  In Arabidopsis, seedlings exposed to bacterial volatile blends from Bacillus
subtilis GB03 and Bacillus amyloliquefaciens IN937a
 Disease severity by the bacterial pathogen Erwinia carotovora subsp.
carotovora was significantly reduced compared with seedlings not exposed
to bacterial volatiles
Bacterial Volatiles Induce Systemic Resistance in Arabidopsis

13. Application of DMDS produced by a Bacillus cereus significantly protected tobacco
against Botrytis cinerea
The highest resistance
to B. cinerea was
observed in tobacco
treated with 1.0 mM
DMDS and disease
severity was reduced by
66%

14. 14

15.  Salt-stressed Arabidopsis plants treated with Bacillus subtilis GB03 VOCs showed
greater biomass production and less Na+ accumulation compared to salt-stressed
plants
 Arabidopsis HKT1 is a xylem parenchyma-expressed Na+ transporter that is
responsible for Na+ exclusion from leaves by removing Na+ from the xylem sap
 SOS3-dependent Na+ exudation is required for the decreased accumulation of Na+
in VOC-treated plants
15

16.  Choline and glycine betaine are
important osmo-protectants that confer
dehydration tolerance in plants
 VOC treatment increased the level of
PEAMT which is an essential enzyme in
the biosynthesis pathway of choline and
glycine betaine
 Under osmotic stress, Arabidopsis
exposed to GB03 VOCs accumulated
higher levels of choline and glycine
betaine than plants without VOC
treatment
 Certain bacterial VOCs such as acetic
acid can induce the formation of
biofilms, which contain
exopolysaccharides that enhance the
ability of the bacteria to maintain soil
moisture content and increase drought
tolerance in plants
Fig. GB03 enhances plant tolerance to osmotic
stress 16

17.  Dimethyl disulfide (DMDS) is an S-containing volatile compound commonly produced
by many soil bacteria and fungi
 Emission of DMDS from Bacillus sp.strain B55, a natural symbiont of Nicotiana
attenuata plants, rescued plant growth retardation caused by S deprivation
17

18.  Indole
 Dimethyl disulfide
 Tridecane
 3-petanol
 1-octen-3-ol
 Indole
 Dimethyl disulfide
 2-pentylfuran
 Dimethylhexadecylamine
18

19. Indole :
 Isolated from soil-borne bacteria
 Increase plant biomass
 Promote lateral root growth
Dimethyl disulfide
 Produce during the interaction between Nicotiana attenuata and root-associated
Bacillus sp. B55
 Enhance plant growth by increasing plant sulfur content
2-Pentylfuran
The fresh weight of Arabidopsis increased approximately two-fold after exposure
Dimethylhexadecylamine
Promoted the growth of Medicago sativa seedlings
(increases root length, stem length, and plant biomass)
19

20. Tridecane
 Promotes plant biomass production
 Functions to control phytopathogens
 Induces systemic resistance in Arabidopsis against Pseudomonas syringae pv.
maculicola ES432
Pentanol
 1-pentanol strongly reduced severity
caused by X. axonopodis and naturally
occurring Cucumber mosaic virus
1-Octen-3-ol
 Produced by mushrooms
 Reduces disease symptoms caused by Botrytis cinerea
 Also reduces germination of Lecanicillium fungicola,
which causes dry bubble disease
20

21.  Volatiles produced by Collimonas pratensis and Serratia plymuthica stimulated the
growth of Pseudomonas fluorescens which promote plant growth by releasing MVOCs
 Tomato plants treated with Serratia plymuthica strongly suppressed Agrobacterium
growth by emitting DMDS
Pseudoalteromonas strains were able to completely inhibit the growth of most
Burkholderia cepacia complex (Bcc) strains
21

22. •
22

23.  Fungal MVOCs exert either potent inhibitory or stimulatory effects on plants
 Sesquiterpenes, chokols A–G have been isolated from Epichloe typhina an
endophytic fungus of Phleum pratense, and have been found to be toxic to
the leaf spot disease pathogen Cladosporium phlei

24. Volatile Compounds Produced by Genetically and
Phenotypically Diverse F. oxysporum Strains Enhanced the
Growth of A. thaliana and Tobacco
Volatiles from NRRL 38499 did not enhance tobacco (N. tabacum) growth, but volatiles from
NRRL 26379 and NRRL 38335 resulted in 2.5- and 3-fold shoot weight increases

25. Analytical tools to study the chemical nature of MVOC
Head space GC-MS
It is the fastest and cleanest method for analyzing volatile organic compounds

26. Fig. Gas syringe system

28. 28

29. Single colonies were transferred to flasks containing
culture medium
Grown aerobically on a rotating shaker
Bacterial suspension was diluted
One node, from aseptically cultured plantlet, was placed on one side of
a specialized plastic Petri dish
Bacteria were grown on nutrient agar
29

30. Suspension culture of various PGPR strains
was applied to the side of the dish
Placed in a growth chamber
Plant growth measurement
Extraction of EOs
30

31. Shoot fresh weight and root dry weight of M. piperita exposed to VOCs from
three PGPR species
31

32. Leaf area of 30-day old M. piperita plants
exposed to VOCs from three PGPR species
Essential oil (EO) yield in M. piperita exposed to
VOCs from three PGPR species.
32

33. Concentrations of major EO components in M. piperita exposed to VOCs
from three PGPR species

34.  VOC-mediated interactions are species-
specific
 Growth parameters of plants exposed to
VOCs were significantly higher than
those of controls
 Increased essential oil biosynthesis
34

35. BACKGROUND: In this study, Arabidopsis plants were exposed to mixtures of volatile organic
compounds (VOCs) emitted by growing cultures of Trichoderma from 20 strains, representing
11 different Trichoderma species.
35

36. Fungus was grown in a Petri dish containing MEA and incubated
Arabidopsis thaliana seeds were sown onto partitioned Petri dish while Tomato
seeds were sown into sterile culture vessel
Exposures of Arabidopsis plants to Trichoderma VOCs
36
Kept in a growth chamber
Fresh weight of plant shoots and total chlorophyll content was measured

37. 37
Fig. Average fresh weight and total chlorophyll content of Arabidopsis thaliana plants grown in a shared atmosphere with
20 different strains of Trichoderma for 14 days

38. 38
Growth of Arabidopsis thaliana after 14 days

39. 39
Tomato seedlings exposed to T. viride (BBA 70239) VOCs for a) 14 days b) 21 days c) Roots of
tomatoes exposed to Trichoderma VOCs for 21 days

40.  Many Trichoderma strains produced
plant growth promoting VOCs
 Different species and strains of
Trichoderma exhibited a range of effects
 Trichoderma species are prolific
producers of VOCs
40

41.  Microbial volatile organic compounds (MVOCs) are produced by a
wide array of microorganisms ranging from bacteria to fungi
 Microbial volatile organic compounds form a bioactive interface
between plants and a myriad of microorganisms above and below
ground where most of the interactions take place
 MVOCs are intriguingly complex and dynamic and understanding
their ecology and evolution is the key to bio prospecting suitable
tools for crop protection and production for sustainable agriculture
perspective
 New understanding of the importance of MVOCs for crop plants
both at the lab and open field conditions will make possible to
adopt and implement sustainable crop protection and to develop
production strategies

42. krashkushwaha24@gmail.com