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Exploration of bioactive metabolites from Streptomyces as natural
insecticides against Helicoverpa armigera
ABSTRACT
Microorganisms produce a range of metabolites which plays key roles in agriculture including pest control properties. With this concept, 15 Streptomyces strains with insecticidal activity against the lepidopteran pests
such as Helicoverpa armigera, Spodoptera litura, and Chilo partellus were identified. Based on the activity units, S. griseoplanus SAI-25 and Streptomyces sp., CAI-155 were further studied to identify the key insecticidal
metabolites against H. armigera. An insecticidal compound called cyclo(Trp-Phe) belongs to the diketopiperazine class was purified from SAI-25 with antifeedant (70%), larvicidal (67%), and pupicidal (59%) activity. The
LD50 and LD90 values were observed to be 619 and 2750 ppm, respectively. In the context of Streptomyces sp., CAI-155, a novel fatty acid amide derivative called N-(1-(2,2-dimethyl-5-undecyl-1,3-dioxolan-4-yl)-2hydroxyethyl)stearamide with insecticidal activity of 70–78% was identified. The LD50 and LD90 values were found to be 627 and 2276 ppm respectively. Further characterization of these metabolites in the field
conditions, will bring out the potentiality of microbial metabolites for the pod borer management.
ESI-MS spectrum and structure of cyclo(Trp-Phe)
INTRODUCTION
RESULTS
Legume pod borer, H. armigera, is one of the
most important lepidopteran pests worldwide
affecting more than 300 species of plants. Though
there are many synthetic pesticides available as
control measures, their indiscriminate use have
developed insect resistance. Therefore, there is a
need to do research on safer alternate products
for pest management, where the microbial
metabolites plays key role as they constitute an
infinite pool for novel secondary metabolites.
Hence, the present work was aimed to identify
microbial metabolites with insecticidal properties
from Streptomyces strains against H. armigera.
Larvicidal activity of extracellular extract
Starch Casein Broth/8 Days/28 °C
Extracellular extract
SAI-25
C18 open
column, HPLC
CAI-155
Silica and C18
open column, TLC
Bioactivity guided fractionation
1. Extraction
Diaion HP-20
3. Identification
S. griseoplanus SAI-25/Streptomyces sp. CAI-155
2. Purification
MATERIALS AND METHODS
EI-MS spectrum and structure of N-(1-(2,2-dimethyl-5-undecyl1,3-dioxolan-4-yl)-2-hydroxyethyl)stearamide
Molecular formula: C20H20N3O2
Molecular mass: 333.3
Molecular formula: C36H71NO4
Molecular mass: 283.3
Each bar depicts the mean (n=3). Error bar indicates SE.
Larvicidal activity of purified compounds
Samples (ppm)
Larvicidal activity (%)
Cyclo(Trp-Phe)
250
23.3±2.7f
500
39.4±5.5def
1000
67.6±3.8bc
N-(1-(2,2-dimethyl-5-undecyl-1,3-dioxolan-4-yl)2-hydroxyethyl)stearamide
250
24.6±2.5ef
500
40.6±2.2de
1000
78.3±1.2b
Azadirachtin (Standard)
250
54.6±4.1cd
500
81.9±4.3ab
1000
97.8±2.2a
Values are mean±SE (n=3). Values followed by different lower-case
superscript letters are significantly different (p < 0.05) by Tukey test.
DISCUSSION
LD50 and LD90 values of purified compounds
Compounds
Cyclo(Trp-Phe)
LD50 ppm
LD90 ppm
(95% LFL-UFL)
(95% LFL-UFL)
χ2 (df) p value
619 (516-776) 2750 (1765-6431) 15.9(7) 0.026*
627 (535-760) 2276 (1589-4271) 15.7(7) 0.027*
N-(1-(2,2-dimethyl-5undecyl-1,3-dioxolan-4-yl)2-hydroxyethyl)stearamide
Azadirachtin
233 (164-286) 627 (511-895)
23.9(7) 0.001*
* χ2 values are significant at p < 0.05; LFL – Lower Fiducial Limits; UFL – Upper
Fiducial Limits; df – degree of freedom.
 Two microbial metabolites with insecticidal properties on
H. armigera were identified.
 Cyclo(Trp-Phe) from , S. griseoplanus SAI-25 is the first report for
its presence and biological activity from the genus Streptomyces.
 N-(1-(2,2-dimethyl-5-undecyl-1,3-dioxolan-4-yl)-2hydroxyethyl)stearamide purified from Streptomyces sp., CAI-155
is a novel metabolite with insecticidal activity
 This study reveal the importance of microbial metabolites in the
development of biopesticide formulation.
 Still, the study warrants further characterization in relation to its
mode of action and efficacy trails under field conditions.
REFERENCES/PUBLICATIONS
FTIR,
1H and 13C NMR,
HR-LCMS
1D and 2D NMR: 1H,
13C, COSY, NOESY,
HMBC and HSQC; EI-MS
 Vijayabharathi R, RatnaKumari B, Sathya A, Srinivas V, Rathore A, Sharma HC,Gopalakrishnan S. Biological activity of entomopathogenic actinomycetes against lepidopteran insects (Noctuidae: Lepidoptera).
Canadian Journal of Plant Science (2014) 94 (4): 759-769
 Sathya A, Vijayabharathi R, Kumari BR, Srinivas V, Sharma HC, Sathyadevi P, Gopalakrishnan S. Assessment of a diketopiperazine, cyclo(Trp-Phe) from Streptomyces griseoplanus SAI-25 against cotton bollworm,
Helicoverpa armigera. Applied Entomology and Zoology (2016) 51:11-20
 Gopalakrishnan S, Vijayabharathi R, Sathya A, Sharma HC, Srinivas V, Bhimineni RK, Gonzalez SV, Melø TM, Simic N. Insecticidal activity of a novel fatty acid amide derivative from Streptomyces species against
Helicoverpa armigera. Natural Products Research (2016) 8:1-10
S. Gopalakrishnan1, Vijayabharathi R1, Sathya A1, Sharma HC1, Srinivas V1, Ratna Kumari B1,
Gonzalez SV2, Melø TM3, Simic N2
1
ICRISAT, Patancheru, India; 2 Department of Chemistry, Norwegian University of Science and
Technology (NTNU), Trondheim, Norway; 3 Department of Biotechnology, NTNU, Trondheim, Norway.
Funding from DBT, GOI for this study is greatly acknowledged. This work was undertaken as part of the
CGIAR Research Program on Grain Legumes. ICRISAT is a member of CGIAR Consortium. Identification
of metabolites through the support of NTNU, Norway is also greatly acknowledged.
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