Isolation of Malathion degrading Pseudomonas xanthomarina with ...

Research Journal of Chemistry and Environment___________________________________Vol.17 (3) March (2013) 

Res. J. Chem. Environ. 

Isolation of Malathion degrading Pseudomonas 

xanthomarina with plant growth promoting activity 

Goyat Pankaj, Bhatia Divya and Malik Deepak Kumar * 

Department of Biotechnology Engineering, University Institute of Engineering and Technology, Kurukshetra University Kurukshetra-136119, INDIA 

*deepmolbio@rediffmail.com 

Abstract 

Malathion is an organophosphorus insecticide used 

all over the world to control adult mosquitoes. A total 

of 10 morphologically different bacterial cultures 

DKM1, DKM2, DKM3, DKM4, DKM5, DKM6, 

DKM7, DKM8, DKM9 and DKM10 were isolated by 

using enrichment method. The growth study of 

isolated strains showed that the bacterial strain 

(DKM8) was able to grow in minimal medium 

containing 0.5 mM Malathion as a sole carbon 

source. The isolated bacterial strain DKM8 was found 

very close to Pseudomonas xanthomarina on the basis 

of morphological, physiological and biochemical 

characteristics. The resting cell study showed that 

strain (DKM8) can degrade Malathion 70.5% within 

two days. The isolated bacterial strain DKM8 was 

also showing plant growth promoting activities (IAA 

production, phosphate solubilization, protease activity 

and antifungal activity). These data indicate that the 

isolated bacterial strain DKM8 can be used for 

degradation of Malathion along with plant growth 

promoting activity in agriculture. 

Keywords: Malathion, Indole acetic acid, PGPR, Resting 

cell study, GC. 

Introduction 

Malathion (O, O-dimethyl-S (1, 2 dicarbethoxyethyl) dithiophosphate) 

is an organophosphate insecticide used 

extensively to control adult mosquitoes. Like most 

organophosphates, Malathion is degraded in soils 27, 45 , in 

aquatic systems 24 and in terrestrial plants and animals 13 . 

Due to the environmental concerns associated with 

accumulation of this pesticide in food products and water 

supplies, efforts are currently underway to develop safe, 

convenient and economically feasible methods for 

pesticides detoxification. Bioremediation takes place in 

order to transform the contaminants into substances that 

can be absorbed and used by autotrophic organisms with no 

toxic effect 43 . The microbial interactions are useful, neutral 

or harmful and influence plant growth accordingly 1 . 

Plant growth-promoting bacteria (PGPB) are rhizosphere 

bacteria that can help plant growth by different 

mechanisms 14 . The detrimental environmental impact of 

chemical fertilizers and their rising cost, the use of PGPB 

as natural fertilizers is beneficial for the development of 

sustainable agriculture. PGPR promote plant growth by 

(59) 

various mechanisms that include: (i) The ability to produce 

or change the concentration of the plant hormones like 

indole acetic acid 42 , gibberelic acid 26 , cytokines 44 and 

ethylene 14 (ii) symbiotic nitrogen fixation 16, 17 (iii) asymbiotic 

nitrogen fixation 5 (iv) phosphate solubilization 49 (v) 

antagonisms against phytopathogenic microorganisms by 

the production of siderophores 42 , β-1, 3- glucanase 40 , 

chitinase 12 , antibiotics 29 and cyanide 11 . 

Material and Methods 

Chemicals: The chemicals, media and reagents used in 

present studies were of AR grade and taken from Hi Media, 

CDH and Rankem etc. Malathion was purchased from New 

Chemi Industries Ltd, India. Analytical and spectroscopic 

grade hexane and acetone were purchased from CDH and 

Rankem respectively. All other chemicals were of AR 

grade commercially available. 

Isolation of Malathion Degrading Bacterial Culture 

from Pesticide Contaminated Soil: The soil sample was 

taken from pesticide contaminated field. The enrichment 

technology was used for the isolation of Malathion 

degrading bacterial strains by using basal salt medium 

(BSM) with the following composition (in g/L) (NH4)2SO4, 

1.0; K2HPO4, 0.1; MgSO4, 0.2; FeSO4.7H2O, 0.001; NaCl, 

1.0; Na2MoO4, 0.0033 4 . Approximately 10 g of soil sample 

was suspended in 250 ml basal salt medium supplemented 

with 0.30 mM Malathion and incubated at 30 ºC. After 7 

days of incubation, 15-20 ml broth culture was used to 

inoculate fresh basal salt medium containing 0.35 mM 

Malathion. 

Subsequently three-four rounds of enrichment were carried 

out in basal salt medium supplemented with increasing 

concentration of Malathion up to 0.5 mM. The enriched 

medium was spreaded over nutrient agar plates containing 

0.5 mM Malathion. After 3 days of incubation, 

morphologically different types of colonies were streaked 

for their purification on nutrient agar plates containing 0.5 

mM Malathion. The isolated bacterial cultures were 

transferred to fresh slants at regular intervals for further 

study. 

Identification and Growth Study of Isolated Bacterial 

Culture: The growth of all isolated bacterial strains was 

observed by taking absorbance at 600 nm at interval of 0, 6, 

12, 24, 48, 96, 120 and 168 hr in basal salt media (BSM) 

supplemented with 0.5 mM malathion. The bacterial strain 

DKM8 was identified on the basis of their morphological, 

physiological and biochemical characteristics from Institute 

of Microbial Technology (IMTECH), Chandigarh.



IAA Production of Isolated Bacterial Cultures: The 

indole acetic acid production of isolated bacterial strain 

was determined by using Salkowski reagent 15 . The 2% 

inoculums of all the isolated bacterial culture were 

transferred individually into 5 ml LB broth supplemented 

with 100 µg/ml L-tryptophan and incubated at 28 ºC for 4 

days. After 2 and 4 days, 2 ml growth suspension was taken 

from culture broth and centrifuged for 5 min at 10,000 rpm. 

Then equal amount of Salkowski reagent (0.5 M FeCl3 in 

35 % Perchloric acid) was added in the supernatant. The 

supernatant was mixed by shaking and allowed to stand at 

room temperature for 30 min till the development of pink 

color. For quantitative estimation of IAA, optical density of 

culture broth was taken at 500 nm. The effect of different 

concentration of Malathion (0.5 mM and 1.0 mM) on IAA 

production was also checked by using the same method. 

Uninoculated broth served as control. 

Phosphate Solubilization and Protease Activity of 

Isolated Bacterial Cultures: The phosphate solubilization 

activity of all isolated bacterial strains was checked by 

using Pikovskaya 32 medium. The bacterial cultures were 

spot inoculated on Pikovskaya medium containing 

tricalcium phosphate [Ca3 (PO4)2] and incubated at 30 ºC 

for 10 days. The development of a clear zone was 

considered as phosphate solubilizing activity. The 

phosphate solubilization was also checked by using same 

method at different concentration of Malathion (0.5 mM 

and 1.0 mM). The protease activity was checked by using 

skimmed milk agar medium 34 . The bacterial strains were 

spot inoculated on skimmed milk agar plates and incubated 

at 30 ºC for 48 hr to check the proteolytic activity. The 

development of a clear zone at the inoculation site on the 

culture plates was considered as an index of proteolytic 

activity. 

Anti-fungal Activity against Aspergillus sp. and 

Antibiotic Resistance Pattern of Isolated Bacterial 

Cultures: The antagonistic ability of isolated bacterial 

cultures was determined with slight modifications 3 . The 

growth suspension of Aspergillus was spread on the surface 

of nutrient agar plates. After the absorption of Aspergillus 

suspension, bacterial strains were spot inoculated. The 

antifungal activity of bacterial strains against the 

Aspergillus was assessed on the basis of inhibition zone 

size after 4 days of incubation at 30 ºC. The antibiotic 

resistant pattern of bacterial strains DKM8 and DKM9 was 

determined by disc diffusion method. The overnight growth 

suspension of strains DKM8 and DKM9 was spread over 

nutrient agar plate. 

After absorption of bacterial suspension antibiotic discs 

were placed, plates without antibiotic discs were 

considered as control. The following antibiotic discs were 

tested, chloromphenicol, oxacillin, ampicillin, 

clarithromycin, gentamycin, amoxyclav, vancomycin, 

cephalothin, amikacin, novobiocin, erythromycin, 

teicoplanin, co-trimoxazole, penicillin, azithromycin, 

(60) 

ofloxacin, methicillin, linezolid, clindamycin and 

tetracycline. The zone of inhibition was obsereved after 48 

hr of incubation at 30 ºC. 

Quantitative Analysis of Malathion Degradation by 

Resting Cell Study: On the basis of plant growth 

promoting activity and growth in BSM medium containing 

0.5 mM malathion, bacterial strain DKM8 was selected for 

their ability to degrade Malathion by resting cell study 23 . 

The isolate DKM8 was grown in 300 ml nutrient broth 

supplemented with 0.5 mM Malathion at 30 ºC up to mid 

log phase. Cells were harvested at 4 ºC and washed twice 

with BSM. These cells were resuspended in 50 ml BSM 

supplemented with 0.5 mM Malathion. Aliquots of 10 ml 

were taken at different time interval of 0, 24 and 48 hrs. 

Heat killed cells of strain DKM8 were used as control. 

Malathion was extracted for 30 min from cell free 

supernatant by using 50 ml hexane in separating funnel 

(neutral extraction). After neutral extraction, the pH of the 

aqueous phase was adjusted to 2.0 with 2 N HCl and again 

extracted for 30 min with 50 ml hexane: acetone (acidic 

extraction). The amount of Malathion at different time was 

analyzed by gas chromatography. 

Results 

Isolation and Identification of Malathion Degrading 

Bacteria: A total of 10 morphologically different bacterial 

cultures (DKM1, DKM2, DKM3, DKM4, DKM5, DKM6, 

DKM7, DKM8, DKM9 and DKM10) were isolated by 

using enrichment method as shown in table 1. All the 

isolated bacterial cultures were showing growth in BSM 

media containing 0.5 mM Malathion. All the isolated 

bacterial cultures were also checked for their plant growth 

promoting activity. Out of the ten cultures, only one 

bacterial strain DKM8 utilized Malathion as a sole carbon 

and energy source along with plant growth promoting 

ability (indole acetic acid, phosphate solubilization, 

antifungal and protease activity), was selected for further 

study. 

The morphological, physiological and biochemical features 

of bacterial strain DKM8 are shown in table 2 and 3. It is a 

motile, gram negative, rod shape and catalse and oxidase 

positive. It was not growing on Maconkey agar as lactose 

fermenting microorganism. This culture can grow at 30 and 

37 o C, but was unable to grow at low temperature (4, 10, 15 

and 25 o C) and high temperature (42 and 60 o C). It can 

grow at different pH (5.0, 8.0 and 10.0) and different 

concentrations of NaCl (2%, 4%, 5% and 8%). This culture 

can utilize citrate as carbon source. The culture DKM8 was 

unable to hydrolyze tween 20, tween 40, starch, gelatin, 

esculin and urea. This isolate did not produce acid from 

sugar lactose. The culture DKM8 was producing acid from 

sugar dextrose. On the basis of these results the culture 

DKM8 was found very closely related to Pseudomonas 

xanthomarina. 

Growth of Isolated Bacterial Strains: On the basis of



growth over BSM agar medium containing 0.5 mM 

malathion, ten bacterial strains were selected for their 

growth in BSM medium containing 0.5 mM malathion, The 

growth of DKM1, DKM2, DKM3, DKM4, DKM5, DKM6, 

DKM7, DKM8, DKM9 and DKM10 is shown in fig. 1. 

The growth of bacterial culture DKM8 was rapid after 1 

day in the presence of 0.5 mM Malathion, showing 

exponential phase of growth. After 4 days, the growth of 

DKM8 declined which may be due to unavailability of 

Malathion as sole carbon source or due to the production of 

some other toxic compounds indicating the death phase. 

Indole Acetic Acid Production of Isolated Bacterial 

Strains: The bacterial isolates DKM3, DKM5, DKM8 and 

DKM9 were found to produce indole acetic acid. The 

intensity of colour change varied depending upon the 

amount of IAA produced by a particular isolate. The 

culture DKM8 and DKM9 were produced (3.7 and 2.2 

µg/ml IAA) after 2 days and (7.3 and 3.3 µg/ml IAA) after 

4 days respectively as shown in table 4. The bacterial 

culture DKM8 produced (3.5 and 3.8 µg/ml IAA) after 2 

days and (6.8 and 6.3 µg/ml IAA) after 4 days and culture 

DKM9 produced (2.4 and 2.1 µg/ml IAA) after 2 days and 

(3.4 and 3.1 µg/ml IAA) after 4 days respectively, at 0.5 

and 1.0 mM concentration of malathion. 

Phosphate Solubilization of Isolated Bacterial Culture: 

All the ten bacterial isolates were screened for their 

phosphate solubilization. Out of ten, only five bacterial 

isolates DKM1, DKM3, DKM5, DKM8 and DKM9 

formed clear zone on Pikovaskaya medium, considered as 

phosphate solubilizing bacteria as shown in table 1. The 

bacterial culture DKM8 was showing more phosphate 

solubilization as compared to DKM1, DKM3, DKM5 and 

DKM9 on the basis of diameter of halo zone in cm. The 

bacterial culture DKM8 was forming 1.1 and 1.2 cm halo 

zone after 7 and 10 days of incubation respectively. At 0.5 

and 1.0 concentration of Malathion, DKM8 bacterial 

culture was forming 1.1 and 1.1 cm halo zone after 7 days 

and 1.3 and 1.1 cm halo zone after 10 days respectively. 

Antifungal against Aspergillus sp. and Protease Activity 

of Isolated Bacterial Cultures: Out of ten, only two 

bacterial isolates DKM8 and DKM9 were forming halo 

zone on the nutrient agar plate containing Aspergillus 

growth suspension at 30 ºC, considered as antifungal active 

bacterial strain as shown in table 1. The halo zone was not 

formed by bacterial isolates DKM1, DKM2, DKM3, 

DKM4, DKM5, DKM6, DKM7 and DKM10. Only two 

bacterial isolates DKM8 and DKM10 were forming clear 

zone on the skimmed milk agar medium at 30 ºC, 

considered as protease producing bacteria as shown in table 

1. The clear zone on skimmed milk agar medium was not 

formed by bacterial isolates DKM1, DKM2, DKM3, 

DKM4, DKM5, DKM6, DKM7 and DKM9. 

Antibiotic Resistance Pattern of Bacterial Strain DKM8 

and DKM9: The antibiotic resistant pattern of DKM8 and 

(61) 

DKM9 was determined by using disc diffusion method. 

The bacterial culture DKM8 was sensitive towards 

antibiotic (cephalothin, teicoplanin, methicillin) and 

resistant towards (chloromphenicol, oxacillin, ampicillin, 

clarithromycin, gentamycin, amoxyclav, vancomycin, 

amikacin, novobiocin, erythromycin, co-trimoxazole, 

penicillin, azithromycin, ofloxacin, linezolid, clindamycin, 

tetracycline). The bacterial culture DKM9 was sensitive 

toward antibiotic (clarithromycin, amoxyclav, 

erythromycin, teicoplanin, ofloxacin, methicillin, linezolid, 

clindamycin) and resistant towards (chloromphenicol, 

oxacillin, ampicillin, gentamycin, vancomycin, amikacin, 

novobiocin, co-trimoxazole, penicillin, azithromycin, 

tetracycline) 

Degradation of Malathion by Bacterial Strain DKM8: 

To elucidate that the bacterial strain DKM8 degrades 

Malathion, resting cell study was performed. From GC 

analysis, it was found that the initial concentration of 

Malathion, 6.9 ppm, reduced to 4.74 ppm after 24 hr and 

further reduced to 2.04 ppm after 48 hr indicating 70.5 % 

depletion of Malathion by bacterial strain DKM8 as shown 

in fig. 2. However, in case of heat killed resting cell, no 

depletion of Malathion was observed. 

Discussion 

During enrichment, the natural selection of microorganisms 

takes place in the presence of xenobiotic compound and its 

rapid biodegradation is known to take place 7 . In most cases, 

the isolated microorganisms are able to utilize the pesticide 

as a source of a single element (C, N, P or S). 

Pseudomonas putida strain was able to use ethoprophos as 

a carbon source but not as a phosphorus source 21 . In the 

present study by using enrichment technique 10 bacterial 

strains (DKM1, DKM2, DKM3, DKM4, DKM5, DKM6, 

DKM7, DKM8, DKM9 and DKM10) were isolated from 

pesticide contaminated soil. All the isolated strains were 

able to grow in both minimal salt agar medium as well as in 

broth medium containing 0.5 mM Malathion as the sole 

carbon source. The different bacterial strains were isolated 

by using enrichment culture technique capable of degrading 

organophosphorus pesticides such as Malathion. These 

include Agrabacterium radiobacte 18 , Pseudomonas and 

Micrococcus sp. 37 and Bacillus thuringiensis 50 . 

The isolated bacterial strain DKM8 was found very close to 

Pseudomonas xanthomarina on the basis of morphological, 

physiological and biochemical characteristics. Most species 

of Pseudomonas can grow in minimal medium with a 

single organic compound as carbon and energy source 31 . 

Pseudomonads possess a variety of diverse catabolic 

pathways that enable them to metabolize an equally diverse 

number of low molecular weight compounds, including 

chlorinated aliphatic hydrocarbons such as 

phenoxyalkanoic acid herbicides 25 . It is known for its 

capacity to degrade phenolic compounds 19 and other 

aromatic substances. Therefore, Pseudomonads are ideal 

choice as the bacteria to be used for degradative



biotechnologies 33, 47 . 

In the present study, the growth of all isolates was observed 

in BSM media containing 0.5 mM Malathion. The growth 

of bacterial culture DKM8 was rapid after 1 day in the 

presence of 0.5 mM Malathion, showing exponential phase 

of growth. After 4 days, the growth of DKM8 declined 

which may be due to unavailability of Malathion as sole 

carbon source or due to the production of some toxic 

compound indicating the death phase. 

The physiologically most active auxin in plants is indole-3acetic 

acid (IAA), which is known to stimulate both rapid 

(e.g. increases in cell elongation) and long-term (e.g. cell 

division and differentiation) responses in plants. In the 

present study, bacterial isolates DKM3, DKM5, DKM8 and 

DKM9 were showing IAA production. The isolate DKM8 

was showing more IAA production as compared to DKM9. 

The IAA production ability of bacterial strain DKM8 was 

also checked in the presence of Malathion. It was found 

that there was no effect on IAA production in presence of 

different concentration of Malathion (0.5 mM, 1.0 mM and 

1.5 mM). Pseudomonas species have shown promising 

results in the production of IAA as plant growth promotion 

activites 42 . 

Phosphate solubilizing microorganism (PSM) is present in 

almost all soils, although their number varies depending 

upon the soil and climatic conditions 22 . First time in 1903, 

tricalcium phosphate (TCP) solubilization was 

demonstrated by soil bacteria in liquid and in solid 

medium 38 . However, the extent of phosphate solubilization 

varies with the source of inorganic phosphate and the 

micro-organisms involved 2 . PSM helps in utilization of 

indigenous rock phosphates 20 . Thus, PSM causes the 

release of nutrients into the soil for naturally balanced 

proportion 6 and exerts beneficial effects on plant 

development 14 . In the present study, all the ten bacterial 

isolates were screened for phosphate solubilization activity. 

The bacterial isolates DKM1, DKM3, DKM5, DKM8 and 

DKM9 were forming clear zone on the Pikovaskaya 

medium, considered as phosphate solubilizing bacteria. The 

bacterial culture DKM8 was showing more phosphate 

solubilization as compared to DKM1, DKM3, DKM5 and 

DKM9. The phosphate solubilizing ability of DKM8 was 

not adversely affected by the presence of Malathion. 

Microbial community composition can also contribute to 

the suppression of germination and mycelia growth of soil 

fungi to a certain extent 9 . In the present study, out of ten, 

only two bacterial strains (DKM8 and DKM9) showed 

antifungal activity against Aspergillus sp. The antifungal 

potential of Bacillus sp., Pseudomonas sp. and 

Streptomyces sp. has also been reported to inhibit the 

mycelial growth of many species of Aspergillus, 

Penicillium and Fusarium 28, 30 . 

For agricultural application, protease producing microorg- 

(62) 

anisms act as biological control agents for eradication of 

some fungal plant pathogens 41 . Regulation of soil protease 

activities in soil is important to maintain the fertility of 

soil 46 . In the present study, out of ten bacterial isolates, 

only two bacterial strains (DKM8 and DKM10) were 

showing protease activity on skimmed milk agar medium. 

The bacterial strain DKM8 showed more protease activity 

as compared to DKM10. 

The antibiotics produced by PGPR include: butyrolactones, 

zwittermycin A, kanosamine, oligomycin A, oomycin A, 

phenazine-1-carboxylic acid, pyoluteorin, pyrrolnitrin, 

viscosinamide, xanthobaccin and 2, 4-diacetyl 

phloroglucinol 48 . The DAPG is one of the most efficient 

antibiotics in the control of plant pathogens 10 and can be 

produced by various strains of Pseudomonas 35 . The isolates 

DKM8 and DKM9 were resistant to antibiotic 

(chloromphenicol, oxacillin, ampicillin, gentamycin, 

vancomycin, amikacin, novobiocin, co-trimoxazole, 

penicillin, azithromycin and tetracycline). 

The resting cell study was performed to check the 

quantitative degradation of Malathion. Resting cells of 

Pseudomonas derived from cultures were grown on 

diazinon or Malathion for extensive destruction of these 

two organophosphates 36 . In the present study, from GC 

analysis, it was found that the initial concentration of 

Malathion (6.9 ppm) reduced to 4.74 ppm after 24 hr and 

further reduced to 2.04 ppm after 48 hr indicating 70.5 % 

depletion of Malathion by strain DKM8. It was reported 

that a strain of Pseudomonas isolated from peppermill 

effluents was capable of degrading Malathion cometabollically 

up to Malathion mono carboxylic acid 39 . 

Several species of Pseudomonas have been reported to 

degrade organophosphorus pesticide 8,33 . 

Conclusion 

This research may have practical applications in 

bioremediation of Malathion contaminated soil, waste 

dump, industrial effluents and contaminated water 

environment. Apart from this, bacterial strain DKM8 can 

be used in the field of agriculture as a tool for plant growth 

promotion. Manipulations of such bacterial strains in 

relation to bioremediation and plant growth promotion are 

promising areas for further development. The bacterial 

strain DKM8 can be used as biofertilizer for sustainable 

crop production system along with remediation of 

Malathion under field conditions. Characterizing the 

pathway for degradation, identifying the genes and 

enzymes involved in this process represents areas for 

further investigation. 

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OD at 600 nm 

0.45 

0.4 

0.35 

0.3 

0.25 

0.2 

0.15 

0.1 

0.05 

0 

0 hr 6 hr 12 hr 24 hr 48 hr 96 hr 120hr 168 hr 

Time (hr) 

(63) 

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DKM1 

DKM2 

DKM3 

DKM4 

DKM5 

DKM6 

DKM7 

Fig. 1: Growth of isolated strains in basal salt medium containing 0.5 mM Malathion 

Malathion 

Concentration 

(ppm) 

8 

7 

6 

5 

4 

3 

2 

1 

0 

6.9 

6.9 

6.8 

4.74 

6.8 

0 hr 24 hr 48 hr 

Time (hr) 

Malathion degradation by 

DKM8 

Malathion degradation by 

heat killed cells 

2.04 

Fig. 2: Degradation of Malathion by bacterial strain DKM8



Table 1 

Growth promoting characteristics (IAA production, Phosphate solubilization, antifungal activity and protease 

activity) of isolated bacterial strains 

Culture Name IAA production Phosphate solubilization Antifungal activity Protease activity 

DKM1 - + - - 

DKM2 - - - - 

DKM3 + + - - 

DKM4 - - - - 

DKM5 + + - - 

DKM6 - - - - 

DKM7 - - - - 

DKM8 + + + + 

DKM9 + + + - 

DKM10 - - - + 

Table 2 

Identification of Malathion degrading bacterial culture DKM8 by morphological and physiological test 

Tests Result 

Colony morphology Circular, Cream, Entire, Flat 

Gram’s reaction - 

Cell shape and size Rod, 0.8x1.5 

Spore (s) - 

Motility + 

Growth at temperatures (°C) 

4, 10, 15, 25, 42, 60 - 

30, 37 + 

Growth at pH 

pH 5.0, 8.0, 10.0 + 

Growth on NaCl (%) 

2.0, 4.0, 5.0 + 

8.0 + 

+: Positive, -: Negative, (+): Weak positive 

Table 3 

Identification of Malathion degrading bacterial culture DKM8 by biochemical test 

Tests DKM8 

Growth on MacConkey - 

Indole test - 

Methyl red test + 

Voges Proskauer test - 

Citrate utilization + 

H2S production - 

Gas production from glucose - 

Gelatin, Esculin, Starch and Urea hydrolysis - 

Nitrate reduction + 

Ornithine and Lysine decarboxylase - 

Catalase and oxidase test + 

Tween 20 and Tween 40 hydrolysis - 

Acid production from Dextrose + 

Acid production from Lactose - 

+: Positive, -: Negative, (+): Weak positive 

(64)



Table 4 

Production of IAA (µg/ml supernantent) by bacterial isolates DKM8 and DKM9 

in the presence and absence of malathion 

Culture Time Control 0.5 mM (Malathion) 1.0 mM (Malathion) 

(days) (IAA µg/ml) (IAA µg/ml) (IAA µg/ml) 

DKM8 2 3.7 3.5 3.8 

4 7.3 6.8 6.3 

DKM9 2 2.2 2.4 2.1 

4 3.3 3.4 3.1 

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(Received 15 th October 2012, accepted 17 th January 2013)

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