IN-VITRO STUDIES ON OIL DEGRADING BACTERIA ISOLATED FROM OIL CONTAMINATED SOIL OF VANIYAMBADI AND AMBUR AREAS OF VELLORE DISTRICT

IN-VITRO STUDIES ON OIL DEGRADING BACTERIA ISOLATED FROM OIL CONTAMINATED SOIL OF VANIYAMBADI AND AMBUR AREAS OF VELLORE DISTRICT

K. Malathi ^* and V. Prabha

Department of Biochemistry, D.K.M College for Women, Vellore-632 001, Tamil Nadu, India

ABSTRACT: The oil polluted soil has many hydrocarbons which can be degraded by microbes. These oil degrading microbes were isolated from the oil contaminated soil through plate and dilution technique. The oil contaminated soils were collected from the oil spilled places of Vaniyambadi and Ambur areas of Vellore District, Tamil nadu, India. Through the biochemical tests, the isolated bacterial strains were identified as Pseudomonas aeruginosa and Bacillus subtilis, the strains were further confirmed by starch hydrolysis test and by growing on cetrimide agar. It is screened for the biosurfactant production through drop collapsing test and Emulsification Index (E₂₄) using diesel, petrol, kerosene and tween 20. Biosurfactants are amphiphilic compounds which reduce surface and interfacial tension. Here, Pseudomonas aeruginosa had shown higher biosurfactant activity, when compared to Bacillus subtilis

Biosurfactants,

Bacterial strains, Bioremediation, Microbes, Soil pollution

INTRODUCTION: Pollution of the soil system with the excess amount of chemicals or other substances resulted in the turndown of its fertility and which resulted in the poor yield of crops. The soil pollution is mainly caused by the accidental oil spills, agricultural activities, waste disposal and industrial outlets which mix with the soil and spoil the nature of the soil. This problem may be overcome by bioremediation. Bioremediation is the biological process to degrade or transform contaminants or impairments from the soil and water.

This process totally depends on microbes, which carry out their metabolic process and use this chemical contaminants as an energy source and converts contaminants into harmless or less toxic products ¹.

Biosurfactants are amphiphilic compounds produced on living surfaces, mostly microbial cell surfaces or excreted extracellularly and contain hydrophobic and hydrophilic moieties that reduce surface tension and interfacial tension between individual molecules at the surface and interface respectively ². Biosurfactants are grouped into six major classes based on the producing microorganism. These classes are glycolipids, phospholipids, polysaccharide lipid complexes, lipoprotein-lipopeptides, hydroxylated and cross linked fatty acids and the complete cell surface ³. Microorganisms exhibit emulsifying activity by producing biosurfactants and utilize contaminants as substrate and mineralize them into harmless products. The present study was focused on the isolation of oil degrading bacteria and screening the biosurfactant activity of the isolated bacterial strains.

MATERIALS AND METHODS:

Collection of soil sample:

The oil contaminated soil samples were collected from the oil spilled places of Vaniyambadi and Ambur areas of Vellore District, Tamil nadu, India.

Isolation of bacteria from the soil:

The bacterial strains were isolated from the soil through serial dilution technique and nutrient agar as a media. Staining techniques and biochemical tests were performed to identify the isolated bacterial strains⁴. These two strains were further confirmed through starch hydrolysis test and growth of the streaked culture on cetrimide agar.

Screening for Biosurfactant Activity:

Biosurfactant activity of the isolated bacterial strains were detected by using emulsification stability testand Drop collapsing test using four different oil sources namely Petrol, Diesel, Kerosene and Tween 20.

Emulsification Test:

The emulsifying capacity was evaluated by an emulsification index E₂₄⁵. The emulsifying activity of the culture supernatant was estimated by adding 3ml of the supernatant and adding equal volume of oil of interest to the same tube. The tube was vortexed for 10 seconds to 1 minute. Then held stationary for 1 minute and then visually examined for turbidity of stable emulsion. Emulsifying power was measured by vortexing equal volumes of the centrifuged culture with the oil for 1 minute and determining the percentage of volume to settle for 24 hours and the height of the emulsion was measured⁶.

E₂₄ (%) = (Height of emulsion formed / Total height of solution) X 100

Drop collapsing test:

2µl of oil was added to each well of plate lid. The lid was equilibrated for 1 hour at room temperature and then 5 microliter of the culture supernatant was added to surface of oil. The shape of the drop on the oil surface was inspected after 1 minute. Biosurfactant producing cultures giving flat drops were scored as ‘positive’. Those cultures that have rounded drop were scored as ‘negative’ indicative of the lack of biosurfactant production⁷.

RESULTS AND DISCUSSION: Totally eight oil contaminated soil samples were collected from the oil spilled places like Petrol bunk, Diesel bunk, Mechanical shop and Coconut oil spills. From these samples, the bacterial strains were isolated by using nutrient agar plate and serial dilution techniques. Table 1 shows the presence (+) and Absence (-) of the growth of bacterial colonies (Fig. 1) from the different soil samples at various dilution conditions. Here, most of the all eight samples have shown better bacterial growth which can be further isolated and subcultured.

FIG. 1: BACTERIAL COLONIES

TABLE 1: ISOLATION OF OIL DEGRADING BACTERIA FROM THE OIL CONTAMINATED SOILS

(+) – Presence, (-) – Absence, P - Petrol, D - Diesel, M - Mechanical Shop,

C - Coconut oil, VNB – Vaniyambadi, AMB – Ambur.

Table 2 shows the biochemical test results for the identification of bacterial isolates. Out of eight different soil samples, totally 15 bacterial strains were isolated using nutrient agar medium and these strains were undergone for gram staining and biochemical tests like Voges-proscauer test (Fig.2), Urease test (Fig. 3), Indole production test (Fig. 4), Simmons citrate agar test (Fig.5), Triple sugar iron test (Fig.6), Methyl red test (Fig.7),Catalase and Oxidase test etc. From these test results the strains 9, 10, 11 and 12 were identified as a gram negative bacteria Pseudomonas aeruginosa   and strains 13, 14 and 15 are identified as a gram positive bacteria Bacillus subtilis.

TABLE 2: BIOCHEMICAL TEST FOR THE IDENTIFICATION OF BACTERIAL ISOLATES

VP - Voges-Proscauer, MR – Methylred test, SCA – Simmon Citrate Agar test, TSI – Triple sugar iron test

Biochemical test for the identification of bacterial isolates:

C- Control, P- Positive, N- Negative

For further confirmation of Pseudomonas aeruginosa, it was streaked on a Cetrimide Agar plate. Cetrimide Agar was used as a selective medium for the isolation of Pseudomonas aeruginosa (Fig. 9). This medium inhibits bacteria other than Pseudomonas aeruginosa. Same way Bacillus subtilis was streaked on starch agar medium. There is no color change found in the medium when organisms hydrolyze the starch, then the plate turns black after the addition of iodine (depending on the concentration of iodine). A clearing zone around the bacterial growth confirms that the organism streaked was Bacillus subtilis (Fig.8).

Confirmation test for the Bacterial isolates:

TABLE 3: SCREENING OF EMULSIFICATION INDEX (E₂₄%) OF BACTERIAL ISOLATES

(+) – Presence, (-) – Absence.

Table 3 shows the Emulsification index (E24%) of the bacterial isolates. The confirmed bacterial strains Pseudomonas aeruginosa and Bacillus subtilis were sceened for the biosurfactant activity. Biosurfactant play a role in emulsifying hydrocarbons. Out of seven isolated bacterial strains, based on the growth five bacterial strains were selected for the screening of biosurfactant production. These 5 bacterial isolates have shown better results against different oils (Fig.10, 11, 12 and 13). In this study S9, S10, S12 were Pseudomonas aeruginosa and S14, S15 were Bacillus subtilis. These two bacterial strains have the ability of emulsifying oils. S9 have shown the best of 62.85% , 68.57% against Kerosene and Tween 20 respectively. Same way S12 shown best of 62.86% against Diesel⁸.

Emulsification activity of bacterial isolates on different oils:

TABLE 4: DROP COLLAPSING TEST FOR THE BACTERIAL ISOLATES

(+) – Presence, (-) – Absence.

FIG.14: DROP COLLAPSING TEST FOR BACTERIAL STRAINS

Table 4 shows thedrop collapsing test for the biosurfactant production from bacterial isolates. Biosurfactant production of bacterial strains were further screened by using the qualitative drop collapsing test against different oils. Here, based on the flat drop appearance(+)  and round drop appearance (-), the biosurfactant production was confirmed (Fig.14). Same way S9 and S14 have given the flat drop appearance against different used oils.This two test results confirms that Pseudomonas aeruginosa and Bacillus subtilis have biosurfactant acrivity^9,10.

CONCLUSION: This study concludes that the oil degrading bacteria has the biosurfactant activity. The microorganisms utilize hydrocarbons present in the oils as a source and convert that as a usable energy. It is very clear that Pseudomonas aeruginosa and Bacillus subtilis has biosurfactant activity. The biosurfactants isolated from the microbes can be used in the bioremediation process to treat the contaminated soil, waste water and gases.

ACKNOWLEDGEMENT: The authors acknowledge the support of the Principal Dr. P.N. Sudha, Principal DKM College for Women (Autonomous) for providing necessary facilities in carry out this work.

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    How to cite this article:

    Malathi K and Prabha V: In-Vitro Studies on Oil Degrading Bacteria Isolated from Oil Contaminated Soil of Vaniyambadi and Ambur Areas of Vellore District. Int J Pharm Sci Res 2015; 6(8): 3478-83.doi: 10.13040/IJPSR.0975-8232.6(8).3478-83.

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