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POTENTIAL OF INDIGENOUS KLEBSILLA SP. FOR CHLORPYRIFOS BIODEGRADATION.

Byline: M.Farhan, A.U.Khan. A.Wahid, A.S.Ali and F.Ahmad

ABSTRACT: Pesticides are one of the major disturbing factors in ecosystems, so their removal/degradation is the need of time. In the present research, 56 microbial strains were isolated from cotton growing areas of Punjab. Strain Ct27 (Klebsiella sp.) was most resistant/effective in chlorpyrifos degradation. Biodegradation potential of Klebsiella sp. was studied under different conditions like; concentration, carbon sources, pH and inoculum densities. Klebsiella sp. showed 90 (Percent) chlorpyrifos biodegradation (200mgL-1) at pH8 and 105CFU/mL with addition of glucose in 18 days. Presence of other nutrients enhanced chlorpyrifos degradation probably due to high growth on easily metabolizable compounds which in turn favors biodegradation. This strain can be used for bioremediation and ecological restoration of sites, contaminated with chlorpyrifos.

Key words: Biodegradation, bioremediation, organochlorines, chlorpyrifos, Klebsiella.

INTRODUCTION

Chlorpyrifos (CP) is "moderately hazardous" pesticide, with annual consumption of 1280 MT (40 million US dollar) all over the world and is ranked 9th in term of use. It is commonly used on vegetables, cereals and cotton for pest control. For domestic purposes it is used against flies, mosquitoes and other house hold pests (Li et al., 2010). Harmful effects of chlorpyrifos include twitching of muscles, skin irritation, depression, respiratory failures, convulsion, subtle neurological effects and death (Ahmad et al., 2012). Chlorpyrifos may persists in environment up to one year, have low water solubility (2mgL-1) and soluble in organic solvents. It accumulates in aquatic plants, blue-green algae, mosquito fish and goldfish. Only limited information is available on the fate of chlorpyrifos in the soil-crop system (Tariq et al., 2007).

Chlorpyrifos degrades into number of toxic products which have bioaccumulation tendency (Fang et al., 2008). 3,5,6-trichloro-2-pyridinol (TCP) is the main metabolite of chlorpyrifos having antimicrobial properties (Thengodkar and Sivakami, 2010).

Biodegradation of organic wastes to an innocuous state or levels is the need of an hour. Bioremediation involving microbes has received much attention (Liu et al., 2012). Microbes that are present in pesticide contaminated sites for long duration, develops the ability to degrade it. Such microbes with advanced/new traits can be used for pesticide degradation. Several unsuccessful efforts were made, to isolate a chlorpyrifos degrading microbial system (Thengodkar and Sivakami, 2010). One of the reason behind such failure is that the chlorpyrifos metabolize/degrade into 3,5,6-trichloro-2-pyridinol TCP) which has antimicrobial effects. Therefore, interest has been shifted to use indigenous microorganisms for biodegradation (Mukherjee et al., 2004). Successful biodegradation by number of isolated have been reported (Lu et al., 2013; Farhan et al., 2012; Liu et al.,2012; Ahmad et al.,2012; Li et al.,2010; Thengodkar and Sivakami, 2010; Singh et al.,2009; Fang et al., 2008; Ghanem et al., 2007; Singh et al., 204).

The aims of the present research are to isolate resistant bacteria from agricultural soils that are under extensive chlorpyrifos spray and investigate the potential of these bacteria against Chlorpyrifos biodegradation. Also explore the major factors that may enhance chlorpyrifos biodegradation.

MATERIALS AND METHODS

Chemicals and soil sampling: Throughout the experiment only analytical grade chemicals were used. Chlorpyrifos (95 (Percent) was obtained from Pak China Chemicals, Lahore. Soil samples were collected by standard methods (Tariq et al., 2007), from cotton growing fields (extensively under the spray of chlorpyrifos) of Multan, Muzaffarghar, Rajanpur, Faisalabad, Bhawalpur, D.G. Khan.

Enrichment, isolation and selection of microbial strain: Chlorpyrifos resistant microbial strain were isolated from collected samples using minimal salt medium (MSM) at pH 7. The medium contained: 200mg MgSO4, 900mg K2HPO4, 200mg KCl, 2mg FeSO4, 2mg MnSO4, 2mg ZnSO4 and 1000mg NH4NO3/L. About 25g - 1 of soil sample, 25mlL chlorpyrifos and 200mL sterile MSM were added in 500ml flask and shaked at 100rpm.

One week later 10ml of the culture was transferred to fresh MSM containing more pesticide as was used previous week. After every week 10ml culture was transferred to fresh MSM and pesticide concentration of 175mlL-1 chlorpyrifos was achieved, successively.

From the last sub-culture, pure cultures were established by serial dilution and streak plate method (Ortiz-Hernandez and Sanchez-Salinas, 2010). Strain exhibiting maximum growth and CP resistance was selected for further studies.

Taxonomic identification and inoculum preparation: Isolated strains were identified using Bergey's Manual of Determinative Bacteriology, on the basis of physiological, morphological and biochemical properties (Holt et al., 1994). Required cell density of cell suspension was adjusted through serial dilution methods and haemocytometer slide-bridge (Butt et al.,2011) Experimental setup for Biodegradation of chlorpyrifos: To study the potential of isolated strain for chlorpyrifos biodegradation, shake flask studies were conducted. 25mL of sterile MSM, inoculum (105 CFU/mL) and known concentration of chlorpyrifos was mixed, shaked (100rpm) and incubated (37oC). In a control flask, 25mL MSM (sterile) and known concentration of pesticide was added, control was not inoculated. All the experiments were conducted in triplicate. After regular interval, samples from these flasks were drawn aseptically and were analyzed for remaining pesticides concentration (Fang et al., 2008).

Extraction and HPLC analysis of chlorpyrifos: For HPLC analysis the extracted samples were centrifuged (at 7200rpm) for about 10min and supernatant was mixed with equal volume of dichloromethane (DCM). Organic layer was collected and DCM was evaporated (under nitrogen) at room temperature. Residues were filtered (0.45 mm diameter) after dissolving in acetonitrile. Varian HPLC, equipped with a ternary gradient pump, UV detector, electric sample valve, column oven and C18 reversed-phase column was used for pesticide analysis using mobile phase of methanol: water (85:15, v:v). HPLC conditions were set as follows, sample volume: 20 (Mu) L, flow rate: 1mLmin-1, retention time: 15min and wavelength: 290nm (Ortiz-Hernandez and Sanchez- Salinas, 2010).

Effect of different conditions on chlorpyrifos degradation: Pesticide concentration of 75-125mgL-1 was investigated to study the effect of concentration on biodegradation process. Experiments were setup as described in previous section with varying chlorpyrifos concentration and keeping all other factors constant. To investigate the optimum temperature range, the experimental setups were incubated at different temperatures. pH range of 6-8.5 was tested in order to optimize chlorpyrifos degradation. Different carbon sources tested for enhancement of chlorpyrifos degradation were glucose, yeast extract and starch.

All the C-sources were added in experimental setup to the final concentration of 5gmL-1. Inoculum ranges of 104-108 CFUmL-1 were tested by using different inoculum and keeping all other factors constant. Statistical analysis: Data was analyzed using Costat and SPSS software.

RESULTS AND DISCUSSION

Indigenous bacteria are considered the best option for bioremediation of bound and aged pesticide, as they provide eco-friendly solution and do not pose any threat to native flora and fauna (Thengodkar and Sivakami, 2010). Soil decontamination/restoration by using isolated microbe has been successful carried out by many researchers (Liu et al., 2012; Ahmad et al., 2012; Li et al., 2010; Thengodkar and Sivakami, 2010; Singh et al., 2009; Fang et al., 2008). Lu et al., (2013) isolated Cupriavidus sp. DT-1 form Chinese contaminated soils, which were under cultivation. The study reported 100 (Percent) degradation of CP and 94 (Percent) degradation of TCP. As compared to the control experiment Cupriavidus sp. DT-1 showed significantly high degradation. The detailed pathway reveled that CP is first broken down into TCP and then de-chlorinated into 2-pyridinol. Pyridine ring were then subjected to cleavage and thus complete mineralization results.

Tortella et al., (2012) achieved 50 (Percent) biodegradation of CP with initial concentration of 480mgKg-1, by using biobeds or biomixtures (mixture of peat: soil: straw in proportion of 25:25:50 by weight).

The main purpose of the biobed was to retain and degrade pesticide. The retention of pesticide in biobed depends on the sorption capacity and degradation depends on the biological activity. The results concluded that higher maturity leads to the more degradation. Ahmad et al.,(2012) investigated the combined use of plants and microbes for CP biodegradation. The plant and microbes used were rye grass and Bacillus cereus. In soil experimentation the combination of plant and microbes degraded 97 (Percent) of CP within 45days. This study highlights the facts that exogenous microbes can be used successfully for the bioremediation process. Farhan et al., (2012) isolated Pseudomonas sp. from industrial drain. This strain showed good degradation efficiency as compared to the control. Complete biodegradation yield carbon source and energy by the process of oxidation. This carbon and energy is used for the growth of microbes.

Potential microbes from other sites can be introduced into the environment where local or indigenous microbes are not available (Kadian et al.,2012).

Isolation and identification of chlorpyrifos degrading bacteria: In the present study 56 isolates were screened, only few were resistant at higher concentration of CP (175mgL-1). Ct27 showed very good growth and is selected for in-depth study of chlorpyrifos degradation. Other isolates were sensitive to increasing concentration of chlorpyrifos. Ct27 was identified as Klebsiella sp. by standard protocol set in Bergey's Manual of Determinative Bacteriology (Holt et al., 1994). To our understanding, this is the enhanced biodegradation of chlorpyrifos by Klebsiella sp. Klebsiella is a versatile genus and previous reports suggested that this genus could degrade a number of pollutants, including pyrene (Zhang and Zhu, 2012), propionitrile (solvent, organonitriles group) (Chen et al., 2010), azo dyes (Franciscon et al., 2009), organophosphate pesticide (Ghanem et al., 2007) and present study also supported their immense biodegradation diversity.

Effect of chlorpyrifos concentration: Among the vital factors that significantly effects CP degradation is the concentration of active material. Very high concentration usually leads to the failure of biodegradation as microbes are not resistant against that. On the other hand very low pesticide concentration, leads to strong affinity with soil particles thus make it non-available to microbes. The maximum degradation of 90 (Percent) was achieved in 18days of incubation at 200mgL-1 (Fig. 1). Klebsiella is best adaptive at low concentration, the chlorpyrifos degradation decreases with the increase in concentration. The growth of Klebsiella sp. also decreases with increase in chlorpyrifos concentration. These results are in correspondence with those of Singh et al. (2004), who reported maximum biodegradation of chlorpyrifos at 250mgL-1. As the concentrations of pesticide increases longer lag phases were observed.

Karpouzas and Walker (2000) suggested that these longer lag phases might because of the requirement of larger microbial number and acclimation period to begin enhanced biodegradation. To our best knowledge this Klebsiella sp. has enhanced abilities for chlorpyrifos degradation.

Effect of media temperature: CP degradation pattern of Klebsiella at different temperature is given in Figure 2, which narrates that Klebsiella prefer 35oC, as maximum degradation was observed at this temperature. Degradation rate at all the temperature ranges differ significantly. At 40oC longer lag phase was revealed up to 12 days, after that degradation rate increased. Degradation at 35oC was 61 (Percent) more as compared to degradation at 40oC. This signifies the importance of temperature in biodegradation (Ahmad et al., 2012) Effect of media pH: One of the important abiotic factors that affect the microbial ability towards biodegradation is pH.

Klebsiella exhibits degradation at most of the pH ranges (alkaline to acidic) but with varying degree (Fig.3). Maximum degradation was observed at pH 8. Singh et al. (2004) reported rapid chlorpyrifos degradation by an Enterobacter sp at higher pH, while it was significantly slow at low pH. Conversely, Karpouzas and Walker (2000) reported Pseudomonas putida (epI and epII) which quickly degraded organophosphate pesticide (ethoprophos) from pH 7.6 to 5.5. In the present study, higher pH shows maximum degradation. Possibly, chlorpyrifos degrading enzymes have optimum activity at high pH (Swetha and Phale, 2005).

Effect of carbon source: Micro and macro nutrients play very promising role in microbial growth and degradation process. These nutrients may boost or retard the growth of microbe being toxic. Without any additional carbon source, Klebsiella sp. degraded 75 (Percent) of chlorpyrifos in 18 days (Fig. 4). However with the addition of nutrients like glucose the degradation increased up to 90 (Percent) . Yeast extract also positively influenced the degradation and increased the process up to 82 (Percent) (Fig. 4). The results of Singh et al. (2004) are contradictory with present study, who reported Enterobacter strain which stops CP degradation with the addition of glucose, and after 1.5 days the degradation process started again. On the other hand, in present study Klebsiella sp. not only carry on chlorpyrifos degradation, but also boost the process. The elevated biodegradation rate with addition of glucose is a sign that glucose has a critical role in initial growth of Klebsiella sp. (Swetha and Phale, 2005).

This boosts in biodegradation is perhaps due to co-metabolism, where addition of easily metabolizable organic matter is used as primary source of energy and carbon. Earlier findings suggested the use of glucose as co-substrate and the process of co-metabolism is widely accepted in biodegradation management (Sarkar et al., 2010).

Effect of inoculum density on degradation of chlorpyrifos: Initial inoculum densities of 104-108 CFU/mL were tested and it was found that the inoculum density has a direct relationship with chlorpyrifos degradation (Fig. 5). With the highest inoculum density of 108 CFU/mL, chlorpyrifos degraded up to 99 (Percent) within 18days of incubation with apparently no lag phase. Whereas, low inoculum density (104 CFU/mL) shows longer lag phase and degraded maximum of 81 (Percent). In general, longer lag phases were observed prior to speedy degradation. At the start of biodegradation process the number of active bacterial population used to be small, longer lag phase represents the time required to maintain the certain significant number of bacterial population. Before that significant number of active bacterial population biodegradation cannot proceeds (Ahmad et al., 2009).

This significant number depends on resistant level of microbial strain and also on the chemical nature of material to be degraded (Fang et al., 2008).

Conclusions: Bioremediation is gaining popularity for ecological restoration. Bioremediation depends of the selection of appropriate/competent microbial strains. The most successful elimination of contaminants may be achieved using inoculants isolated from contaminated environments (where contamination had occurred over years). These indigenous microbe give duel benefit, first they detoxify the contaminant and secondly do not pose any serious threat to other native microbes. Many biotic and abiotic factors significantly influence the process of biodegradation. In conclusion, present results validate the potential of Klebsiella sp. for chlorpyrifos degradation. This strain can be used for bioremediation of contaminated sites.

Acknowledgments: The authors are thankful to GC University for providing funding necessary for the study. We are also grateful to University of Veterinary and Animal Sciences (Lahore) and Pakistan Council of Scientific and Industrial Research (Lahore) for providing lab facilities and BahuDin Zakaria University (Multan) for technical support.

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Sustainable Development Study Centre, GC, University, Lahore Department of Environmental Science, Bahudin Zakria, University, Multan Corresponding Author: m.farhan_gcu@yahoo.com
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Date:Mar 31, 2013
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