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تأثیر رطوبت خاک بر تخریب زیستی هیدروکربن‌های آروماتیک چندحلقه‌ای (PAHs) توسط سویه‌های باکتریایی | ||
| زیست شناسی خاک | ||
| مقالات آماده انتشار، پذیرفته شده، انتشار آنلاین از تاریخ 18 شهریور 1404 | ||
| نوع مقاله: مقاله پژوهشی | ||
| شناسه دیجیتال (DOI): 10.22092/sbj.2025.370068.282 | ||
| نویسندگان | ||
| رضا محمدی کیا* 1؛ علیرضا فلاح نصرت آباد2؛ بهمن خوشرو3 | ||
| 1محقق/ مؤسسه تحقیقات خاک و آب/ سازمان تحقیقات، آموزش و ترویج کشاورزی | ||
| 2استاد، بخش تحقیقات بیولوژی و بیوتکنولوژی، مؤسسه تحقیقات خاک و آب، سازمان تحقیقات، آموزش و ترویج کشاورزی، کرج، ایران. | ||
| 3محقق پسادکترا، بخش تحقیقات بیولوژی و بیوتکنولوژی، مؤسسه تحقیقات خاک و آب، سازمان تحقیقات، آموزش و ترویج کشاورزی، کرج، ایران | ||
| چکیده | ||
| چکیده آلودگی خاک با هیدروکربن‌های آروماتیک چندحلقه‌ای (PAHs) به‌دلیل پایداری بالا، سمیت زیاد و تجمع زیستی، یکی از چالش‌های زیست‌محیطی مهم به‌شمار می‌رود. زیست‌پالایی با بهره‌گیری از ریزجانداران تجزیهکننده، روشی مؤثر و پایدار برای کاهش این آلاینده‌ها محسوب می‌شود. در این پژوهش، تأثیر سطوح مختلف رطوبت خاک با چهار سطح از تخلیه آب آبیاری به-مقدار 30%، 50%، 70% و90% آب قابل استفاده و سه سویه باکتریایی منتخب (Pseudomonas alcaligenes، Pseudomonas stutzeri و Enterobacter cloacae) بر کارایی تخریب زیستی PAHs در یک خاک لوم‌رسی آلوده به مواد نفتی در شرایط آزمایشگاهی و در قالب طرح فاکتوریل با پایه بلوک‌های کامل تصادفی (RCBD) در سه تکرار انجام گرفت. نتایج نشان داد که رطوبت خاک اثر معناداری بر کاهش غلظت کل PAHs داشت (P<0.05) و بیشترین کاهش غلظت (8/56٪) در رطوبت نزدیک به ظرفیت زراعی مشاهده شد. با وجود آن‌که اثر آماری سویه‌های باکتریایی معنادار نبود، اما عملکرد آن‌ها در کاهش غلظت PAHs متفاوت بود؛ طوری‌که E. cloacae و P. alcaligenes به‌ترتیب موجب کاهش 57/50 و 65/45 درصدی غلظت کل PAHs شدند. همچنین، برخی ترکیبات سبک‌تر مانند فلوران و فنانتـرن تجزیه‌پذیری بالاتری داشتند، در حالی‌که برخی ترکیبات سنگین‌تر نظیرBenzo(a)pyrene در برخی تیمارها افزایش یافتند که احتمالاً ناشی از تجزیه ناقص یا تولید واسطه‌های مقاوم‌تر بود. یافته‌ها بر اهمیت بهینه‌سازی هم‌زمان شرایط محیطی و انتخاب سویه‌های میکروبی مناسب در افزایش اثربخشی زیست‌پالایی تأکید دارند. | ||
| کلیدواژه‌ها | ||
| زیست‌پالایی؛ فنانترن؛ ریزجانداران تجزیهکننده؛ Enterobacter cloacae؛ آلودگی نفتی | ||
| عنوان مقاله [English] | ||
| The impact of soil moisture on the bioremediation of polycyclic aromatic hydrocarbons (PAHs) by bacterial strains | ||
| نویسندگان [English] | ||
| Reza Mohammadikia1؛ Alireza Fallah Nosratabad2؛ Bahman Khoshrou3 | ||
| 1Researcher / Soil and Water Research Institute / Agricultural Research, Education and Extension Organization&quot; | ||
| 2Professor, Department of Biology and Biotechnology Research, Soil and Water Research Institute (SWRI), Agricultural Research, Education and Extension Organization (AREEO), Karaj, Iran. | ||
| 3Postdoctoral Researcher, Department of Biology and Biotechnology Research, Soil and Water Research Institute (SWRI), Agricultural Research, Education and Extension Organization (AREEO), Karaj, Iran. | ||
| چکیده [English] | ||
| Extended Abstract Background and Objectives: Soil contamination by petroleum hydrocarbons, particularly Polycyclic Aromatic Hydrocarbons (PAHs), due to industrial activities, poses significant environmental and health risks. PAHs are persistent, toxic organic compounds, and their presence in soil alters its physicochemical and biological properties, threatening ecosystem health and food security. Bioremediation, utilizing microorganisms to degrade pollutants, offers an eco-friendly and cost-effective solution. The efficacy of bacterial degradation of PAHs is, however, critically influenced by environmental factors, especially soil moisture, which affects microbial activity, nutrient and oxygen availability, and pollutant accessibility. While optimal moisture (often 40-60% of water-holding capacity) is known to enhance degradation, and various soil amendments and bacterial strains can influence outcomes, a comprehensive understanding of the interactive effects of specific bacterial strains and varying moisture regimes on PAH bioremediation remains incomplete. Many studies focus on limited variables, leaving a gap in understanding these complex interactions, especially concerning less-studied bacterial strains. This study aimed to address this gap by investigating the effects of different soil moisture regimes and three selected bacterial strains on PAH bioremediation in a contaminated loamy-clay soil under laboratory conditions. The main hypothesis was that both bacterial strain type and soil moisture level, along with their interaction, would significantly impact PAH degradation efficiency. This research is distinguished by its simultaneous examination of multiple moisture levels and the comparative efficacy of three bacterial strains, including the less frequently studied Enterobacter cloacae, in degrading a spectrum of PAHs, coupled with an assessment of bacterial population dynamics. Materials and Methods: A factorial pot experiment based on a Completely Randomized Design (CRD) with three replicates was conducted. Treatments included four bacterial applications (three individual strains: Pseudomonas alcaligenes (B1), Pseudomonas stutzeri (B2), Enterobacter cloacae (B3); and an uninoculated control (B0)) and four soil moisture regimes. Surface soil (0–30 cm) from an oil-contaminated site near Tehran refinery was sieved, characterized (loamy-clay, pH, EC, organic matter, FC, PWP), and autoclaved at 121°C for 60 minutes. Bacterial strains were cultured in Nutrient Broth, harvested, washed, and resuspended to an OD600 of 0.6–0.8 (approx. 1.5–2.8 × 10⁹ CFU/mL). Thirty mL of inoculum (or sterile water for control) were added to each pot. The four moisture regimes were: I1 (30% depletion of available water, AWC), I2 (50% AWC depletion), I3 (70% AWC depletion), and I4 (90% AWC depletion), maintained daily by weighing. Pots were kept at 25 ± 2°C. After a 20-day bacterial stabilization period (at 60% FC), the moisture regimes were imposed for 65 days. Soil sampling occurred on days 32, 45, and 67 (destructive sampling of one pot per treatment). Bacterial populations were enumerated (CFU/g dry soil) on Nutrient Agar. Concentrations of 14 target PAHs were determined by HPLC (Agilent 1260, fluorescence detector, C18 column) following USEPA method 8310 after Soxhlet extraction (hexane/acetone 1:1) and silica/alumina column cleanup. Data were analyzed by two-way ANOVA, with means compared by Duncan's Multiple Range Test (P ≤ 0.05) using SAS and SPSS software; data normality was confirmed. Results: The results of this study showed that the examined soil, with an initial concentration of 33.4 mg/kg of polycyclic aromatic hydrocarbons (PAHs), was classified as highly contaminated, with fluoranthene being the dominant compound. Bacterial populations did not show significant changes across treatments; however, the performance of bacterial strains in reducing PAH concentrations was notable—particularly in treatments B1 and B3, which achieved reductions of 45.65% and 50.57%, respectively, indicating effective bioremediation. Moisture regimes also had a significant effect, with the highest reduction observed in treatment I1 (56.8%). Lighter compounds such as phenanthrene and naphthalene were more biodegradable, while heavier compounds like benzo(a)pyrene showed increases due to incomplete degradation or greater chemical stability. These findings highlight the importance of optimizing moisture conditions and selecting effective bacterial strains to enhance bioremediation of petroleum-contaminated soils. Conclusion: This study was designed to investigate the effects of different soil moisture levels and three selected bacterial strains on the bioremediation of polycyclic aromatic hydrocarbons (PAHs) in petroleum-contaminated soil. The results indicated that soil moisture, as a key environmental factor, had a significant impact on enhancing bioremediation efficiency. The greatest reduction in PAH concentrations was observed at moderate moisture levels, particularly in treatment I1 (with 30% depletion of available water), suggesting that optimal moisture conditions—by improving soil aeration, increasing contaminant mobility, and creating a suitable environment for microbial activity—can facilitate effective degradation of organic pollutants. On the other hand, although no statistically significant effect was observed for bacterial treatments, a comparison of the strains' performance revealed that certain strains, particularly Enterobacter cloacae and Pseudomonas alcaligenes, showed considerable capacity in reducing total PAHs. This suggests that the functional quality, enzymatic potential, and environmental adaptability of microbial strains are more important than merely increasing bacterial population. Moreover, the observed increase in concentrations of some toxic compounds in certain treatments raises the possibility of incomplete degradation and the formation of hazardous intermediate products, which should be considered in the design of remediation processes. Overall, this study emphasizes that successful bioremediation of petroleum-contaminated soils requires the simultaneous consideration of multiple factors, including optimal moisture, selection of effective microbial strains, and precise monitoring of organic compound behavior throughout the process. The findings can serve as a valuable guide for the design and implementation of soil remediation projects. | ||
| کلیدواژه‌ها [English] | ||
| Bioremediation, Phenanthrene, hydrocarbon-degrading microorganisms, Enterobacter cloacae, petroleum contamination | ||
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