糙皮侧耳和鞘脂菌NS7对多环芳烃污染土壤的生物强化与协同作用

Bioaugmentation of polycyclic aromatic hydrocarbons-contaminated soil with Pleurotus ostreatus and Sphingobium sp. NS7 and their synergistic effect

摘要:

[背景] 真菌和细菌被认为在多环芳烃污染土壤生物修复过程中发挥协同作用，目前在真实土壤体系中开展真菌-细菌协同降解研究较少。[目的] 研究真菌和细菌对不同种类多环芳烃降解的差异及对蒽和苯并[a]蒽的生物强化与协同作用。[方法] 选用多环芳烃降解真菌和细菌各一株，在液体纯培养体系下分析它们对不同种类多环芳烃降解的差异，在土壤体系中采用放射性同位素示踪技术研究2种微生物对蒽和苯并[a]蒽的生物强化与协同作用。[结果] 供试细菌鞘脂菌NS7能够很好地降解低环种类多环芳烃，以蒽作为唯一碳源时可以将其完全降解，在复合污染条件下对菲、蒽、荧蒽、芘等降解效果突出（>90%），对苯并[a]芘降解效果较差（9.76%）。相比而言，供试真菌糙皮侧耳菌对苯并[a]芘具有更好的降解效果（21.18%），对低环多环芳烃降解效果明显不如降解菌NS7。在自然土壤中，蒽和苯并[a]蒽具有明显不同的矿化效率，分别为18.61%和4.28%，在蒽污染土壤中加入鞘脂菌NS7并未显著提高蒽的矿化率（P>0.05），相比而言，苯并[a]蒽污染土壤中加入糙皮侧耳显著提高了污染物矿化效率（2.24倍），表明真菌和细菌在土壤环境中的定殖存活能力可能影响了生物强化效果。采用灭菌土壤排除土著微生物的竞争排斥作用，研究了真菌菌丝对生物强化降解的影响，发现在蒽污染土壤中，真菌菌丝的迁移作用显著提高了细菌鞘脂菌NS7对污染物的矿化率，从1.75%提高到5.91%；而在苯并[a]蒽灭菌污染土壤中，接种糙皮侧耳却没有发现苯并[a]蒽矿化率提高的现象，表明自然土壤中真菌强化降解苯并[a]蒽的作用可能是源于真菌菌丝促进污染物和土著降解菌的接触，而非直接来自真菌本身。[结论] 细菌能够很好地降解低环种类多环芳烃，而真菌对高环种类多环芳烃降解效果较好。真菌可能通过菌丝促进土著微生物在土壤中的迁移，增大多环芳烃和土著降解菌的接触，从而促进了多环芳烃降解。研究加深了对多环芳烃污染土壤生物强化修复的认识，对发展基于真菌-细菌协同作用的生物强化与调控技术提供理论指导。

关键词:多环芳烃;生物强化;真菌;细菌;同位素示踪

Abstract:

[Background] Fungi and bacteria are considered to play a synergistic role in the bioremediation of polycyclic aromatic hydrocarbons (PAHs)-contaminated soil. However, there are limited studies on their synergistic degradation in soil. [Objective] This paper aims to investigate the different PAHs-degrading abilities of Pleurotus ostreatus and Sphingobium sp. NS7 and reveal their synergistic role in the biodegradation of anthracene and benzo[a]anthracene in soil. [Methods] The PAH degradation by P. ostreatus and Sphingobium sp. NS7 was performed in liquid culture. Soil microcosms were set up with radiolabeled anthracene and benzo[a]anthracene to investigate the fate of PAHs after bioaugmentation. [Results] NS7 can efficiently degrade low-molecular-weight (LMW) PAHs, as it removed almost all the anthracene when anthracene was the only carbon source. In the case of compound contamination, the bacterium removed >90% of phenanthrene, anthracene, fluoranthene, and pyrene while degraded benzo[a]pyrene with a low rate (9.76%). By contrast, P. ostreatus demonstrated relatively high removal rate (21.18%) of benzo[a]pyrene. The degradation rate of LMW PAHs by P. ostreatus was much lower than that by NS7. In the natural soil, the mineralization rate of anthracene and benzo[a]anthracene was 18.61% and 4.28%, respectively. P. ostreatus promoted benzo[a]anthracene mineralization in natural soil (increased by 2.24 folds) but NS7 failed to significantly improve anthracene mineralization. Thus, the competition of indigenous microbial communities might affect the survival of exogenous microorganisms. A sterile soil system excluding the microbial competition was used to investigate the helper role of fungal hyphae in the synergistic degradation. With the help of fungal hyphae, the mineralization of anthracene was enhanced by NS7 (mineralization rate up from 1.75% to 5.91%), but no promotion effect was observed in benzo[a]anthracene mineralization. Therefore, the reason for the enhancement of benzo[a]anthracene mineralization in natural soil by P. ostreatus might be that the fungal hyphae promoted the migration of indigenous PAHs-degrading bacteria in soil matrix and thus enhanced the contact of them with the contaminant. [Conclusion] Bacteria can efficiently degrade LMW PAHs while fungi showed high degradation rate of high-molecular-weight PAHs like benzo[a]pyrene. Enhanced PAH mineralization in natural soil was observed after P. ostreatus inoculation, and the mechanism might be that the fungal hyphae promoted migration of indigenous bacteria in the soil matrix. This study deepens our understanding of the synergistic degradation of PAHs in soil by fungus and bacterium and lays a theoretical basis for soil bioremediation based on the synergistic effect of fungi and bacteria.

Key words:polycyclic aromatic hydrocarbons;bioaugmentation;fungus;bacterium;radiolabeling