浅析植物根分泌物与根际微生物的相互作用关系

综述了根分泌物与根际微生物、病原微生物的相互影响以及根际微生物作用几方面内容。根分泌物作用于周围环境产生根际效应,影响根际微生物的生态分布、种群组成,不同抗性品种根分泌物对病原微生物表现出促进或抑制的作用;而根际微生物又会对根分泌物起到修饰限制作用,通过各种途径改变根分泌物的数量、组成。根分泌物与根际微生物间的作用是相互的。此外,根际微生物在植物养分转化与吸收、病虫草害控制、物质循环等方面发挥着不可替代的作用。     

Efficiency of phenol biodegradation by planktonic Pseudomonas pseudoalcaligenes (a constructed wetland isolate) vs. root and gravel biofilm

In the last two decades, constructed wetland systems gained increasing interest in wastewater treatment and as such have been intensively studied around the world. While most of the studies showed excellent removal of various pollutants, the exact contribution, in kinetic terms, of its particular components (such as: root, gravel and water) combined with bacteria is almost nonexistent.In the present study, a phenol degrader bacterium identified as Pseudomonas pseudoalcaligenes was isolated from a constructed wetland, and used in an experimental set-up containing: plants and gravel. Phenol removal rate by planktonic and biofilm bacteria (on sterile Zea mays roots and gravel surfaces) was studied. Specific phenol removal rates revealed significant advantage of planktonic cells (1.04 × 10⁻⁹ mg phenol/CFU/h) compared to root and gravel biofilms: 4.59 × 10⁻¹¹-2.04 × 10⁻¹⁰ and 8.04 × 10⁻¹¹-4.39 × 10⁻¹⁰ (mg phenol/CFU/h), respectively.In batch cultures, phenol biodegradation kinetic parameters were determined by biomass growth rates and phenol removal as a function of time. Based on Haldane equation, kinetic constants such as μ_max = 1.15/h, K_s = 35.4 mg/L and K_i = 198.6 mg/L fit well phenol removal by P. pseudoalcaligenes.Although P. pseudoalcaligenes planktonic cells showed the highest phenol removal rate, in constructed wetland systems and especially in those with sub-surface flow, it is expected that surface associated microorganisms (biofilms) will provide a much higher contribution in phenol and other organics removal, due to greater bacterial biomass.Factors affecting the performance of planktonic vs. biofilm bacteria in sub-surface flow constructed wetlands are further discussed.     

Rhizoremediation of hydrocarbon contaminated soil using Australian native grasses

Rhizoremediation involves the breakdown of contaminants in soil resulting from microbial activity that is enhanced in the plant root zone. The objective of this study was to assess Australian native grasses for their ability to stimulate removal of aliphatic hydrocarbons from a mine site soil. Time-course pot experiments were conducted in a greenhouse with three grass species (Cymbopogon ambiguus, Brachiaria decumbens, and Microlaena stipoides) in a mine site soil experimentally contaminated with a 60:40 diesel:oil mixture at 1% (w/w) concentration. Plants were cultivated for 100 days with periodic evaluation of changes in soil total petroleum hydrocarbon (TPH) concentration, soil lipase activity, and abundance of hydrocarbon-degrading microorganisms. Results were compared to unplanted control treatments. Significantly lower endpoint TPH concentrations were recorded in planted soil compared to unplanted soil (p = 0.01). Final TPH concentrations and rates of TPH removal varied between grass species, with total TPH removal of between 50% and 88% achieved in planted treatments. The presence of grasses significantly increased the abundance of hydrocarbon-degrading microorganisms and soil lipase activity relative to unplanted soil (p < 0.05). Residual TPH concentration was found to be closely (negatively) correlated with abundance of hydrocarbon-degrading microorganisms and to a lesser extent with soil lipase activity. Australian native grass species were identified that effectively enhance the remediation of diesel/oil contaminated soil, without any requirement for nutrient supplementation. Results may have extensive application to the nationwide problems associated with hydrocarbon contaminated sites.     

Enrichment of bacteria possessing catechol dioxygenase genes in the rhizosphere of Spirodela polyrrhiza: A mechanism of accelerated biodegradation of phenol

The bacterial community structure in bulk water and in rhizosphere fractions of giant duckweed, Spirodela polyrrhiza, was quantitatively and qualitatively investigated by PCR-based methods using 6 environmental water samples to elucidate the mechanisms underlying selective accumulation of aromatic compound-degrading bacteria in the rhizosphere of S. polyrrhiza. S. polyrrhiza selectively accumulated a diverse range of aromatic compound-degrading bacteria in its rhizosphere, regardless of the origin of water samples, despite no exposure to phenol. The relative abundances of the catechol 1,2-dioxygenase (C12O) gene (C12O DNA) and catechol 2,3-dioxygenase (C23O) gene (C23O DNA) were calculated as the ratios of the copy numbers of these genes to the copy number of 16S rDNA and are referred to as the rhizosphere effect (RE) value. The RE values for C12O DNA and C23O DNA were 1.0 × 10¹–9.3 × 10³ and 1.7 × 10²–1.5 × 10⁴ times as high, respectively, in rhizosphere fractions as in bulk water fractions, and these higher values were associated with a notably higher sequence diversity of C12O DNA and C23O DNA. The RE values during phenol degradation were 3.6 × 10⁰–4.3 × 10² and 2.2 × 10⁰–1.7 × 10², respectively, indicating the ability of S. polyrrhiza to selectively accumulate aromatic compound-degrading bacteria in its rhizosphere during phenol degradation. The bacterial communities in the rhizosphere fractions differed from those in the bulk water fractions, and those in the bulk water fractions were notably affected by the rhizosphere bacterial communities. S. polyrrhiza released more than 100 types of phenolic compound into its rhizosphere as root exudates at the considerably high specific release rate of 1520 mg TOC and 214 mg phenolic compounds/d/g root (wet weight). This ability of S. polyrrhiza might result in the selective recruitment and accumulation of a diverse range of bacteria harboring genes encoding C12O and C23O, and the subsequent accelerated degradation of phenol in the rhizosphere.     

复合生防菌群对连作大豆根际土壤可培养微生物区系的影响

采用盆栽试验,研究了复合生防菌群对大豆根际土壤可培养微生物区系的调节作用。结果表明,复合生防菌群可以明显改变大豆根际微生物区系组成。在大豆不同时期,复合生防菌群处理的大豆根际细菌、真菌和放线菌在数量上发生了较大改变。在大豆真叶期和复叶期,复合生防菌群接种处理大豆根际细菌较对照增幅分别达到71.8%和114.3%,而根际真菌较对照减少12.9%和22.3%。在大豆真叶期,复合生防菌群接种处理大豆根际放线菌数量较对照减少9.9%,而在复叶期,根际放线菌数量较对照增加27.4%。此外,施用复合生防菌群可有效降低土传病原菌镰孢菌属（Fusarium）和丝核菌属（Rhizoctonia）的比例,并且提高根瘤菌（Rhizobium）、固氮菌（Azoto-bacter）、木霉属（Trichoderma）、假单胞菌属（Pseudomonas）和芽孢杆菌属（Bacillus）等有益菌的比例。     

有机污染物根际胁迫及根际修复研究进展

根际环境及根际微生物是植物降解有毒有害有机污染物的基础。污染土壤植物修复的纵深研究产生了根际修复新技术。通过总结近20年来有机污染物胁迫的根际效应的研究,探讨了有机物污染士壤根际修复的可能性,为加强有机污染物在环境中的迁移、调控研究及土壤有机物污染的原位修复提供有利信息。     

有机毒物甲磺隆胁迫下根际微生物种群生态的动态变化研究

运用根箱盆栽法进行定期测定土壤中微生物的数量,确定甲磺隆胁迫下,小麦根际土壤微生物种群生态的动态变化。表明甲磺隆胁迫下根际土壤中的细菌、真菌、放线菌数量均大于非根际土壤,并初步分离和鉴定了优势菌群。     

A rapid and efficient method for directed screening of lipase-producing Burkholderia cepacia complex strains with organic solvent tolerance from rhizosphere

Lipase from Burkholderia cepacia strain is one of the most versatile biocatalysts and is used widely in many biotechnological application fields including detergent additives, the resolution of racemic compounds, etc. Based on the known whole genomic information of B. cepacia strain, both ampicillin and kanamycin were added to the TB-T medium to screen B. cepacia complex stains from rhizosphere soil samples. The selected colonies from the modified TB-T medium were then qualitatively determined the ability to produce extracellular lipase on the rhodamine B-olive oil agar plates. A total of 35 lipolytic pseudo-B. cepacia complex strains were isolated and the positive rate of lipolytic bacteria was 65%. Among them, 15 pseudo-B. cepacia complex strains showed tolerance to benzene, n-hexane and n-heptane at concentration of 10% (V/V) and were identified by the recA gene sequence. All of the 14 lipolytic bacteria were identified as B. cepacia complex strains except that the recA gene sequence of one lipolytic bacterium, strain ZMB009, was not obtained.     

可持续性有机污染物根际微界面化学过程的研究进展

土壤-植物系统关系着人类生存与健康,土壤-植物根际微界面过程更是日益受到研究者们的重视。本文主要阐述在根际微界面过程中的污染物、根系分泌物和根际微生物三者之间的相互作用、影响;探讨了植物体内界面过程、植物修复的机理和根际界面微生态过程;同时,对今后土壤-植物根际微界面过程研究方向进行了建议和展望。     

Effects of light intensity and water temperature on oxygen release from roots into water lettuce rhizosphere

The oxygen release rate into the rhizosphere by a floating aquatic plant-water lettuce-was determined under various light intensities (0.0-1.2x10(5)lx) and water temperatures (10-35 degrees C). The net specific oxygen release rate was expressed by a model equation comprising the gross oxygen release rate and the rhizosphere respiration terms. Experimental and simulated results show that the net specific oxygen release rate increased with light intensity up to the optimal value, but slight inhibition by higher light intensities was observed at 10-20 degrees C. With increased water temperature, the respiration rate became larger than the gross oxygen release rate. The maximum net specific oxygen release rate of 11.0-12.5mg-O(2)kg-wet(-1)h(-1) was obtained at the optimal condition of about 25 degrees C and 9.0x10(4)-1.1x10(5)lx. The net oxygen release rate was negligible at 35 degrees C at any light intensity because the respiration rate was much greater than the gross oxygen release rate into the rhizosphere.