Nitrogen uptake in barley after spring incorporation of 15N-labelled Italian ryegrass into sandy soils

A 5-month laboratory incubation experiment was conducted to study the immobilization-mineralization of N in soil to which dried or composted ¹⁵N labelled ryegrass (Lolium italicum L.) had been added. Cellulose was added to dried ryegrass to give a C/N ratio similar to that of composted ryegrass. Exchangeable NH₄ ⁺ and NO₃ ^–, HCl-hydrolyzable N forms, microbial biomass N, NaOH-soluble and insoluble N were monitored during incubation. Dried ryegrass brought about a significant increase in total and labelled exchangeable NH₄ ⁺, while a rapid immobilization and a subsequent slow release of exchangeable NH₄ ⁺ was observed in soil with composted ryegrass, together with a resistance to degradation of the labelled humic substances. Compounds synthesized during the composting process and resistant to microbial decomposition probably caused an increase in the amino-acid fraction of soil. These findings suggest that composting can reduce the risk of N losses.     

Exchange of chromosomal markers by natural transformation between the soil isolate,Pseudomonas stutzeri JM300, and the marine isolate,Pseudomonas stutzeri strain ZoBell

Both the soil isolate,Pseudomonas stutzeri JM300, and the marine isolate,Pseudomonas stutzeri strain ZoBell, have been shown previously to be naturally transformable. This study reports the detection of genetic exchange by natural transformation between these two isolates. Transformation frequency was determined by filter transformation procedures. Three independent antibiotic resistance loci were used as chromosomal markers to monitor this exchange event: resistance to rifampicin, streptomycin, and nalidixic acid. The maximum frequencies of transformation were on the order of 3.1 to 3.8×10^-6 transformants per recipient; frequencies over an order of magnitude greater than those for spontaneous antibiotic resistance, although they are lower than those observed for soil: soil or marine: marine strain crosses. This exchange was inhibited by DNase I. Transformation was observed between soil and marine strains, both by filter transformation using purified DNA solutions and when transforming DNA was added in the form of viable donor cells. The results from this study support the close genetic relationship betweenP. stutzeri JM300 andP. stutzeri strain ZoBell. These results also further validate the utility ofP. stutzeri as a benchmark organism for modeling gene transfer by natural transformation in both soil and marine habitats.     

Development of genetic markers in cyanobacteria and stability of genetically marked strains in soil

Reporter marker GUS (-glucuronidase gene from Escherichia coli) and luc operon from the American firefly were introduced into cyanobacteria and the stability of these markers in soil was examined. To transfer the integrational vector into cyanobacteria, the genomic DNA library of Synechocystis sp. or Anabaena cylindrica maintained in pBR 322, pCY 100 and pCY 101 were transformed with HB 101 containing pRL 528 and selected for Cm^r and Amp^r. These clones of HB 101 containing pRL 528 and the vectors carrying different cyanobacterial chromosomal DNA fragments were used for triparental mating with HB 101 [pRK 2013/pRK 2073] and cyanobacteria. The frequency of transconjugants for integrational vectors was between 2.1 × 10^–5 and 4.0 × 10^–4. The transfer frequency of RSF 1010 based vectors (pDSK 519 and pCY 106) was 1.0–4.5 × 10^–4 in Synechocystis sp. whereas A. cylindrica failed to maintain these vectors. Low frequency transfer (2.0–2.3 × 10^–6) of RK 2 based vectors pVK 100 and pCY 104 was observed in A. cylindrica but these were unable to replicate in Synechocystis sp. The vectors in general were stable at least by 74.9% for 60 days of incubation in BG-11 medium. The markers were less stable in A. cylindrica (74.9–84.2%) compared to Synechocystis sp. (80.1–88.8%) at 60 days of incubation. Integrational vectors were almost 85% stable in both the strains. The RK 2 derivative of pCY 104 was less stable in A. cylindrica (74.9–77.3%) than the RSF 1010-based vector pCY 106 in Synechocystis sp. (80.1–81.0%). A maximum of 64.7% of the markers were lost in soil. The chromosomal markers through integrational vectors were found to be highly stable and 68.2–72.7% of these markers were retained in cyanobacteria at 60 days of incubation. Plasmid markers were less stable, with a loss of 64.7–48.7% at the end of the experiment. In A. cylindrica 58–65% of the RK 2 vector was lost whereas in Synechocystis sp. 49–61% of RSF 1010 was lost at 60 days of incubation.     

Transformation of14C labelled plant components in soil in relation to immobilization and remineralization of15N fertilizer

Summary Uniformly¹⁴C labelled glucose, cellulose and wheat straw and specifically¹⁴C labelled lignin component in corn stalks were aerobically incubated for 12 weeks in a chernozem soil alongwith¹⁵N labelled ammonium sulphate. Glucose was most readily decomposed, followed in order by cellulose, wheat straw and corn stalk lignins labelled at methoxyl-, side chain 2-and ring-C. More than 50% of¹⁴C applied as glucose, cellulose and wheat straw evolved as CO₂ during the first week. Lignin however, decomposed relatively slowly. A higher proportion of¹⁴C was transformed into microbial biomass whereas lignins contributed a little to this fraction.After 12 weeks of incubation nearly 60% of the lignin¹⁴C was found in humic compounds of which more than 70% was resistant to hydrolysis with 6N HCl. Maximum incorporation of¹⁵N in humic compounds was observed in cellulose amended soil. However, in this case more than 80% of the¹⁵N was in hydrolysable forms.Immobilization-remineralization of applied¹⁵N was most rapid in glucose treated soil and a complete immobilization followed by remineralization was observed after 3 days. The process was much slow in soil treated with cellulose, wheat straw or corn stalks. More than 70% of the newly immobilized N was in hydrolysable forms mainly reepresenting the microbial component.Serial hydrolysis of soil at different incubation intervals showed a greater proportion of 6N HCl hydrolysable¹⁴C and¹⁵N in fractions representing microbial material.¹⁴C from lignin carbons was relatively more uniformly distributed in different fractions as compared to glucose, cellulose and wheat straw where a major portion of¹⁴C was in easily hydrolysable fractions.     

Screening of soil fungi for in vitro degradation of endosulfan

Intensive use of endosulfan has resulted in contamination of soil and water environments at various sites in Pakistan. This study was conducted to isolate efficient endosulfan-degrading fungal strains from contaminated soils. Sixteen fungal strains were isolated from fifteen specific sites by employing enrichment techniques while using endosulfan as a sole sulfur source, and tested for their potential to degrade endosulfan. Among these fungal strains, Chaetosartorya stromatoides, Aspergillus terricola, and Aspergillus terreus degraded both α- and β-endosulfan upto 75% in addition to ∼20% abiotic degradation of the spiked amount (100 mg l⁻¹) in the broth within 12 days of incubation. Biodegradation of endosulfan by soil fungi was accompanied by a substantial decrease in pH of the broth from 7.0 to 3.2. The major metabolic product was endosulfan diol along with very low concentrations of endosulfan ether. Maximum biodegradation of endosulfan by these selected fungal strains was found at an initial broth pH of 6, incubation temperature of 30°C and under agitation conditions. This study indicates that the isolated strains carried efficient enzyme systems required for bioremediation of endosulfan-contaminated soil and water environments.     

A simple technique for producing 13C or 14C-labelled fronds of Lemna gibba and their use in soil incubation investigations

The duckweed Lemna gibba required light and a suitable energy source such as sucrose, glucose or fructose, for maximum growth in culture. The requirement for light was relatively unimportant and the plants grew well in a photon flux density of only 52 μmol m^-2s^-1 PAR. The uptake and incorporation of uniformly labelled ¹⁴C-glucose into fronds was related only to the concentration of the sugar. When incubated with soil, labelled L. gibba behaved in a manner similar to that of labelled ryegrass roots which had been produced by a more elaborate technique using a ¹⁴CO₂ labelled atmosphere. During incubation with soil for 224 days the L. gibba material (specific activity 6133 Bq mg^-1 d. wt) lost 64% of its radioactivity as ¹⁴CO₂ and ryegrass (specific activity 6634 Bq mg^-1 d. wt) lost 49%. Alkaline extracted humic and fulvic acids from soil had specific activities for the L. gibba incubation of 3409 and 407 Bq mg^-1 solid and for ryegrass roots of 4609 and 546 Bq mg^-1 solid respectively. The production of ¹³C or ¹⁴C-labelled L. gibba can be undertaken using only simple equipment producing material the specific radioactivity of which can be controlled by adjusting the activity of the sugar energy source.     

Bacterial conjugation betweenEscherichia coli andPseudomonas spp. donor and recipient cells in soil

Summary Experiments conducted in microcosms containing loam soil samples inoculated with eitherE. coli orPseudomonas spp. donor and recipient cells showed that bacterial cells survived and conjugated over a 24-h incubation period.E. coli transconjugants were detected 6 h after donor and recipient strains were introduced into sterile soil samples. In non-sterile soil samples, transconjugants were detected between 8 and 24 h incubation.Pseudomonas transconjugants were recovered from sterile soil samples between 6 and 12 h after their introduction and as early as 2 h in non-sterile soil. The results show that genetic interactions occur in non-sterile soil in relatively short periods of time at relatively high transfer frequencies (10^–3 to 10^–4). Studies on genetic interactions in soil are becoming necessary in risk assessment/environmental impact studies prior to the release of genetically engineered or modified organisms into uncontained environments.     

Factors affecting survival of <Emphasis Type="Italic">Listeria monocytogenes</Emphasis> and <Emphasis Type="Italic">Listeria innocua</Emphasis> in soil samples

We investigated the ability of several strains of L. monocytogenes and Listeria innocua strains to survive in local soil samples in vitro. Survival of three L. monocytogenes strains, EGDe, CD83, and CD1038, and three L. innocua strains, CLIP, FH2117, FH2152, was monitored in soil samples by direct enumeration of colony-forming units on selective agar. The study did not demonstrate any species-specific difference in soil survival, and all Listeria strains exhibited a marked decline in numbers over time. Bioluminescence imaging approaches to detect lux-tagged strains in soil proved largely ineffective, most likely due to the reduced metabolic activity of strains in this environment. We investigated the influence of specific factors including the presence of a background microbiota, growth temperature, moisture and strain motility upon persistence in this environment. A sequenced L. monocytogenes strain, EGDe, was capable of active growth in sterile soil yet exhibited a decline in the presence of the normal soil microbiota. Furthermore, greater survival was seen at lower incubation temperatures in normal soil. Finally, we demonstrated a direct correlation between motility and survival of L. monocytogenes in soil with highly motile L. monocytogenes strains exhibiting greater soil survival than non-motile mutants.     

Establishment and persistence of the entomopathogenic fungus Metarhizium anisopliae in maize fields

The entomopathogenic fungus Metarhizium anisopliae (Metsch.) Sorokin (Hypocreales: Clavicipitaceae) was applied in maize fields to control the Western Corn Rootworm Diabrotica virgifera virgifera Le Conte (Coleoptera: Chrysomelidae). Establishment and persistence of two strains of M. anisopliae were investigated after application as ‘fungal colonized barley kernels’ (FCBK) into the soil and as a spore suspension on maize leaves and on the soil surface in 2006 and 2007 at two locations in Hungary. The applied fungal strains were able to establish at both locations and a long‐term persistence of at least 15 months could be recorded in the soil. A positive correlation between density of colony forming units (CFU) in the soil and the soil inhabiting stages of the host insect D. v. virgifera could be found. M. anisopliae spores applied on maize leaves were able to survive for no longer than 3 days after application, whereas on the soil surface a noticeably increase of fungus densities were found after treatments. Molecular markers were used to identify the applied M. anisopliae strains before and after application of FCBK into the soil of the maize field.     

Survival and Nodulating Ability of Indigenous and Inoculated Rhizobium leguminosarum biovar trifolii in Sterilized and Unsterilized Soil Treated with Sewage Sludge

Rhizobium leguminosarum biovar trifolii was detected in soil from 41 of 47 plots, within nine sewage sludge-treated sites with different soil characteristics and heavy metal contents. However, although population size varied widely, there was no consistent correlation with soil heavy metal concentration. Indigenous populations in 20 plots within four selected sites retained their ability to induce effective nodule formation after incubation of soil in the dark for 165 days. In sterilized (γ-irradiated) soil, Rhizobium survival varied from 0.01% to 95% depending on the soil sample and strain used. Metal-resistant strains with non-mucoid colonies survived less well than mucoid metal-sensitive strains. Received: 26 June 2000/Accepted: 31 July 2000     

Genetic transformation in higher plants

Successful transformation of plant cells has been obtained utilizing vectors and DNA delivery methods derived from the plant pathogen, Agrobacterium tumefaciens. This soil bacterium is capable of transferring a DNA segment (T‐DNA), located between specific nucleotide border sequences, from its large tumor inducing (Ti) plasmid into the nuclear DNA of infected plant cells. The exploitation of the Agrobacterium/Ti plasmid system for plant cell transformation has been facilitated by (1) the construction of modified Agrobacterium strains in which the genes responsible for pathogenicity have been deleted; (2) the design of intermediate vectors containing selectable drug markers for introducing foreign genes into the Ti plasmid and subsequently into plant cells; and (3) the development of efficient in vitro methods for transforming plant cells and tissues with engineered Agrobacterium strains. These modifications have led to the development of a simple, efficient, and reproducible transformation system from which morphologically normal transformed plants can be readily regenerated. The foreign genes are stably maintained and expressed in the resulting plants and are inherited by progeny as typical Mendelian traits. The availability of transformation systems has already facilitated numerous studies on gene expression and regulation in plants and should eventually allow for the modification of various crop species in an agronomically significant manner. The needs and possibilities for the development of alternate vectors and transformation procedures will be discussed.     

Biodegradation of α- and β-endosulfan by soil bacteria

Extensive applications of persistent organochlorine pesticides like endosulfan on cotton have led to the contamination of soil and water environments at several sites in Pakistan. Microbial degradation offers an effective approach to remove such toxicants from the environment. This study reports the isolation of highly efficient endosulfan degrading bacterial strains from soil. A total of 29 bacterial strains were isolated through enrichment technique from 15 specific sites using endosulfan as sole sulfur source. The strains differed substantially in their potential to degrade endosulfan in vitro ranging from 40 to 93% of the spiked amount (100 mg l⁻¹). During the initial 3 days of incubation, there was very little degradation but it got accelerated as the incubation period proceeded. Biodegradation of endosulfan by these bacteria also resulted in substantial decrease in pH of the broth from 8.2 to 3.7 within 14 days of incubation. The utilization of endosulfan was accompanied by increased optical densities (OD₅₉₅) of the broth ranging from 0.511 to 0.890. High performance liquid chromatography analyses revealed that endosulfan diol and endosulfan ether were among the products of endosulfan metabolism by these bacterial strains while endosulfan sulfate, a persistent and toxic metabolite of endosulfan, was not detected in any case. The presence of endosulfan diol and endosulfan ether in the bacterial metabolites was further confirmed by GC-MS. Abiotic degradation contributed up to 21% of the spiked amount. The three bacterial strains, Pseudomonas spinosa, P. aeruginosa, and Burkholderia cepacia, were the most efficient degraders of both α- and β-endosulfan as they consumed more than 90% of the spiked amount (100 mg l⁻¹) in the broth within 14 days of incubation. Maximum biodegradation by these three selected efficient bacterial strains was observed at an initial pH of 8.0 and at an incubation temperature of 30°C. The results of this study may imply that these bacterial strains could be employed for bioremediation of endosulfan polluted soil and water environments.     

Temperature responses of carbon mineralization in conifer forest soils from different regional climates incubated under standard laboratory conditions

¹⁴C‐labelled straw was mixed with soils collected from seven coniferous forests located on a climatic gradient in Western Europe ranging from boreal to Mediterranean conditions. The soils were incubated in the laboratory at 4°, 10°, 16°, 23° and 30 °C with constant moisture over 550 days. The temperature coefficient (Q₁₀) for straw carbon mineralization decreased with increasing incubation temperatures. This was a characteristic of all the soils with a difference of two Q₁₀ units between the 4–10° and the 23? 30 °C temperature ranges. It was also found that the magnitude of the temperature response function was related to the period of soil incubation. Initial temperature responses of microbial communities were different to those shown after a long period of laboratory incubation and may have reflected shifts in microbial species composition in response to changes in the temperature regime. The rapid exhaustion of the labile fractions of the decomposing material at higher temperatures could also lead to underestimation of the temperature sensitivity of soils unless estimated for carbon pools of similar qualities. Finally, the thermal optima for the organic soil horizons (Of and Oh) were lower than 30 °C even after 550 days of incubation. It was concluded that these responses could not be attributed to microbial physiological adaptations, but rather to the rates at which recalcitrant microbial secondary products were formed at higher temperatures. The implication of these variable temperature responses of soil materials is discussed in relation to modelling potential effects of global warming.     

Introduction and recovery of Clavibacter michiganensis subsp. michiganensis from agricultural soil

Twelve phytopathogenic Clavibacter michiganensis subsp. michiganensis strains were introduced into non-sterile agricultural loam soil at an inoculum density of about log. 6.0 cfu g^–1 dry weight soil. The soil samples were incubated at 22°C under a 12h light, 12h dark cycle and the population densities followed over a 30-day period by plating subsamples of serial dilutions of soil on Brain Heart Infusion agar amended with 0.5% (w/v) yeast extract and 30 g mL^–1 nalidixic acid. In 5 soil samples C. michiganensis cfu were not detected after 30 days incubation. Initially, C. michiganensis cfu accounted for about 90% of the cfu recovered but decreased to less than 10% after 30 days. These results suggested that some C. michiganensis strains survive in this particular soil, while other strains exhibit poor survival and/or may be difficult to detect when present in low numbers.     

Metabolism of Atrazine in Liquid Cultures and Soil Microcosms by Nocardioides Strains Isolated from a Contaminated Nigerian Agricultural Soil

Atrazine-degrading microorganisms designated EAA-3 and EAA-4, belonging to the genus Nocardioides, were obtained from an agricultural soil in Nigeria. The degradation kinetics of the two strains revealed total disappearance of 25 mg l^?1 of atrazine in less than 72 h of incubation at the rate of 0.42 mg l^?1 h^?1 and 0.35 mg l^?1 h^?1, respectively. Screening for atrazine catabolic genes in these organisms revealed the presence of trzN, atzB, and atzC. Other genes, specifically atzA, atzD, and trzD, were not detected. Potential intermediates of atrazine catabolic route such as hydroxyatrazine, desethylatrazine, and desisopropylatrazine were utilized as sources of carbon and energy, while desisopropyl desethyl-2-hydroxyatrazine and desisopropyl-2-hydroxyatrazine were attacked but in the presence of glucose. A soil microcosm study showed that degradation was faster in microcosms contaminated with 13 mg of atrazine per g^?1 of soil compared with 480 mg g^?1 of soil. In the former, degradation was 10% higher in the inoculated soil than the non-inoculated control (natural attenuation) over the 28-day study period. Corresponding value obtained for the latter was nearly 70% higher. This study has demonstrated that the bacterial strains isolated enhanced atrazine degradation and the catabolic activities of these strains were not affected with increasing soil atrazine concentration.     

Biodegradation of pentachorophenol by tropical basidiomycetes in soils contaminated with industrial residues

Summary The ability of tropical Brazilian basidiomycetes to degrade pentachlorophenol (PCP) in soils from areas contaminated with organochlorine industrial residues was studied. Thirty-six basidiomycetes isolated from different tropical ecosystems were tested for tolerance to high PCP concentrations in soil. Peniophoracinereaand Psilocybecastanella, two strains of Trametes villosa,Agrocybe perfecta, Trichaptum bisogenumand Lentinus villosuswere able to colonize soil columns containing up to 4600 mg pentachlorophenol kg⁻¹soil. The first four species were inoculated into soil containing 1278 mg pentachlorophenol kg⁻¹ soil supplemented with gypsum and sugar cane bagasse. P. cinerea,P.castanella, T. villosaCCB176 and CCB213 and Agrocybe perfectareduced the PCP present in the contaminated soil by 78, 64, 58, 36 and 43%, respectively, after 90 days of incubation. All fungi mineralized [¹⁴C] pentachlorophenol, mainlyP. cinereaandT. villosawith the production of 7.11 and 8.15% ¹⁴CO₂, respectively, during 120 days of incubation. All fungi produced chloride ions during growth on soil containing PCP, indicating dehalogenation of the molecule. Conversion of PCP to pentachloroanisole was observed only after 90 days of incubation in soils inoculated with A. perfecta, P.cinereaand one of T. villosastrain. The present study shows the potential of Brazilian fungi for the biodegradation of toxic and persistent pollutants and it is the first to report fungal growth and PCP depletion in soils with high pentachlorophenol concentrations.     

Guaiacol and isovanillic acid as metabolites in the transformation of methoxyphenolic acids by Nocardia autotrophica

The transformation ofmethoxy derivatives of benzoic acid ¹⁴C labelled in the ring or in the methoxyl or carboxyl groups were determined in the cultures of five selected strains of Nocardia autotrophica. It was shown that the transformation of vanillic acid to protocatechuic acid might proceed through guaiacol and isovanillic acid as intermediates. This metabolic conversion was found in three of the five bacterial strains examined.     

Transformation of15N-labelled urea in rice-wheat cropping system

Summary In a udic chromusterts the transformation of an initial application of¹⁵N-urea @ 80 kg N ha^–1 to rice (Oryza sativa L.) in rice-wheat (R-W) and to wheat (Triticum aestivum L.) in wheat-rice (W-R) rotations was followed in 6 successive crops in each rotation. All rice crops were grown in irrigated wetland and wheat in irrigated upland conditions.The first wheat crop in W-R rotation utilized 22 kg fertilizer N ha^–1 as compared to 19 kg by the corresponding rice crop in R-W rotation. But the latter absorbed more soil N than the former. About 69% of the total N uptake in rice was derived from mineralization of soil organic N as compared to 61% in wheat.The succeeding wheat crop in R-W rotation utilized 6.7% of the residual fertilizer N in the soil but the corresponding rice crop in W-R rotation only 2.2%. The higher utilization appeared to be related to a greater incorporation of labelled fertilizer N in mineral and hexosamine fractions of the soil N. After the second crop in each rotation, the average residual fertilizer N utilization in the next 4 crops ranged between 3 and 4%.The total recovery of¹⁵N-urea in all crops amounted to 21.7 and 24.3 kg N ha^–1 in R-W and W-R rotation, respectively. At the end of the experiment, about 9 to 10 kg ha^–1 of the applied labelled N was found in soil upto 60 cm depth. Most of the labelled soil N (69–76%) was located in the upper 0–20 cm soil layer indicating little movement to lower depths despite intensive cropping for 4 years.     

Aerobic biodegradation of methyl tert-butyl ether (MTBE) by pure bacterial cultures isolated from contaminated soil

Summary Methyl tert-Butyl Ether (MTBE) has been used in gasoline as a substitute for lead-based additives, which have been demonstrated to be toxic. MTBE however, is persistent in soil and water, showing high affinity for water and low affinity for soil, and has become an important contaminant. Therefore, the aim of this work was to isolate and identify soil microorganisms capable of degrading MTBE. Two samples were taken from a gasoline-contaminated soil at a service station and 59 different bacterial strains were isolated by enrichment culture with three consecutive selective transfers. Biochemical and morphological characterization of the bacterial isolates classified them into the following groups: Bacillus, Rhodococcus, Micrococcus, Aureobacterium and Proteus. Twelve strains were selected for evaluation of MTBE biodegradation depending on visual growth and biomass production of the isolates in minimal salt broth. Six strains significantly reduced MTBE concentration (22–37%) compared to an abiotic control after 5 days of incubation. Although it has been considered that MTBE is degraded mainly by cometabolism, our results demonstrate that these microorganisms are able to reduce MTBE concentration when MTBE is the sole source of carbon.     

酸性旱地红壤无机氮同化菌株筛选及其全基因组分析

微生物执行的无机氮同化作用可固定施入土壤后未被作物直接吸收的化学氮肥,有效减少化学氮肥损失、降低环境氮素污染风险。土壤无机氮同化作用不是由大量冗余微生物共同执行的,而是由一小部分功能微生物优先执行。【目的】对酸性旱地红壤中的优势无机氮同化细菌进行富集、菌株分离鉴定及全基因组测序,并明确菌株在土壤中的氮同化能力,为酸性土壤化学氮肥应用及其转化过程研究提供菌株资源和理论依据。【方法】在酸性旱地红壤中添加KNO3或(NH4)2SO4作为无机氮源,以葡萄糖作为碳源,在好氧条件下进行富集预培养,采用稀释分离法筛选出优势无机氮同化细菌菌株;将菌株回接至土壤中从而验证其无机氮同化能力,并通过全基因组测序分析菌株的氮素代谢途径及相关功能基因。【结果】酸性旱地红壤经富集预培养一周后,优势无机氮同化微生物的16SrRNA基因相对丰度从0.20%–0.94%增长至20.2%–30.2%;分离筛选后得到的3株优势无机氮同化细菌菌株,鉴定为伯克霍尔德氏菌(Burkholderia sp.) M6-3、索状芽孢杆菌(Bacillus funiculus) M2-4和节杆菌(Arthrobacter sp.) M7...