Isolation and characterization of Arthrobacter sp. strain MCM B-436, an atrazine-degrading bacterium, from rhizospheric soil

Atrazine is one of the most environmentally prevalent s-triazine-ring herbicides. The widespread use of atrazine and its toxicity necessitates search for remediation technology. As atrazine is still used in India as a major herbicide, exploration of atrazine-degrading bacterial community is of immense importance. Considering lack of reports on well characterized atrazine-degrading bacterial cultures from India and wide diversity and density of microorganisms in rhizosphere, soil sample from rhizosphere of atrazine-resistant plant was studied. Arthrobacter sp. strain isolated in this investigation utilizes atrazine as the sole nitrogen source. In addition, the bacterium degrades other triazines such as ametryn, cyanizine, propazine and simazine. PCR analysis confirms the presence of atzBCD and triazine hydrolase (trzN) genes on chromosomal DNA. Sequencing of the trzN gene reveals high sequence similarity with trzN from Nocardioides sp. C190. An inducible and intracellular atrazine chlorohydrolase enzyme was isolated and partially purified from this isolate. This study confirms the presence of atrazine-degrading microbial population in Indian soils and could be used efficiently for remediation of contaminated soils. Presence of trzN gene indicates possible presence of bacterial community with more efficient and novel enzymatic capabilities. Comparison of enzyme and gene structure of this isolate with other geographically distinct atrazine-degrading strains will help us in the better understanding of gene transfer and evolution.     

Isolation and characterization of atrazine-degrading Arthrobacter sp. strains from Argentine agricultural soils

Three bacterial strains capable of degrading atrazine were isolated from Manfredi soils (Argentine) using enrichment culture techniques. These soils were used to grow corn and were treated with atrazine for weed control during 3 years. The strains were nonmotile Gram-positive bacilli which formed cleared zones on atrazine solid medium, and the 16S rDNA sequences indicated that they were Arthrobacter sp. strains. The atrazine-degrading activity of the isolates was characterized by the ability to grow with atrazine as the sole nitrogen source, the concomitant herbicide disappearance, and the chloride release. The atrazine-degrader strain Pseudomonas sp. ADP was used for comparative purposes. According to the results, all of the isolates used atrazine as sole source of nitrogen, and sucrose and sodium citrate as the carbon sources for growth. HPLC analyses confirmed herbicide clearance. PCR analysis revealed the presence of the atrazine catabolic genes trzN, atzB, and atzC. The results of this work lead to a better understanding of microbial degradation activity in order to consider the potential application of the isolated strains in bioremediation of atrazine-polluted agricultural soils in Argentina.     

Metabolic ability and gene characteristics of Arthrobacter sp. strain DNS10, the sole atrazine-degrading strain in a consortium isolated from black soil

Strain DNS10 was the only member that could utilize atrazine as the sole nitrogen source for growth in an atrazine-degrading consortium which was isolated from black soil previously in our laboratory. It belongs to the genus Arthrobacter according to the sequence of 16S rRNA gene and is designated as Arthrobacter sp. DNS10. 16S rRNA gene phylogenetic analysis showed that strain DNS10 was located in a different evolutionary branch comparing with other Arthrobacter sp. atrazine-degrading strains. The degrading genes such as trzN, atzB and atzC harbored in strain DNS10 revealed high sequence similarity with those in Arthrobacter aurescens TC1 and Pseudomonas sp. ADP. These genes enabled the strain DNS10 to decompose atrazine to cyanuric acid. This was further proved by the results that the strain DNS10 (10⁸ CFU mL⁻¹) could degrade the whole atrazine (100 mg L⁻¹) in the medium within 24 h at 30 °C and there was 66.13 ± 2.11 mg L⁻¹ cyanuric acid accumulated at 24 h. These results imply that the strain DNS10 seems to be an excellent atrazine-degrading strain. Furthermore, this paper helps us in the better understanding of the strain evolution by comparing the metabolic ability and gene characteristics of strain DNS10 with other geographically distinct atrazine-degrading strains.     

Isolation and characterization of novel atrazine-degrading microorganisms from an agricultural soil

Six previously undescribed microorganisms capable of atrazine degradation were isolated from an agricultural soil that received repeated exposures of the commonly used herbicides atrazine and acetochlor. These isolates are all Gram-positive and group with microorganisms in the genera Nocardioides and Arthrobacter, both of which contain previously described atrazine degraders. All six isolates were capable of utilizing atrazine as a sole nitrogen source when provided with glucose as a separate carbon source. Under the culture conditions used, none of the isolates could utilize atrazine as the sole carbon and nitrogen source. We used several polymerase-chain-reaction-based assays to screen for the presence of a number of atrazine-degrading genes and verified their identity through sequencing. All six isolates contain trzN and atzC, two well-characterized genes involved in the conversion of atrazine to cyanuric acid. An additional atrazine-degrading gene, atzB, was detected in one of the isolates as well, yet none appeared to contain atzA, a commonly encountered gene in atrazine impacted soils and atrazine-degrading isolates. Interestingly, the deoxyribonucleic acid sequences of trzN and atzC were all identical, implying that their presence may be the result of horizontal gene transfer among these isolates.     

Use of atrazine sensitive leguminous plants as biological indicators to evaluate the atrazine degradation efficiency of a bacterial inoculum

Atrazine sensitive leguminous plants were grown in a soil spiked with atrazine and augmented with an atrazine-degrading bacterium, Arthrobacter sp. strain MCM B-436, to ascertain its degradative efficiency. Germination and survival of plants was correlated with atrazine removal from soil. This experiment was carried out at laboratory as well as field level, showing consistent results. This bioindicator approach serves as an efficient measure for atrazine removal and could be easily adapted to determine atrazine degradation efficiency of other microbial strains.     

Combined metabolic activity within an atrazine-mineralizing community enriched from agrochemical factory soil

The main objective of this work was to characterize an atrazine-mineralizing community originating from agrochemical factory soil, especially to elucidate the catabolic pathway and individual metabolic and genetic potentials of culturable members. A stable four-member bacterial community, characterized by colony morphology and 16S rDNA sequencing, was rapidly able to mineralize atrazine to CO₂ and NH₃. Two primary organisms were identified as Arthrobacter species (ATZ1 and ATZ2) and two secondary organisms (CA1 and CA2) belonged to the genera Ochrobactrum and Pseudomonas, respectively. PCR assessment of atrazine-degrading genetic potential of the community, revealed the presence of trzN, trzD, atzB and atzC genes. Isolates ATZ1 and ATZ2 were capable of dechlorinating atrazine to hydroxyatrazine and contained the trzN gene. ATZ2 further degraded hydroxyatrazine to cyanuric acid and contained atzB and atzC genes whereas ATZ1 contained atzC but not atzB. Isolates CA1 and CA2 grew on cyanuric acid and contained the trzD gene. Complete atrazine degradation was a result of the combined metabolic attack on the atrazine molecule, and complex interactions may exist between the community members sharing carbon and nitrogen from atrazine mineralization.Scientific relevance: Despite numerous reports on atrazine degradation by pure bacterial cultures, the pathways and the atrazine-degrading gene combinations harboured by bacterial communities are only poorly described. In this work, we characterized a four-member atrazine-mineralizing community enriched from an agrochemical factory soil, which was capable of rapidly metabolizing atrazine to CO₂. This study will contribute towards better understanding of the genetic potential and metabolic activities of atrazine-degrading communities, which are generally considered to be responsible for atrazine mineralization in the natural environment.     

Isolation and Characterization of Atrazine Mineralizing Bacillus subtilis Strain HB-6

Atrazine is a widely used herbicide with great environmental concern due to its high potential to contaminate soil and waters. An atrazine-degrading bacterial strain HB-6 was isolated from industrial wastewater and the 16S rRNA gene sequencing identified HB-6 as a Bacillus subtilis. PCR assays indicated that HB-6 contained atrazine-degrading genes trzN, atzB and atzC. The strain HB-6 was capable of utilizing atrazine and cyanuric acid as a sole nitrogen source for growth and even cleaved the s-triazine ring and mineralized atrazine. The strain demonstrated a very high efficiency of atrazine biodegradation with a broad optimum pH and temperature ranges and could be enhanced by cooperating with other bacteria, suggesting its huge potential for remediation of atrazine-contaminated sites. To our knowledge, there are few Bacillus subtilis strains reported that can mineralize atrazine, therefore, the present work might provide some new insights on atrazine remediation.     

Impact of the Maize Rhizosphere on the Genetic Structure, the Diversity and the Atrazine-degrading Gene Composition of Cultivable Atrazine-degrading Communities

Sixty-six atrazine-degrading bacterial communities utilizing atrazine as sole N source and citrate as principal C source were isolated from unplanted and maize planted soils treated with atrazine. Ribosomal intergenic spacer analysis (RISA) fingerprints revealed that the genetic structure of atrazine-degrading bacterial communities was modified in the maize rhizosphere. To assess the underlying microbial diversity, 16S rDNA sequences amplified from each bacterial community were cloned. Libraries containing 660 16S rDNA clones were screened by restriction fragment length polymorphism (RFLP) analysis. In all, 63 clone families were identified. Rarefaction curves did not reach a clear saturation, indicating that the analysis of a greater number of clones would have revealed further diversity. Recovered 16S rDNA sequences were related to Actinobacteria, Bacteroidetes and Proteobacteria. The four dominant RFLP families were highly similar to Variovorax paradoxus, Burkholderia cepacia, Arthrobacter sp. and Bosea sp. The composition of most of the atrazine-degrading bacterial communities consisted of 2–7 different bacterial species. Various atrazine-degrading gene compositions were observed, two of these atzABCDEF, trzND and atzBCDEF, trzN being largely dominant. The first was more frequently detected in bacterial communities isolated from the maize rhizosphere whereas the second was more frequently detected in communities isolated from bulk soil. Monitoring of atrazine-degrading activity showed that 76% of the bacterial communities degraded up to 80% of the initially added atrazine within 15 days of culture. Altogether our results indicate that the maize rhizosphere has an impact on the genetic structure, the diversity and atrazine-degrading gene composition of the atrazine-degrading communities.     

Characterization of an Atrazine-Degrading Pseudaminobacter sp. Isolated from Canadian and French Agricultural Soils

Atrazine, a herbicide widely used in corn production, is a frequently detected groundwater contaminant. Fourteen bacterial strains able to use this herbicide as a sole source of nitrogen were isolated from soils obtained from two farms in Canada and two farms in France. These strains were indistinguishable from each other based on repetitive extragenic palindromic PCR genomic fingerprinting performed with primers ERIC1R, ERIC2, and BOXA1R. Based on 16S rRNA sequence analysis of one representative isolate, strain C147, the isolates belong to the genus Pseudaminobacter in the family Rhizobiaceae. Strain C147 did not form nodules on the legumes alfalfa (Medicago sativa L.), birdsfoot trefoil (Lotus corniculatus L.), red clover (Trifolium pratense L.), chickpea (Cicer arietinum L.), and soybean (Glycine max L.). A number of chloro-substituted s-triazine herbicides were degraded, but methylthio-substituted s-triazine herbicides were not degraded. Based on metabolite identification data, the fact that oxygen was not required, and hybridization of genomic DNA to the atzABC genes, atrazine degradation occurred via a series of hydrolytic reactions initiated by dechlorination and followed by dealkylation. Most strains could mineralize [ring-U-¹⁴C]atrazine, and those that could not mineralize atrazine lacked atzB or atzBC. The atzABC genes, which were plasmid borne in every atrazine-degrading isolate examined, were unstable and were not always clustered together on the same plasmid. Loss of atzB was accompanied by loss of a copy of IS1071. Our results indicate that an atrazine-degrading Pseudaminobacter sp. with remarkably little diversity is widely distributed in agricultural soils and that genes of the atrazine degradation pathway carried by independent isolates of this organism are not clustered, can be independently lost, and may be associated with a catabolic transposon. We propose that the widespread distribution of the atrazine-degrading Pseudaminobacter sp. in agricultural soils exposed to atrazine is due to the characteristic ability of this organism to utilize alkylamines, and therefore atrazine, as sole sources of carbon when the atzABC genes are acquired.     

Bioremediation of atrazine-contaminated soil by repeated applications of atrazine-degrading bacteria

Bioaugmentation has previously been unreliable for the in situ clean-up of contaminated soils because of problems with poor survival and the rapid decline in activity of the bacterial inoculum. In an attempt to solve these problems, a 500-l batch fermenter was investigated for its ability to deliver inoculum repeatedly to contaminated soils via irrigation lines. In a field experiment, mesocosms were filled with 350 kg soil containing 100 mg kg⁻¹ atrazine, and inoculated one, four or eight times with an atrazine-degrading bacterial consortium that was produced in the fermenter. After 12 weeks, no significant degradation of atrazine had occurred in soil that was inoculated only once; whereas, mesocosms inoculated four and eight times mineralized 38% and 72% of the atrazine respectively. Similar results were obtained in a laboratory experiment using soil contaminated with 100 mg kg⁻¹ [¹⁴C]atrazine. After 35 days, soil that was inoculated once with 10⁸ cfu ml⁻¹ of the consortium or with the atrazine-degrading bacterium, Pseudomonas sp. strain ADP, mineralized 17% and 35% of the atrazine respectively. In comparison, microcosms inoculated every 3 days with the consortium or with Pseudomonas sp. (ADP) mineralized 64% or 90% of the atrazine over this same period. Results of these experiments suggest that repeated inoculation from an automated fermenter may provide a strategy for bioaugmentation of contaminated soil with xenobiotic-degrading bacteria. Received: 20 November 1998 / Received revision: 8 February 1999 / Accepted: 12 February 1999     

Characterization of Arthrobacter nicotinovorans HIM, an atrazine-degrading bacterium, from agricultural soil New Zealand

Arthrobacter nicotinovorans HIM was isolated directly from an agricultural sandy dune soil 6 months after a single application of atrazine. It grew in minimal medium with atrazine as sole nitrogen source but was unable to mineralize 14C-ring-labelled atrazine. Atrazine was degraded to cyanuric acid. In addition to atrazine the bacterium degraded simazine, terbuthylazine, propazine, cyanazine and prometryn but was unable to grow on terbumeton. When added to soil, A. nicotinovorans HIM did enhance mineralization of 14C-ring-labelled atrazine and simazine, in combination with naturally occurring cyanuric acid degrading microbes resident in the soil. Using PCR, the atrazine-degradation genes atzABC were identified in A. nicotinovorans HIM. Cloning of the atzABC genes revealed significant homology (>99%) with the atrazine degradation genes of Pseudomonas sp. strain ADP. The atrazine degradation genes were held on a 96 kbp plasmid.     

Characterization of S-Triazine Herbicide Metabolism by a Nocardioides sp. Isolated from Agricultural Soils

Atrazine, a herbicide widely used in corn production, is a frequently detected groundwater contaminant. Nine gram-positive bacterial strains able to use this herbicide as a sole source of nitrogen were isolated from four farms in central Canada. The strains were divided into two groups based on repetitive extragenic palindromic (rep)-PCR genomic fingerprinting with ERIC and BOXA1R primers. Based on 16S ribosomal DNA sequence analysis, both groups were identified as Nocardioides sp. strains. None of the isolates mineralized [ring-U-¹⁴C]atrazine. There was no hybridization to genomic DNA from these strains using atzABC cloned from Pseudomonas sp. strain ADP or trzA cloned from Rhodococcus corallinus. S-Triazine degradation was studied in detail in Nocardioides sp. strain C190. Oxygen was not required for atrazine degradation by whole cells or cell extracts. Based on high-pressure liquid chromatography and mass spectrometric analyses of products formed from atrazine in incubations of whole cells with H₂¹⁸O, sequential hydrolytic reactions converted atrazine to hydroxyatrazine and then to the end product N-ethylammelide. Isopropylamine, the putative product of the second hydrolytic reaction, supported growth as the sole carbon and nitrogen source. The triazine hydrolase from strain C190 was isolated and purified and found to have a K_m for atrazine of 25 μM and a V_max of 31 μmol/min/mg of protein. The subunit molecular mass of the protein was 52 kDa. Atrazine hydrolysis was not inhibited by 500 μM EDTA but was inhibited by 100 μM Mg, Cu, Co, or Zn. Whole cells and purified triazine hydrolase converted a range of chlorine or methylthio-substituted herbicides to the corresponding hydroxy derivatives. In summary, an atrazine-metabolizing Nocardioides sp. widely distributed in agricultural soils degrades a range of s-triazine herbicides by means of a novel s-triazine hydrolase.     

Atrazine biodegradation by a bacterial community immobilized in two types of packed-bed biofilm reactors

Through selective enrichment of atrazine-metabolizing microorganisms, a microbial community was selected from agricultural soil. Bacterial isolates, identified by their closest similarity with 16S rDNA sequences stored in NCBI GeneBank, belonged to the genera: Massilia, Stenotrophomonas, Klebsiella, Sphingomonas, Ochrobactrum, Arthrobacter, Microbacterium, Xanthomonas and Ornithinimicrobium. From these strains, only the first six used atrazine as nitrogen and carbon source. The microbial community attached to a non-porous support was evaluated for its atrazine biodegradation rate and removal efficiency under aerobic conditions in two types of packed-bed biofilm reactors fed with a mineral salt medium containing glucose plus atrazine, or atrazine as the sole carbon and nitrogen source. Removal efficiencies near 100% were obtained at loading rates up to 10 mg l⁻¹ h⁻¹. After long periods of continuous operation, the richness of microbial species in biofilm reactors diminished to only three bacterial strains; Stenotrophomonas sp., Ochrobactrum sp. and Arthrobacter sp. By PCR analysis of their DNA, the presence of atzABC genes codifying for the enzymes of the upper catabolic pathway of atrazine, was confirmed in the three strains. The gene atzD that encodes for the cyanuric acid amidohydrolase enzyme was detected only in Stenotrophomonas sp.     

阿特拉津降解菌ATR3的分离鉴定与土壤修复

阿特拉津因效率高、价格低廉,是我国玉米田施用最广泛的除草剂之一,但其结构稳定,残留时间长,因此对生态环境和人类健康造成了一定的危害。从长期受阿特拉津污染的玉米田土壤中筛选并鉴定阿特拉津降解菌,明确其在不同类型土壤中的去除能力。对分离出的阿特拉津降解菌ATR3进行生理生化分析和16S rRNA序列鉴定,确定菌株ATR3为节杆菌属（Arthrobacter sp.）。该菌株以阿特拉津为唯一氮源,培养48 h后对1 000 mg/L阿特拉津的去除率达到97%以上。敏感作物盆栽试验结果表明,阿特拉津在棕壤上去除最快,褐土次之,黑土最慢,说明阿特拉津在土壤中的去除过程与土壤本身的理化性质呈相关关系。同时,该菌株处理14 d后,能明显恢复玉米的各项生物学指标,说明该菌株对阿特拉津污染土壤具有良好的修复能力。为阿特拉津降解菌剂的推广利用提供参考。     

Classification of Achromobacter genogroups 2, 5, 7 and 14 as Achromobacter insuavis sp. nov., Achromobacter aegrifaciens sp. nov., Achromobacter anxifer sp. nov. and Achromobacter dolens sp. nov., respectively

The phenotypic and genotypic characteristics of seventeen Achromobacter strains representing MLST genogroups 2, 5, 7 and 14 were examined. Although genogroup 2 and 14 strains shared a DNA–DNA hybridization level of about 70%, the type strains of both genogroups differed in numerous biochemical characteristics and all genogroup 2 and 14 strains could by distinguished by nitrite reduction, denitrification and growth on acetamide. Given the MLST sequence divergence which identified genogroups 2 and 14 as clearly distinct populations, the availability of nrdA sequence analysis as a single locus identification tool for all Achromobacter species and genogroups, and the differential phenotypic characteristics, we propose to formally classify Achromobacter genogroups 2, 5, 7 and 14 as four novel Achromobacter species for which we propose the names Achromobacter insuavis sp. nov. (with strain LMG 26845^T [= CCUG 62426^T] as the type strain), Achromobacter aegrifaciens sp. nov. (with strain LMG 26852^T [= CCUG 62438^T] as the type strain), Achromobacter anxifer sp. nov. (with strain LMG 26857^T [= CCUG 62444^T] as the type strain), and Achromobacter dolens sp. nov. (with strain LMG 26840^T [= CCUG 62421^T] as the type strain).     

Degradation and Mineralization of Nanomolar Concentrations of the Herbicide Dichlobenil and Its Persistent Metabolite 2,6-Dichlorobenzamide by Aminobacter spp. Isolated from Dichlobenil-Treated Soils

2,6-Dichlorobenzamide (BAM), a persistent metabolite from the herbicide 2,6-dichlorobenzonitrile (dichlobenil), is the pesticide residue most frequently detected in Danish groundwater. A BAM-mineralizing bacterial community was enriched from dichlobenil-treated soil sampled from the courtyard of a former plant nursery. A BAM-mineralizing bacterium (designated strain MSH1) was cultivated and identified by 16S rRNA gene sequencing and fatty acid analysis as being closely related to members of the genus Aminobacter, including the only cultured BAM degrader, Aminobacter sp. strain ASI1. Strain MSH1 mineralized 15 to 64% of the added [ring-U-¹⁴C]BAM to ¹⁴CO₂ with BAM at initial concentrations in the range of 7.9 nM to 263.1 μM provided as the sole carbon, nitrogen, and energy source. A quantitative enzyme-linked immunoassay analysis with antibodies against BAM revealed residue concentrations of 0.35 to 18.05 nM BAM following incubation for 10 days, corresponding to a BAM depletion of 95.6 to 99.9%. In contrast to the Aminobacter sp. strain ASI1, strain MSH1 also mineralized the herbicide itself along with several metabolites, including ortho-chlorobenzonitrile, ortho-chlorobenzoic acid, and benzonitrile, making it the first known dichlobenil-mineralizing bacterium. Aminobacter type strains not previously exposed to dichlobenil or BAM were capable of degrading nonchlorinated structural analogs. Combined, these results suggest that closely related Aminobacter strains may have a selective advantage in BAM-contaminated environments, since they are able to use this metabolite or structurally related compounds as a carbon and nitrogen source.     

Biodegradation of Atrazine by Agrobacterium radiobacter J14a and Use of This Strain in Bioremediation of Contaminated Soil

We examined the ability of a soil bacterium, Agrobacterium radiobacter J14a, to degrade the herbicide atrazine under a variety of cultural conditions, and we used this bacterium to increase the biodegradation of atrazine in soils from agricultural chemical distribution sites. J14a cells grown in nitrogen-free medium with citrate and sucrose as carbon sources mineralized 94% of 50 μg of [¹⁴C-U-ring]atrazine ml⁻¹ in 72 h with a concurrent increase in the population size from 7.9 × 10⁵ to 5.0 × 10⁷ cells ml⁻¹. Under these conditions cells mineralized the [ethyl-¹⁴C]atrazine and incorporated approximately 30% of the ¹⁴C into the J14a biomass. Cells grown in medium without additional carbon and nitrogen sources degraded atrazine, but the cell numbers did not increase. Metabolites produced by J14a during atrazine degradation include hydroxyatrazine, deethylatrazine, and deethyl-hydroxyatrazine. The addition of 10⁵ J14a cells g⁻¹ into soil with a low indigenous population of atrazine degraders treated with 50 and 200 μg of atrazine g⁻¹ soil resulted in two to five times higher mineralization than in the noninoculated soil. Sucrose addition did not result in significantly faster mineralization rates or shorten degradation lag times. However, J14a introduction (10⁵ cells g⁻¹) into another soil with a larger indigenous atrazine-mineralizing population reduced the atrazine degradation lag times below those in noninoculated treatments but did not generally increase total atrazine mineralization.     

Achromobacter animicus sp. nov., Achromobacter mucicolens sp. nov., Achromobacter pulmonis sp. nov. and Achromobacter spiritinus sp. nov., from human clinical samples

The phenotypic and genotypic characteristics of fourteen human clinical Achromobacter strains representing four genogroups which were delineated by sequence analysis of nusA, eno, rpoB, gltB, lepA, nuoL and nrdA loci, demonstrated that they represent four novel Achromobacter species. The present study also characterized and provided two additional reference strains for Achromobacter ruhlandii and Achromobacter marplatensis, species for which, thus far, only single strains are publicly available, and further validated the use of 2.1% concatenated nusA, eno, rpoB, gltB, lepA, nuoL and nrdA sequence divergence as a threshold value for species delineation in this genus. Finally, although most Achromobacter species can be distinguished by biochemical characteristics, the present study also highlighted considerable phenotypic intraspecies variability and demonstrated that the type strains may be phenotypically poor representatives of the species. We propose to classify the fourteen human clinical strains as Achromobacter mucicolens sp. nov. (with strain LMG 26685^T [=CCUG 61961^T] as the type strain), Achromobacter animicus sp. nov. (with strain LMG 26690^T [=CCUG 61966^T] as the type strain), Achromobacter spiritinus sp. nov. (with strain LMG 26692^T [=CCUG 61968^T] as the type strain), and Achromobacter pulmonis sp. nov. (with strain LMG 26696^T [=CCUG 61972^T] as the type strain).     

Growth in Coculture Stimulates Metabolism of the Phenylurea Herbicide Isoproturon by Sphingomonas sp. Strain SRS2

Metabolism of the phenylurea herbicide isoproturon by Sphingomonas sp. strain SRS2 was significantly enhanced when the strain was grown in coculture with a soil bacterium (designated strain SRS1). Both members of this consortium were isolated from a highly enriched isoproturon-degrading culture derived from an agricultural soil previously treated regularly with the herbicide. Based on analysis of the 16S rRNA gene, strain SRS1 was assigned to the β-subdivision of the proteobacteria and probably represents a new genus. Strain SRS1 was unable to degrade either isoproturon or its known metabolites 3-(4-isopropylphenyl)-1-methylurea, 3-(4-isopropylphenyl)-urea, or 4-isopropyl-aniline. Pure culture studies indicate that Sphingomonas sp. SRS2 is auxotrophic and requires components supplied by association with other soil bacteria. A specific mixture of amino acids appeared to meet these requirements, and it was shown that methionine was essential for Sphingomonas sp. SRS2. This suggests that strain SRS1 supplies amino acids to Sphingomonas sp. SRS2, thereby leading to rapid metabolism of ¹⁴C-labeled isoproturon to ¹⁴CO₂ and corresponding growth of strain SRS2. Proliferation of strain SRS1 suggests that isoproturon metabolism by Sphingomonas sp. SRS2 provides unknown metabolites or cell debris that supports growth of strain SRS1. The role of strain SRS1 in the consortium was not ubiquitous among soil bacteria; however, the indigenous soil microflora and some strains from culture collections also stimulate isoproturon metabolism by Sphingomonas sp. strain SRS2 to a similar extent.     

Ageing of atrazine in manure amended soils assessed by bioavailability to Pseudomonas sp. strain ADP

Animal manure is applied to agricultural land in areas of high livestock production. In the present study, we evaluated ageing of atrazine in two topsoils with and without addition of manure and in one subsoil. Ageing was assessed as the bioavailability of atrazine to the atrazine mineralizing bacteria Pseudomonas sp. strain ADP. Throughout an ageing period of 90 days bioavailability was investigated at days 1, 10, 32, 60 and 90, where ~10⁸ cells g^?1 of the ADP strain was inoculated to the ¹⁴C-atrazine exposed soil and ¹⁴CO₂ was collected over 7 days as a measure of mineralized atrazine. Even though the bioavailable residue decreased in all of the three soils as time proceeded, we found that ageing occurred faster in the topsoils rich in organic carbon than in subsoil. For one topsoil rich in organic carbon content, Simmelkær, we observed a higher degree of ageing when treated with manure. Contrarily, sorption experiments showed less sorption to Simmelkær treated with manure than the untreated soil indicating that sorption processes are not the only mechanisms of ageing. The other topsoil low in organic carbon content, Ringe, showed no significant difference in ageing between the manure-treated and untreated soil. The present study illustrates that not simply the organic carbon content influences adsorption and ageing of atrazine in soil but the origin and composition of organic matter plays an important role.