Bioaugmentation of a 4-chloronitrobenzene contaminated soil with Pseudomonas putida ZWL73

Bioaugmentation of Atrazine-Contaminated Soil With Paenarthrobacter sp. Strain AT-5 and Its Effect on the Soil Microbiome

Atrazine, a triazine herbicide, is widely used around the world. The residue of atrazine due to its application in the fore-rotating crop maize has caused phytotoxicity to the following crop sweet potato in China. Bioaugmentation of atrazine-contaminated soil with atrazine-degrading strains is considered as the most potential method to remove atrazine from soil. Nevertheless, the feasibility of bioaugmentation and its effect on soil microbiome still need investigation. In this study, Paenarthrobacter sp. AT-5, an atrazine-degrading strain, was inoculated into agricultural soils contaminated with atrazine to investigate the bioaugmentation process and the reassembly of the soil microbiome. It was found that 95.9% of 5 mg kg⁻¹ atrazine was removed from the soils when inoculated with strain AT-5 with 7 days, and the phytotoxicity of sweet potato caused by atrazine was significantly alleviated. qRT-PCR analysis revealed that the inoculated strain AT-5 survived well in the soils and maintained a relatively high abundance. The inoculation of strain AT-5 significantly affected the community structure of the soil microbiome, and the abundances of bacteria associated with atrazine degradation were improved.

Identification and Differentiation of Pseudomonas Species in Field Samples Using an rpoD Amplicon Sequencing Methodology

Species of the genus Pseudomonas are used for several biotechnological purposes, including plant biocontrol and bioremediation. To exploit the Pseudomonas genus in environmental, agricultural, or industrial settings, the organisms must be profiled at the species level as their bioactivity potential differs markedly between species. Standard 16S rRNA gene amplicon profiling does not allow for accurate species differentiation. Thus, the purpose of this study was to develop an amplicon-based high-resolution method targeting a 760-nucleotide (nt) region of the rpoD gene enabling taxonomic differentiation of Pseudomonas species in soil samples. The method was benchmarked on a 16-member Pseudomonas species mock community. All 16 species were correctly and semiquantitatively identified using rpoD gene amplicons, whereas 16S rRNA V3-V4 amplicon sequencing only correctly identified one species. We analyzed the Pseudomonas profiles in 13 soil samples in northern Zealand, Denmark, where samples were collected from grassland (3 samples) and agriculture soil (10 samples). Pseudomonas species represented up to 0.7% of the 16S rRNA gene abundance, of which each sampling site contained a unique Pseudomonas composition. Thirty culturable Pseudomonas strains were isolated from each grassland site and 10 from each agriculture site and identified by Sanger sequencing of the rpoD gene. In all cases, the rpoD amplicon approach identified more species than were found by cultivation, including hard-to-culture nonfluorescent pseudomonads, as well as more than were found by 16S rRNA V3-V4 amplicon sequencing. Thus, rpoD profiling can be used for species profiling of Pseudomonas, and large-scale prospecting of bioactive Pseudomonas may be guided by initial screening using this method.

IMPORTANCE A high-throughput sequencing-based method for profiling of Pseudomonas species in soil microbiomes was developed and identified more species than 16S rRNA gene sequencing or cultivation. Pseudomonas species are used as biocontrol organisms and plant growth-promoting agents, and the method will allow tracing of specific species of Pseudomonas as well as enable screening of environmental samples for further isolation and exploitation.

Quantitative detection of economically important Fusarium oxysporum f. sp. cubense strains in Africa in plants, soil and water

Banana is an important food crop and source of income in Africa. Sustainable production of banana, however, is at risk because of pests and diseases such as Fusarium wilt, caused by the soil-borne fungus Fusarium oxysporum f. sp. cubense (Foc). Foc can be disseminated from infested to disease-free fields in plant material, water and soil. Early detection of Foc using DNA technologies is thus required to accurately identify the fungus and prevent its further dissemination with plants, soil and water. In this study, quantitative (q)PCR assays were developed for the detection of Foc Lineage VI strains found in central and eastern Africa (Foc races 1 and 2), Foc TR4 (vegetative compatibility groups (VCG) 01213/16) that is present in Mozambique, and Foc STR4 (VCG 0120/15) that occurs in South Africa. A collection of 127 fungal isolates were selected for specificity testing, including endophytic Fusarium isolates from banana pseudostems, non-pathogenic F. oxysporum strains and Foc isolates representing the 24 VCGs in Foc. Primer sets that proved to be specific to Foc Lineage VI, Foc TR4 and Foc STR4 were used to produce standard curves for absolute quantification, and the qPCR assays were evaluated based on the quality of standard curves, repeatability and reproducibility, and limits of quantification (LOQ) and detection (LOD). The qPCR assays for Foc Lineage VI, TR4 and STR4 were repeatable and reproducible, with LOQ values of 10⁻³–10⁻⁴ ng/μL and a LOD of 10⁻⁴–10⁻⁵ ng/μL. The quantitative detection of Foc strains in Africa could reduce the time and improve the accuracy for identifying the Fusarium wilt pathogen from plants, water and soil on the continent.

Complete metabolic study by dibutyl phthalate degrading Pseudomonas sp. DNB-S1

The primary purpose of this study was to systematically explore the complete metabolic pathway and tolerance mechanism of strain DNB-S1 to dibutyl phthalate (DBP), and the effect of DBP on energy metabolism of DNB-S1. Here, DNB-S1, a strain of Pseudomonas sp. that was highly effective in degrading DBP, was identified, and differentially expressed metabolites and metabolic networks of DBP were studied. The results showed that the differentially expressed metabolites were mainly aromatic compounds and lipid compounds, with only a few toxic intermediate metabolites. It speculated that phthalic acid, salicylic acid, 3-hydroxybenzoate acid, 3-Carboxy-cis, cis-muconate, fumarypyravate were intermediate metabolites of DBP. Their up-regulation indicated that there were two metabolic pathways in the degradation of DBP (protocatechuate pathway and gentisate pathway), which had been verified by peak changes at 290 nm, 320 nm, 330 nm, and 375 nm in the enzymatic method. Also, aspartate, GSH, and other metabolites were up-regulation, indicating that DNB-S1 had a high tolerance to DBP and maintained cell homeostasis, which was also one of the essential reasons to ensure the efficient degradation of DBP. Altogether, this study firstly proposed two pathways to degrade DBP and comprehensively explored the effect of DBP on the metabolic function of DNB-S1, which enriched the study of microbial metabolism of organic pollutants, and which provided a basis for the application of metabolomics.

Microbial degradation kinetics and molecular mechanism of 2,6-dichloro-4-nitrophenol by a Cupriavidus strain

2,6-Dichloro-4-nitrophenol (2,6-DCNP) is an emerging chlorinated nitroaromatic pollutant, and its fate in the environment is an important question. However, microorganisms with the ability to utilize 2,6-DCNP have not been reported. In this study, Cupriavidus sp. CNP-8 having been previously reported to degrade various halogenated nitrophenols, was verified to be also capable of degrading 2,6-DCNP. Biodegradation kinetics assay showed that it degraded 2,6-DCNP with the specific growth rate of 0.124 h^-1, half saturation constant of 0.038 mM and inhibition constant of 0.42 mM. Real-time quantitative PCR analyses indicated that the hnp gene cluster was involved in the catabolism of 2,6-DCNP. The hnpA and hnpB gene products were purified to homogeneity by Ni-NTA chromatography. Enzymatic assays showed that HnpAB, a FAD-dependent two-component monooxygenase, converted 2,6-DCNP to 6-chlorohydroxyquinol with a K_m of 3.9 ± 1.4 μM and a k_cat/K_m of 0.12 ± 0.04 μΜ^-1 min^-1. As the oxygenase component encoding gene, hnpA is necessary for CNP-8 to grow on 2,6-DCNP by gene knockout and complementation. The phylogenetic analysis showed that the hnp cluster originated from the cluster involved in the catabolism of chlorophenols rather than nitrophenols. To our knowledge, CNP-8 is the first bacterium with the ability to utilize 2,6-DCNP, and this study fills a gap in the microbial degradation mechanism of this pollutant at the molecular, biochemical and genetic levels. Moreover, strain CNP-8 could degrade three chlorinated nitrophenols rapidly from the synthetic wastewater, indicating its potential in the bioremediation of chlorinated nitrophenols polluted environments.

Biodegradation of 2,6-dibromo-4-nitrophenol by Cupriavidus sp. strain CNP-8: Kinetics, pathway, genetic and biochemical characterization

Compound 2,6-dibromo-4-nitrophenol (2,6-DBNP) with high cytotoxicity and genotoxicity has been recently identified as an emerging brominated disinfection by-product during chloramination and chlorination of water, and its environmental fate is of great concern. To date, the biodegradation process of 2,6-DBNP is unknown. Herein, Cupriavidus sp. strain CNP-8 was reported to be able to utilize 2,6-DBNP as a sole source of carbon, nitrogen and energy. It degraded 2,6-DBNP in concentrations up to 0.7 mM, and the degradation of 2,6-DBNP conformed to Haldane inhibition model with μ_max of 0.096 h^-1, K_s of 0.05 mM and K_i of 0.31 mM. Comparative transcriptome and real-time quantitative PCR analyses suggested that the hnp gene cluster was likely responsible for 2,6-DBNP catabolism. Three Hnp proteins were purified and functionally verified. HnpA, a FADH₂-dependent monooxygenase, was found to catalyze the sequential denitration and debromination of 2,6-DBNP to 6-bromohydroxyquinol (6-BHQ) in the presence of the flavin reductase HnpB. Gene knockout and complementation revealed that hnpA is essential for strain CNP-8 to utiluze 2,6-DBNP. HnpC, a 6-BHQ 1,2-dioxygenase was proposed to catalyze the ring-cleavage of 6-BHQ during 2,6-DBNP catabolism. These results fill a gap in the understanding of the microbial degradation process and mechanism of 2,6-DBNP.

Dynamic response of biofilm microbial ecology to para-chloronitrobenzene biodegradation in a hydrogen-based, denitrifying and sulfate-reducing membrane biofilm reactor

The dynamic response of biofilm microbial ecology to para-chloronitrobenzene (p-CNB) biodegradation was systematically evaluated according to the composition and loading of electron acceptors and H₂ availability (controlled by H₂ pressure) in a hydrogen-based, denitrifying and sulfate-reducing membrane biofilm reactor (MBfR). To accomplish this, a laboratory-scale MBfR was set up and operated with different influent p-CNB concentrations (0, 2, and 5 mg p-CNB/L) and H₂ pressures (0.04 and 0.05 MPa). Polymerase chain reaction-denaturing gel electrophoresis (PCR-DGGE) and cloning were then applied to investigate the bacterial diversity response of biofilm during p-CNB biodegradation. The results showed that denitrification and sulfate reduction largely controlled the total demand for H₂. Additionally, the DGGE fingerprint demonstrated that the addition of p-CNB, which acted as an electron acceptor, was a critical factor in the dynamics of the MBfR biofilm microbial ecology. The presence of p-CNB also had a more advantageous effect on the biofilm microbial community. Additionally, clone library analysis showed that Proteobacteria (especially beta- and gamma-) comprised the majority of the microbial biofilm response to p-CNB biodegradation, and that Pseudomonas sp. (Gammaproteobacteria) played a significant role in the biotransformation of p-CNB to aniline.

Biodegradation of 2-chloro-4-nitrophenol via a hydroxyquinol pathway by a Gram-negative bacterium, Cupriavidus sp. strain CNP-8

Cupriavidus sp. strain CNP-8 isolated from a pesticide-contaminated soil was able to utilize 2-chloro-4-nitrophenol (2C4NP) as a sole source of carbon, nitrogen and energy, together with the release of nitrite and chloride ions. It could degrade 2C4NP at temperatures from 20 to 40 °C and at pH values from 5 to 10, and degrade 2C4NP as high as 1.6 mM. Kinetics assay showed that biodegradation of 2C4NP followed Haldane substrate inhibition model, with the maximum specific growth rate (μ_max) of 0.148/h, half saturation constant (K_s) of 0.022 mM and substrate inhibition constant (K_i) of 0.72 mM. Strain CNP-8 was proposed to degrade 2C4NP with hydroxyquinol (1,2,4-benzenetriol, BT) as the ring-cleavage substrate. The 2C4NP catabolic pathway in strain CNP-8 is significant from those reported in other Gram-negative 2C4NP utilizers. Enzymatic assay indicated that the monooxygenase initiating 2C4NP catabolism had different substrates specificity compared with previously reported 2C4NP monooxygenations. Capillary assays showed that strain CNP-8 exhibited metabolism-dependent chemotactic response toward 2C4NP at the optimum concentration of 0.5 mM with a maximum chemotaxis index of 37.5. Furthermore, microcosm studies demonstrated that strain CNP-8, especially the pre-induced cells, could remove 2C4NP rapidly from the 2C4NP-contaminated soil. Considering its adaptability to pH and temperature fluctuations and great degradation efficiency against 2C4NP, strain CNP-8 could be a promising candidate for the bioremediation of 2C4NP-contaminated sites.

A Novel Method for Enhancing Strains' Biodegradation of 4-Chloronitrobenzene

This paper introduces a novel approach to enhance the strains' biodegradation of 4-chloronitrobenzene by utilizing the synergistic effect of the organic reductant mannitol and the substrate beef extraction. Our results demonstrate that 4-chloronitrobenzene could not be an available nitrogen source to support target strains' growth, which induced the limited 4-chloronitrobenzene biodegradation. In addition, the organic reducing agent and substrate had a better synergistic effect than inorganic reducing agent and substrate to enhance the strains' 4-chloronitrobenzene cometabolic biodegradation. Employing the synergistic effect of the optimal mixture (mannitol and beef extraction), the biodegradation rates of 50mgL^-1 4-chloronitrobenzene by seven of the ten target strains were enhanced up to 100% from previous removals of no more than 19.1% after 7days. Three of the strains could even completely degrade 100mgL^-1 4-chloronitrobenzene while five strains degraded over 91.4%. The method has good potential to enhance bioremediation of various 4-Chloronitrobenzene-contaminated environments as mannitol and beef extraction are non-toxic to the environment.

Effect of inoculation of Burkholderia sp. strain SJ98 on bacterial community dynamics and para-nitrophenol, 3-methyl-4-nitrophenol, and 2-chloro-4-nitrophenol degradation in soil

para-Nitrophenol (PNP), 3-methyl-4-nitrophenol (3M4NP), and 2-chloro-4-nitrophenol (2C4NP) are highly toxic compounds that have caused serious environmental issues. We inoculated an artificially contaminated soil with Burkholderia sp. strain SJ98, which has the ability to degrade PNP, 3M4NP, and 2C4NP, and quantified bioremediation. There was accelerated degradation of all nitrophenols in inoculated treatments compared to the un-inoculated treatments. The indigenous bacteria were able to degrade PNP, but not 3M4NP or 2C4NP. Real-time PCR targeting the catabolic gene pnpA showed that levels of strain SJ98 remained stable over the incubation period. High-throughput sequencing revealed that both contamination and bioaugmentation influenced the bacterial community structure. Bioaugmentation seemed to protect Kineosporia, Nitrososphaera, and Schlesneria from nitrophenol inhibition, as well as led to a sharp increase in the abundance of Nonomuraea, Kribbella, and Saccharopolyspora. There was a significant increase in the relative abundances of Thermasporomyces, Actinomadura, and Streptomyces in both contaminated and bioaugmented treatments; this indicated that these bacteria are likely directly related to nitrophenol degradation. To our knowledge, this is the first report of the simultaneous removal of PNP, 3M4NP, and 2C4NP using bioaugmentation. This study provides valuable insights into the bioremediation of soils contaminated with nitrophenols.

Biodegradation of Xenobiotic Compounds

The continuous accumulation of recalcitrant xenobiotic compounds into the ecosystem released from various sources caused a serious global concern. Xenobiotics compounds are carcinogenic, mutagenic, causing teratogenic effect and persist over a long period of time in the environment. Therefore there is an urgent need for the detoxification of these compounds. Biodegradation is a technique that employs natural biological processes to completely degrade toxic contaminants from the environment. The microorganisms possess a wide range of catabolic biodegradation pathways and, thus, use these toxic xenobiotics as the sole source of carbon and energy. Bacteria and fungi are source of xenobiotic degradation. For the development of successful and improved bioremediation processes, understanding of the biochemical and molecular aspects of xenobiotics biodegradation is required. The chapter aims to provide an overview of xenobiotic compounds, factors affecting biodegradation, the metabolic pathways and genetic adaptation in microorganisms for degradation of recalcitrant xenobiotic compounds.

Exploring the potential of novel biomixtures and Lentinula edodes fungus for the degradation of selected pesticides. Evaluation for use in biobed systems

An approach to reduce the contamination of water sources with pesticides is the use of biopurificaction systems. The active core of these systems is the biomixture. The composition of biomixtures depends on the availability of local agro-industrial wastes and design should be adapted to every region. In Portugal, cork processing is generally regarded as environmentally friendly and would be interesting to find applications for its industry residues. In this work the potential use of different substrates in biomixtures, as cork (CBX); cork and straw, coat pine and LECA (Light Expanded Clay Aggregates), was tested on the degradation of terbuthylazine, difenoconazole, diflufenican and pendimethalin pesticides. Bioaugmentation strategies using the white-rot fungus Lentinula edodes inoculated into the CBX, was also assessed. The results obtained from this study clearly demonstrated the relevance of using natural biosorbents as cork residues to increase the capacity of pesticide dissipation in biomixtures for establishing biobeds. Furthermore, higher degradation of all the pesticides was achieved by use of bioaugmented biomixtures. Indeed, the biomixtures inoculated with L. edodes EL1 were able to mineralize the selected xenobiotics, revelling that these white-rot fungi might be a suitable fungus for being used as inoculum sources in on-farm sustainable biopurification system, in order to increase its degradation efficiency. After 120 days, maximum degradation of terbuthylazine, difenoconazole, diflufenican and pendimethalin, of bioaugmented CBX, was 89.9%, 75.0%, 65.0% and 99.4%, respectively.. The dominant metabolic route of terbuthylazine in biomixtures inoculated with L. edodes EL1 proceeded mainly via hydroxylation, towards production of terbuthylazine-hydroxy-2 metabolite. Finally, sorption process to cork by pesticides proved to be a reversible process, working cork as a mitigating factor reducing the toxicity to microorganisms in the biomixture, especially in the early stages.

Metabolic pathway for degradation of 2-chloro-4-aminophenol by Arthrobacter sp. SPG

A degradation pathway of 2-chloro-4-aminophenol (2C4AP) was studied in an Arthrobacter sp. SPG that utilized 2C4AP as its sole source of carbon and energy. The 2C4AP degradation was initiated by a 2C4AP-deaminase that catalyzed the conversion of 2C4AP into chlorohydroquinone (CHQ) with removal of ammonium ion. In the next step, a CHQ-dehalogenase dehalogenated CHQ to hydroquinone (HQ) that cleaved into γ-hydroxymuconic semialdehyde by a HQ-dioxygenase. The 2C4AP degradation was also investigated in sterile and non-sterile soil microcosms using strain SPG. The results show that the SPG cells degraded 2C4AP more rapidly in sterile soil than non-sterile soil. Our studies showed that strain SPG may be used for bioremediation of 2C4AP-contaminated sites. This is the first report of the 2C4AP degradation by any bacteria.

Bacterial degradation of nitrophenols and their derivatives

This review intends to provide an overview of bacterial degradation of nitrophenols (NPs) and their derivatives. The main scientific focus is on biochemical and genetic characterization of bacterial degradation of NPs. Other aspects such as bioremediation and chemotaxis correlated with biodegradation of NPs are also discussed. This review will increase our current understanding of bacterial degradation of NPs and their derivatives.

Simazine biodegradation and community structures of ammonia-oxidizing microorganisms in bioaugmented soil: impact of ammonia and nitrate nitrogen sources

The objective of the present study was to investigate the impact of ammonia and nitrate nitrogen sources on simazine biodegradation by Arthrobacter sp. strain SD1 and the community structures of ammonia-oxidizing archaea (AOA) and bacteria (AOB) in non-agricultural soil. Soil microcosms with different treatments were constructed for herbicide biodegradation test. The relative abundance of the strain SD1 and the structures of AOA and AOB communities were assessed using quantitative PCR (q-PCR) and terminal restriction fragment length polymorphism (TRFLP), respectively. The co-existence of two inorganic nitrogen sources (ammonia and nitrate) had certain impact on simazine dissipation by the strain SD1. Bioaugmentation could induce a shift in the community structures of both AOA and AOB, but AOA were more responsive. Nitrogen application had significant impacts on AOA and AOB communities in bioaugmented soils. Moreover, in non-bioaugmented soil, the community structure of AOA, instead of AOB, could be quickly recovered after herbicide application. This study could add some new insights towards the impacts of nitrogen sources on s-triazine bioremediation and ammonia-oxidizing microorganisms in soil ecosystem.

Simazine degradation in bioaugmented soil: urea impact and response of ammonia-oxidizing bacteria and other soil bacterial communities

The objective of this study was to investigate the impact of exogenous urea nitrogen on ammonia-oxidizing bacteria (AOB) and other soil bacterial communities in soil bioaugmented for simazine remediation. The previously isolated simazine-degrading Arthrobacter sp. strain SD1 was used to degrade the herbicide. The effect of urea on the simazine degradation capacity of the soil bioaugmented with Arthrobacter strain SD1 was assessed using quantitative PCR targeting the s-triazine-degrading trzN and atzC genes. Structures of bacterial and AOB communities were characterized using terminal restriction fragment length polymorphism. Urea fertilizer could affect simazine biodegradation and decreased the proportion of its trzN and atzC genes in soil augmented with Arthrobacter strain SD1. Bioaugmentation process could significantly alter the structures of both bacterial and AOB communities, which were strongly affected by urea amendment, depending on the dosage. This study could provide some new insights towards s-triazine bioremediation and microbial ecology in a bioaugmented system. However, further studies are necessary in order to elucidate the impact of different types and levels of nitrogen sources on s-triazine-degraders and bacterial and AOB communities in bioaugmented soil.

Anaerobic biotransformation of fluoronitrobenzenes and microbial communities in methanogenic systems

The fluorinated compounds are becoming a ubiquitous class of environmental contaminants because of their widespread applications, and their fate is a matter of great concern under anaerobic environment. In this work, the biotransformation of five fluoronitrobenzenes (FNBs), i.e., 2-fluoronitrobenzene (2-FNB), 3-fluoronitrobenzene (3-FNB), 4-fluoronitrobenzene (4-FNB), 2,4-difluoronitrobenzene (2,4-DFNB), and 2,3,4-trifluoronitrobenzene (2,3,4-TFNB), under methanogenic conditions had been studied by semicontinuous and batch tests for the first time. In 245 days, the five FNBs except 3-FNB were transformed mainly via nitro-reduction, and the reductive defluorination was not observed. During the biotransformation of 3-FNB, the reductive defluorination occurred after 98 days; however, its product was not aniline. The maximum transformation rates of 2-FNB, 3-FNB, 4-FNB, 2,4-DFNB, and 2,3,4-TFNB were 21.21 ± 1.73, 32.14 ± 2.33, 21.33 ± 2.48, 33.89 ± 6.87, and 10.87 ± 0.84 mg FNB (g VSS h)(-1), respectively. With the increase in the number of the fluorous groups, the transformation rates did not increase. Besides, the microbial communities were characterized by means of denaturing gradient gel electrophoresis (DGGE). Results showed that the predominant archaea were Methanobacterium, Methanosphaerula, Methanofollis, Methanospirillum, Methanolinea, and Methanosaeta; the predominant bacteria were Sphingbacteriales, Flavobacteriales, bacteroidales, Deltaproteobacteria, Desulfovibrionales, Clostridates, and Pseudomonadates. Few bacteria found were with high similarity to dechlorinating microorganisms reported. The results demonstrated that the pathways of FNBs biotransformation were different from those of the chloronitrobenzenes under methanogenic conditions.

Bioaugmentation with a consortium of bacterial nitrophenol-degraders for remediation of soil contaminated with three nitrophenol isomers

A consortium consisting of para-nitrophenol utilizer Pseudomonas sp. strain WBC-3, meta-nitrophenol utilizer Cupriavidus necator JMP134 and ortho-nitrophenol utilizer Alcaligenes sp. strain NyZ215 was inoculated into soil contaminated with three nitrophenol isomers for bioaugmentation. Accelerated removal of all nitrophenols was achieved in inoculated soils compared to un-inoculated soils, with complete removal of nitrophenols in inoculated soils occurring between 2 and 16 days. Real-time polymerase chain reaction (PCR) targeting nitrophenol-degradation functional genes indicated that the three strains survived and were stable over the course of the incubation period. The abundance of total indigenous bacteria (measured by 16S rRNA gene real-time PCR) was slightly negatively impacted by the nitrophenol contamination. Denaturing gradient gel electrophoresis profiles of total and group-specific indigenous community suggested a dynamic change in species richness occurred during the bioaugmentation process. Furthermore, Pareto-Lorenz curves and Community organization parameters indicated that the bioaugmentation process had little impact on species evenness within the microbial community.

Degradation of chlorinated nitroaromatic compounds

Chlorinated nitroaromatic compounds (CNAs) are persistent environmental pollutants that have been introduced into the environment due to the anthropogenic activities. Bacteria that utilize CNAs as the sole sources of carbon and energy have been isolated from different contaminated and non-contaminated sites. Microbial metabolism of CNAs has been studied, and several metabolic pathways for degradation of CNAs have been proposed. Detoxification and biotransformation of CNAs have also been studied in various fungi, actinomycetes and bacteria. Several physicochemical methods have been used for treatment of wastewater containing CNAs; however, these methods are not suitable for in situ bioremediation. This review describes the current scenario of the degradation of CNAs.

Reductive transformation and detoxification mechanism of 2,4-dinitrochlorobenzene in combined zero valent iron and anaerobic-aerobic process

A combined zero valent iron (ZVI) and anaerobic-aerobic process was adopted for the treatment of 2,4-dinitrochlorobenzene (DNCB)-containing wastewater. The transformation pathway, reduction of acute toxicity and enhancement of biodegradability were investigated. After pretreatment by ZVI, DNCB in wastewater could be completely converted into 2,4-diaminochlorobenzene (DACB). The ratio of BOD5/COD increased from 0.005 +/- 0.001 to 0.168 +/- 0.007, while EC(50, 48 hr) (V/V) increased from 0.65% to 5.20%, indicating the enhancement of biodegradability and reduction of acute toxicity with the pretreatment by ZVI. DACB was further dechlorinated to m-phenylenediamine during the anaerobic process using methanol as electron donor, with EC(50, 48 hr) increasing from 5.20% to 48.2%. After the subsequent anaerobic-aerobic process, m-phenylenediamine was degraded completely, with effluent COD of 67.5 +/- 10.8 mg/L. This effluent of the subsequent anaerobic-aerobic process was not toxic to zebrafish. The combined ZVI and anaerobic-aerobic process offers bright prospects for the treatment of chlorinated nitroaromatic compound-containing wastewater.

Isolation and bioaugmentation of an estradiol-degrading bacterium and its integration into a mature biofilm

Bioaugmentation can alter the potential activity as well as the composition of the naturally occurring microbial biota during bioremediation of a contaminated site. The focus of the current study is the pollutant 17β-estradiol (E2), which can cause endocrine effects and is potentially harmful to aquatic biota and to public health. The community composition and function of biofilms, originating from a wetland system, as affected by augmentation of an estradiol-degrading bacterium (EDB-LI1) under different conditions, were investigated. EDB-LI1 inoculation into biofilm from two wetland ponds representing early and advanced water treatment stages, respectively, yielded three significant observations, as follows: (i) EDB-LI1, enriched from a biofilm of a constructed wetland wastewater treatment system, was detected (by quantitative PCR [qPCR] analysis) in this environment in the augmented biofilm only; (ii) the augmented biofilm acquired the ability to remove estradiol; and (iii) the bacterial community composition (analyzed by PCR-denaturing gradient gel electrophoresis [DGGE]) of the augmented biofilm differed from that of the control biofilm. Furthermore, EDB-LI1 bioaugmentation showed a higher level of removal of estradiol with biofilms that originated from the advanced-treatment-stage wetland pond than those from the early-treatment-stage pond. Hence, the bioaugmentation efficiency of EDB-LI1 depends on both the quality of the feed water and the microbial community composition in the pond.

Bioaugmentation as a strategy for cleaning up of soils contaminated with aromatic compounds

The contamination of soil with aromatic compounds is of particular environmental concern as they exhibit carcinogenic and mutagenic properties. One of the methods of their removal from soil is bioaugmentation, defined as a technique for improvement of the degradative capacity of contaminated areas by introduction of specific competent strains or consortia of microorganisms. The efficiency of bioaugmentation is determined by many abiotic and biotic factors discussed in this paper. The first include chemical structure, concentration and availability of pollutants as well as physico-chemical properties of soil. In turn, among biotic factors the most important is the selection of proper microorganisms that can not only degrade contaminants but can also successfully compete with indigenous microflora. Several strategies are being developed to make augmentation a successful technology particularly in soils without degrading indigenous microorganisms. These approaches involve the use of genetically engineered microorganisms and gene bioaugmentation. The enhancement of bioaugmentation may be also achieved by delivering suitable microorganisms immobilized on various carriers or use of activated soil.