Highly Efficient Removal of 2,4,5-Trichlorophenoxyacetic Acid by Adsorption and Photocatalysis Using Nanomaterials with Surface Coating by the Cationic Surfactant

Extensive removal of 2,4,5-trichlorophenoxyacetic acid (2,4,5-T) using titania (TiO2) nanoparticles by adsorption and photocatalysis with a surface coating by cetyltrimethylammonium bromide (CTAB) is reported. The CTAB-coated TiO2 nanoparticles (CCTN) were characterized by FT-IR, zeta-potential measurements, and UV-vis diffuse reflectance spectroscopy (UV-vis-DRS). 2,4,5-T removal increased significantly after surface modification with CTAB compared with bare TiO2 nanoparticles. Optimal parameters affecting 2,4,5-T removal were found to be pH 4, CCTN dosage 10 mg/mL, and adsorption time 180 min. The maximum adsorptive removal of 2,4,5-T using CCTN reached 96.2% while highest adsorption capacity was 13.4 mg/g. CCTN was also found to be an excellent photocatalyst that achieved degradation efficiency of 99.2% with an initial concentration of 25 mg/L. The removal mechanisms of 2,4,5-T using CCTN by both adsorption and photocatalysis are discussed in detail based on changes in functional group vibrations and surface charge. Our results indicate that CCTN is an excellent material for 2,4,5-T removal in water by both adsorption and photocatalysis.

Pesticide-tolerant microbial consortia: Potential candidates for remediation/clean-up of pesticide-contaminated agricultural soil

Reclamation of pesticide-polluted lands has long been a difficult endeavour. The use of synthetic pesticides could not be restricted due to rising agricultural demand. Pesticide toxicity has become a pressing agronomic problem due to its adverse impact on agroecosystems, agricultural output, and consequently food security and safety. Among different techniques used for the reclamation of pesticide-polluted sites, microbial bioremediation is an eco-friendly approach, which focuses on the application of resilient plant growth promoting rhizobacteria (PGPR) that may transform or degrade chemical pesticides to innocuous forms. Such pesticide-resilient PGPR has demonstrated favourable effects on soil-plant systems, even in pesticide-contaminated environments, by degrading pesticides, providing macro-and micronutrients, and secreting active but variable secondary metabolites like-phytohormones, siderophores, ACC deaminase, etc. This review critically aims to advance mechanistic understanding related to the reduction of phytotoxicity of pesticides via the use of microbe-mediated remediation techniques leading to crop optimization in pesticide-stressed soils. The literature surveyed and data presented herein are extremely useful, offering agronomists-and crop protectionists microbes-assisted remedial strategies for affordably enhancing crop productivity in pesticide-stressed soils.

Pesticide bioremediation in liquid media using a microbial consortium and bacteria-pure strains isolated from a biomixture used in agricultural areas

Microorganisms' role in pesticide degradation has been studied widely. Insitu treatments of effluents containing pesticides such as biological beds (biobeds) are efficient biological systems where biomixture (mixture of substrates) and microorganisms are the keys in pesticide treatment; however, microbial activity has been studied poorly, and its potential beyond biobeds has not been widely explored. In this study, the capacity of microbial consortium and bacteria-pure strains isolated from a biomixture (soil-straw; 1:1, v/v) used to treat agricultural effluents under real conditions were evaluated during a bioremediation process of five pesticides commonly used Yucatan Mexico. Atrazine, carbofuran, and glyphosate had the highest degradations (>90%) using the microbial consortium; 2,4-D and diazinon were the most persistent (DT50 = 8.64 and 6.63 days). From the 21 identified bacteria species in the microbial consortium, Pseudomonas nitroreducens was the most abundant (52%) according to identified sequences. For the pure strains evaluation 2,4-D (DT50 = 9.87 days), carbofuran (DT50 = 8.27 days), diazinon (DT50 = 8.80 days) and glyphosate (DT50 = 8.59 days) were less persistent in the presence of the mixed consortium (Ochrobactrum sp. DGG-1-3, Ochrobactrum sp. Ge-14, Ochrobactrum sp. B18 and Pseudomonas citronellolis strain ADA-23B). Time, pesticide, and strain type were significant (P < 0.05) in pesticide degradation, so this process is multifactorial. Microbial consortium and pure strains can be used to increase the biobed efficiency by inoculation, even in the remediation of soil contaminated by pesticides in agricultural areas.

Microbial Degradation of Pesticide Residues and an Emphasis on the Degradation of Cypermethrin and 3-phenoxy Benzoic Acid: A Review

Nowadays, pesticides are widely used in preventing and controlling the diseases and pests of crop, but at the same time pesticide residues have brought serious harm to human's health and the environment. It is an important subject to study microbial degradation of pesticides in soil environment in the field of internationally environmental restoration science and technology. This paper summarized the microbial species in the environment, the study of herbicide and pesticides degrading bacteria and the mechanism and application of pesticide microbial degrading bacteria. Cypermethrin and other pyrethroid pesticides were used widely currently, while they were difficult to be degraded in the natural conditions, and an intermediate metabolite, 3-phenoxy benzoic acid would be produced in the degradation process, causing the secondary pollution of agricultural products and a series of problems. Taking it above as an example, the paper paid attention to the degradation process of microorganism under natural conditions and factors affecting the microbial degradation of pesticide. In addition, the developed trend of the research on microbial degradation of pesticide and some obvious problems that need further solution were put forward.

Geosmin-producing Species of Coelosphaerium (Synechococcales, Cyanobacteria) in Lake Shinji, Japan

In Lake Shinji, Japan, periodic outbreaks of musty odour have occurred since mid-May 2007. Although the substance responsible for the odour was identified as geosmin, the odour-producing organism was unknown. We cultivated an axenic unialgal strain and determined that a species of Coelosphaerium (Synechococcales) was responsible for the production of geosmin in Lake Shinji. Our analysis was conducted using gas chromatography/mass spectrometry to determine the odorous compound. To determine the algae species, it was observed by optical microscopy to describe its morphological characteristics and the polymerase chain reaction was used to characterise the nucleotide sequence of the 16S rRNA gene and the 16S-23S rRNA internal transcribed spacer region. In addition, we explored the relationship between the number of cells of the Coelosphaerium sp. and the concentration of geosmin. In conclusion, geosmin, the cause of the musty odour in Lake Shinji in autumn 2009, was produced by Coelosphaerium sp., and to our knowledge, this is the first report of a geosmin-producing species in the family Coelosphaeriaceae.

Bacterial population dynamics in a reverse-osmosis water purification system determined by fluorescent staining and PCR-denaturing gradient gel electrophoresis

The bacterial population dynamics in an industrial scale reverse-osmosis (RO) water purification system were analyzed by fluorescent staining methods and denaturing gradient gel electrophoresis (DGGE). Bacterial numbers increased with storage in a tank, and bacterial diversity changed during the water purification process. A DNA sequence-based analysis of the major bands on the DGGE gel revealed that Simonsiella sp. (Betaproteobacteria) was abundant in the source water (activated sludge-treated waste effluent), while Bosea sp. and Rhizobium sp. (Alphaproteobacteria), which usually exist in an oligotrophic environment, became abundant during the water purification process. These results suggest the importance of microbiological monitoring by culture-independent methods for quality control in RO water purification systems. These methods could provide an early warning of impending problems and clarify critical steps in controlling specific bacteria contributing to the contamination of RO water systems.

A great leap forward in microbial ecology

Ribosomal RNA (rRNA) sequence-based molecular techniques emerged in the late 1980s, which completely changed our general view of microbial life. Coincidentally, the Japanese Society of Microbial Ecology (JSME) was founded, and its official journal "Microbes and Environments (M&E)" was launched, in 1985. Thus, the past 25 years have been an exciting and fruitful period for M&E readers and microbiologists as demonstrated by the numerous excellent papers published in M&E. In this minireview, recent progress made in microbial ecology and related fields is summarized, with a special emphasis on 8 landmark areas; the cultivation of uncultured microbes, in situ methods for the assessment of microorganisms and their activities, biofilms, plant microbiology, chemolithotrophic bacteria in early volcanic environments, symbionts of animals and their ecology, wastewater treatment microbiology, and the biodegradation of hazardous organic compounds.

Soil clone library analyses to evaluate specificity and selectivity of PCR primers targeting fungal 18S rDNA for denaturing-gradient gel electrophoresis (DGGE)

We evaluated the fungal specificity and detection bias of four fungal 18S rRNA gene (18S rDNA) primer sets for denaturing-gradient gel electrophoresis (DGGE). We constructed and compared clone libraries amplified from upland and paddy field soils with each primer set (1, NS1/GCFung; 2, FF390/FR1-GC; 3, NS1/FR1-GC; and 4, NS1/EF3 for the first PCR and NS1/FR1-GC for the second PCR). Primer set 4 (for nested PCR) showed the highest specificity for fungi but biased specific sequences. Sets 1, 2, and 3 (for single PCR) amplified non-fungal eukaryotic sequences (from 7 to 16% for upland soil and from 20 to 31% for paddy field soil) and produced libraries with similar distributions of fungal 18S rDNA sequences at both the phylum and the class level. Set 2 tended to amplify more diverse fungal sequences, maintaining higher specificity for fungi. In addition, clone analyses revealed differences among primer sets in the frequency of chimeras. In upland field soil, the libraries amplified with primer sets 3 and 4, which targeted long fragments, contained many chimeric 18S rDNA sequences (18% and 48%, respectively), while the libraries obtained with sets 1 and 2, which targeted short fragments, contained fewer chimeras (5% and 10%, respectively).

Isolation of effective 3-chlorobenzoate-degraders in soil using community analyses by PCR-DGGE

The screening of pollutant degraders by relying solely on cultivation techniques such as liquid enrichment often fails to isolate the actual degraders in the environment. Community analyses by PCR-denaturing gradient gel electrophoresis (DGGE) were performed to isolate bacteria that can degrade 3-chlorobenzoate (3CB) effectively in soil. A forest soil sample was repeatedly dosed with 3CB (500 mg kg(-1)) to enrich it with indigenous 3CB-degraders, and changes in the bacterial community were monitored by PCR-DGGE of the 16S rRNA gene and benzoate 1,2-dioxygenase alpha subunit gene (benA). Initially, it required about 3 weeks to degrade 3CB in the soil, whereas it took only 3 days after the third dose. With this accelerated degradation, several intensified bands appeared in the DGGE profiles of both 16S rRNA gene and benA. We succeeded in isolating five 3CB-degrading Burkholderia strains corresponding to these bands by direct plating, while most of them were eliminated by liquid enrichment. Inoculation of the strains into the soil demonstrated that the five strains could degrade 3CB effectively in the soil. This study clearly shows significant bias during the liquid enrichment process and the advantage of using PCR-DGGE in screening effective degraders under environmental conditions.

Growth of the cyanobacterium Synechococcus leopoliensis CCAP1405/1 on agar media in the presence of heterotrophic bacteria

The cyanobacterium Synechococcus leopoliensis CCAP1405/1 does not grow on common solid media made of agar, agarose HT, noble agar, gelrite and gelatin, although it grows in liquid media with the same components. The inoculation of S. leopoliensis CCAP1405/1 at a high initial cell density allowed it to grow on the agar media, and co-inoculation with one of the heterotrophic bacterial strains belonging to a wide range of phylogeny, showed the same effects even at a low initial cell density of S. leopoliensis CCAP1405/1. The addition of thiosulfate and high concentrations of vitamin B(12), biotin and thiamine also supported growth on solid media, but catalase had no effect. On inorganic solid media, the autotrophic cyanobacterial strain supported the growth of heterotrophic bacteria, suggesting mutual interaction.

Construction of river model biofilm for assessing pesticide effects

Due to the high importance of biofilms on river ecosystems, assessment of pesticides' adverse effects is necessary but is impaired by high variability and poor reproducibility of both natural biofilms and those developed in the laboratory. We constructed a model biofilm to evaluate the effects of pesticides, consisting in cultured microbial strains, Pedobacter sp. 7-11, Aquaspirillum sp. T-5, Stenotrophomonas sp. 3-7, Achnanthes minutissima N71, Nitzschia palea N489, and/or Cyclotella meneghiniana N803. Microbial cell numbers, esterase activity, chlorophyll-a content, and the community structure of the model biofilm were examined and found to be useful as biological factors for evaluating the pesticide effects. The model biofilm was formed through the cooperative interaction of bacteria and diatoms, and a preliminary experiment using the herbicide atrazine, which inhibits diatom growth, indicated that the adverse effect on diatoms inhibited indirectly the bacterial growth and activity and, thus, the formation of the model biofilm. Toxicological tests using model biofilms could be useful for evaluating the pesticide effects and complementary to studies on actual river biofilms.

Bioremediation of soil contaminated with pentachlorophenol by Anthracophyllum discolor and its effect on soil microbial community

Bioaugmentation is a promising technology to clean up sites contaminated with recalcitrant chemicals. White-rot fungi have proven to be effective in the degradation of pentachlorophenol. Here, we report the bioremediation of soil contaminated with pentachlorophenol (PCP) by Anthracophyllum discolor and its impact on the soil microbial community. In this study three types of microcosms were established: fresh soil (C(0)), fresh soil plus wheat straw (WS(0)) and, fresh soil plus wheat straw inoculated with A. discolor (WSAD(0)). Additionally, similar treatments and a control of sterile soil spiked with PCP (C(250), WS(250) and WSAD(250)) were used to evaluate the remediation and adsorption of PCP. The PCP removal, total microbial activity, and enzymatic activities were evaluated. This study also investigated the structure of soil microbial community by denaturing gradient gel electrophoresis (DGGE), identifying some of the dominant bacterial and fungal species. The results showed that PCP was effectively degraded in soils by A. discolor and by indigenous soil microorganisms. The addition of wheat straw increased the PCP degradation and enzymatic activities. Only laccase activity was negatively affected by PCP contamination. The PCP degradation was associated with changes in microbial communities, mainly stimulation of members of bacterial phylum Proteobacteria (Xanthomonadaceae, Burkholderiaceae and Enterobacteriaceae), and fungal phylum Ascomycota and Basidiomycota. This study shows the ability of A. discolor to degrade PCP from contaminated soil, and demonstrates that agricultural residues, such as wheat straw, can be used as growth substrate by microorganisms in PCP-contaminated soil, demonstrating a great potential of autochthonous microorganisms for soil remediation.

The earthworm Aporrectodea caliginosa stimulates abundance and activity of phenoxyalkanoic acid herbicide degraders

2-Methyl-4-chlorophenoxyacetic acid (MCPA) is a widely used phenoxyalkanoic acid (PAA) herbicide. Earthworms represent the dominant macrofauna and enhance microbial activities in many soils. Thus, the effect of the model earthworm Aporrectodea caliginosa (Oligochaeta, Lumbricidae) on microbial MCPA degradation was assessed in soil columns with agricultural soil. MCPA degradation was quicker in soil with earthworms than without earthworms. Quantitative PCR was inhibition-corrected per nucleic acid extract and indicated that copy numbers of tfdA-like and cadA genes (both encoding oxygenases initiating aerobic PAA degradation) in soil with earthworms were up to three and four times higher than without earthworms, respectively. tfdA-like and 16S rRNA gene transcript copy numbers in soil with earthworms were two and six times higher than without earthworms, respectively. Most probable numbers (MPNs) of MCPA degraders approximated 4 × 10(5) g(dw)(-1) in soil before incubation and in soil treated without earthworms, whereas MPNs of earthworm-treated soils were approximately 150 × higher. The aerobic capacity of soil to degrade MCPA was higher in earthworm-treated soils than in earthworm-untreated soils. Burrow walls and 0-5 cm depth bulk soil displayed higher capacities to degrade MCPA than did soil from 5-10 cm depth bulk soil, expression of tfdA-like genes in burrow walls was five times higher than in bulk soil and MCPA degraders were abundant in burrow walls (MPNs of 5 × 10(7) g(dw)(-1)). The collective data indicate that earthworms stimulate abundance and activity of MCPA degraders endogenous to soil by their burrowing activities and might thus be advantageous for enhancing PAA degradation in soil.

Analysis of genes encoding the 2,4-dichlorophenoxyacetic acid-degrading enzyme from Sphingomonas agrestis 58-1

A 2,4-dichlorophenoxy acetic acid (2,4-D)-degrading bacterium, strain 58-1, was newly isolated from soil samples collected in the Fukuoka Prefecture, Japan, and grown on an enrichment culture medium containing 2,4-D as the sole carbon source. Phylogenic analysis identified strain 58-1 as Sphingomonas agrestis. In 2,4-D degraders, classes I, II, and III inherit the tfdA, cadA, and tfdAalpha genes, respectively, and the results from degenerate-PCR indicated that this strain belongs to the class II degraders. A clone that includes the cadA gene homolog of S. agrestis 58-1 was screened from a library by using the PCR amplified fragment as a DNA probe. The cloned fragment was sequenced and found to consist of 5043 nucleotides and include 3 open reading frames (orfs). The orf1, orf2, and orf3 genes encode polypeptides consisting of 412, 448, and 177 amino acids, respectively. The Orf2 product shares a high degree of sequence similarity (92%) with the large subunit of 2,4-D oxygenase from the Bradyrhizobium sp. strain HW13, which belongs to the class III 2,4-D degraders, while the orf3 product shared 63% sequence similarity with the small subunit of 2,4-D oxygenase from the strain HW13. The results of the functional expression analysis using various deletion mutants in Escherichia coli revealed that the expression of both orf2 and orf3 genes, but not orf1, is essential for the conversion of 2,4-D to 2,4-DCP. From these results, we conclude the first isolation of 2,4-D oxygenase genes from a class II 2,4-D degrader.