Hang Min

EFFECTS OF BUTACHLOR ON MICROBIAL POPULATIONS AND ENZYME ACTIVITIES IN PADDY SOIL

This paper reports the influences of the herbicide butachlor (n-butoxymethl-chloro -2′,6′ -diethylacetnilide) on microbial populations, respiration, nitrogen fixation andnitrification, and on the activities of dehydrogenase and hydrogen peroxidase in paddy soil. The results showed that the number of actinomycetes declined significantly after the application of butachlor at different concentrations ranging from 5.5μg g−1 to 22.0μg g−1 dried soil, while that of bacteria and fungi increased. Fungi were easily affected by butachlor compared to the bacteria. The growth of fungi was retarded by butachlor at higher concentrations. Butachlor however, stimulated the growth of anaerobic hydrolytic fermentative bacteria, sulfate-reducing bacteria (SRB) and denitrifying bacteria. The increased concentration of butachlor applied resulted in the higher number of SRB. Butachlor inhibited the growth of hydrogen-producing acetogenic bacteria. The effect of butachlor varied on methane-producing bacteria (MPB) at different concentrations. Butachlor at the concentration of 11.0μg g−1 dried soil or less than this concentration accelerated the growth of MPB, while at 22.0μg g−1 dried soil showed an inhibition. Butachlor enhanced the activity of dehydrogenase at increasing concentrations. The soil dehydrogenase showed the highest activity on the 16th day after application of 22.0μg g−1 dried soil of butachlor. The hydrogen peroxidase could be stimulated by butachlor. The soil respiration was depressed during the period from several days to more than 20 days, depending on concentrations of butachlor applied. Both the nitrogen fixation and nitrification were stimulated in the beginning but reduced greatly afterwards in paddy soil.

Bioaugmentation with the nicotine-degrading bacterium Pseudomonas sp. HF-1 in a sequencing batch reactor treating tobacco wastewater: degradation study and analysis of its mechanisms.

The highly effective nicotine-degrading bacterium Pseudomonas sp. HF-1 was augmented in an SBR system that is used to treat tobacco wastewater. Compared to the non-bioaugmented (non-BA) system, the bioaugmented (BA) system exhibited considerably stronger pollution disposal abilities, with 100% nicotine degradation and more than 84% chemical oxygen demand (COD) removal within 12h. Nicotine degradation had a significant effect on COD removal in SBRs (r=0.928, p<0.01). The mechanisms of bioaugmentation were systematically investigated using a combination of polymerase chain reaction and denaturing gradient gel electrophoresis (PCR-DGGE) and a toxicity assay (protein carbonyl (PC) and DNA-protein crosslinking (DPC)). DGGE fingerprint profiles showed that the number of bands and the Shannon-Wiener index decreased at a nicotine load of 250mg/L compared to a 40-130mg/L nicotine load in the non-BA system. However, a stepwise increase in the Shannon-Wiener index was found during all periods in the BA system. A comparison of sequences excised from DGGE gels demonstrated significant differences in the dominant microbial species between the two SBRs. This result suggested that bioaugmentation of strain HF-1 could select cooperators for treating complicated tobacco wastewater. The PC content and the DPC coefficient increased significantly at levels higher than 80mg/L in the non-BA system; nevertheless, no increase was observed in the BA system during the stepwise nicotine load. This indicated that bioaugmentation of strain HF-1 resulted in the maintenance of high treatment activity by minimizing the nicotine toxicity for other microbes in the BA system. In conclusion, the rapid nicotine degradation of strain HF-1 performed a vital function in SBR by influencing the microbial community structure, dynamics and activity of the activated sludge system.

Isolation, identification and characterization of a novel Rhodococcus sp. strain in biodegradation of tetrahydrofuran and its medium optimization using sequential statistics-based experimental designs.

Statistics-based experimental designs were applied to optimize the culture conditions for tetrahydrofuran (THF) degradation by a newly isolated Rhodococcus sp. YYL that tolerates high THF concentrations. Single factor experiments were undertaken for determining the optimum range of each of four factors (initial pH and concentrations of K(2)HPO(4).3H(2)O, NH(4)Cl and yeast extract) and these factors were subsequently optimized using the response surface methodology. The Plackett-Burman design was used to identify three trace elements (Mg(2+), Zn(2+)and Fe(2+)) that significantly increased the THF degradation rate. The optimum conditions were found to be: 1.80 g/L NH(4)Cl, 0.81 g/L K(2)HPO(4).3H(2)O, 0.06 g/L yeast extract, 0.40 g/L MgSO(4).7H(2)O, 0.006 g/L ZnSO(4).7H(2)O, 0.024 g/L FeSO(4).7H(2)O, and an initial pH of 8.26. Under these optimized conditions, the maximum THF degradation rate increased to 137.60 mg THF h(-1) g dry weight in Rhodococcus sp. YYL, which was nearly five times of that by the previously described THF degrading Rhodococcus strain.

Studies on biosorption equilibrium and kinetics of Cd2+ by Streptomyces sp. K33 and HL-12.

The sorption of Cd(2+) by Streptomyces sp. K33 and HL-12 was investigated. The removal efficiency increased with pH, but no obvious differences with different temperatures. Fourier transform infrared (FT-IR) was used to characterize the interaction between Cd(2+) and K33 and HL-12. Results revealed that the presence of amino, carboxyl, hydroxyl and carbonyl groups were responsible for the biosorption of Cd(2+). Strain HL-12 had more changes in the functional groups than K33. Biosorption equilibrium was established earlier by strain K33 than that by HL-12, and K33 had higher adsorption ratio. Langmuir, Freundlich and Dubinin-Radushkevich (D-R) isotherms were used to describe the adsorption experiment, Langmuir model fitted the experiment data best. Strain K33 showed greater sorption capacities with 38.49 mg Cd(2+)/g dry cells. Pseudo-first-order and second-order kinetic models were used to describe the kinetic data, and second-order kinetic model fitted better. About 70% recovery of Cd(2+) could be obtained at pH <or= 3 from metal-loaded biomass of strains HL-12 and K33.

Isolation and characterization of phenanthrene-degrading Sphingomonas paucimobilis strain ZX4

Phenanthrene-degrading bacterium strain ZX4 was isolated from an oil-contaminated soil, and identified as Sphingomonaspaucimobilis based on 16S rDNA sequence, cellular fatty acid composition, mol% G + C and Biolog-GN tests. Besides phenanthrene, strain ZX4 could also utilize naphthalene, fluorene and other aromatic compounds. The growth on salicylic acid and catechol showed that the strain degraded phenanthrene via salicylate pathway, while the assay of catechol 2, 3-dioxygenase revealed catechol could be metabolized through meta-cleavage pathway. Three genes, including two of meta-cleavage operon genes and one of GST encoding gene were obtained. The order of genes arrangement was similar to S-type meta-pathway operons. The phylogenetic trees based on 16S rDNA sequence and meta-pathway gene both revealed that strain ZX4 is clustered with strains from genus Sphingomonas.

Biodegradation of di-n-butyl phthalate by a stable bacterial consortium, HD-1, enriched from activated sludge.

HD-1, a stable microbial consortium capable of mineralizing di-n-butyl phthalate (DBP), was developed from activated sludge. The dominant microorganisms in the consortium, Gordonia sp., Burkholderia sp. and Achromobacter sp., were identified by denaturing gradient gel electrophoresis (DGGE). The consortium could mineralize approximately 90% of 1200 mg/L DBP after 48 h of cultivation. The optimal DBP degradation conditions were 25-30 °C and pH 8.0-9.0. The addition of yeast (0.5 g/L), sodium acetate (0.5 g/L, 1.0 g/L), Brij 35 (0.2%, 0.5%, 1.0%), or Triton X-100 (0.2%) enhanced DBP degradation. The DBP degradation rate was influenced by the presence of dimethyl phthalate (DMP) and diethyl phthalate (DEP). Only one main intermediate, phthalic acid, could be monitored by gas chromatography-mass spectrometry (GC-MS) during the degradation process. The HD-1 consortium also utilized phenol, o-dihydroxybenzene as the sole carbon and energy source. The results indicate the consortium may represent a promising application for DBP bioremediation.

Catalase and superoxide dismutase activities in a Stenotrophomonas maltophilia WZ2 resistant to herbicide pollution.

Quinclorac bensulfuron-methyl is a mixed herbicide widely used on paddy rice field to effectively control barnyard grass and most broad-leaved grasses and sedges. We analyzed superoxide dismutase (SOD) and catalase activities in the quinclorac-highly degrading strain Stenotrophomonas maltophilia WZ2 and Gram-negative standard strain Escherichia coli K12 in an attempt to understand antioxidant enzymes in bacteria are produced in response to quinclorac or bensulfuron-methyl, which increases the virulence of the bacteria. MnSOD and two additional catalase isozymes were induced by quinclorac or bensulfuron-methyl in S. maltophilia WZ2, but not in E. coli K12. Quinclorac turned out to be a more sensitive inducer of SOD, whereas bensulfuron-methyl is a more sensitive one of catalase. A mixture of both has effects similar to quinclorac. Results indicate that catalase has a much weakly role in the defense against quinclorac or bensulfuron-methyl induced oxidative stress, whereas SOD could be critical.

Assessment of toxicity of tetrahydrofuran on the microbial community in activated sludge.

Activated sludge is widely used to treat industrial wastewater, but its efficiency is affected by a variety of factors, including toxic substances such as tetrahydrofuran (THF). In this study, we examined the toxicity of THF at different concentrations (0-320 mM) on the microbial community in activated sludge. A remarkable dose-dependent decrease in the total organic compound removal rate and culturable bacteria and fungi was observed. At THF concentrations higher than 160 mM, a decrease in pH to 3.0 was observed. The activities of five enzymes (catalase, dehydrogenase, urease, phosphatase and protease) analyzed were all significantly inhibited (p<0.01) at THF concentrations higher than 160 mM, especially dehydrogenase activity, which lost 95.4% of its activity at 320 mM THF. Microbial community analysis by PCR-DGGE revealed a substantial shift in the community structure and a reduction in diversity at a low THF concentration (20mM). These results suggest that THF is much more toxic than reported in the literature, indicating its acute toxicity to microorganisms.

The combination of glycerol metabolic engineering and drug resistance marker-aided genome shuffling to improve very-high-gravity fermentation performances of industrial Saccharomyces cerevisiae.

A challenge associated with the ethanol productivity under very-high-gravity (VHG) conditions, optimizing multi-traits (i.e. byproduct formation and stress tolerance) of industrial yeast strains, is overcome by a combination of metabolic engineering and genome shuffling. First, industrial strain Y12 was deleted with a glycerol exporter Fps1p and hetero-expressed with glyceraldehydes-3-phosphate dehydrogenase, resulting in the modified strain YFG12 with lower glycerol yield. Second, YFG12 was subjected to three rounds of drug resistance marker-aided genome shuffling to increase its ethanol tolerance, and the best shuffled strain TS5 was obtained. Compared with wild strain Y12, shuffled strain TS5 not only decreased glycerol formation by 14.8%, but also increased fermentation rate and ethanol yield by 3.7% and 7.6%, respectively. Moreover, the system of genetic modification and Cre/loxP in aid of three different drug-resistance markers presented in the study significantly improved breeding efficiency and will facilitate the application of breeding technologies in prototrophic industrial microorganisms.

Effects of butachlor on microbial enzyme activities in paddy soil

The 16 priority PAHs (Polycyclic Aromatic Hydrocarbons) designated by US Environmental Protection Agency were analyzed for some digested sludges from wastewater treatment plants in Korea. PAHs are an important group of organic contaminants present in sewage sludge due to their persistence and toxic potential. PAHs were extracted from freeze-dried sludges using a methylene chloride-methanol (2:1) mixture in a soxhlet extractor. The extracts were cleaned-up by silica gel/alumina combination column and subsequently fed into gas chromatograph/mass spectrometer (GC/MS) for determining PAH contents. The sum of the 16 PAHs in the sewage sludge varied from 534.8 to , dry wt.. In the sewage sludge, phenanthrene appears as the most abundant PAHs, followed by naphthalene, pyrene, fluoranthene. Source of the investigated sewage sludges relatively predominated pyrogenic. PAHs levels of sewage sludges in Korea appeared to be lower than those in other countries.