Miao Hu

Metabolic ability and individual characteristics of an atrazine-degrading consortium DNC5.

A stable four-member bacterial consortium, DNC5 that was capable of metabolizing atrazine was isolated from corn-planted soil. The main objective of this paper is to characterize the individual metabolic characteristics and the mutualism of the cultivable members in the consortium DNC5. Substrates utilizing character of each community member indicate that the primary organism in this consortium is Arthrobacter sp. DNS10, which was the only strain capable of mineralizing atrazine to cyanuric acid. Two secondary strains (Bacillus subtilis DNS4 and Variovorax sp. DNS12) utilized cyanuric acid during the atrazine degradation process. Meanwhile, we found that a metabolite (isopropylamine) inhibited the atrazine degrading species Arthrobacter sp. DNS10. The last strain (Arthrobacter sp. DNS9) of this consortium played a role in reducing this inhibition by utilizing isopropylamine for its growth. Altogether this is a new combination of isolates in an atrazine degrading consortium. The growth and the degradation rate of consortium DNC5 were faster than that of the single strain DNS10. The high degradation ability of the consortium showed good potential for atrazine biodegradation. This study will contribute toward a better understanding about metabolic activities of atrazine degrading consortium, which are generally considered to be responsible for atrazine mineralization in the natural environment.

Influence of humic acid on the trichloroethene degradation by Dehalococcoides-containing consortium.

By taking an anaerobic Dehalococcoides-containing consortium (designated UC-1) as the research object, the influence of humic acid on the degradation of TCE by UC-1 was examined. The results indicated that (i) TCE was more rapidly degraded in the presence of humic acid compared with the control and the TCE removal efficiencies increased with the increase of concentrations of humic acid; and (ii) at the end of experiments, in the presence of humic acid, much more ethene was produced compared with the control, whereas less VC was accumulated in the medium. Presumably, humic acid improves the activity of organisms in dechlorinating populations resulting in more ethene accumulated in the medium, and (iii) the degradation of TCE stimulated by humic acid by UC-1 might be a biotic process or an abiotic process. Thus, humic acid could influence the degradation of TCE by UC-1 directly via enhancing electron transfer between UC-1 and TCE. This work is a preliminary step for accelerating the degradation of TCE in the groundwater environment using a kind of natural organic matter - humic acid.

Acclimation of the trichloroethylene-degrading anaerobic granular sludge and the degradation characteristics in an upflow anaerobic sludge blanket reactor

The granulation process was examined in an 8 L laboratory upflow anaerobic sludge blanket (UASB) reactor using synthetic wastewater contained trichloroethylene (TCE). Glucose and lactate were used as primary substrates. The anaerobic bacteria biomass were acclimated and granulated by increasing the chemical oxygen demand (COD) and TCE loadings. Anaerobic sludge was acclimated successfully in 120 days in the anaerobic sludge acclimation appliance. Since start-up, the UASB was operated as a continuous-flow reactor under the following operation conditions: temperature of (35 ± 1)°C, pH ≈ 7.2, hydraulic retention time of 10 h, COD of 2.5 g L(-1) and TCE loading rate from 50.5 to 252.3 mg · (L d)(-1). The UASB reactor was started successfully. The sludge volume index was 13 mL g(-1). The maximum specific methanogenic activity was 1.42 gCOD · (gVSS(.)d)(-1). After 90 days, 85% of COD and 85% of TCE removal efficiencies were achieved. The TCE degrading granular sludge had an average diameter of 2.7 mm and total suspended solid of 52 g L(-1). Anaerobic sludge adsorption of TCE reached adsorption equilibrium in 0.5 h, and in 1 h reached desorption equilibrium. Furthermore, cis-dichloroethylene and vinyl chloride were detected, which showed that the removal of TCE was caused by both adsorption and biodegradation but mainly by biodegradation.

Efforts on membrane properties and enzymes by adding divalent cations and sodium carboxymethyl cellulose

In this paper, the addition of sodium carboxymethyl cellulose (NACMC) and cobalt ions to alginate gel significantly improved the inner and outer surface properties of membranes and the activity of the enzymes. The results showed the optimization was sodium alginate (SA) and NACMC at ratio 1:1, and the concentration of CoCl2 at 0.05 mol/L. The combined SA-NACMC gel bead apparently had a more porous and higher mechanical strength than that of the SA gel bead by scanning electron microscopy (SEM). The microcapsule surface roughness was measured by atomic force microscopy (AFM), the roughness was 155 ± 15.82 mm. Otherwise, the Brunauer-Emmett-Teller (BET) analysis showed that with the addition of NACMC the surface area and most of pore size of the microcapsules was 76.471 m(2)/g, and distributed in 3-25 nm, respectively. In 28 d, immobilized enzyme had a higher degradation rate, and the atrazine residue of the immobilized enzyme with 5% content was 21.79%.

Chemotaxis to atrazine and detection of a xenobiotic catabolic plasmid in Arthrobacter sp. DNS10

IntroductionA plasmid named pDNS10 was detected from an atrazine-degrading strain Arthrobacter sp. DNS10 which has been isolated previously in our laboratory.Materials and methodsIn this paper, a special plasmid-detecting method and drop assays experiments were mainly used to achieve research goals.Results and discussionpDNS10 exhibited an excellent stability because it also could be detected even when the strain DNS10 has been subcultured under nonselective conditions for eight times. Over a 48-h incubation period, the OD600 of samples inoculated with strain DNS10 and strain DNS10-ST (both of them contained pDNS10) were 0.31 ± 0.042 and 0.305 ± 0.034, respectively ,whereas the OD600 of samples inoculated strain without pDNS10 (strain DNS10-PE) was only 0.138 ± 0.018. No atrazine was detected in the inoculated strain DNS10 and strain DNS10-ST samples at this period. Contrarily, the atrazine-degrading rate of strain DNS10-PE was only 5.23 ± 0.71%. Furthermore, both the two types of strains containing pDNS10 confirmed the presence of known degrading genes such as trzN, atzB, and atzC. It suggests that pDNS10 is an atrazine catabolic plasmid. In drop assays experiments, the wild-type strain DNS10 cells were chemotactically attracted to atrazine, whereas strain DNS10-PE showed no chemotaxis to atrazine and hydroxyatrazine. There was some relationship between atrazine degradation and the chemotactic response towards atrazine in strain DNS10.ConclusionsThe biochemical characteristics of pDNS10 and the chemotaxis characteristics of strain DNS10 could help us in better understanding of the mechanism of atrazine degradation by strain DNS10.

Effect of anthraquinone-2,6-disulfonate on the trichloroethene degradation by Dehalococcoides-containing consortium

This paper reports the findings of an examination on the influence of anthraquinone-2,6-disulfonate (AQDS) on the degradation of trichloroethene (TCE) by Dehalococcoides-containing consortium (designated UC-1). Compared with the control, the results indicated that (i) in 100 μmol/L AQDS, TCE was rapidly degraded. More ethene was produced, while less vinyl chloride (VC) was accumulated. AQDS might improve the activity of organisms in dechlorinating populations which resulted in more ethene being accumulated in the medium; (ii) in 500 μmol/L AQDS, TCE was incompletely degraded. Presumably, 500 μmol/L AQDS might have an inhibition effect on methanogens in the UC-1. The inhibition effect might influence the interactions among methanogens, Dehalococcoides species and other organisms in the UC-1.

The effects of sugar beet rinse water irrigation on the soil enzyme activities

ABSTRACT Sugar beet rinse water (SBRW) irrigation is a widely used practice in the northeast of China that reduces the amount of fresh water needed for agricultural irrigation. In addition, soil enzyme activities are important indicators of soil functions such as nutrient cycling and soil fertility. The effects of SBRW irrigation on five types of soil enzymatic activities including invertase, urease, neutral phosphatase, catalase, and polyphenol oxidase were examined at five depths (0–20, 20–40, 40–60, 60–80, and 80–100 cm) of soil. The pre-irrigation and well water (WW) irrigation plots served as background values and control, respectively. The results showed that SBRW irrigation exerted no negative effects on soil enzymatic activities during 2009–2011 experimental period. Invertase, urease, and neutral phosphatase activities significantly increased in soil irrigated with SBRW compared to that of pre-irrigation and that irrigated with WW. Evidence indicates that SBRW irrigation might strengthen the transformation of nutrients such as carbon, nitrogen, and phosphorus and enhance soil nutrients which were required for plant growth. Moreover, catalase activity also significantly rose in soil irrigated with SBRW, suggesting that SBRW irrigation helped remove the adverse effects of hydrogen peroxide. Overall, these results suggest that irrigation with SBRW might be of agricultural interest because of its organic matter concentration and nutrients input, and may be used as a fertilizer source to improve soil quality of irrigated landscapes.