Tianming Cai

The biodegradation pathway of triethylamine and its biodegradation by immobilized Arthrobacter protophormiae cells

A bacterial strain named R4 was isolated from a wastewater treatment pool containing triethylamine (TEA) as the sole source of carbon and nitrogen. Strain R4 was identified as Arthrobacter protophormiae based on 16S rRNA gene sequence analysis and morphological and physiological properties. The optimal pH, temperature and concentration of NaCl for TEA degradation by strain R4 were 7.0, 30°C and 0.5%, respectively. Strain R4 could completely degrade 100 mg l(-1) TEA to ammonia in 32 h, and could also effectively degrade diethylamine (DEA) and ethylamine (EA) to ammonia. The degradation of TEA was strongly inhibited by some metal ions (Cu(2+), Mn(2+), Zn(2+), Co(2+), Ni(2+) and Ag(+)) (1.0mM). Addition of either SO(4)(2-) or NH(4)(+) reduced the degradation efficiency of TEA by strain R4 to a certain extent. The inhibition became significant when the concentration of SO(4)(2-) and NH(4)(+) reached to 11 mM and 30 mM, respectively. Cell-free extracts prepared from cells grown in TEA exhibited TEA monooxygenase, DEA monooxygenase and EA monooxygenase activity. Here, we propose the metabolic pathway of TEA degradation in strain R4. The efficiency of TEA removal by immobilized cells of strain R4 was found to be equivalent to that of free cells. In addition, the immobilized cells could be reused without reduction in their ability to degrade TEA.

Remediation of radiocesium-contaminated liquid waste, soil, and ash: a mini review since the Fukushima Daiichi Nuclear Power Plant accident.

The radiation contamination after the Fukushima Daiichi Nuclear Power Plant accident attracts considerable concern all over the world. Many countries, areas, and oceans are greatly affected by the emergency situation other than Japan. An effective remediation strategy is in a highly urgent demand. Though plenty of works have been carried out, progressive achievements have not yet been well summarized. Here, we review the recent advances on the remediation of radiocesium-contaminated liquid waste, soil, and ash. The overview of the radiation contamination is firstly given. Afterwards, the current remediation strategies are critically reviewed in terms of the environmental medium. Special attentions are paid on the adsorption/ion exchange and electrically switched ion exchange methods. Finally, the present review outlines the possible works to do for the large-scale application of the novel remediation strategies.

Selective removal of cesium by ammonium molybdophosphate – polyacrylonitrile bead and membrane

The selective removal of radionuclides with extremely low concentrations from environmental medium remains a big challenge. Ammonium molybdophosphate possess considerable selectivity towards cesium ion (Cs+) due to the specific ion exchange between Cs+ and NH4+. Ammonium molybdophosphate - polyacrylonitrile (AMP-PAN) membrane was successfully prepared for the first time in this study. Efficient removal of Cs+ (95.7%, 94.1% and 91.3% of 1mgL-1) from solutions with high ionic strength (400mgL-1 of Na+, Ca2+ or K+) was achieved by AMP-PAN composite. Multilayer chemical adsorption process was testified through kinetic and isotherm studies. The estimated maximum adsorption capacities even reached 138.9±21.3mgg-1. Specifically, the liquid film diffusion was identified as the rate-limiting step throughout the removal process. Finally, AMP-PAN membrane could eliminate Cs+ from water effectively through the filtration adsorption process.

Natural ageing process accelerates the release of Ag from functional textile in various exposure scenarios

Natural ageing process occurs throughout the life cycle of textile products, which may possess influences on the release behavior of additives such as silver nanoparticles (Ag NPs). In this study, we assessed the releasability of Ag NPs from a Ag NPs functionalized textile in five different exposure scenarios (i.e. tap water (TW), pond water (PW), rain water (RW), artificial sweat (AS), and detergent solution (DS) along with deionized water (DW) as reference), which were very likely to occur throughout the life cycle of the textile. For the pristine textile, although the most remarkable release was found in DW (6–15 μg Ag/g textile), the highest release rate was found in RW (around 7 μg Ag/(g textile·h)). After ageing treatment, the total released Ag could be increased by 75.7~386.0% in DW, AS and DS. Morphological analysis clearly showed that the Ag NPs were isolated from the surface of the textile fibre due to the ageing treatment. This study provides useful information for risk assessment of nano-enhanced textile products.

Biodegradation of 3-methyldiphenylether (MDE) by Hydrogenophaga atypical strain QY7-2 and cloning of the methy-oxidation gene mdeABCD

3-Methyldiphenylether (MDE) is an important alkyl-substituted diphenyl ether compound that is widely used as an intermediate in the synthesis of pyrethroid insecticides. An efficient MDE-degrading strain QY7-2, identified as Hydrogenophaga atypical, was isolated from activated sludge for the first time. Strain QY7-2 can utilize MDE as the sole carbon and energy source and completely mineralize MDE. The degradation pathway of MDE was proposed in the strain through metabolites identification. A gene cluster involving in methy-oxidation of MDE was cloned from QY7-2 and expressed in Escherichia coli BL21 (DE3), and the products were purified by SDS-PAGE. The specific activities of the recombinant enzymes MdeAB, MdeC and MdeD were 113.8 ± 3.5, 274.5 ± 6.2 and 673.4 ± 8.7 nmol min−1 mg−1, respectively. These results provide the biochemical and genetic foundation of microbial degradation pathway of MDE and benefit the bioremediation of MDE-contaminated environments.

Biodegradation of 2-hydroxyl-1,4 naphthoquinone (lawsone) by Pseudomonas taiwanensis LH-3 isolated from activated sludge

Abstract2-hydroxy-1,4 naphthoquinone (lawsone) is widely used and induces environmental pollutions during its production and application. In the present study, a lawsone-degrading bacterium strain, LH-3 was successfully isolated from the activated sludge. Based on the 16S rRNA gene analysis, the strain LH-3 phylogenetically belonged to the Pseudomonas taiwanensis. It could degrade 200 mg L−1 lawsone completely in 9 h with an inoculum quantity of 1% (v/v). The effects of environmental conditions on the degradation process and the degradation pathway were systematically investigated. LH-3 could maintain its high degradation efficiency under high salt condition. The identified intermediates of salicylic acid, 2-hydroxy-4-oxo-chroman-2-carboxylic acid, and catechol elucidated the potential degradation pathway. Furthermore, the immobilized LH-3 strain cells prepared with alginate gel and biochar performed excellent stability in nine successive degradation runs. It could sucessfully survive in laboratory scale sequencing batch reactor and become to be the dominant species. This study clearly revealed that LH-3 could serve as an attractive candidate for the microbial remediation of lawsone-containing wastewater.

Degradation of Diphenyl Ether in Sphingobium phenoxybenzoativorans SC_3 Is Initiated by a Novel Ring Cleavage Dioxygenase

ABSTRACT Sphingobium phenoxybenzoativorans SC_3 degrades and utilizes diphenyl ether (DE) or 2-carboxy-DE as its sole carbon and energy source. In this study, we report the degradation of DE and 2-carboxy-DE initiated by a novel ring cleavage angular dioxygenase (diphenyl ether dioxygenase [Dpe]) in the strain. Dpe functions at the angular carbon and its adjacent carbon (C-1a, C-2) of a benzene ring in DE (or the 2-carboxybenzene ring in 2-carboxy-DE) and cleaves the C-1a—C-2 bond (decarboxylation occurs simultaneously for 2-carboxy-DE), yielding 2,4-hexadienal phenyl ester, which is subsequently hydrolyzed to muconic acid semialdehyde and phenol. Dpe is a type IV Rieske non-heme iron oxygenase (RHO) and consists of three components: a hetero-oligomer oxygenase, a [2Fe-2S]-type ferredoxin, and a glutathione reductase (GR)-type reductase. Genetic analyses revealed that dpeA1A2 plays an essential role in the degradation and utilization of DE and 2-carboxy-DE in S. phenoxybenzoativorans SC_3. Enzymatic study showed that transformation of 1 molecule of DE needs two molecules of oxygen and two molecules of NADH, supporting the assumption that the cleavage of DE catalyzed by Dpe is a continuous two-step dioxygenation process: DE is dioxygenated at C-1a and C-2 to form a hemiacetal-like intermediate, which is further deoxygenated, resulting in the cleavage of the C-1a—C-2 bond to form one molecule of 2,4-hexadienal phenyl ester and two molecules of H2O. This study extends our knowledge of the mode and mechanism of ring cleavage of aromatic compounds. IMPORTANCE Benzene ring cleavage, catalyzed by dioxygenase, is the key and speed-limiting step in the aerobic degradation of aromatic compounds. As previously reported, in the ring cleavage of DEs, the benzene ring needs to be first dihydroxylated at a lateral position and subsequently dehydrogenated and opened through extradiol cleavage. This process requires three enzymes (two dioxygenases and one dehydrogenase). In this study, we identified a novel angular dioxygenase (Dpe) in S. phenoxybenzoativorans SC_3. Under Dpe-mediated catalysis, the benzene ring of DE is dioxygenated at the angular position (C-1a, C-2), resulting in the cleavage of the C-1a—C-2 bond to generate a novel product, 2,4-hexadienal phenyl ester. This process needs only one angular dioxygenase, Dpe. Thus, the ring cleavage catalyzed by Dpe represents a novel mechanism of benzene ring cleavage.