Dong-Qi Liu

A bacterial strain that could degrade bromoamine acid (BAA) as the sole carbon source was isolated. It was identified as Sphingomonas sp. based on 16S rRNA gene sequence analysis and physio-biochemical characteristics. Under the optimal growth conditions, with temperature of 30 degrees C, pH of 7.0, rotating rate of 100 r/min and (NH4)2SO4 as the nitrogen source, the decolorization percentage of BAA (100 mg/L) could reach 99% within 14 h. NaCl of low concentration ( < 2%) facilitated the decolorization, while NaCl of higher concentration (> or = 2%) had inhibition effect. The effect of initial BAA concentration on decolorization could be described by the Haldane model, and the optimal specific decolorization rate of 1.4 h(-1) could be obtained when the initial concentration of BAA was 1393.5 mg/L. The strain could not mineralize BAA completely, and 52.4% of the total organic carbon was removed at the end of the reaction. The analysis of metabolites using GC-MS and HPLC-MS showed that phthalic acid was the metabolic intermediate which could be further degraded through 3, 4-dihydroxybenzoic acid route and serve as the growth substrate, and the end product was estimated to be either 2-amino-3-hydroxy-5-bromobenzenesulfonic acid or 2-amino-4-hydroxy-5-bromobenzenesulfonic acid.

A quinoline-degrading bacterium QL2, which utilizes quinoline as sole source of carbon, nitrogen and energy, was isolated from activated sludge in a coke-plant wastewater biological treatment system. According to the morphological characteristics, physiological and biochemical characteristics, and sequence analysis of 16S rRNA, the strain was identified as Rhodococcus sp.. The optimal temperature, initial pH, and shaker rotary speed for strain QL2 utilizing quinoline are 35-42 degrees C, pH 8-9, and 150 r/min, respectively. Extra nitrogen sources stimulate the isolate growth on quinoline, and inorganic nitrogen better than organic nitrogen, NH4+ -N better than NO3(-) -N. The degradation reaction of quinoline by strain QL2 can be described with zero order kinetic equation within the initial quinoline concentrations of 60-680 mg/L. When the initial concentration was 150 mg/L, quinoline was degraded completely in 8 hours and TOC removal efficiency was 70% in 14 hours. This bacterium produced pigmented compounds, and ring nitrogen was released into the growth medium as ammonium. The main intermediate in the degradation pathway was 2-hydroxyquinoline by the analysis of HPLC and GC/MS. With a broad range of substrate utilization, the strain can degrade phenol, naphthalene, pyridine, and some other kinds of aromatic compounds.

A 1,125-bp long ORF encoding a novel gentisate 1,2-dioxygenase with two-domain bicupins was cloned from Silicibacter pomeroyi DSS-3 and expressed in Escherichia coli. The resulting product was purified to homogeneity and partially characterized. Non-reductive SDS-PAGE and gel filtration showed that the active recombinant gentisate 1,2-dioxygenase had an estimated molecular mass of 132 kDa, and reductive SDS-PAGE indicated an approximate size of 45 kDa. The enzyme thus appears to be a homotrimeric protein. This is in contrast to the homotetrameric or dimeric protein of the gentisate 1,2-dioxygenases that have been characterized thus far. The K _m and K _cat/K _m for gentisate were 12 μM and 653 × 10⁴ M⁻¹ s⁻¹; the pI was 4.6–4.8. It was optimally active at 40°C and pH 8.0.