Enhancement of phenol biodegradation by Pseudochrobactrum sp. through ultraviolet-induced mutation.

The phenol-degrading efficiency of Pseudochrobactrum sp. was enhanced by ultraviolet (UV) irradiation. First, a bacterial strain, Pseudochrobactrum sp. XF1, was isolated from the activated sludge in a coking plant. It was subjected to mutation by UV radiation for 120 s and a mutant strain with higher phenol-degrading efficiency, Pseudochrobactrum sp. XF1-UV, was selected. The mutant strain XF1-UV was capable of degrading 1800 mg/L phenol completely within 48 h and had higher tolerance to hydrogen ion concentration and temperature variation than the wild type. Haldane's kinetic model was used to fit the exponential growth data and the following kinetic parameters were obtained: µmax = 0.092 h-1, Ks = 22.517 mg/L, and Ki = 1126.725 mg/L for XF1, whereas µmax = 0.110 h-1, Ks = 23.934 mg/L, and Ki = 1579.134 mg/L for XF1-UV. Both XF1 and XF1-UV degraded phenol through the ortho-pathway; but the phenol hydroxylase activity of XF1-UV1 was higher than that of XF1, therefore, the mutant strain biodegraded phenol faster. Taken together, our results suggest that Pseudochrobactrum sp. XF1-UV could be a promising candidate for bioremediation of phenol-containing wastewaters.

[Study on the fluorescence characteristics of BOD sensing films immobilizing different limnetic microorganism].

Taking tetramethoxysilane (TMOS) and dimethyldimethoxysilane (DiMe-DMOS) as precursors for the synthesis of an organically-modified silicates (ORMOSILs), optical BOD sensing films immobilizing five kinds of limnetic microorganisms were composed by poly(vinyl alcohol) ormosils matrix. Their fluorescence characteristics were studied with a home-made optical BOD apparatus. According to the experimental results, linearity between BOD and the corresponding fluorescence intensity ranging from 0-60 mg x L(-1) to 0-120 mg x L(-1) could be obtained on the sensing films immobilizing limnetic microorganisms and their mixture. In addition, the linearity coefficient was from 0.976 to 0.997, and the respond time was 0.5 to 8.7 min. In the experiment, effects of the measurement condition such as temperature and pH on the fluorescent responses of BOD sensing films were investigated. These sensing films presented excellent reproducibility and stability since they could be continuously employed for 30 days, and kept 85% of their original activity when stored for 12 months at 4 degrees C. The approved approach could be applied in the BOD determination of real limnetic samples according to the obtained results.

[Fluorescence characterization of oxygen sensing film for BOD determination].

The film doped with tris-(4,7-diphenyl-1,10-phenanthroline) ruthenium (II) ([Ru(dpp)3]2+) as an oxygen quenching indicator exhibited a good linear relationship, fast response time, long-term stability, and enhanced sensitivity to dissolved oxygen after optimizing the sol-gel processing parameters. Fiber-optical microbial sensors for the determination of biochemical oxygen demand (BOD) were described. The sensing films consist of two layers of an oxygen-sensitive fluorescent material, and three different kinds of seawater microorganisms immobilized in poly(vinyl alcohol) sol-gel matrix. The fluorescent properties and the response behaviors of the film were investigated. The effects of temperature, pH and sodium chloride concentration on the sensing films were studied as well. For low biochemical oxygen demand, the film of sieved bacteria from seawater was superior in respect of sensitivity and is expected for further development.