Xiaosong Cheng

Immobilization of Rhodococcus rhodochrous BX2 (an acetonitrile-degrading bacterium) with biofilm-forming bacteria for wastewater treatment

In this study, a unique biofilm consisting of three bacterial strains with high biofilm-forming capability (Bacillus subtilis E2, E3, and N4) and an acetonitrile-degrading bacterium (Rhodococcus rhodochrous BX2) was established for acetonitrile-containing wastewater treatment. The results indicated that this biofilm exhibited strong resistance to acetonitrile loading shock and displayed a typical spatial and structural heterogeneity and completely depleted the initial concentration of acetonitrile (800mgL(-1)) within 24h in a moving-bed-biofilm reactor (MBBR) after operation for 30days. The immobilization of BX2 cells in the biofilm was confirmed by PCR-DGGE. It has been demonstrated that biofilm-forming bacteria can promote the immobilization of contaminant-degrading bacteria in the biofilms and can subsequently improve the degradation of contaminants in wastewater. This approach offers a novel strategy for enhancing biological oxidation of toxic pollutants in wastewater.

Survival of GFP-tagged Rhodococcus sp. D310-1 in chlorimuron-ethyl-contaminated soil and its effects on the indigenous microbial community.

The recently isolated bacterial strain Rhodococcus sp. D310-1 can degrade high concentrations of chlorimuron-ethyl (up to 1000 mg L(-1)), indicating its potential for the bioremediation of soil contaminated with high levels of chlorimuron-ethyl. In this study, Rhodococcus sp. D310-1 was tagged with green fluorescent protein gene (gfp) to track its survival in soil. Subsequently, degradation activity of the gfp-tagged strain and its effects on indigenous microbial community were analyzed. Results showed the cell numbers of Rhodococcus sp. D310-1::gfp in non-sterilized soil maintained at 8.5 × 10(4) cells g(-1) dry soil 45 days after inoculation of 7.74 × 10(6) cells g(-1) dry soil and approximately 49% of chlorimuron-ethyl was removed. However, The cell numbers of Rhodococcus sp. D310-1::gfp in sterilized samples increased gradually to 7.85 × 10(7) cells g(-1) dry soil and approximately 78% of chlorimuron-ethyl was removed. PCR-DGGE demonstrated that inoculation of this gfp-tagged strain in chlorimuron-ethyl-contaminated soil has negligible impact on the community structure of bacteria, actinomycetes and fungi. These results indicate that Rhodococcus sp. D310-1 is effective for the remediation of chlorimuron-ethyl-contaminated soil and also provides valuable information about the behavior of the inoculant population during bioremediation, which could be directly used in the risk assessment of inoculant population and optimization of bioremediation process.

Toxicity of TiO₂ nanoparticle to denitrifying strain CFY1 and the impact on microbial community structures in activated sludge.

The antibacterial activity of titanium dioxide nanoparticles (TiO2 NPs) is well described, but little is known of their impact on specific microbial functions such as denitrification, nor on microbial community structure. In this study, a denitrifier (named as Pseudomonas stutzeri CFY1), which was isolated from the activated sludge and could remove up to 111.68 mg/L of NO3(-)-N under aerobic conditions, was utilized to evaluate the influences of TiO2 NPs on its nitrogen removal ability and associated gene expression under aerobic conditions. The variations of the bacterial diversity of activated sludge were also observed. The results showed that antibacterial activity increased with increasing concentrations of TiO2 NPs. Increased production of reactive oxygen species was responsible for TiO2 NPs toxicity. An up-regulation of denitrification genes was observed with increasing concentrations of TiO2 NPs under aerobic conditions. Accordingly, denitrification by P. stutzeri was accelerated when the concentration of TiO2 NPs was increased to 50 mg/L. However, the denitrification of CFY1 was inhibited at low concentrations of TiO2 NPs (5-25 mg/L), indicating that assimilatory and dissimilatory denitrification were synchronized in P. stutzeri CFY1; the latter process plays a major role in denitrification. Further study of the community using 454 pyrosequencing showed that after 7 days of exposure to 50 mg/L TiO2 NPs, the microbial composition of the activated sludge was significantly different and had a lower diversity compared to the controls.

Insights into the degradation of chlorimuron-ethyl by Stenotrophomonas maltophilia D310-3

In this study, the effects of cultivation conditions on the degradation of chlorimuron-ethyl by Stenotrophomonas maltophilia D310-3, which exhibits a high chlorimuron-ethyl-degrading capability, were investigated. To improve the biodegradation efficiency, the cultivation conditions were optimized using response surface methodology (RSM) based on Box-Behnken design (BBD). The maximum biodegradation rate (89.9%) was obtained at the optimal conditions (culture time, 6 d; substrate concentration, 50.21 mg L(-1); pH, 5.95; temperature, 30.15 °C). The Andrews model was used to describe the dynamic change regularity of the specific degradation rate as the substrate concentration increased, and the values of the maximum specific degradation rate (q(max)), half-saturation constant (K(S)) and inhibition constant (K(i)) were 78.87 d(-1), 9180.97 mg L(-1) and 0.28 mg L(-1), respectively. Eight degradation products were captured and identified by liquid chromatography-mass spectrometry (LC-MS) and Fourier transform infrared (FTIR) spectrometry, and three possible degradation pathways are proposed based on the results of high-performance liquid chromatography (HPLC), LC-MS and FTIR analyses as well as results reported in relevant literature. To the best of our knowledge, this is the first systematic study of the degradation pathway of chlorimuron-ethyl by S. maltophilia D310-3. This study provides valuable information for further exploration of the microbial degradation of other sulfonylurea herbicides.

Immobilization of iron- and manganese-oxidizing bacteria with a biofilm-forming bacterium for the effective removal of iron and manganese from groundwater.

In this study, three bacteria with high Fe- and Mn-oxidizing capabilities were isolated from groundwater well sludge and identified as Acinetobacter sp., Bacillus megaterium and Sphingobacterium sp. The maximum removal ratios of Fe and Mn (99.75% and 96.69%) were obtained by an optimal combination of the bacteria at a temperature of 20.15°C, pH 7.09 and an inoculum size of 2.08%. Four lab-scale biofilters were tested in parallel for the removal of iron and manganese ions from groundwater. The results indicated that the Fe/Mn removal ratios of biofilter R4, which was inoculated with iron- and manganese-oxidizing bacteria and a biofilm-forming bacterium, were approximately 95% for each metal during continuous operation and were better than the other biofilters. This study demonstrated that the biofilm-forming bacterium could promote the immobilization of the iron- and manganese-oxidizing bacteria on the biofilters and enhance the removal efficiency of iron and manganese ions from groundwater.

Protoplast Formation and Regeneration of Rhodococcus sp. BX2

In order to construct a multi-functional genetic strain which could both degrade bensulfuron-meghyl and butachlor efficiently by protoplast fusion of Rhodococcus sp. BX2 and Acinetobacter sp. LYC-1, conditions for protoplast formation and cell wall regeneration of Rhodococcus sp. BX2 were investigated. Protoplasts from Rhodococcus sp. BX2 were obtained by treatment with the combination of 0.5% glycine preprocessing culture solution at 35°Cfor 6 h and 6 mg·mL− 1 lysozyme incubating bacterial suspension at 35°Cfor 3 h. Consequently protoplast formation rate was up to 91%. The best medium for protoplast regeneration was RNB containing 1.5% polyvinylpyrrolidone; the regeneration rate of protoplasts was 14.83 %.