Zhencheng Su

Responses of Soil Bacteria to Long-Term and Short-Term Cadmium Stress as Revealed by Microbial Community Analysis

Soil pollution by cadmium has been a long standing ecological problem in Zhangshi Irrigation Area, Shenyang, China, as a result of the 30-year practice of irrigation with wastewater containing high levels of heavy metals. To evaluate the adverse impact of cadmium contamination on soil ecosystems, the responses of soil microbiota to both long-term and short-term cadmium stress were studied by molecular microbial community profiling with denaturating gradient gel electrophoresis (DGGE) analysis. Our results show that soil characteristics and nutrient conditions were likely more important than cadmium toxicity in shaping the soil bacterial community structure in the long term. In comparison, soil microbial genetic diversity was shown to be more closely correlated to cadmium levels under short-term cadmium stress, with the highest microbial genetic diversity occurring at mild cadmium stress conditions, which might be attributed to the enrichment of metal-resistant microbial populations through mechanisms of competitive selection and genetic adaptation. In contrast, severe cadmium stress likely presented a condition that fewer microbial populations could survive, thus leading to reduced microbial genetic diversity.

Bioremediation of chlorimuron-ethyl-contaminated soil by Hansschlegelia sp. strain CHL1 and the changes of indigenous microbial population and N-cycling function genes during the bioremediation process.

Long-term and excessive application of the herbicide chlorimuron-ethyl has led to soil degradation and crop rotation barriers. In the current study, we isolated bacterial strain Hansschlegelia sp. CHL1, which can utilize chlorimuron-ethyl as its sole carbon and energy source, and investigated its application in soil bioremediation. Indigenous microbial populations and N-cycling function in the soil were also investigated during the bioremediation process by monitoring the copy numbers of bacterial and fungal marker genes, as well as N-cycling functional genes (nifH, amoA, nirS, and nirK). Results showed that >95% of chlorimuron-ethyl could be degraded within 45 days in soils inoculated with CHL1. Inoculation at two time points resulted in a higher remediation efficiency and longer survival time than a single inoculation. At the end of the 60-day incubation, the copy numbers of most indicator genes were recovered to the level of the control, even in the single-inoculation soils. A double inoculation was necessary for recovery of nifH. However, the abundance of nirK and ammonia-oxidizing bacterial genes were significantly inhibited regardless of inoculum. The results suggested that CHL1 is effective for the remediation of chlorimuron-ethyl-contaminated soil, and could partially reduce the toxic effects of chlorimuron-ethyl on soil microorganisms.

The cadA gene in cadmium-resistant bacteria from cadmium-polluted soil in the Zhangshi Area of Northeast China

Cadmium-resistant bacteria were isolated from the farmland soil in Zhangshi Irrigation Area in Shenyang of Northeast China, an area has been polluted by heavy metals, especially cadmium, for more than 40 years. The cadA gene was detected in 4 Bacillus strains and for the first time in one Flavobacterium strain. The high sequence identity (93%–99%) of cadA gene, shared indels in different bacterial species and genera, and the phylogenetic incongruence between 16S rDNA gene tree and cadA gene tree suggested that lateral gene transfer (LGT) occurred among Bacillus and Flavobacterium spp. The LGT of cadA gene might play a vital role in promoting the spread of cadmium-resistant phenotypes throughout soil microbial communities.

Improved stability and enhanced efficiency to degrade chlorimuron-ethyl by the entrapment of esterase SulE in cross-linked poly (γ-glutamic acid)/gelatin hydrogel.

Free enzymes often undergo some problems such as easy deactivation, low stability, and less recycling in biodegradation processes, especially in soil condition. A novel esterase SulE, which is responsible for primary degradation of a wide range of sulfonylurea herbicides by methyl or ethyl ester de-esterification, was expressed by strain Hansschlegelia sp. CHL1 and entrapped for the first time in an environment-friendly, biocompatible and biodegradable cross-linked poly (γ-glutamic acid)/gelatin hydrogel (CPE). The activity and stability of CPE-SulE were compared with free SulE under varying pH and temperature condition by measuring chlorimuron-ethyl residue. Meanwhile, the three-dimensional network of CPE-SulE was verified by scanning electron microscopy (SEM). The results showed that CPE-SulE obviously improved thermostability, pH stability and reusability compared with free SulE. Furthermore, CPE-SulE enhanced degrading efficiency of chlorimuron-ethyl in both soil and water system, especially in acid environment. The characteristics of CPE-SulE suggested the great potential to remediate chlorimuron-ethyl contaminated soils in situ.

TNF-α produced by SEC2 mutant (SAM-3)-activated human T cells induces apoptosis of HepG2 cells.

Staphylococcal enterotoxins C2 (SEC2) is a classical model of superantigens (SAg), which has the powerful ability to activate T cells as well as induce massive cytokine production. This property makes SEC2 and its mutants well concerned as a potential new immune-regulatory agent for cancer therapy. We previously constructed a SEC2 mutant named SAM-3, which had prominently antitumor activity in BALB/c mice model. But, the underlying molecular mechanism for stimulation of human peripheral blood mononuclear cells (PBMCs) and antitumor effect on human tumor cells induced by SAM-3 is not clear. Here, we showed that SAM-3 could activate human TCR Vβ 12, 13A, 14, 15, 17, and 20 CD8+ subgroup T cells, which secreted the cytokines IL-2, IFN-γ, and TNF-α, and exhibit stimulation activity in a dose-dependent manner. TNF-α secreted from activated T cells could induce apoptosis and G1-phase arrest and lead to the antitumor effect in HepG2 cells. Meanwhile, SAM-3 upregulated the expression of tumor necrosis factor receptor 1 (TNFR1) mRNA and activity of caspase-3 and caspase-8. We also found that the antitumor activity and activity of caspase-3 and caspase-8 were decreased when the neutralizing TNF-α monoclonal antibody presented. These data suggest that TNF-α secreted by SAM-3-activated T cells is an important factor in inducing apoptosis in HepG2 cells.

The effect of polycyclic aromatic hydrocarbon contamination on distribution of the Sphingomonas community in the Shenfu irrigation area of Northeast China

Information about the diversity and community structure of indigenous Sphingomonas communities in natural environments is lacking. In this study, denaturing gradient gel electrophoresis (DGGE) was used to investigate Sphingomonas communities at nine selected sites from the up-, mid- and downstream regions of a wastewater channel, which once flowed with sewage containing high concentrations of polycyclic aromatic hydrocarbons (PAHs). From each region, three samples from channel sediment, rice soil and corn soil were collected. Sediment sites had significantly higher PAH contamination, followed by rice sites and corn sites. In addition, upstream sites had higher PAH accumulation, followed by mid- and downstream sites. For each sample type (sediment, rice and corn soils), the Shannon diversity indices of the Sphingomonas community increased slightly with increasing PAH contamination. Upstream sites had obviously higher diversity than mid- and downstream sites. Both cluster analysis and canonical correspondence analysis indicated that the Sphingomonas community was clearly different among sediment, rice and corn soils. Besides, the Sphingomonas community was affected by different PAH compounds in sediment, rice and corn sites. The Sphingomonas community might degrade mainly benzo[b]fluoranthene, fluorene and fluoranthene in sediment sites by co-metabolism, but degraded mainly pyrene and phenanthrene in corn and rice sites, which provides some suggestions for pollution remediation.

Microbial Community Dynamics during the Bioremediation Process of Chlorimuron-Ethyl-Contaminated Soil by Hansschlegelia sp. Strain CHL1

Long-term and excessive application of chlorimuron-ethyl has led to a series of environmental problems. Strain Hansschlegelia sp. CHL1, a highly efficient chlorimuron-ethyl degrading bacterium isolated in our previous study, was employed in the current soil bioremediation study. The residues of chlorimuron-ethyl in soils were detected, and the changes of soil microbial communities were investigated by phospholipid fatty acid (PLFA) analysis. The results showed that strain CHL1 exhibited significant chlorimuron-ethyl degradation ability at wide range of concentrations between 10μg kg-1 and 1000μg kg-1. High concentrations of chlorimuron-ethyl significantly decreased the total concentration of PLFAs and the Shannon-Wiener indices and increased the stress level of microbes in soils. The inoculation with strain CHL1, however, reduced the inhibition on soil microbes caused by chlorimuron-ethyl. The results demonstrated that strain CHL1 is effective in the remediation of chlorimuron-ethyl-contaminated soil, and has the potential to remediate chlorimuron-ethyl contaminated soils in situ.

Dynamic changes in microbial communities during the bioremediation of herbicide (chlorimuron-ethyl and atrazine) contaminated soils by combined degrading bacteria

Chlorimuron-ethyl and atrazine are two herbicides with long half-lives in soil; their long-term and excessive application has led to a series of environmental problems. In this study, the strains Chenggangzhangella methanolivorans CHL1 and Arthrobacter sp. ART1 were combined and used for the remediation of chlorimuron-ethyl, atrazine and combined contaminated soils in a microcosm experiment. Changes in chlorimuron-ethyl and atrazine concentrations in soils were monitored, and variations in the soil microbial community were studied by phospholipid fatty acid (PLFA) analysis. The two inoculated degrading strains accelerated the degradation of chlorimuron-ethyl and atrazine in soil, especially in the combined contaminated soil. Addition of the two herbicides and their combination generally decreased the concentrations of total PLFAs, total bacterial PLFAs, Gram-negative and Gram-positive bacterial PLFAs and Shannon-Wiener indices, and changed microbial community composition, whilst stimulating fungal PLFA concentrations. In addition, the combined herbicide treatment had more impact on microbial biomass than the single herbicide treatments. Inoculation treatments significantly relieved the effects of herbicides on soil microbial biomass, diversity and community structure. This study demonstrated that strains CHL1 and ATR1 have the potential to remediate chlorimuron-ethyl, atrazine and combined contaminated soils, and provided valuable information for remediation of chlorimuron-ethyl, atrazine and combined contaminated soils in situ.

Catabolic profiles dynamics during the bioremediation process of chlorimuron-ethyl contaminated soil by Methanolivorans CHL1 T

Excessive application of the long-term herbicide chlorimuron-ethyl has resulted in series of environmental problems. Bioaugmentation usually a useful method in contaminated-environment remediation. In this study, the strain Methanolivorans CHL1T with highly chlorimuron-ethyl degrading efficiency was employed to assess its remediation effects on chlorimuron-ethyl-contaminated soil. The chlorimuron-ethyl residues in the soils and the survival condition of strain CHL1T were detected. Meanwhile, the shifts of soil microbial catabolic profile were investigated by MicroResp™ analysis for the first time. The results indicated that strain CHL1T significantly shorten the half-life (6-17 days) of chlorimuron-ethyl and removed 95-100% of chlorimuron-ethyl by the end of the experiment. Meanwhile, the strain CHL1 could inhabit in soil steadily (4.2-4.7 × 107 per g dry soil) for a long time. The inoculation with strain CHL1 significantly shorten and relieved the disturbance effects of chlorimuron-ethyl on soil CLPPs. After inoculation with strain CHL1 60 days, the basal respiration rates and Shannon-Wiener indices of groups S10+ and S30+ had recovered to the control level. Even in the high chlorimuron-ethyl-treated groups (S100), the basal respiration rates and Shannon-Wiener indices were significantly higher in S100+ than that in S100-. These results show the outstanding remediation effects of strain CHL1 and provide new insights into the assessment of the remediation process of chlorimuron-ethyl contaminated soils.