Textile effluent is one of the main contributors of water pollution and it adversely affects fauna and flora. Constructed wetland is a promising approach to remediate the industrial effluent. The detoxification of industrial effluent in a constructed wetland system may be enhanced by applying beneficial bacteria that are able to degrade contaminants present in industrial effluent. The aim of this study was to evaluate the influence of inoculation of textile effluent-degrading endophytic bacteria on the detoxification of textile effluent in a vertical flow constructed wetland reactor. A wetland plant, Typha domingensis, was vegetated in reactor and inoculated with two endophytic bacterial strains, Microbacterium arborescens TYSI04 and Bacillus pumilus PIRI30. These strains possessed textile effluent-degrading and plant growth-promoting activities. Results indicated that bacterial inoculation improved plant growth, textile effluent degradation and mutagenicity reduction and were correlated with the population of textile effluent-degrading bacteria in the rhizosphere and endosphere of T. domingensis. Bacterial inoculation enhanced textile effluent-degrading bacterial population in rhizosphere, root and shoot of T. domingensis. Significant reductions in COD (79%), BOD (77%) TDS (59%) and TSS (27%) were observed by the combined use of plants and bacteria within 72 h. The resultant effluent meets the wastewater discharge standards of Pakistan and can be discharged into the environment without any risks. This study revealed that the combined use of plant and endophytic bacteria is one of the approaches to enhance textile effluent degradation in a constructed wetland system.
A hyperaccumulating ecotype (HE) and a non-hyperaccumulating ecotype (NHE) of Sedum alfredii were grown in a pot experiment to investigate the chemical characteristics of the rhizosphere. The results indicated that HE accumulated more Zn in the shoot than NHE after growing in both heavily and slightly polluted soil. The water soluble Zn and mobile Zn (extractable with 1M NH(4)NO(3)) fraction in both rhizosphere and bulk soils decreased considerably after growth of HE compared to NHE. However, the decreases in mobile fraction accounted for less than 8.5% of the total Zn uptake by HE indicating that HE was effective in mobilizing Zn from the non-mobile fractions. Zinc-induced root exudates reduced the soil pH (by 0.6-0.8 units) and increased dissolved organic carbon concentrations in the rhizosphere of HE compared to the bulk soil. The dissolved organic matter (DOM) from the rhizosphere of HE showed greater (1.7-2.5 times) extracting ability of Zn from various Zn minerals than those of NHE-DOM (P<0.05). Results from this study suggests that rhizosphere acidification and the exudation of high amounts of DOM with great metal extracting ability might be two important mechanisms by which HE S. alfredii is involved in activating metal in the rhizosphere.
Hydroponics experiments were conducted to underpin the nature of interactions between Zn, an essential micronutrient and Pb, a nonessential element on plant growth and root morphology, as well as antioxidant adaptation in mined ecotype (ME) and nonmined ecotype (NME) of Elsholtzia argyi. Plants were exposed to 50 ?M Pb having normal Zn (0.5 ?M), and two other treatments of the same Pb with low (0.05 ?M) and high (20 ?M) Zn, respectively for 12 days. Application of Pb with normal Zn caused adverse effects on the overall growth and antioxidant capacity of both ecotypes, however; effects were more pronounced in NME. The addition of high Zn along with Pb improved the growth and antioxidant capacity of both the ecotypes, while low Zn failed to show significant changes in NME plants; however slightly aggravated the Pb toxicity in the plants of ME. Zinc antagonized Pb concentrations in root and stem of both ecotypes and leaf of ME, while no significant differences were noted in Pb concentrations of NME leaf. It is suggested that in E. argyi, mechanisms of Pb and Zn uptake and translocation as well as their interactions within the plant cell may be different for both ecotypes and need to be further investigated.
A bacterial strain QZ2 was isolated from sludge of anoxic sulfide-oxidizing (ASO) reactor. Based on 16S rDNA sequence analysis and morphology, the isolate was identified as Ochrobactrum sp. QZ2. The strain was facultative chemolithotroph, able of using sulfide to reduce nitrite anaerobically. It produced either elemental sulfur or sulfate as the product of sulfide oxidation, depending on the initial sulfide and nitrite concentrations. The optimum growth pH and temperature for Ochrobactrum sp. QZ2 were found as 6.5-7.0 and 30 degrees C, respectively. The specific growth rate (micro) was found as 0.06 h(-1) with a doubling time of 19.75h; the growth seemed more sensitive to highly alkaline pH. Ochrobactrum sp. QZ2 catalyzed sulfide oxidation to sulfate was more sensitive to sulfide compared with nitrite as indicated by IC(50) values for sulfide and nitrite utilization implying that isolate was relatively more tolerant to nitrite. The comparison of physiology of Ochrobactrum sp. QZ2 with those of other known sulfide-oxidizing bacteria suggested that the present isolate resembled to Ochrobactrum anthropi in its denitrification ability.
Present study reports the results of three pot experiments, conducted to investigate the chelate-assisted phytoextraction of Pb contaminated soils. The optimum phytoextraction was observed when 2.5mM ethylene diamine disuccinic acid (EDDS) was added in single dosage for 14 days to low Pb soil (treated with 400 mg kg(-1)soil). On the contrary, for high Pb soil (treated with 1200 mg kg(-1)soil), 5mM EDDS concentration in single dosage for 10 days produced better results. Post-harvest effects of EDDS on the concentrations of available Pb and dissolved organic carbon (DOC) were significantly higher as compared with check (CK i.e. without EDDS addition), and consequently decreased with the passage of time. Our results suggested that chelate-assisted phytoextraction was more suitable for slightly contaminated soils.
Effects of zinc (Zn) and cadmium (Cd) interactions on root morphology and metal translocation in the hyperaccumulating ecotype (HE) and non-hyperaccumulating ecotype (NHE) of S. alfredii were investigated under hydroponic conditions. Specific root lengths (SRL), specific root surface areas (SRA) and specific root volumes (SRV) of the HE increased significantly when plant were treated with 500 microM Zn or 100 microM Cd+500 microM Zn, whereas these root parameters were significantly decreased for the NHE when plant were treated with 100 microM Cd, 500 microM Zn or 100 microM Cd+500 microM Zn. SRL and SRA of the HE were mainly constituted by roots with diameter between 0.2-0.4mm (diameter class 3 and 4) which were significantly increased in treatment of 500 microM Zn or 100 microM Cd+500 microM Zn, whereas in the NHE, metal treatments caused a significant decrease in SRL and SRA of the finest diameter class root (diameter between 0.1-0.3mm). The HE of S. alfredii could maintain a fine, widely branched root system under contaminated conditions compared with the NHE. Relative root growth, net Cd uptake and translocation rate in the HE were significantly increased by adding 500 microM Zn, as compared with the second growth period, where 100 microM Cd was supplied alone. Cadmium and Zn concentrations in the shoots of the HE were 12-16 times and 22-27 times higher than those of the NHE under 100 microM Cd+500 microM Zn combined treatment. These results indicate strong positive interactions of Zn and Cd occurred in the HE under 100 microM Cd+500 microM Zn treatment and Cd uptake and translocation was enhanced by adding 500 microM Zn.
The combined use of plants and associated microorganisms has great potential for remediating soil contaminated with organic compounds such as pesticides. The objective of this study was to determine whether the bacterial inoculation influences plant growth promotion and chlorpyrifos (CP) degradation and accumulation in different parts of the plant. Ryegrass was grown in soil spiked with CP and inoculated with a pesticide degrading bacterial strain Bacillus pumilus C2A1. Inoculation generally had a beneficial effect on CP degradation and plant biomass production, highest CP degradation (97%) was observed after 45 days of inoculation. Furthermore, inoculated strain efficiently colonized in the rhizosphere of inoculated plant and enhanced CP and its primary metabolite 3,5,6-trichloro-2-pyridinol (TCP) degradation. There was significantly less CP accumulation in roots and shoots of inoculated plants as compared to uninoculated plants. The results show the effectiveness of inoculated exogenous bacteria to boost the remediation of CP contaminated sites and decrease levels of toxic pesticide residues in crop plants.
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