The microbiota of an unpolluted calcareous soil faces up chlorophenols: Evidences of resistant strains with potential for bioremediation

To highlight the effects of a variety of chlorophenols (CP) in relation to the response of an indigenous bacterial community, an agricultural Mediterranean calcareous soil has been studied in microcosms incubated under controlled laboratory conditions. Soil samples were artificially polluted with 2-monochlorophenol (MCP), 2,4,6-trichlorophenol (TCP) and pentachlorophenol (PCP), at concentrations ranging from 0.1 up to 5000 mg kg⁻¹. Both activity and composition of the microbial community were assessed during several weeks, respectively, by respirometric methods and PCR-DGGE analysis of extracted DNA and RNA. Significant decreases in soil respirometric values and changes in the bacterial community composition were observed at concentrations above 1000 mg kg⁻¹ MCP and TCP, and above 100 mg kg⁻¹ PCP. However, the persistence of several active bacterial populations in soil microcosms contaminated with high concentration of CP, as indicated by DGGE fingerprints, suggested the capacity of these native bacteria to survive in the presence of the pollutants, even without a previous adaptation or contact with them.The isolation of potential CP degraders was attempted by culture plating from microcosms incubated with high CP concentrations. Twenty-three different isolates were screened for their resistance to TCP and PCP. The most resistant isolates were identified as Kocuria palustris, Lysobacter gummosus, Bacillus sp. and Pseudomonas putida, according to 16S rRNA gene homology. In addition, these four isolates also showed the capacity to reduce the concentration of TCP and PCP from 15% to 30% after 5 d of incubation in laboratory assays (initial pollutant concentration of 50 mg L⁻¹). Isolate ITP29, which could be a novel species of Bacillus, has been revealed as the first known member in this bacterial group with potential for CP bioremediation applications, usually wide-spread in the soil natural communities, which has not been reported to date as a CP degrader.     

Geochemical and microbiological processes contributing to the transformation of hexahydro-1,3,5-trinitro-1,3,5-triazine (RDX) in contaminated aquifer material

Hexahydro-1,3,5-trinitro-1,3,5-triazine (RDX) is a potential human carcinogen, and its contamination of subsurface environments is a significant threat to public health. This study investigated abiotic and biological degradation of RDX in contaminated aquifer material. Anoxic batch systems were started with and without pre-aeration of aquifer material to distinguish initial biological RDX reduction from abiotic RDX reduction. Aerating the sediment eliminated chemical reductants in the native aquifer sediment, primarily Fe(II) sorbed to mineral surfaces. RDX (50 μM) was completely reduced and transformed to ring cleavage products when excess concentrations (2 mM) of acetate or lactate were provided as the electron donor for aerated sediment. RDX was reduced concurrently with Fe(III) when acetate was provided, while RDX, Fe(III), and sulfate were reduced simultaneously with lactate amendment. Betaproteobacteria were the dominant microorganisms associated with RDX and Fe(III)/sulfate reduction. In particular, Rhodoferax spp. increased from 21% to 35% and from 28% to 60% after biostimulation by acetate and lactate, respectively. Rarefaction analyses demonstrated that microbial diversity decreased in electron-donor-amended systems with active RDX degradation. Although significant amounts of Fe(III) and/or sulfate were reduced after biostimulation, solid-phase reactive minerals such as magnetite or ferrous sulfides were not observed, suggesting that RDX reduction in the aquifer sediment is due to Fe(II) adsorbed to solid surfaces as a result of Fe(III)-reducing microbial activity. These results suggest that both biotic and abiotic processes play an important role in RDX reduction under in situ conditions.     

Biodegradation of Poly(ε-caprolactone) (PCL) Film by <Emphasis Type="Italic">Alcaligenes faecalis</Emphasis>

The biodegradation behavior of PCL film with high molecular weight (80,000 Da) in presence of bacterium Alcaligenes faecalis and the analysis of degraded polymer film have been carried out. Thin Films of PCL were prepared by means of solution casting method and the bacterial degradation behavior was carried in basal medium, in presence of bacteria with time variation after UV treatment. It was observed that after UV treatment the degradation of polymer film was increased and the degradation rate followed a three steps degradation mechanism. The degraded polymer film was analyzed by means of Differential Scanning Calorimeter (DSC), Thermo Gravimetric Analyzer (TGA) and Fourier Transform Infrared Spectroscope (FTIR). DSC results revealed that at the initial stages of the degradation up to 15–20 days, the bacterium preferentially degrades the amorphous parts of the polymer film over the crystalline zone. Thermo gravimetric analysis highlighted the low temperature stability of degraded films with extent of degradation. FTIR results showed the chain scission mechanism of the polymer chains and also supported the preferential degradation of amorphous phase over crystalline phase in the initial stages of the degradation.     

A laboratory study on risk assessment of microcystin-RR in cropland

The persistence time and risk of microcystin-RR (MC-RR) in cropland via irrigation were investigated under laboratory conditions. In order to evaluate the efficiency of the potential adsorption and biodegradation of MC-RR in cropland and the persistence time of MC-RR for crop irrigation, high performance liquid chromatography (HPLC) was used to quantify the amount of MC-RR in solutions. Our study indicated that MC-RR could be adsorbed and biodegraded in cropland soils. MC-RR at 6.5mg/L could be completely degraded within 6 days with a lag phase of 1-2 days. In the presence of humic acid, the same amount of MC-RR could be degraded within 4 days without a lag phase. Accordingly, the persistence time of MC-RR in cropland soils should be about 6 days. This result also suggested the beneficial effects of the organic fertilizer utilization for the biodegradation of MC-RR in cropland soils. Our studies also demonstrated that MC-RR at low concentration (<10microg/L) could accelerate the growth of plants, while high concentration of MC-RR (>100microg/L) significantly inhibited the growth of plants. High sensitivity of the sprouting stage plants to MC-RR treatments as well as the strong inhibitory effects resulting from prolonged irrigation further indicated that this MC-RR growth-inhibition may vary with the duration of irrigation and life stage of the plants.     

Variations in expression of carbon isotope fractionation of chlorinated ethenes during biologically enhanced PCE dissolution close to a source zone

The stable carbon isotope values of tetrachloroethene (PCE) and its degradation products were monitored during studies of biologically enhanced dissolution of PCE dense nonaqueous phase liquid (DNAPL) to determine the effect of PCE dissolution on observed isotope values. The degradation of PCE was monitored in a 2-dimensional model aquifer and in a pilot test cell (PTC) at Dover Air Force Base, both with emplaced PCE DNAPL sources. Within the plume down gradient from the source, the isotopic fractionation of dissolved PCE and its degradation products were consistent with those observed in biodegradation laboratory studies. However, close to the source zone significant shifts in the isotope values of dissolved PCE were not observed in either the model aquifer or PTC due to the constant input of newly dissolved, non fractionated PCE, and the small isotopic fractionation associated with PCE reductive dechlorination by the mixed microbial culture used. Therefore the identification of reductive dechlorination in the presence of PCE DNAPL was based upon the appearance of daughter products and the isotope values of those daughter products. An isotope model was developed to simulate isotope values of PCE during the dissolution and degradation of PCE adjacent to a DNAPL source zone. With the exception of very high degradation rate constants (>1/day) stable carbon isotope values of PCE estimated by the model remained within error of the isotope value of the PCE DNAPL, consistent with measured isotope values in the model aquifer and in the PTC.     

Biodegradation and sorption of nodularin (NOD) in fine-grained sediments

Nodularin (NOD) is a cyclic pentapeptide hepatotoxin produced by the bloom forming cyanobacterium Nodularia spumigena. The fate of the toxin in the aquatic environment has not been fully evaluated. In the current study the changes in NOD concentration caused by biodegradation and sorption in samples from the Baltic were studied. Seawater of various salinities (0, 4, 8 and 12 PSU) and three forms of fine-grained sediment (sterile wet sediment, non-sterile wet sediment, and combusted sterile sediment) were incubated with 34.7 μg of NOD. The toxin was seen to be highly stable both in sterile and non-sterile seawater. During the 21-day experiment NOD concentrations in solutions overlying the combusted sediment and the sterile wet sediment were reduced to 12.5 ± 2.6% and 59.8 ± 2.4% of the initial value. The greatest loss of the toxin (up to 100%) was observed in the non-sterile seawater incubated with non-sterile wet sediment. These results indicate an important role of benthic microbial community in nodularin removal. Two biodegradation products with similar spectral characteristics to NOD were detected; one of which was identified as Adda amino acid.     

专性好氧菌降解苯胺废水的动力学研究

研究了苯胺在专性好氧菌Ｏｃｈｒｏｂａｃｔｒｕｍａｎｔｈｒｏｐｉ(人苍白杆菌)作用下的降解规律,讨论苯胺初始浓度及菌种接种量对苯胺降解速率的影响,当初始浓度低于８００ｍｇ／Ｌ时降解速率随浓度增加而加快,高于１０００ｍｇ／Ｌ时则表现出抑制作用;在可降解浓度范围内,该专性好氧菌能将苯胺完全降解而消除其污染;此外,通过对解降过程动力学实验数据的分析计算,得出苯胺的降解反应在不同浓度范围内分别表现为零级或一级关系      

环境污染物的处理技术

综述了环境污染的治理方法,侧重介绍了生物技术在三废治理、土壤及地下水污染治理中的应用,并介绍了一些污染治理技术的典型应用。     

Biodegradation of insecticide carbofuran by Paracoccus sp. YM3

A bacterium (Paracoccus sp. YM3) capable of degrading carbofuran was isolated from carbofuran-contaminated sludge. The strain was shown to metabolize carbofuran (50 mg L^?1) to carbofuran-7-phenol in minimal salt medium within 6 days in which the pesticide was the only source of carbon. Carbofuran and its main metabolite were analyzed by high performance liquid chromatography (HPLC). The addition of an other carbon source led to accelerated biodegradation. The relevant degrading-enzyme was intracellular and inducible. A tobacco hypersensitivity experiment showed that YM3 could eliminate carbofuran in soils effectively and safely. This is the first report of a Paracoccus sp. that could degrade carbofuran. The present study may provide a basis for biotreatment of wastewaters and bioremediation of carbofuran-contaminated soils.