Microbial degradation of metal complexed cyanides and thiocyanate from mining wastewaters

A microbiological examination of the soil from a cyanide wastewater storage basin was carried out. The storage basin contained water from the cyanidation process of gold extraction, and it was composed principally of simple cyanide, metal complexed cyanide, mainly cuprocyanide, ferro-ferricyanides and thiocyanate. Pseudomonas species were the principal bacteria identified in the soil. Using the storage basin soil as a seed sludge, its potential for the biodegradation of all the cyanide complexes in the mining wastewater was studied in the laboratory, using batch, fed-batch and continuous processes. The ammonia and sulphate produced were quantified. The presence of intermediate products was suspected. In the continuous process, total degradation of all cyanide was observed at a dilution rate of 0.066 day(-1).     

Microbial transformation and degradation of polychlorinated biphenyls

This paper reviews the potential of microorganisms to transform polychlorinated biphenyls (PCBs). In anaerobic environments, higher chlorinated biphenyls can undergo reductive dehalogenation. Meta- and para-chlorines in PCB congeners are more susceptible to dechlorination than ortho-chlorines. Anaerobes catalyzing PCB dechlorination have not been isolated in pure culture but there is strong evidence from enrichment cultures that some Dehalococcoides spp. and other microorganisms within the Chloroflexi phylum can grow by linking the oxidation of H(2) to the reductive dechlorination of PCBs. Lower chlorinated biphenyls can be co-metabolized aerobically. Some aerobes can also grow by utilizing PCB congeners containing only one or two chlorines as sole carbon/energy source. An example is the growth of Burkholderia cepacia by transformation of 4-chlorobiphenyl to chlorobenzoates. The latter compounds are susceptible to aerobic mineralization. Higher chlorinated biphenyls therefore are potentially fully biodegradable in a sequence of reductive dechlorination followed by aerobic mineralization of the lower chlorinated products.     

Microbial transformation products of benzoxazolinone and benzoxazinone allelochemicals--a review

Cyclic hydroxamic acids and lactams are allelochemicals present in the common agricultural crops wheat, rye, and maize. The hydroxamic acids are mainly present in the plants as glucosides. Upon injury or insect attack or when exuded to the soil environment, the hydroxamic acids occur in their unstable agluconic form. In the first step in the transformation of hydroxamic acids, benzoxazolinones are formed spontaneously. It is necessary to elucidate the further microbial transformation of these compounds in the soil environment for a purposeful exploitation of the allelopathic properties of wheat, rye, and maize. In the present paper, the existing knowledge on microbial transformation products of benzoxazolin-2-one (BOA), 6-methoxy-benzoxazolin-2-one (MBOA), and 2-hydroxy-1,4-benzoxazin-3-one (HBOA) was reviewed. Three main groups of transformation products were identified: aminophenoxazinones, malonamic acids, and acetamides. Future research needs concerning the transformation of these chemicals in soil are discussed, when their properties for suppressing weeds and soil-borne diseases are going to be exploited.     

Microbial transformation of dissolved organic matter from different sources and its influence on disinfection byproduct formation potentials

Biodegradation-induced changes in the characteristics of dissolved organic matter (DOM) and the subsequent effects on disinfection byproduct formation potentials (DBPFPs) were investigated using six different sources of DOM (algae, leaf litter, reed, compost, paddy water, and treated municipal sewage effluent). Microbial incubation of the DOM samples increased the specific ultraviolet absorbance and humic-like fluorescence but decreased the protein/tannin-like fluorescence and relative distribution of smaller-sized DOM components. Comparison of the original versus biodegraded DOM samples using resin fractionation and pyrolysis–gas chromatography/mass spectrometry revealed that the biodegradation-induced changes were highly dependent on DOM sources and exhibited no consistent trends among the different sources. Changes in DBPFPs also differed with DOM source. Vascular plant-derived DOM (leaf litter and reed) demonstrated an enhancement in specific DBPFP after biodegradation, whereas little change or even a slight decrease was observed for the other DOM sources. Correlations that were significant between specific DBPFPs and the aromatic content or humic-like fluorescence for the original DOM samples were no longer significant after microbial degradation. The relative abundance of hydrophobic to hydrophilic structures in DOM is suggested to be a general indicator for the formation potential of trihalomethanes irrespective of DOM source and the state of biodegradation.     

Microbial utilization and transformation of humic acid-like substances extracted from a mixture of municipal refuse and sewage sludge disposed of in a landfill

The purpose of the research was to establish whether humic acid-like substances (HA) related to municipal refuse disposed of in a landfill can resist microbial degradation and if they contribute, in that way, to long-term stabilization of landfill refuse. Using a mixture of 0.1 M Na(4)P(2)O(7) + 0.1 M NaOH, we extracted HA from municipal refuse mixed with sewage sludge and disposed of for up to 12 months, in a 40-m(3) model landfill. In laboratory experiments under aerobic conditions, up to 50% of HA was utilized as a supplementary source of nutrients by an assemblage of soil microorganisms in only 21 days. The microbial utilization was enhanced to over 80%, and up to 98%, respectively, if HA served as the sole source of carbon or nitrogen. Remaining HA which could be re-isolated from microbial cultures were lower in carbon (<12%) and nitrogen (<2.3%). Spectroscopic analysis (UV, Vis, FTIR) indicated losses, especially in aliphatic structural units, and a relative enhancement in aromatic structures. It was postulated that for their high degree of degradability, HA indigenous to that anthropogenic environment would not play an important role in the long-term stabilization of landfill refuse.     

化学沉淀法脱除HPF脱硫废液中的硫氰酸盐

硫氰酸根(SCN-)普遍存在于HPF脱硫废液中,其含量高达90~140 g/L,对COD、色度等指标构成影响。首先对HPF脱硫废液做预处理,即以加酸的方法脱除其中的S2O32-,然后利用氯酸根将废水中高浓度SCN-氧化脱除,实验通过交替向废液中加入氯酸钠和浓硫酸,维持溶液pH值在1以下,使反应停留在轻度氧化阶段以使SCN-定向转化为沉淀,处理后SCN-的浓度由初始的69.76 g/L降至0.67 g/L,溶液COD由初始的98600 mg/L降至2400 mg/L。用较少的化学试剂将硫氰酸根基本脱除,达到了化学降解的目的。     

焦化废水中COD、挥发酚和硫氰化物同步高效去除

采用两级膨胀颗粒污泥床(EGSB)反应器在微氧条件下处理焦化废水,考察了该工艺对焦化废水中挥发酚、硫氰化物、氰化物和COD的去除效果。研究结果表明,在进水流量为1 L/h,总水力停留时间(HRT)为24 h的条件下,两级EGSB反应器对COD的去除效果较好。稳定运行时,在进水挥发酚为56.8~185.1 mg/L、硫氰化物为287.1~539.9 mg/L、氰化物为0.17~0.72 mg/L的条件下,系统对其平均去除率分别为99.9%、96.8%和82.6%,出水挥发酚和氰化物均能达到《污水综合排放标准(GB8978-1996)》的一级标准。进水COD浓度在1 084~1 880 mg/L之间,平均去除率为76.9%,出水平均浓度为325 mg/L。     

Transcriptome analysis of Oryza sativa in responses to different concentrations of thiocyanate

Environmental Science and Pollution Research - Effective concentrations of potassium thiocyanate (KSCN) to rice seedlings were experimentally determined using relative growth rate as a sensitive...     

Microbial degradation of pendimethalin

Microbial degradation of pendimethalin (N-(1-Ethylpropyl)-3, 4-dimethyl-2, 6-dinitroaniline) in vitro was studied. Fusarium oxysporum and Paecilomyces varioti, two soil fungi, in culture media degraded pendimethalin to two metabolites namely N-(1-Ethylpropyl)-3, 4-dimethyl-2-nitrobenzene-1, 6-diamine (II) and 3,4-Dimethyl-2, 6-dinitroaniline (IV). Rhizoctonia bataticola, another soil fungus, decomposed pendimethalin yielding only the latter metabolite (IV). Fungal decomposition of pendimethalin involved nitro reduction and dealkylation.     

Microbial degradation of guanidinium ion

Guanidinium ion was degraded by microorganisms in a variety of surface water samples. Degradation of the cation was characterized by long and variable periods prior to enhanced microbial activity and was considerably slower than the degradation of the amino acid arginine. A carbon source could potentiate the degradation of guanidinium ion, in which case its carbon was mineralized and its nitrogen could be used for growth; but at nutrient levels in surface water, only slight mineralization of the cation's carbon was demonstrated and was considerably slower than that of urea carbon. Degradation of guanidinium ion by microorganisms capable of growing on it as a sole carbon source was estimated to be slow relative to two xenobiotic compounds. The development of such populations in surface water samples was dependent on the concentration of guanidinium ion.     

Microbial degradation of chlorinated dioxins

Polychlorinated dibenzo-p-dioxins (PCDD) and polychlorinated dibenzofurans (PCDF) were introduced into the biosphere on a large scale as by-products from the manufacture of chlorinated phenols and the incineration of wastes. Due to their high toxicity they have been the subject of great public and scientific scrutiny. The evidence in the literature suggests that PCDD/F compounds are subject to biodegradation in the environment as part of the natural chlorine cycle. Lower chlorinated dioxins can be degraded by aerobic bacteria from the genera of Sphingomonas, Pseudomonas and Burkholderia. Most studies have evaluated the cometabolism of monochlorinated dioxins with unsubstituted dioxin as the primary substrate. The degradation is usually initiated by unique angular dioxygenases that attack the ring adjacent to the ether oxygen. Chlorinated dioxins can also be attacked cometabolically under aerobic conditions by white-rot fungi that utilize extracellular lignin degrading peroxidases. Recently, bacteria that can grow on monochlorinated dibenzo-p-dioxins as a sole source of carbon and energy have also been characterized (Pseudomonas veronii). Higher chlorinated dioxins are known to be reductively dechlorinated in anaerobic sediments. Similar to PCB and chlorinated benzenes, halorespiring bacteria from the genus Dehalococcoides are implicated in the dechlorination reactions. Anaerobic sediments have been shown to convert tetrachloro- to octachlorodibenzo-p-dioxins to lower chlorinated dioxins including monochlorinated congeners. Taken as a whole, these findings indicate that biodegradation is likely to contribute to the natural attenuation processes affecting PCDD/F compounds.     

Microbial biotransformation of aryl sulfanylpentafluorides

We report, for the first time, the biotransformation of potential pollutants bearing the pentafluorosulfanyl (SF₅-) functional group in a fungus and bacteria. Cunninghamella elegans transformed p-methoxy phenyl SF₅ via demethylation; Pseudomonas knackmussii and P. pseudoalcaligenes KF707 transformed amino-, hydroxyamino- and diamino- substituted phenyl SF₅, forming the N-acetylated derivatives as the main product. Cell-free extract of Streptomyces griseus transformed 4-amino-3-hydroxy-phenyl SF₅ to the N-acetylated derivative in the presence of acetyl CoA, confirming that an N-acetyltransferase is responsible for the bacterial biotransformations. Approximately 25 % of drugs and 30 % of agrochemicals contain fluorine, and the trifluoromethyl group is a prominent feature of many of these since it improves lipophilicity and stability. The pentafluorosulfanyl substituent is seen as an improvement on the trifluoromethyl group and research efforts are underway to develop synthetic methods to incorporate this moiety into biologically active compounds. It is important to determine the potential environmental impact of these compounds, including the potential biotransformation reactions that may occur when they are exposed to microorganisms.     

Microbial conversion of fungicide vinclozolin

An ecological safety study of using vinclozolin in field and laboratory experiments showed that the effect of the preparation led to a decrease in the abundance of actinomycetes and mycelial fungi and an enhancement of nitrification. The residual amounts of vinclozolin in soil after 12 months were 6-12% of the dose introduced. The persistent chlorinated derivatives of the toxicant were found. Microbial strains pertaining to the genera Pseudomonas and Bacillus were isolated that utilized vinclozolin as the sole source of carbon and energy.     

羽毛角蛋白的生物降解

羽毛角蛋白是自然界中丰富的蛋白资源,由于其难以被解解而造成环境污染,近些年来对它的生物降解及有关角蛋白酶的研究取得了一定进展,对此作一简要综述。     

Individual and combined inhibition of phenol and thiocyanate on microbial activity of partial nitritation

This study evaluated the individual and interactive effect of phenol and thiocyanate (SCN⁻) on partial nitritation (PN) activity using batch test and response surface methodology. The IC₅₀ of phenol and SCN⁻ on PN sludge were 5.6 and 351 mg L⁻¹, respectively. The PN sludge was insensitive to phenol and SCN⁻ at levels lower than 1.77 and 43.3 mg L⁻¹, respectively. A regression model equation was developed and validated to predict the relative specific respiration rate (RSRR) of PN sludge exposed to different phenol and SCN⁻ concentrations. In the range of independent variables, the most severe inhibition was observed with a valley value (17%) for RSRR, when the phenol and SCN⁻ concentrations were 4.08 and 198 mg L⁻¹, respectively. An isobole plot was used to judge the combined toxicity of phenol and SCN⁻, and the joint inhibitory effect was variable depending on the composition and concentration of the toxic components. Furthermore, the toxic compounds showed independent effects, which is the most common type of combined toxicity.

     

Microbial phytotoxins as potential herbicides

Abstract

Microbes are sources of a diverse array of phytotoxic compounds. These compounds are generally structurally different from commercial herbicides, targeting different molecular sites of action within the plant. These novel structures and sites can be excellent leads for the discovery and development of safer synthetic herbicides. Microbial phytotoxins are often more environmentally benign than synthetic herbicides. Examples of phytotoxins from fungi (AAL‐toxin, cornexistin, cyperin, and tentoxin) with novel structures and sites of action are discussed. AAL‐toxin is toxic to a wide variety of weeds at very low dose rates. AAL‐toxin and many of its analogues kill plants by inhibiting a ceramide synthase‐like enzyme, causing rapid accumulation of free sphingoid bases that disrupt membranes. Cornexistin appears to be metabolically cnverted to an inhibitor of certain aspartate amino transferase isoenzymes. Its activity can be reversed by feeding aspartate and glutamate or with tricarboxylic acid cycle intermediates. Its activity is much like that of (aminooxy)acetate. Cyperin is a diphenylether phytotoxin that inhibits protoporphyrinogen oxidase, but does not kill plants by this mechanism. It appears to have other effects on porphyrin metabolism. Tentoxin is toxic by two mechanisms. It disrupts chloroplast development by inhibiting the processing of a nuclear‐coded plastid protein, and it also inhibits photophosphorylation by acting as an energy transfer inhibitor of coupling factor 1 ATPase. Other examples of phytotoxins from microbes with promise as herbicides will be mentioned.     

Microbial growth with vapor-phase substrate

Limited information exists on influences of the diffusive transport of volatile organic contaminants (VOC) on bacterial activity in the unsaturated zone of the terrestrial subsurface. Diffusion of VOC in the vapor-phase is much more efficient than in water and results in effective VOC transport and high bioavailability despite restricted mobility of bacteria in the vadose zone. Since many bacteria tend to accumulate at solid-water, solid-air and air-water interfaces, such phase boundaries are of a special interest for VOC-biodegradation. In an attempt to evaluate microbial activity toward air-borne substrates, this study investigated the spatio-temporal interplay between growth of Pseudomonas putida (NAH7) on vapor-phase naphthalene (NAPH) and its repercussion on vapor-phase NAPH concentrations. Our data demonstrate that growth rates of strain PpG7 were inversely correlated to the distance from the source of vapor-phase NAPH. Despite the high gas phase diffusivity of NAPH, microbial growth was absent at distances above 5 cm from the source when sufficient biomass was located in between. This indicates a high efficiency of suspended bacteria to acquire vapor-phase compounds and influence headspace concentration gradients at the centimeter-scale. It further suggests a crucial role of microorganisms as biofilters for gas-phase VOC emanating from contaminated groundwater or soil.     

Light induced transformation of tribenuron-methyl

To study the photostability of sulfonylurea herbicide tribenuron-methyl (methyl 2-[[[[ N-(4-methoxy-6-methyl-1,3,5-triazin-2-yl) methylamino] carbonyl]amino]sulfonyl]benzoate), in the field, model experiments with organic solvents were performed. Irradiation of tribenuron-methyl in methanol, isopropanol and cyclohexane yielded 4-methoxy-6-methyl-2-aminomethyl-1,3,5-triazine; methyl-2-(aminosulfonyl) benzoate; N-(4-methoxy-6-methyl-1,3,5-triazin-2-yl)-N-methyl urea; N-(2-carbomethoxy phenyl)-N-(4-methoxy-6-methyl-1,3,5-triazin-2-yl)-N'-methyl urea; 2-(aminosulfonyl) benzoic acid, N-methyl saccharin and saccharin in considerable amounts. The rate of degradation in different solvents followed first-order kinetics with a statistically significant correlation coefficient.