Biological destruction of CCl(4): I. Experimental design and data

A denitrifying consortium capable of transforming carbon tetrachloride (CCl(4)) was cultured from aquifer sediment from the U.S. Department of Energy's Hanford Site in southeastern Washington State. To understand the kinetics of the biological destruction of CCl(4) by these microbes, a set of experiments, the conditions of which were chosen according to a fractional factorial experimental design, were completed. This article reports on the experimental design along with the results for CCl(4), biomass, acetate, nitrate, and nitrite concentrations. These data indicate that growth is inhibited by high nitrite concentrations, whereas CCl(4) degradation is slowed by the presence of nitrate and/or nitrite. (c) 1994 John Wiley & Sons, Inc.     

好氧反硝化细菌及其在微污染水源水修复中的应用研究进展

相比于氨氮,天然水体中的硝酸盐氮通常更稳定,导致更难将其从水中去除。由于好氧反硝化可以在有氧环境下进行反硝化作用去除硝酸盐氮,该过程对含有较高溶解氧的天然水体中硝酸盐氮处理有重要作用。本文综述了好氧反硝化菌的分离纯化现状、微生物代谢机制和环境影响因子,并介绍了功能菌群在微污染饮用水源水生物修复的应用研究进展。与一般的厌氧反硝化类似,好氧反硝化菌的种属分布较广,常见的如假单胞菌属(Pseudomoas)、产碱杆菌属(Alcaligenes)、副球菌属(Paracoccus)和芽孢杆菌属(Bacillus)等所属部分微生物均有好氧反硝化能力。大部分好氧反硝化菌株在最佳生长条件下(25–37℃、溶解氧浓度为3–5mg/L、pH为7–8、碳氮比为5–10)具有高效的脱氮效率。但目前好氧反硝化作用在微污染饮用水源水的生物修复方面的应用仍有着脱氮性能不稳定、菌剂流失等不足。此外,目前较少相关中试及实际工程应用的研究,需要进一步的深入探究。     

微生物镉解毒机制及微生物-植物互作修复研究进展

镉(cadmium,Cd)是引起粮食减产的主要金属之一,具有高溶解性及高迁移性,易被植物吸收和积累。微生物长期在镉胁迫的条件下进化出一系列的镉解毒机制。微生物对镉的解毒包括抑制Cd(Ⅱ)的进入、促进Cd(Ⅱ)的外排,以及将进入胞内的Cd(Ⅱ)进行“扣押”。微生物的Cd(Ⅱ)钝化是通过细胞吸附和胞外沉淀将游离态的Cd(Ⅱ)进行钝化,这类微生物具有较强的土壤镉污染治理潜力。本文主要介绍微生物的镉解毒机制、微生物-微生物互作、微生物-植物互作机制及其在镉污染生物修复中应用的最新研究进展。     

Biotechniques for air pollution control

This paper gives an overview of present biological techniques for the treatment of off-gases and the techniques that are being developed at the moment. The characteristics, advantages, disadvantages, costs and application area are discussed and compared. Biological off-gas treatment is based on the absorption of volatile contaminants in an aqueous phase or biofilm followed by oxidation by the action of microorganisms. Biofilters, bioscrubbers and biotrickling filters are used for elimination of odour and bioconvertable volatile organic and inorganic compounds and are enjoying increasing popularity. This popularity is a result of the low investment and operational costs involved compared to physico-chemical techniques and the elimination efficiencies that can be obtained. The operational envelop is still extending to higher concentrations and gas flow rates (exceeding 200,000 m³ h^–1) and a broader spectrum of degradable compounds. Research and development on the use of membranes and the addition of activated carbon or a second liquid phase to the biological systems may lead to a more efficient elimination of hydrophobic compounds and buffering of fluctuating loads. Shorter adaptation periods can be obtained by inoculation with specialized microorganisms. Improved design and operation are made possible by the growing insights in the kinetics and microbiology and supported by the development of models describing biological off-gas treatment. In conclusion, biotechniques are efficient and cost effective in treating off-gases with concentrations of biodegradable contaminants up to 1–5 g/m³. They could play a justified and important role in air pollution control in the coming years.Abbreviations VOC volatile organic compound - NO _x gaseous oxides of nitrogen     

Metabolic diversity of aromatic hydrocarbon-degrading bacteria from a petroleum-contaminated aquifer

We characterized bacteria from contaminated aquifers for their ability to utilize aromatic hydrocarbons under hypoxic (oxygen-limiting) conditions (initial dissolved oxygen concentration about 2 mg/l) with nitrate as an alternate electron acceptor. This is relevant to current intense efforts to establish favorable conditions forin situ bioremediation. Using samples of granular activated carbon slurries from an operating groundwater treatment system, we isolated bacteria that are able to use benzene, toluene, ethylbenzene, orp-xylene as their sole source of carbon under aerobic or hypoxic-denitrifying conditions. Direct isolation on solid medium incubated aerobically or hypoxically with the substrate supplied as vapor yielded 10³ to 10⁵ bacteria ml^–1 of slurry supernatant, with numbers varying little with respect to isolation substrate or conditions. More than sixty bacterial isolates that varied in colony morphology were purified and characterized according to substrate utilization profiles and growth condition (i.e., aerobic vs. hypoxic) specificity. Strains with distinct characteristics were obtained using benzene compared with those isolated on toluene or ethylbenzene. In general, isolates obtained from direct selection on benzene minimal medium grew well under aerobic conditions but poorly under hypoxic conditions, whereas many ethylbenzene isolates grew well under both incubation conditions. We conclude that the conditions of isolation, rather than the substrate used, will influence the apparent characteristic substrate utilization range of the isolates obtained. Also, using an enrichment culture technique, we isolated a strain ofPseudomonas fluorescens, designated CFS215, which exhibited nitrate dependent degradation of aromatic hydrocarbons under hypoxic conditions.Abbreviations BTEX benzene, toluene, ethylbenzene, andp-xylene - HPLC high performance liquid chromatography - GAC granular activated carbon     

A comparison of carbon/energy and complex nitrogen sources for bacterial sulphate-reduction: potential applications to bioprecipitation of toxic metals as sulphides

Detailed nutrient requirements were determined to maximise efficacy of a sulphate-reducing bacterial mixed culture for biotechnological removal of sulphate, acidity and toxic metals from waste waters. In batch culture, lactate produced the greatest biomass, while ethanol was more effective in stimulating sulphide production and acetate was less effective. The presence of additional bicarbonate and H₂ only marginally stimulated sulphide production. The sulphide output per unit of biomass was greatest using ethanol as substrate. In continuous culture, ethanol and lactate were used directly as efficient substrates for sulphate reduction while acetate yielded only slow growth. Glucose was utilised following fermentation to organic acids and therefore had a deleterious effect on pH. Ethanol was selected as the most efficient substrate due to cost and efficient yield of sulphide. On ethanol, the presence of additional carbon sources had no effect on growth or sulphate reduction in batch culture but the presence of complex nitrogen sources (yeast extract or cornsteep) stimulated both. Cornsteep showed the strongest effect and was also preferred on cost grounds. In continuous culture, cornsteep significantly improved the yield of sulphate reduced per unit of ethanol consumed. These results suggest that the most efficient nutrient regime for bioremediation using sulphate-reducing bacteria required both ethanol as carbon source and cornsteep as a complex nitrogen source.     

Expression of mouse metallothionein in the cyanobacteriumSynechococcus PCC7942

A cDNA encoding mouse metallothionein was cloned into the shuttle vector pUC303, creating a translational fusion with the bacterial chloramphenicol acetyltransferase gene. The resulting fusion protein has been expressed in the cyanobacteriumSynechococcus PCC7942. Cyanobacterial transformants expressed mouse metallothionein-specific mRNA species as detected by RNA slot blots. In addition, the transformants expressed a unique cadmium ionbinding protein corresponding to the predicted size of the mouse metallothionein fusion protein. Expression of this fusion protein conferred a two-to five-fold increase in cadmium ion tolerance and accumulation onSynechococcus PCC7942.     

Environmental biotechnology in India: prospects and case studies

The emergence and acceptance of the concept of sustainable development warrants that the scope of environmental biotechnology be enlarged to address issues like environmental monitoring, restoration of environmental quality, resource/residue/waste-recovery/utilization/treatment, and substitution of the non-renewable resource base with renewable resources. This paper delineates the current and prospective applications in these sub-areas of environmental biotechnology, and documents case studies on environmental monitoring (enteric viruses), restoration of environmental quality (oil spill remediation), resource recovery (hydrocarbon recovery from oily sludges, biosurfactants from distillery spentwash, desulphurization of coal & sour gases), and substitution of non-renewable resources with renewables (conversion of lignocellulisics into value added chemicals).The author is with the National Environmental Engineering Research Institute, Nagpur: 440 020, India     

Microbiological aspects of surfactant use for biological soil remediation

Biodegradation of hydrophobic organic compounds in polluted soil is a process involving interactions among soil particles, pollutants, water, and micro-organisms. Surface-active agents or surfactants are compounds that may affect these interactions, and the use of these compounds may be a means of overcoming the problem of limited bioavailability of hydrophobic organic pollutants in biological soil remediation. The effects of surfactants on the physiology of micro-organisms range from inhibition of growth due to surfactant toxicity to stimulation of growth caused by the use of surfactants as a co-substrate. The most important effect of surfactants on the interactions among soil and pollutant is stimulation of mass transport of the pollutant from the soil to the aqueous phase. This can be caused by three different mechanisms: emulsification of liquid pollutant, micellar solubilisation, and facilitated transport. The importance of these mechanisms with respect to the effect of surfactants on bioavailability is reviewed for hydrophobic organic pollutants present in different physical states. The complexity of the effect of surfactants on pollutant bioavailability is reflected by the results in the literature, which range from stimulation to inhibition of desorption and biodegradation of polluting compounds. No general trends can be found in these results. Therefore, more research is necessary to make the application of surfactants a standard tool in biological soil remediation. This revised version was published online in August 2006 with corrections to the Cover Date.