Remediation of dyes in textile effluent: a critical review on current treatment technologies with a proposed alternative

This review focuses on some important and challenging aspects of soil extracellular enzyme research. We report on recent discoveries, identify key research needs and highlight the many opportunities offered by interactions with other microbial enzymologists. The biggest challenges are to understand how the chemical, physical and biological properties of soil affect enzyme production, diffusion, substrate turnover and the proportion of the product that is made available to the producer cells. Thus, the factors that regulate the synthesis and secretion of extracellular enzymes and their distribution after they are externalized are important topics, not only for soil enzymologists, but also in the broader context of microbial ecology. In addition, there are many uncertainties about the ways in which microbes and their extracellular enzymes overcome the generally destructive, inhibitory and competitive properties of the soil matrix, and the various strategies they adopt for effective substrate detection and utilization. The complexity of extracellular enzyme activities in depolymerising macromolecular organics is exemplified by lignocellulose degradation and how the many enzymes involved respond to structural diversity and changing nutrient availabilities. The impacts of climate change on microbes and their extracellular enzymes, although of profound importance, are not well understood but we suggest how they may be predicted, assessed and managed. We describe recent advances that allow for the manipulation of extracellular enzyme activities to facilitate bioremediation, carbon sequestration and plant growth promotion. We also contribute to the ongoing debate as to how to assay enzyme activities in soil and what the measurements tell us, in the context of both traditional methods and the newer techniques that are being developed and adopted. Finally, we offer our collective vision of the future of extracellular enzyme research: one that will depend on imaginative thinking as well as technological advances, and be built upon synergies between diverse disciplines.

Soil enzymes in a changing environment: Current knowledge and future directions

Bioremediation of high molecular weight polycyclic aromatic hydrocarbons: a review of the microbial degradation of benzo[a]pyrene.

We have compared the total microbial biomass and the fungal/bacterial ratio estimated using substrate-induced respiration (SIR) in combination with the selective inhibition technique and using the phospholipid fatty acid (PLFA) technique in a pH gradient (3.0-7.2) consisting of 53 mature broad-leaved forest soils. A fungal/bacterial biomass index using the PLFA technique was calculated using the PLFA 18:2w6,9 as an indicator of fungal biomass and the sum of 13 bacterial specific PLFAs as indicator of the bacterial biomass. Good linear correlation (p 0.8); for example the PLFAs 16:1w5 and 16:1w7c increased with increasing soil pH, while i16:0 and cy19:0 decreased. A principal component analysis of the total PLFA pattern gave a first component that was strongly correlated to soil pH (R-2 = 0.85, p < 0.001) indicating that the microbial community composition in these beech/beech-oak forest soils was to a large extent determined by soil pH. (Less)

Comparison of soil fungal/bacterial ratios in a pH gradient using physiological and PLFA-based techniques

The ligninolytic enzymes of white-rot fungi have a broad substrate specificity and have been implicated in the transformation and mineralization of organopollutants with structural similarities to lignin. This review presents evidence for the involvement of these enzymes in white-rot fungal degradation of munitions waste, pesticides, polychlorinated biphenyls, polycyclic aromatic hydrocarbons, bleach plant effluent, synthetic dyes, synthetic polymers, and wood preservatives. Factors relating to the feasibility of using white-rot fungi in bioremediation treatments for organopollutants are discussed.

Feasibility of bioremediation by white-rot fungi.

During the last decade, high pH anion exchange chromatography with pulsed amperometric detection (HPAEC/PAC) has gained increasing acceptance as the method of choice for analysis of neutral sugars commonly occurring in woods, pulps, and other lignocellulosics. This paper describes modified chromatographic conditions and discusses other critical factors that improve the precision and efficiency of this application. The method involves a controlled loading of acetate onto the column prior to equilibration with water and injection of sample. In-line solid-phase extraction is used to remove hydrophobic substances that have the potential to foul the analytical column. Critical operational parameters for the successful application of the method include a metal-free flowpath and a consistent application of anions with sample. Resolution of rhamnose is achieved while maintaining the resolution of xylose and mannose. Simplified sample pretreatment allows a ca. five-fold increase in sample through-put comp...

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A Rapid Modified Method for Compositional Carbohydrate Analysis of Lignocellulosics by High pH Anion-Exchange Chromatography with Pulsed Amperometric Detection (HPAEC/PAD)

Two methods were evaluated to extract ergosterol for quantitation of fungal biomass in Marshan, Zurich, and Batavia soils. Yields of ergosterol from hyphae and from fungal-colonized soil were greater when fungal tissue was extracted with an alkaline solvent mixture than when base was added to neutral extracts following removal of solids. A lyophilization treatment prior to extraction increased yields from Marshan but not from Zurich and Batavia soils. Losses of ergosterol during lyophilization were prevented by a rapid freezing treatment before lyophilization of soil samples. Recoveries from soil fortified with pure ergosterol did not accutately model recoveries from fungal tissue in these substrates. Thus, determinations of extraction efficiencies should be based upon recoveries from fungal tissue added to soils. Ergosterol was quantitatively recovered from Marshan and Zurich soils fortified with fungal tissue; however, only ca 66% was recovered from Batavia soil, a subsoil with a high clay content. The limit of detection of Phanerochaete chrysosporium from the three soils ranged from 8 to 15 μg biomass g soil−1.

Evaluation of methods to extract ergosterol for quantitation of soil fungal biomass

A field study to determine the ability of selected lignin-degrading fungi to remediate soil contaminated with pentachlorophenol and creosote was performed at a wood treating facility in south central Mississippi in the Autumn of 1991. The study was designed to evaluate 7 fungal treatments and appropriate control treatments. Soil concentrations of 14 priority pollutant polycyclic aromatic hydrocarbon (PAH) components of creosote were measured over time to determine treatment efficacies. Fungal treatments involved mixing fungal inocula and aspen chips into the contaminated soil and maintaining moisture by irrigation and aeration by tillage. PAHs of more than 4 rings persisted at their original concentrations during the 8 wk course of the study for all treatments and controls.

Field evaluation of the lignin-degrading fungus Phanerochaete sordida to treat creosote-contaminated soil

The feasibility of large-scale fungal bioaugmentation was evaluated by assessing the ability of the lignin-degrading fungus Phanerochaete sordida to decrease the soil concentrations of pentachlorophenol (PCP) and 13 priority pollutant polynuclear aromatic (PNA) creosote components in a field-demonstration study. Inoculation of the contaminated soil with the fungus (fungal treatment) at a rate of 10% (dry wt fungal hyphae and inoculum substrate dry wt soil−1) was compared to amending the soil (amended control) with sterile inoculum substrate also at a 10% rate (dry wt substrate dry wt soil−1) and no treatment (non-amended control), for their effects on PCP and PNA concentrations over 20 wk. The initial soil PCP and total measured PNA concentrations for the three treatments averaged 1058 and 1210mg kg−1, respectively. Despite very low initial amounts of fungal biomass, determined from ergosterol concentrations in the inoculum and inoculated soil, there was a 64% PCP decrease to a residual concentration of 362 mg kg−1 in the fungal-treated soil after 20 wk of treatment. This residual concentration was statistically less than the 715 mg kg−1 (26% decrease) and the 985 mg kg−1 (18% decrease) PCP concentrations observed in the amended control and the non-amended control soils, respectively. There were significant decreases in the concentrations of 3- and 4-ring PNAs in all treatments. With the exception of acenapthene, decreases in the concentrations of 3-ring PNAs were significantly greater in the non-amended control soil than in either the amended control or fungal-treated soils. Conversely, decreases in the concentration of 4-ring PNAs tended to be greater in the fungal-treated and amended control soils than in the non-amended control soils. The concentrations of 5- and 6-ring PNAs were not decreased significantly by any of the treatments.

Mark W. Davis

Papers

A Rapid Modified Method for Compositional Carbohydrate Analysis of Lignocellulosics by High pH Anion-Exchange Chromatography with Pulsed Amperometric Detection (HPAEC/PAD)

Evaluation of methods to extract ergosterol for quantitation of soil fungal biomass

Field evaluation of the lignin-degrading fungus Phanerochaete sordida to treat creosote-contaminated soil

Treatment of a pentachlorophenol- and creosote-contaminated soil using the lignin-degrading fungus phanerochaete sordid a: A field demonstration