Itziar Alkorta

Phytoextraction: a cost-effective plant-based technology for the removal of metals from the environment.

Phytoremediation is an emerging technology that uses plants to clean up pollutants (metals and organics) from the environment. Within this field of phytoremediation, the utilization of plants to transport and concentrate metals from the soil into the harvestable parts of roots and above-ground shoots is usually called phytoextraction. Most traditional remediation methods do not provide acceptable solutions for the removal of metals from soils. By contrast, phytoextraction of metals is a cost-effective approach that uses metal-accumulating plants to clean up these soils. Subsequently, the harvestable parts, rich in accumulated metals, can be easily and safely processed by drying, ashing or composting. Some extracted metals can also be reclaimed from the ash, generating recycling revenues. Phytoextraction appears a very promising technology for the removal of metal pollutants from the environment and may be, at present, approaching commercialization.

Industrial applications of pectic enzymes: a review

Abstract Although pectic enzymes have long been used to increase the yield and clarity of fruit juices, it is only recently that technological innovations, such as the use of immobilization supports and continuous-flow systems, have been considered to optimize these fruit processing procedures. To our knowledge, this is the first review to focus on the benefits brought to the field by these new technologies and their potential for commercial applications.

Phytoremediation of organic contaminants in soils

Soil pollution, a very important environmental problem, has been attracting considerable public attention over the last decades. Unfortunately, the enormous costs associated with the removal of pollutants from soils by means of traditional physicochemical methods have been encouraging companies to ignore the problem. Phytoremediation is an emerging technology that uses plants to clean up pollutants in the environment. As overwhelmingly positive results have become available regarding the ability of plants to degrade certain organic compounds, more and more people are getting involved in the phytoremediation of organic contaminants. Phytoremediation of organics appears a very promising technology for the removal of these contaminants from polluted sites.

Aerobic chromate reduction by Bacillus subtilis

We have studied the reduction of hexavalent chromium (chromate) to the less toxic trivalent form by using cell suspensions and cell-free extracts from the common soil bacterium, Bacillus subtilis. B. subtilis was able to grow and reduce chromate at concentrations ranging from 0.1 to 1 mM K2CrO4. Chromate reduction was not affected by a 20-fold excess of nitrate-compound that serves as alternate electron acceptor and antagonizes chromate reduction by anaerobic bacteria. Metabolic poisons including sodium azide and sodium cyanide inhibited chromate reduction. Reduction was effected by a constitutive system associated with the soluble protein fraction and not with the membrane fraction. The reducing activity was heat labile and showed a Km of 188 μm CrO42-. The reductase can mediate the transfer of electrons from NAD(P)H to chromate. The results suggest that chromate is reduced via a detoxification system rather than dissimilatory electron transport.

Soil enzyme activities as biological indicators of soil health.

Soil health can be defined as the continued capacity of a specific kind of soil to function as a vital living system, within natural or managed ecosystem boundaries, to sustain plant and animal productivity, to maintain or enhance the quality of air and water environments, and to support human health and habitation. Because of the conflicting pressures increasingly applied to the soil, it is clear that relevant indicators are urgently needed to assess and monitor soil health. Biological indicators of soil health offer certain advantages over physicochemical methods. Among the various biological indicators that have been proposed to monitor soil health, soil enzyme activities have great potential to provide a unique integrative biological assessment of soils and the possibility of assessing the health of the soil biota. Besides, soil enzyme activities provide an easy, relatively rapid, and low cost procedure to monitor soil health. Nevertheless, soil enzyme activities also present some limitations and must always be considered in conjunction with other biological and physicochemicals measurements if we are to diagnose soil health correctly.

Microbial Monitoring of the Recovery of Soil Quality During Heavy Metal Phytoremediation

Soil pollution with heavy metals is a worldwide environmental problem. Phytoremediation through phytoextraction and phytostabilization appears to be a promising technology for the remediation of polluted soils. It is important to strongly emphasize that the ultimate goal of a heavy metal remediation process must be not only to remove the heavy metals from the soil (or instead to reduce their bioavailability and mobility) but also to restore soil quality. Soil quality is defined as the capacity of a given soil to perform its functions. Soil microbial properties are increasingly being used as biological indicators of soil quality due to their quick response, high sensitivity, and, above all, capacity to provide information that integrates many environmental factors. Indeed, microbial properties are among the most ecologically relevant indicators of soil quality. Consequently, microbial monitoring of the recovery of soil quality is often carried out during heavy metal phytoremediation processes. However, soil microbial properties are highly context dependent and difficult to interpret. For a better interpretation of microbial properties as indicators of soil quality, they may be grouped within categories of higher ecological relevance, such as soil functions, ecosystem health attributes, and ecosystem services.

Immobilization of pectin lyase from Penicillium italicum by covalent binding to nylon

Abstract Pectin lyase [PNL, poly(methoxygalacturonide) lyase; E.C. 4.2.2.10] from Penicillium italicum was immobilized by covalent binding to Nylon 6 in order to compare physico-chemical and kinetic properties of the soluble and immobilized counterpart. Optimum conditions for the immobilization process, kinetic parameters, and pH and temperature behavior of the enzyme were determined. The pH activity curve of the immobilized enzyme shifted toward a low pH compared with that of the soluble one. Similarly, the immobilized PNL was more stable at lower pHs than the soluble enzyme. The immobilization caused a marked increase in the thermal stability of the enzyme. The immobilized PNL was extraordinarily stable during storage at 4°C. No loss of activity was observed when the immobilized enzyme was used for 12 consecutive cycles of operation. In comparison with the soluble enzyme, the immobilized PNL caused a lower decrease in the viscosity of pectin solutions. Nevertheless, when fruit juices were used, the drop in initial viscosity was as marked as that observed when the soluble enzyme was used to clarify pectin solutions. Nylon-immobilized PNL appears promising for the clarification of fruit juices at 40°C and approximate pH of 3.0.

Bioluminescent bacterial biosensors for the assessment of metal toxicity and bioavailability in soils.

A major factor governing the toxicity of heavy metals in soils is their bioavailability. Traditionally, sequential extraction procedures using different extractants followed by chemical analysis have been used for determining the biologically available fraction of metals in soils. Yet, the transfer of results obtained on non-biological systems to biological ones is certainly questionable. Therefore, bioluminescence-based bacterial biosensors have been developed using genetically engineered microorganisms, constructed by fusing transcriptionally active components of metal resistance mechanisms to lux genes from naturally bioluminescent bacteria like Vibrio fischeri for the assessment of metal toxicity and bioavailability in polluted soils. As compared to chemical methods, bacterial biosensors present certain advantages, such as selectivity, sensitivity, simplicity, and low cost. Despite certain inherent limitations, bacterial bioluminescent systems have proven their usefulness in soils under laboratory and field conditions. Finally, green fluorescent protein-based bacterial biosensors are also applicable for determining with high sensitivity the bioavailability of heavy metals in soil samples.

Utilization of genetically engineered microorganisms (GEMs) for bioremediation

The wide metabolic and physiological versatility of microorganisms can be used to degrade many pollutants. Bioremediation is the technological process whereby biological systems are harnessed to effect the clean-up of environmental pollutants. Nowadays, microbial systems are employed in bioremediation programmes, generally in the treatment of soils and waters contaminated with organic pollutants. There are instances where natural populations are not suitable for use in the remediation of polluted sites and therefore the utilization of genetically engineered microorganisms (GEMs) is being considered for in-situ bioremediation of contaminated ecosystems. The deliberate release of GEMs into the environment is a subject of considerable public concern. The potential risks associated with the release of GEMs into the environment has led to the construction of biological containment systems by which bacteria are killed in a controlled suicide process. Active biological containment systems usually consist of two different components, a killing element designed to induce cell death and a control element which modulates the expression of the killing function. © 1999 Society of Chemical Industry

Phytostabilization of Metal Contaminated Soils

The contamination of soils with heavy metals represents a worldwide environmental problem of great concern. Traditional methods for the remediation of metal contaminated soils are usually very expensive and frequently induce adverse effects on soil properties and biological activity. Consequently, biological methods of soil remediation like phytoremediation (the use of green plants to clean up contaminated sites) are currently receiving a great deal of attention. In particular, chemophytostabilization of metal contaminated soils (the use of metal tolerant plants together with different amendments like organic materials, liming agents, or phosphorus compounds and such) to reduce metal mobility and bioavailability in soils appears most promising for sites contaminated with high levels of several metals when phytoextraction is not a feasible option. During chemophytostabilization processes, one must at all times be cautious with a possible future reversal of soil metal immobilization, with concomitant adverse environmental consequences.