Bioavailability of selenium accumulated by selenite-reducing bacteria

The bioavailability of selenium (Se) was determined in bacterial strains that reduce selenite to red elemental Se (Se^o). A laboratory strain ofBacillus subtilis and a bacterial rod isolated from soil in the vicinity of the Kesterson Reservoir, San Joaquin Valley, CA, (Microbacterium arborescens) were cultured in the presence of 1 mM sodium selenite (Na₂SeO₃). After harvest, the washed, lyophilizedB. subtilis andM. arborescens samples contained 2.62 and 4.23% total Se, respectively, which was shown to consist, within error, entirely of Se^o. These preparations were fed to chicks as supplements to a low-Se, vitamin E-free diet. Three experiments showed that the Se in both bacteria had bioavailabilities of approx 2% that of selenite. A fourth experiment revealed that gray Se^o had a bioavailability of 2% of selenite, but that the bioavailability of red Se^o depended on the way it was prepared (by reduction of selenite). When glutathione was the reductant, bioavailability resembled that of gray Se^o and bacterial Se; when ascorbate was the reductant, bioavailability was twice that level (3–4%). These findings suggest that aerobic bacteria such asB. subtilis andM. arborescens may be useful for the bioremediation of Se-contaminated sites, i.e., by converting selenite to a form of Se with very low bioavailability.     

Viscosity decrease of pectin and fruit juices catalyzed by pectin lyase from Penicillium italicum in batch and continuous-flow membrane reactors

Summary The extracellular pectin lyase (PNL, E.C. 4.2.2.10) from Penicillium italicum was utilized in batch and confined in a continuous-flow ultrafiltration membrane reactor. The enzyme catalyzed the decrease in viscosity of pectin solutions at pH 6.0 as well as of different fruit juices at their respective pH. PNL decreased the viscosity of pectin solutions in the membrane (60% after 30 min) more than in the batch (46% after 70 min) reactors, but similar viscosity reduction of fruit juices was achieved in both reactors. The enzyme decreased the viscosity of grape, peach and melon juices to different extents, but failed to do so with apple or pear juices. It can be concluded that the utilization of PNL in a membrane reactor appears of interest for the clarification of fruit juices.     

Removal of nitrate from water by foam-immobilizedPhormidium laminosum in batch and continuous-flow bioreactors

Cells of the non-N₂-fixing cyanobacteriumPhormidium laminosum were immobilized in polyurethane (PU) foams either by absorption or by entrapment in the PU prepolymer followed by polymerisation and by adsorption onto polyvinyl (PV) foams. Although entrapment caused toxicity problems which lead to rapid death of the immobilized cells, they were immobilized successfully by adsorption onto PU or PV foams and maintained their photosynthetic electron transport activities (PS I, II, I + II) for at least 7 weeks. Changes in the morphology resulting from immobilization, as revealed by scanning electron microscopy (SEM) and low temperature-SEM, were investigated. Batch cultures and a continuous-flow packed bed photobioreactor were used to study nitrate removal from water. The effects of light intensity and CO₂ concentration on bioreactor performance were studied with respect to the nitrate uptake efficiency of the system. It was concluded thatP. laminosum immobilized on polymer foams is of potential value for biological nitrate removal in a continuous-flow system. author for correspondence     

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 K_m of 188 m CrO₄ ^2-. 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.     

Native plant communities in an abandoned Pb-Zn mining area of northern Spain: implications for phytoremediation and germplasm preservation

Plants growing on metalliferous soils from abandoned mines are unique because of their ability to cope with high metal levels in soil. In this study, we characterized plants and soils from an abandoned Pb-Zn mine in the Basque Country (northern Spain). Soil in this area proved to be deficient in major macronutrients and to contain toxic levels of Cd, Pb, and Zn. Spontaneously growing native plants (belonging to 31 species, 28 genera, and 15 families) were botanically identified. Plant shoots and rhizosphere soil were sampled at several sites in the mine, and analyzed for Pb, Zn and Cd concentration. Zinc showed the highest concentrations in shoots, followed by Pb and Cd. Highest Zn concentrations in shoots were found in the Zn-Cd hyperaccumulator Thlaspi caerulescens (mean = 18,254 mg Zn kg(-1) DW). Different metal tolerance and accumulation patterns were observed among the studied plant species, thus offering a wide germplasm assortment for the suitable selection of phytoremediation technologies. This study highlights the importance of preserving metalliferous environments as they shelter a unique and highly valuable metallicolous biodiversity.     

From phytoremediation of soil contaminants to phytomanagement of ecosystem services in metal contaminated sites

Since the emergence of phytoremediation, much research has focused on its development for (i) the removal of metals from soil and/or (ii) the reduction of metal bioavailability, mobility, and ecotoxicity in soil. Here, we review the lights and shades of the two main strategies (i.e., phytoextraction and phytostabilization) currently used for the phytoremediation of metal contaminated soils, irrespective of the level of such contamination. Both strategies face limitations to become successful at commercial scale and, then, often generate skepticism regarding their usefulness. Recent innovative approaches and paradigms are gradually establishing these phytoremediation strategies as suitable options for the management of metal contaminated soils. The combination of these phytotechnologies with a sustainable and profitable site use (a strategy called phytomanagement) grants value to the many benefits that can be obtained during the phytoremediation of metal contaminated sites, such as, for instance, the restoration of important ecosystem services, e.g. nutrient cycling, carbon storage, water flow regulation, erosion control, water purification, fertility maintenance, etc.     

Thioredoxin h overexpressed in barley seeds enhances selenite resistance and uptake during germination and early seedling development

The uptake, distribution and metabolism of selenite were examined in germinating homozygous barley (Hordeum vulgare L.) grain with thioredoxin h overexpressed in starchy endosperm. Results were related to the null segregant in which the transgene had segregated out during crossing. Compared with the null segregant, the homozygote showed enhanced germination and root and shoot growth in the presence of 1 and 2 mM sodium selenite. The rate of incorporation of selenite by the homozygote was approximately twice that of the null segregant. Based on X-ray absorption spectroscopy, the major products in both cases were selenomethionine-like species and the red, monoclinic form of elemental selenium, a derivative not previously reported in green plants. Selenite and selenate made up the balance. The distribution of the products formed differed as to the tissue — root, shoot, aleurone, endosperm — but the ratios were similar in the homozygote and null segregant. The results provide evidence that, in addition to the accelerated germination observed previously in water, barley grain overexpressing thioredoxin h are resistant to the inhibitory effects of selenite. These properties raise the possibility that plants overexpressing thioredoxin h could find application in the remediation of polluted environments.