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Applied Microbiology and Biotechnology (v.48, #2)
Safe biotechnology. 8. Transport of infectious and biological materials by H. L. M. Lelieveld; H. Bachmayer; B. Boon; A. Bennett; G. Brunius; K. Bürki; M. Cantley; J.M. Collard; C.H. Collins; P.Crooy; O. Doblhoff-Dier; R. Dubakiene; I. Economidis; A. Elmqvist; C. Frontali-Botti; R. Havenaar; H. Haymerle; O. Käppeli; G. Leaver; M. Lex; S. Lund; J. L. Mahler; R. Marris; L. J. Martinez; C. Mosgaard; M. Nicu; C. Normand-Plessier; J. Olsen; J. Pazlerova; M. Romantschuk; F. Rudan; M. Sarvas; H.-D. Schlumberger; G. Szvoboda; H. Stepankova; G. Tzotzos; V. Vaicuivenas; K. Wagner; R. G. Werner; A. Zhilevicha (pp. 135-140).
The transport of infectious and biological material is regulated by a number of international organizations. This mini-review has been compiled to increase awareness within the scientific community of problems caused by differences in terminology (such as infectious materials/substances, biological products, diagnostic specimens, genetically modified microorganisms) and certain technical aspects of the main international guidelines, and to assist policy makers in the creation of harmonized guidelines. A list of relevant Internet resources has been compiled.
Production of d-ribose by fermentation by P. De Wulf; E. J. Vandamme (pp. 141-148).
The production of d-ribose by fermentation has received much attention lately, possibly because of the use of this pentose to synthesize antiviral and anticancer drugs. This review briefly outlines the methods that have been used to synthesize d-ribose since it was identified in yeast RNA, and focuses in particular on the latest developments in d-ribose fermentation, which have led to d-ribose yields that exceed 90 g/l. Furthermore, the various transketolase-deficient d-ribose-producing mutants that are used, and the biochemical and genetic rationales applied to select them or to enhance their d-ribose productivities, are dealt with. Attention is also drawn to the unusual pleiotropic characteristics of the mutant strains, as well as to the industrial and academic applications of d-ribose.
Plant cell suspension culture in a bench-scale fermenter with a newly designed membrane stirrer for bubble-free aeration by C. Böhme; M.-B. Schröder; H. Jung-Heiliger; J. Lehmann (pp. 149-154).
In this paper, tests of an optimized membrane-stirrer geometry for bubble-free aeration of a plant cell suspension culture are described. Cell attachment and clogging of a previously described system [Piehl et al. (1988) Appl Microbiol Biotechnol 29:456–461] led to the development of a new stirrer. The volumetric oxygen transfer capacity has been measured in aqueous medium. The mass transfer coefficient, k l a, was 3.75 h−1 at 25 °C and at a stirrer speed of 34 rpm. The overall oxygen transfer capacity was investigated with a suspension culture of Aesculus hippocastanum. It was shown that the oxygen mass transfer was sufficient even at the maximum biomass of 10–12 g dry weight/l, which was obtained by using this system. Furthermore, special attention was given to medium components like C and N sources, to avoid growth limitation due to a shortage of nutrients.
Hollow-fibre bioreactors compared to batch and chemostat culture for the production of a recombinant toxoid by a marine Vibrio by J. R. Lloyd; T. R. Hirst; A. W. Bunch (pp. 155-161).
Bioreactor selection is important for maximising the productivity of recombinant organisms. In this paper a comparison is made between growth and recombinant protein synthesis in three types of bioreactor containing a marine Vibrio capable of heterologous expression and secretion of the non-toxic B-subunit pentamer of Escherichia coli heat-labile enterotoxin, EtxB. The heterologous gene was located on the plasmid pMMB68. Resistance to carbenicillin was used to select for plasmid-containing cells. In batch and continuous culture, volumetric productivities were highest when cells were grown in the presence of carbenicillin. Without antibiotic selection, the highest volumetric productivity (9.4 mg EtxB−1 h−1) was observed in hollow-fibre bioreactors, and the production phase could be maintained for over 50 h. The highest specific productivity under these conditions was found in batch culture, but the maximal production phase was only of 5 h duration. In hollow-fibre reactors the type of fibre used significantly affected productivity, both with regards to the maintenance of reactor integrity and by allowing passage of the recombinant toxoid through the selectively permeable membrane. Where contamination of the product with carbenicillin is to be avoided, these bioreactors are superior to batch or continuous culture.
Production of zeaxanthin in Escherichia coli transformed with different carotenogenic plasmids by A. Ruther; N. Misawa; P. Böger; G. Sandmann (pp. 162-167).
Carotenoids are of great commercial interest and attempts are made to produce different carotenoids in transgenic bacteria and yeasts. Development of appropriate systems and optimization of carotenoid yield involves transformation with several new genes on suitable plasmids. Therefore, the non-carotenogenic bacterium Escherichia coli JM101 was transformed in our study with several genes that mediated the biosynthetic production of the carotenoid zeaxanthin in this host. Selection of plasmids for the introduction of five essential genes for zeaxanthin formation showed that a pACYC-derived plasmid was the best. Multiplasmid transformation generally decreased production of zeaxanthin. By cotransformation with different plasmids, limitations in the biosynthetic pathway were found at the level of geranylgeranyl-pyrophosphate synthase and β-carotene hydroxylase. In our study a maximum zeaxanthin content of 289 μg/g dry weight was obtained. This involved the construction of a plasmid that mediated high-level expression of β-carotene hydroxylase. The level of expression was demonstrated on protein gels and solubilization by the mild detergent Brij 78 revealed that a significant portion of the expressed enzyme is located in the E. coli membranes where it can exert its catalytic function. Based on the results obtained, new strategies for vector construction and strain selection were proposed which could increase the present concentrations drastically. Optimal growth conditions of the transfomed E. coli strains for carotenoid formation were found at a temperature of 28 °C and a cultivation period of 2 days.
On-line enzyme activity determination using the stopped-flow technique: application to laccase activity in pulp mill waste-water treatment by X. Font; G. Caminal; X. Gabarrell; J. Lafuente; M. T. Vicent (pp. 168-173).
An automated system for on-line measurement of enzyme activity is proposed. The system uses a flow injection manifold in the stopped-flow mode to measure initial reaction rates. The time during which the flow is halted is selected in such a way as to optimise the enzyme/substrate ratio for the correct determination of activity values. The proposed system was used to determine the activity of laccase produced by the fungus Trametes versicolor immobilised on nylon in a fixed-bed reactor used for treating pulp mill waste water.
Bioconversion of 2-cyanopyrazine to 5-hydroxypyrazine-2-carboxylic acid with Agrobacterium sp. DSM 6336 by M. Wieser; K. Heinzmann; A. Kiener (pp. 174-176).
5-Hydroxypyrazine-2-carboxylic acid, a versatile building block for the synthesis of new antituberculous agents, was prepared by whole-cell biotransformation from 2-cyanopyrazine via pyrazinecarboxylic acid using Agrobacterium sp. DSM 6336. By developing a fermentation process for this two-enzyme-step bioconversion, a product concentration of 286 mM (40 g/l) was obtained. After the isolation method had been optimized the total yield was 80%.
Family-10 and Family-11 xylanases differ in their capacity to enhance the bleachability of hardwood and softwood paper pulps by J. H. Clarke; J. E. Rixon; A. Ciruela; H. J. Gilbert; G. P. Hazlewood (pp. 177-183).
Enzyme-aided bleaching of softwood and hardwood kraft pulps by glycosyl hydrolase family-10 and -11 xylanases and a family-26 mannanase was investigated. The ability to release reducing sugar from pulp xylan and to enhance bleachability is not a characteristic shared by all xylanases. Of the six enzymes tested, two xylanases belonging to family 11 were most effective at increasing bleachability and improving final paper brightness. None of the enzymes had a deleterious effect on pulp fibre integrity. The efficiency of individual xylanases as bleach enhancers was not dependent on the source microorganism, and could not be predicted solely on the basis of the quantity or nature of products released from pulp xylan. Cooperative interactions between xylanase/xylanase and xylanase/mannanase combinations, during the pretreatment of softwood and hardwood pulps, were investigated. Synergistic effects on reducing-sugar release and kappa number reduction were elicited by a combination of two family-10 xylanases. Pretreatment of kraft pulp with mannanase A from Pseudomonas fluorescens subsp. cellulosa and any one of a number of xylanases resulted in increased release of reducing sugar and a larger reduction in kappa number than obtained with the xylanases alone, confirming the beneficial effects of family-26 mannanases on enzyme-aided bleaching of paper pulp.
Determination of the kinetic parameters during continuous cultivation of the lipase-producing thermophile Bacillus sp. IHI-91 on olive oil by P. Becker; I. Abu-Reesh; S. Markossian; G. Antranikian; H. Märkl (pp. 184-190).
A thermostable lipase was produced in continuous cultivation of a newly isolated thermophilic Bacillus sp. strain IHI-91 growing optimally at 65 °C. Lipase activity decreased with increasing dilution rate while lipase productivity showed a maximum of 340 U l−1 h−1 at a dilution rate of 0.4 h−1. Lipase productivity was increased by 50% compared to data from batch fermentations. Up to 70% of the total lipase activity measured was associated to cells and by-products or residual substrate. Kinetic and stoichiometric parameters for the utilisation of olive oil were determined. The maximal biomass output method led to a saturation constant K S of 0.88 g/l. Both batch growth data and a washout experiment yielded a maximal specific growth rate, μmax, of 1.0 h−1. Oxygen uptake rates of up to 2.9 g l−1h−1 were calculated and the yield coefficient, Y X/O, was determined to be 0.29 g dry cell weight/g O2. From an overall material balance the yield coefficient, Y X/S, was estimated to be 0.60 g dry cell weight/g olive oil.
Stabilization of Escherichia coli penicillin G acylase against thermal inactivation by cross-linking with dextran dialdehyde polymers by D. Kazan; H. Ertan; A. Erarslan (pp. 191-197).
The thermostabilization of penicillin G acylase (PGA) obtained from a mutant of Escherichia coli ATCC 11105 by cross-linking with dextran dialdehyde molecules, at a molecular mass of 11 500, 37 700 and 71 000 Da, was studied. The thermal inactivation mechanisms of the native and modified PGA were both considered to obey first-order inactivation kinetics during prolonged heat treatment, forming fully active but temperature-sensitive transient states. The highest enhancement to the thermostability of PGA was obtained using dextran-71000-dialdehyde modification, as a␣nearly ninefold increase at temperatures above 50 °C. The modification of PGA by dextran-11500-dialdehyde resulted in a considerable reduction of the V m and K m parameters of the enzyme. However, other dextran dialdehyde derivatives used for modification did not cause a meaningful change in either V m and K m. Modification by dextran dialdehyde derivatives did not result in significant change to either the optimal temperature or the activation energy of PGA. All modified PGA preparations showed lower inactivation rate constants but higher half-lives for inactivation than those of the native PGA at all temperatures studied. As indicated by the half-life times and k i values, dextran 71000-dialdehyde was found to be more effective at cross-linking in the thermo-stabilization of PGA than any other agent studied in this work.
The effect of oxidative stress on the production of the recombinant protein, interferon γ, produced by Chinese hamster ovary cells in stirred-batch culture by C. A. Dunster; K. H. Cheeseman; S. P. Maddix (pp. 198-203).
The CHO320 cell line, engineered to produce human interferon γ was investigated with regard to its susceptibility to oxidative stress. Batch cultures of the cells grown in a bench-top bioreactor exhibited no marked response to changes in oxygen concentration between 6% and 14% whereas cell growth and recombinant protein production were inhibited by increasing the oxygen to 20%. High concentrations of hydrogen peroxide (in excess of 200 μM) were required to inhibit growth of the CHO320 cells whereas concentrations of 50 μm and 100 μM had no effect on recombinant protein production. Buthionine sulphoximine (50 μM and 100 μM) completely depleted the cells of glutathione within 24 h; however, no quantitative effect on recombinant protein production was seen. It is concluded that the CHO320 cells are, possibly as a consequence of the long selection process they have undergone, very resistant to oxidative stress.
A counter-selectable marker for genetic transformation of the yeast Schwanniomyces alluvius by M. N. Dave; B. B. Chattoo (pp. 204-207).
We report here a counter-selectable marker system for genetic transformation of the yeast Schwanniomyces alluvius, based on the complementation of uracil auxotrophs defective in either orotidine-5′-phosphate decarboxylase (URA3) or orotidine-5′-pyrophosphatase (URA5). Uracil auxotrophs of S. alluvius were obtained by ethyl methanesulphonate mutagenesis and complemented using the ura3 gene from S. cerevisiae. A␣transformation frequency of approximately 104/μg DNA was obtained, which is tenfold higher than results described in earlier reports. Transformants were analysed by Southern blot hybridisation and were found to be mitotically stable. The extrachromosomal nature of the transforming DNA was confirmed by Southern hybridisation and plasmid rescue. The rescued plasmid DNA had a restriction pattern identical to that of the parent plasmid.
Cloning, expression in Streptomyces lividans and biochemical characterization of a thermostable endo-β-1,4-xylanase of Thermomonospora alba UL JB1 with cellulose-binding ability by J. Blanco; J. J. R. Coque; J. Velasco; J. F. Martín (pp. 208-217).
Several thermophilic actinomycetes were isolated from urban solid waste. One of them, Thermomonospora alba ULJB1, showed a broad degradative activity on xylan, cellulose, starch and other polymers. Xylanase and cellulase activities were quantified and compared with those of Thermomonospora fusca. Genes encoding two different endo-β-1,4-xylanases were cloned from T.␣alba ULJB1. One of them, xylA, was sequenced, subcloned and overexpressed in Streptomyces lividans. It encodes a protein of 482 amino acids with a deduced molecular mass of 48 456 Da. The protein contains a 38-amino-acid leader peptide with six Arg+ residues in its amino-terminal end, a catalytic domain and a cellulose-binding domain connected by a linker region rich in proline and glycine. The XylA protein was purified to near homogeneity from S. lividans/xylA cultures. Two forms of the extracellular xylanase, of 48 kDa and 38 kDa, were produced that differed in their cellulose-binding ability. The 48-kDa protein showed a strong binding to cellulose whereas the 38-kDa form did not bind to this polymer, apparently because of the removal during processing of the cellulose-binding domain. Both forms were able to degrade xylans form different origins but not lichenam or carboxymethylcellulose. The major degradation product was xylobiose with traces of xylose. The xylanase activity was thermostable, showing a good activity up to 95 °C, and had broad pH stability in the range from pH 4.0 to pH 10.0.
Expression of different levels of enzymes from the Pichia stipitis XYL1 and XYL2 genes in Saccharomyces cerevisiae and its effects on product formation during xylose utilisation by M. Walfridsson; M. Anderlund; X. Bao; B. Hahn-Hägerdal (pp. 218-224).
Saccharomyces cerevisiae was transformed with the Pichia stipitis CBS 6054 XYL1 and XYL2 genes encoding xylose reductase (XR) and xylitol dehydrogenase (XDH) respectively. The XYL1 and XYL2 genes were placed under the control of the alcohol dehydrogenase 1 (ADH1) and phosphoglycerate kinase (PGK1) promoters in the yeast vector YEp24. Different vector constructions were made resulting in different specific activities of XR and XDH. The XR:XDH ratio (ratio of specific enzyme activities) of the transformed S. cerevisiae strains varied from 17.5 to 0.06. In order to enhance xylose utilisation in the XYL1-, XYL2-containing S. cerevisiae strains, the native genes encoding transketolase and transaldolase were also overexpressed. A strain with an XR:XDH ratio of 17.5 formed 0.82 g xylitol/g consumed xylose, whereas a strain with an XR:XDH ratio of 5.0 formed 0.58 g xylitol/g xylose. The strain with an XR:XDH ratio of 0.06, on the other hand, formed no xylitol and less glycerol and acetic acid compared with strains with the higher XR:XDH ratios. In addition, the strain with an XR:XDH ratio of 0.06 produced more ethanol than the other strains.
Site-directed mutagenesis of a fungal β-1,4-endoglucanase increases the minimum size required for the substrate by H. Wang; R. W. Jones (pp. 225-231).
Conserved regions within a family-5 β-1,4-endoglucanase (Egl1), produced by the fungus Macrophomina phaseolina, have been modified through site-directed mutagenesis, resulting in production of an enzyme with novel substrate requirements. The engineered form was generated through mutagenesis of D232A, which lies within the substrate-binding cleft of Egl1. Wild-type Egl1 requires a minimum substrate size of five glucosyl units, while the engineered form requires a minimum of six glucosyl units. Screening was facilitated by the unique ability to obtain functional expression of the fungal endoglucanase in Escherichia coli. Wild-type and mutated Egl1 have equivalent activity on cellohexaose, and both release cellobiose from the reducing end of the cellodextrin. This is the first example of protein engineering of an endoglucanase that results in a novel minimum substrate requirement for cellohexaose. This substrate specificity has not been reported for any native endoglucanases, thus the modified Egl1 may prove useful in applications requiring specific hydrolysis of complex carbohydrates such as β-glucans.
One-step transformation of the dimorphic yeast Yarrowia lipolytica by D.-C. Chen; J.-M. Beckerich; C. Gaillardin (pp. 232-235).
An efficient one-step transformation method for the dimorphic yeast Yarrowia lipolytica is described. Using cells grown overnight on agar plates, the whole process is carried out within 1 h. The transformant clones could be recovered on selective plates as early as 36–48 h after plating. The efficiency was better than 105 transformants/μg replicative plasmid DNA. Effects of cell density, dithiothreitol, heat shock, poly(ethylene glycol) 4000 concentration and the wetness of selective plates were investigated.
Effect of citrate on growth of Lactococcus lactis subsp. lactis in milk by S. Haddad; I. Sodini; C. Monnet; E. Latrille; G. Corrieu (pp. 236-241).
The effect of citrate on the growth of Lactococcus lactis subsp. lactis var. diacetylactis in milk has been investigated. Five strains of Lactococcus lactis subsp. lactis var. diacetylactis were compared to their citrate-negative variants, which lack the plasmid coding for citrate permease. In most cases, acidification kinetics and the final bacterial concentration of pure cultures of parental and variant strains did not differ significantly. Co-cultures of parental and variant strains, however, systematically tended towards the predominance of parental strains. Citrate metabolism is responsible for this change, since the predominance of citrate-positive strains was not observed in the absence of citrate. Continuous culture in milk enabled the difference in growth rates between the parental strain Lactococcus lactis subsp. lactis var. diacetylactis CDI1 and its citrate-negative variant to be quantified by following changes in the populations of the two co-cultured strains. At 26 °C, the growth rate of the parental strain was 7% higher than that of its citrate-negative variant. These results show that citrate metabolism slightly stimulates the growth of lactococci in milk.
Production of Spirulina sp. in sea water supplemented with anaerobic effluents in outdoor raceways under temperate climatic conditions by E. J. Olguín; S. Galicia; R. Camacho; G. Mercado; T. J. Pérez (pp. 242-247).
The use of untreated sea water supplemented with anaerobic effluents from digested pig waste and sodium bicarbonate was evaluated as a low-cost medium for semi-continuous cultivation of a mixed culture of two Spirulina strains in outdoor raceways under temperate climatic conditions (pond temperature in the range 21–26 °C and light intensity in the range 225–957␣μE m−2 s−1). The mixed culture had a predominant population (86.6 ± 3.9%) of an atypical Spirulina strain consisting of straight filaments, which appeared spontaneously after the strain with helicoidal trichomes had been subcultured. Morphological studies for the identification of the type and size of trichomes of the two strains (HF and SF) were carried out. The proportions of the two strains were observed to be stable during the monitoring period (30 days). Three different sets of semicontinuous cultures were carried out. Sets 1 and 2 were operated under regime 1 (a single addition of anaerobic effluents at time zero and no pH control) during the same season (June and July) of different years. Set 3 was operated under regime 2 (semi-continuous addition of anaerobic effluents and pH control) during the autumn. A minimum productivity of 3.6 g m−2 day−1 was obtained at one of the lowest temperatures (22.1 °C) and light intensities (245 μE m−2 s−1) and a maximum productivity of 10.9 g m−2 day−1 was observed at the highest temperature (25 °C) and highest average light intensity (618 μE m−2 s−1) registered for sets 1 and 2. The protein content in the Spirulina biomass harvested from these two sets varied from 17% to 65.6%. In set 3, a maximum productivity of 9.0 g m−2 day−1 was recorded at an average temperature of 24.4 °C and at an average light intensity of 668 μE m−2 s−1. The protein content in this set under regime 2 varied within a narrower range than in set 1 and set 2 (from 34.8% to 49.1%), apparently because of a continuous availability of ammonia nitrogen at a level of 30–50 mg l−1. However, in terms of the removal of ammonia nitrogen and chemical oxygen demand, regime 1 was more efficient than regime␣2.
Overexpression of cytosolic malate dehydrogenase (MDH2) causes overproduction of specific organic acids in Saccharomyces cerevisiae by O. Pines; S. Shemesh; E. Battat; I. Goldberg (pp. 248-255).
Saccharomyces cerevisiae accumulates l-malic acid through a cytosolic pathway starting from pyruvic acid and involving the enzymes pyruvate carboxylase and malate dehydrogenase. In the present study, the role of malate dehydrogenase in the cytosolic pathway was studied. Overexpression of cytosolic malate dehydrogenase (MDH2) under either the strong inducible GAL10 or the constitutive PGK promoter causes a 6- to 16-fold increase in cytosolic MDH activity in growth and production media and up to 3.7-fold increase in l-malic acid accumulation in the production medium. The high apparent K m of MDH2 for l-malic acid (11.8 mM) indicates a low affinity of the enzyme for this acid, which is consistent with the cytosolic function of the enzyme and differs from the previously published K m of the mitochondrial enzyme (MDH1, 0.28 mM). Under conditions of MDH2 overexpression, pyruvate carboxylase appears to be a limiting factor, thus providing a system for further metabolic engineering of l-malic acid production. The overexpression of MDH2 activity also causes an elevation in the accumulation of fumaric acid and citric acid. Accumulation of fumaric acid is presumably caused by high intracellular l-malic acid concentrations and the activity of the cytosolic fumarase. The accumulation of citric acid may suggest the intriguing possibility that cytosolic l-malic acid is a direct precursor of citric acid in yeast.
A para-site-specific hydroxylation of aromatic compounds by Mycobacterium sp. strain 12523: stabilization of the hydroxylation activity by H. Semba; K. Sakano (pp. 256-260).
Mycobacterium sp. strain 12523 has a para-site-specific hydroxylation activity, which produce para-substituted phenols from various aromatic compounds. However, the activity is unstable and the reactions are inactivated within 24 h. In order to extend the reaction period, the factors that affected reaction stability were examined. The hydroxylation activity of the cells incubated in buffer was significantly stabilized by the inclusion of an inducer such as methyl ethyl ketone. It is suggested that a regulatory mechanism is involved in controlling the activity. This study resulted in the development of a convenient method to stabilize the hydroxylation activity, involving the addition of an inducer, such as acetone, to the reaction system. This method permitted the hydroxylation reaction to continue for more than 67 h.
Biodegradation of azo and phthalocyanine dyes by Trametes versicolor and Bjerkandera adusta by A. Heinfling; M. Bergbauer; U. Szewzyk (pp. 261-266).
Eighteen fungal strains, known for their ability to degrade lignocellulosic material or lignin derivatives, were screened for their potential to decolorize commercially used reactive textile dyes. Three azo dyes, Reactive Orange 96, Reactive Violet 5 and Reactive Black 5, and two phthalocyanine dyes, Reactive Blue 15 and Reactive Blue 38, were chosen as representatives of commercially used reactive dyes. From the 18 tested fungal strains only Bjerkandera adusta, Trametes versicolor and Phanerochaete chrysosporium were able to decolorize all the dyes tested. During degradation of the nickel-phthalocyanine complex, Reactive Blue 38, by B. adusta and T. versicolor respectively, the toxicity of this dye to Vibrio fischeri was significantly reduced. In the case of Reactive Violet 5, a far-reaching detoxification was achieved by treatment with B. adusta. Reactive Blue 38 and Reactive Violet 5 were decolorized by crude exoenzyme preparations from T. versicolor and B. adusta in a H2O2-dependent reaction. Specific activities of the exoenzyme preparations with the dyes were determined and compared to oxidation rates by commercial horseradish peroxidase.
Nitrate removal from drinking water using a membrane-fixed biofilm reactor by W. Fuchs; G. Schatzmayr; R. Braun (pp. 267-274).
Biological treatment of drinking water is a cost-effective alternative to conventional physico/chemical processes. A new concept was tested to overcome the main disadvantage of biological denitrification, the intensive post-treatment process to remove microorganisms and remnant carbon source. The biological reaction zone and carbon supply were separated from the raw water stream by a nitrate-permeable membrane. Denitrification takes place in a biofilm, which is immobilized at the membrane. In a series of bench-scale runs, different types of membranes and reactor configurations were investigated. The best denitrification rates achieved were 1230 mg NO3 −-N m−2 day−1. In one run, raw water containing 100 mg NO3 − l−1 was completely freed from nitrate. The membrane and the attached biofilm also represent a barrier against the passage of the C source and nutrients into the raw water. At concentrations of 20 mg l−1 ethanol and 15 mg l−1 phosphate in the bioreactor no diffusion through the membrane into the treated water was observed. Without any post-treatment, the effluent met nearly all the relevant criteria for drinking water; only the colony count was slightly increased.
Microbial degradation of tetraethyl lead in soil monitored by microcalorimetry by H. Teeling; H. Cypionka (pp. 275-279).
Sieved agricultural soil samples were treated with the anti-knock agent tetraethyl lead (Et4Pb), and the resulting effects were analyzed by microcalorimetry. Et4Pb additions resulted in an increase of the heat production rate, provided that oxygen was present and that the soil was not autoclaved. The increased heat production rate was accompanied by degradation of Et4Pb, as verified by speciation analysis (GC-MS) of the remaining Et4Pb and its ionic degradation products (triethyl lead and diethyl lead cations). Conclusive evidence was obtained that these transformations were mediated mainly by microbes. At an initial Et4Pb concentration of 2 g Pb/kg dry weight the biodegradation rate was about 780 μmol day−1 kg dry weight−1, whilst the chemical decomposition was only 50 μmol day−1 kg dry weight−1. A fivefold rise of the initial Et4Pb concentration resulted in a decrease of the biodegradation rate to 600 μmol day−1 kg dry weight−1 and an increase of the chemical decomposition to 200 μmol day−1 kg dry weight−1. The biodegradation rate was not influenced by the addition of glucose, which means that no indication for a cometabolic attack of Et4Pb was found.