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Applied Microbiology and Biotechnology (v.64, #4)
Anaerobic degradation of monoaromatic hydrocarbons by R. Chakraborty; J. D. Coates (pp. 437-446).
Over the last two decades significant advances have been made in our understanding of the anaerobic biodegradability of monoaromatic hydrocarbons. It is now known that compounds such as benzene, toluene, ethylbenzene, and all three xylene isomers can be biodegraded in the absence of oxygen by a broad diversity of organisms. These compounds have been shown to serve as carbon and energy sources for bacteria growing phototrophically, or respiratorily with nitrate, manganese, ferric iron, sulfate, or carbon dioxide as the sole electron acceptor. In addition, it has also been recently shown that complete degradation of monoaromatic hydrocarbons can also be coupled to the respiration of oxyanions of chlorine such as perchlorate or chlorate, or to the reduction of the quinone moieties of humic substances. Many pure cultures of hydrocarbon-degrading anaerobes now exist and some novel biochemical and genetic pathways have been identified. In general, a fumarate addition reaction is used as the initial activation step of the catabolic process of the corresponding monoaromatic hydrocarbon compounds. However, other reactions may alternatively be involved depending on the electron acceptor utilized or the compound being degraded. In the case of toluene, fumarate addition to the methyl group mediated by benzylsuccinate synthase appears to be the universal mechanism of activation and is now known to be utilized by anoxygenic phototrophs, nitrate-reducing, Fe(III)-reducing, sulfate-reducing, and methanogenic cultures. Many of these biochemical pathways produce unique extracellular intermediates that can be utilized as biomarkers for the monitoring of hydrocarbon degradation in anaerobic natural environments.
Properties and applications of microbial transglutaminase by K. Yokoyama; N. Nio; Y. Kikuchi (pp. 447-454).
Some properties and applications of the transglutaminase (TGase) referred to as microbial TGase (MTGase), derived from a variant of Streptomyces mobaraensis (formerly classified as Streptoverticillium mobaraense), are described. MTGase cross-linked most food proteins, such as caseins, soybean globulins, gluten, actin, myosins, and egg proteins, as efficiently as mammalian TGases by forming an ε-(γ-glutamyl)lysine bond. However, unlike many other TGases, MTGase is calcium-independent and has a relatively low molecular weight. Both of these properties are of advantage in industrial applications; a number of studies have illustrated the potential of MTGase in food processing and other areas. The crystal structure of MTGase has been solved. It provides basic structural information on the MTGase and accounts well for its characteristics. Moreover, an efficient method for producing extracellular MTGase has been established using Corynebacterium glutamicum. MTGase may be expected to find many uses in both food and non-food applications.
Lincomycin, clindamycin and their applications by J. Spížek; T. Řezanka (pp. 455-464).
Lincomycin and clindamycin are lincosamide antibiotics used in clinical practice. Both antibiotics are bacteriostatic and inhibit protein synthesis in sensitive bacteria. They may even be bactericidal at the higher concentrations that can be reached in vivo . Clindamycin is usually more active than lincomycin in the treatment of bacterial infections, in particular those caused by anaerobic species; and it can also be used for the treatment of important protozoal diseases, e.g. malaria, most effectively in combination with primaquine. Resistance to lincomycin and clindamycin may be caused by methylation of 23S ribosomal RNA, modification of the antibiotics by specific enzymes or active efflux from the periplasmic space.
Studies on molecular mechanisms of Ginkgo biloba extract by J. V. Smith; Y. Luo (pp. 465-472).
In the past decade, interest by the general public in the use of herbal dietary supplements has risen exponentially. As throughout history, individuals are now turning to the use of “natural” therapies for the prevention, treatment and cure of almost every ailment and aging malady imaginable... often without substantial proof of safety or efficacy. One of the most popular herbal supplements is Ginkgo biloba extract, taken for its perceived “memory enhancing” properties. Given the inordinate popularity, growing use, and substantial number of pharmaceutical products containing G. biloba, coupled with demands for product safety and “hard evidence,” science has followed this trend closely with an ever-expanding body of pharmacological and clinical data on such preparations. Claims that standardized G. biloba extract (EGb 761) can modulate the cellular environment of an organism under both physiological and stress conditions may be attributed to its multivalent or totipotent properties, and can now be substantiated by the availability of modern molecular techniques. As opposed to pharmacologically manufactured or synthetic drugs, which provide a single target for a single receptor as the mechanism of action, EGb 761 is able to up- or down-regulate signaling pathways, gene transcription, cellular metabolism, etc., and thus assist in the regulation of the general physiological status of the cell and/or organism in response to stressors posed by both intracellular and extracellular conditions. Presumably, this is one of the biggest advantages of using natural products for the prevention and treatment of infirmity, as well as the maintenance of health in an organism.
Temperature optima of enzyme-catalysed reactions in microemulsion systems by K. Mlejnek; B. Seiffert; T. Demberg; M. Kämper; M. Hoppert (pp. 473-480).
Ternary phase systems (water/surfactant/organic solvent) were utilised to increase and broaden the temperature optima of enzyme-catalysed reactions. Alcohol dehydrogenases from yeast and Thermoanaerobium brockii (EC 1.1.1.1 and EC 1.1.1.2), lactate dehydrogenase from Lactobacillus delbrueckii (EC 1.1.1.28) and the particulate hydrogenase from Ralstonia eutropha (EC 1.18.99.1) were used as model enzymes in microemulsions, consisting of the surfactant Aerosol OT, and various alkane solvent and aqueous phases. All enzymes exhibited, besides an increase in specific activity, an upshift of the temperature optimum of the catalysed reaction. The temperature optimum could be further shifted by variation of the chain length of the solvent used and/or the addition of compatible solutes to the aqueous phase. Under optimised conditions, catalytic reactions of enzymes from mesophilic microorganisms had temperature optima in the range generally obtained with enzymes from thermophilic organisms.
Enantioselective transesterification using lipase-displaying yeast whole-cell biocatalyst by T. Matsumoto; M. Ito; H. Fukuda; A. Kondo (pp. 481-485).
An enantioselective transesterification in non-aqueous organic solvent was developed by utilizing a lipase-displaying yeast whole cell biocatalyst constructed in our previous study. As a model reaction, optical resolution of (RS)-1-phenylethanol, which serves as one of chiral building blocks, was carried out by enantioselective transesterification with vinyl acetate. Recombinant Rhizopus oryzae lipase displayed on the yeast cell surface retained its activity in hexane, heptane, cyclohexane and octane. The effective amount of whole-cell biocatalyst in the reaction mixture was 10 mg/ml solvent. In a reaction mixture incubated for 36 h with molecular sieves 4A, the concentration of (R)-1-phenylethyl acetate reached 39.8 mM (97.3% yield) with high enantiomeric excess (93.3%ee). In contrast, a reaction mixture incubated without molecular sieves 4A produced little (R)- and (S)-1-phenylethyl acetate. The results obtained in this study demonstrate the applicability of the lipase-displaying yeast whole cell biocatalyst to bioconversion processes in non-aqueous organic solvents.
Biotransformation of halophenols using crude cell extracts of Pseudomonas putida F6 by S. J. Brooks; E. M. Doyle; C. Hewage; J. P. G. Malthouse; W. Duetz; K. E. O’ Connor (pp. 486-492).
Crude cell extracts of Pseudomonas putida F6 transformed 4-substituted fluoro-, chloro-, bromo- and iodo-phenol without the exogenous addition of cofactors. The rate of substrate consumption decreased with increasing substituent size (F>Cl>Br>I). Biotransformations resulted in greater than 95% utilisation of the halogenated substrate. Product accumulation was observed in incubations with 4-chloro, 4-bromo- and 4-iodo-phenol. These products were identified as the corresponding 4-substituted catechols. Transformation of 4-fluorophenol did not result in the accumulation of the corresponding catechol; however, manipulation of the reaction conditions by incorporation of ascorbic acid culminated in the formation of 4-fluorocatechol. Cell extracts of P. putida F6 also showed activity towards a 3-substituted phenol, namely 3-fluorophenol, resulting in the formation of a single product, 4-fluorocatechol.
Investigation of hydroxamic acids as laccase-mediators for pulp bleaching by X. Geng; K. Li; F. Xu (pp. 493-496).
A number of hydroxamic acids have been synthesized and investigated as laccase-mediators for pulp bleaching. As compared with N-hydroxyacetanilide (NHA), one of the most effective laccase-mediators reported so far, N-(4-cyanophenyl)acetohydroxamic acid (NCPA), resulted in the highest brightness and lowest kappa number of hardwood kraft pulp of all the laccase-mediators studied. The bleaching efficacy of a laccase/7-cyano-4-hydroxy-2H-1,4-benzoxazin-3-one system was also comparable with that of a laccase/NHA system. A laccase/NCPA system was further studied for the bleaching of unbleached softwood kraft pulp. The effects of pulp consistency, laccase dosage, NCPA dosage, incubation time, and oxygen pressure on the bleaching efficacy of a laccase/NCPA system were studied.
Diglucosyl-glycerolipids from the marine sponge-associated Bacillus pumilus strain AAS3: their production, enzymatic modification and properties by W. Ramm; W. Schatton; I. Wagner-Döbler; V. Wray; M. Nimtz; H. Tokuda; F. Enjyo; H. Nishino; W. Beil; R. Heckmann; V. Lurtz; S. Lang (pp. 497-504).
The marine strain Bacillus pumilus strain AAS3, isolated from the Mediterranean sponge Acanthella acuta, produced a diglucosyl-glycerolipid, 1,2-O-diacyl-3-[β-glucopyranosyl-(1–6)-β-glucopyranosyl)]glycerol, with 14-methylhexadecanoic acid and 12-methyltetradecanoic acid as the main fatty acid moieties (GGL11). On a 30 l scale, using artificial seawater supplemented with glucose (20 g/l), yeast extract (10 g/l), and suitable nitrogen/phosphate sources, growth-associated glycoglycerolipid production reached its maximum yield of 90 mg/l after 11 h. Lipase-catalyzed modification of the native substance led to the deacylated parent compound (GG11), which could be reacylated using the same enzyme system to afford a new dipentenoyl-diglucosylglycerol (GGL12) as the major product upon addition of 4-pentenoic acid to the medium. GGL11 decreased the surface tension of water from 72 mN/m to 29 mN/m and the interfacial tension of the water/n-hexadecane system from 44 to 5 mN/m. Anti-tumor-promoting studies on this class of diglucosyl glycerol products showed that the carbohydrate/glycerol backbone (GG11) has a more potent inhibitory activity than the acylated compounds. The diglucosyl-glycerol GG11 strongly inhibited growth of the tumor cell lines HM02 and Hep G2 (50% inhibition at ~1 μg/ml), while the glycerolipids GGL11 and GGL12 were less active or had no effect.
Enzymatic properties and nucleotide and amino acid sequences of a thermostable β-agarase from a novel species of deep-sea Microbulbifer by Y. Ohta; Y. Hatada; Y. Nogi; M. Miyazaki; Z. Li; M. Akita; Y. Hidaka; S. Goda; S. Ito; K. Horikoshi (pp. 505-514).
An agar-degrading bacterium, strain JAMB-A7, was isolated from the sediment in Sagami Bay, Japan, at a depth of 1,174 m and identified as a novel species of the genus Microbulbifer. The gene for a novel β-agarase from the isolate was cloned and sequenced. It encodes a protein of 441 amino acids with a calculated molecular mass of 48,989 Da. The deduced amino acid sequence showed similarity to those of known β-agarases in glycoside hydrolase family 16, with only 34–55% identity. A sequence similar to a carbohydrate-binding module was found in the C-terminal region of the enzyme. The recombinant agarase was hyper-produced extracellularly using Bacillus subtilis as the host, and the enzyme purified to homogeneity had a specific activity of 398 U (mg protein)–1 at pH 7.0 and 50°C. It was thermostable, with a half-life of 502 min at 50°C. The optimal pH and temperature for activity were around 7 and 50°C, respectively. The pattern of agarose hydrolysis showed that the enzyme was an endo-type β-agarase, and the final main product was neoagarotetraose. The activity was not inhibited by NaCl, EDTA, and various surfactants at high concentrations. In particular, sodium dodecyl sulfate had no inhibitory effect up to 2%.
Gene expression in Escherichia coli biofilms by D. Ren; L. A. Bedzyk; S. M. Thomas; R. W. Ye; T. K. Wood (pp. 515-524).
DNA microarrays were used to study the gene expression profile of Escherichia coli JM109 and K12 biofilms. Both glass wool in shake flasks and mild steel 1010 plates in continuous reactors were used to create the biofilms. For the biofilms grown on glass wool, 22 genes were induced significantly (p≤0.05) compared to suspension cells, including several genes for the stress response (hslS, hslT, hha, and soxS), type I fimbriae (fimG), metabolism (metK), and 11 genes of unknown function (ybaJ, ychM, yefM, ygfA, b1060, b1112, b2377, b3022, b1373, b1601, and b0836). The DNA microarray results were corroborated with RNA dot blotting. For the biofilm grown on mild steel plates, the DNA microarray data showed that, at a specific growth rate of 0.05/h, the mature biofilm after 5 days in the continuous reactors did not exhibit differential gene expression compared to suspension cells although genes were induced at 0.03/h. The present study suggests that biofilm gene expression is strongly associated with environmental conditions and that stress genes are involved in E. coli JM109 biofilm formation.
Molecular cloning and expression of the pyranose 2-oxidase cDNA from Trametes ochracea MB49 in Escherichia coli by B. Večerek; H. Marešová; M. Kočanová; P. Kyslík (pp. 525-530).
A cDNA of a structural gene encoding pyranose 2-oxidase (P2O) from Trametes ochracea strain MB49 was cloned into Escherichia coli strain BL21(DE3) on a multicopy plasmid under the control of the trc promoter. Synthesis of P2O was studied in batch cultures in LB or M9-based mineral medium at 28°C. While there was a low specific activity of P2O in LB medium, the enzyme was synthesised constitutively in mineral medium and represented 3% of the cell soluble protein (0.3 U mg−1). The effect of isopropyl β-d-thiogalactoside on the expression of P2O was studied in mineral medium at 25 and 28°C. The synthesis of P2O at 28°C corresponded to 39% of the cell soluble protein but the major portion of P2O (93%) was in the form of non-active inclusion bodies (activity of P2O equalled 0.19 U mg−1). At 25°C, the amount of P2O represented 14% of the cell soluble protein and the activity of P2O was 1.1 U mg−1. The soluble enzyme represented 70% of the total amount of P2O.
Heterologous expression of metabotropic glutamate receptor subtype 1 in Saccharomyces cerevisiae by K. Sugiyama; T. P. Niki; K. Inokuchi; Y. Teranishi; M. Ueda; A Tanaka (pp. 531-536).
The upstream region of the isocitrate lyase gene (UPR-ICL) from the n-alkane-utilizing yeast Candida tropicalis serves as a useful promoter of gene expression in the yeast Saccharomyces cerevisiae. The production of rat metabotropic glutamate receptor 1α (mGluR1α), which belongs to the G-protein-coupled receptor (GPCR) family, was tested under the control of UPR-ICL. Expression of mGluR1α was found in recombinant clones and enhanced by replacing the signal sequence of mGluR1α with the corresponding region of the α-factor receptor (Ste2), which is a GPCR found in S. cerevisiae. Moreover, the membrane fraction from a recombinant clone associated with Vesl-1S/Homer-1a protein binds the mGluR1α in rat cerebellum. These results suggest that the UPR-ICL-controlled gene expression system is useful for heterologous GPCRs in S. cerevisiae.
A screening system for antioxidants using thioredoxin-deficient yeast: discovery of thermostable antioxidant activity from Agaricus blazei Murill by S. Izawa; Y. Inoue (pp. 537-542).
Previously, we found that cytosolic thioredoxin is a negative regulator for an oxidative stress responsive transcription factor, Yap1p (yeast AP-1-like transcription factor), i.e., this transcription factor is constitutively concentrated in the nucleus in the thioredoxin-deficient mutant (trx1Δtrx2Δ) due to an impairment of the reactive oxygen species-scavenging activity of this mutant [Izawa et al. (1999) J Biol Chem 274:28459–28465]. Based on these findings, we developed a screening method to discover substances that show antioxidant activity. With this method, antioxidant activity was evaluated by monitoring the subcellular localization of Yap1p. Since Yap1p is oxidized and accumulates in the nucleus in trx1Δtrx2Δ cells, it is easy to identify antioxidant activity by observing the localization of green fluorescent protein (GFP)-tagged Yap1p. If exogenous substances taken in by trx1Δtrx2Δ cells were able to function as antioxidants to reduce the oxidized form of Yap1p, GFP1-Yap1p would diffuse into the cytoplasm. We used this system to screen for antioxidant activity in mushrooms, and found that the edible mushroom Agaricus blazei Murill is an excellent source of antioxidants.
The relative glucose uptake abilities of non-Saccharomyces yeasts play a role in their coexistence with Saccharomyces cerevisiae in mixed cultures by P. Nissen; D. Nielsen; N. Arneborg (pp. 543-550).
The growth and glucose uptake of single cultures of the wine-related yeasts Kluyveromyces thermotolerans, Torulaspora delbrueckii, and Saccharomyces cerevisiae were investigated. The yeasts had different specific glucose uptake rates (q s) that depended on the residual glucose concentration and the oxygen availability. In mixed cultures, the q s values of the yeasts were not subject to any interaction effects over a wide range of glucose concentrations. Our results strongly indicate that the relative glucose uptake abilities of both non-Saccharomyces yeasts, i.e. the q s(non-Saccharomyces)/q s(S. cerevisiae) ratios, regulated their abilities to compete for space in mixed cultures with S. cerevisiae, which, in turn, regulated their early deaths. This hypothesis enabled us to explain why K. thermotolerans was less able than T. delbrueckii to coexist with S. cerevisiae in mixed cultures. Furthermore, it enabled us to explain why oxygen increased the abilities of K. thermotolerans and T. delbrueckii to coexist with S. cerevisiae in the mixed cultures.
An easy method for screening and isolating rod mutants of Bacillus subtilis by S.-H. Cheung; W.-P. Lai; T.-W. Ng; M.-W. Lam; H.-Y. Cheung (pp. 551-555).
A convenient and rapid method for screening and identifying rod mutants of Bacillus subtilis is described. At the restrictive temperature (45 °C), all rod mutants of B. subtilis screened lost their ability to sporulate. The morphology and colour of mutant colonies grown on sporulation agar plates differed from those of rod+ cells, which were able to sporulate even at elevated temperature. These characteristics provide an alternative approach for the identification of rod mutants in B. subtilis culture by streaking the cells onto a minimal glucose agar plate and incubating at the restrictive temperature. After 30 h of incubation at this temperature, rod mutants are easily identified. This method will facilitate the screening and isolation of rod mutants of B. subtilis.
Enzymatic assay for perfluoro-tagged metabolites of l-DOPA using crude lysate from E. coli transformed with pKKAADCII by S. Dingman; T. Snyder-Leiby; D. J. Mack; R. Thomas; C. Guo (pp. 556-559).
Isomers of l-DOPA and dopamine with a nine-atom 19F atom tag were exposed to aromatic acid decarboxylase (AADC) in the lysate of Escherichia coli JM109 that had been transformed with the plasmid pKKAADCII. The resulting samples were analyzed with HPLC. The first study investigated the conversion of the tagged l-DOPA into tagged dopamine, using the tagged dopamine as a standard. A second study was undertaken to identify the source of peaks seen in the enzymatic assays. l-DOPA with the tag bonded at position 5 served as the best substrate for AADC. Isomers that fit into the active site of AADC are likely to follow the biosynthetic path for dopamine in vivo and are potentially useful in magnetic resonance studies. The enzymatic assay described here provides an efficient and cost-effective tool for screening new compounds for use in the fluorine imaging of neural pathways.
Cloning of the pelA gene from Bacillus licheniformis 14A and biochemical characterization of recombinant, thermostable, high-alkaline pectate lyase by S. Berensmeier; S. A. Singh; J. Meens; K. Buchholz (pp. 560-567).
The pectate lyase gene pelA from alkaliphilic Bacillus licheniformis strain 14A was cloned and sequenced. The nucleotide sequence corresponded to an open reading frame of 1,026 bp that codes for a 39 amino acid signal peptide and a mature protein with a molecular mass of 33,451 Da. The mature PelA showed significant homology to other pectate lyases belonging to polysaccharide lyase family 1, such as enzymes from different Bacillus spp. and Erwinia chrysanthemi. The pelA gene was expressed in Escherichia coli as a recombinant fusion protein containing a C-terminal His-tag, allowing purification to near homogeneity in a one-step procedure. The values for the kinetic parameters K m and V max of the fusion protein were 0.56 g/l and 51 µmol/min, respectively. The activity of purified PelAHis was inhibited in the presence of excess substrate. Characterization of product formation revealed unsaturated trigalacturonate as the main product. The yields of unsaturated trigalacturonic acids were further examined for the substrates polygalacturonic acid, citrus pectin and sugar-beet pectin.
Assessment of microbial populations in methyl ethyl ketone degrading biofilters by denaturing gradient gel electrophoresis by C. Li; W. M. Moe (pp. 568-575).
Denaturing gradient gel electrophoresis (DGGE) analysis of polymerase chain reaction-amplified genes coding for 16S rRNA was used to assess differences in bacterial community structure as a function of spatial location along the height of two biofilters used to treat a model waste gas stream containing methyl ethyl ketone (MEK). One of the laboratory-scale biofilters was operated as a conventional continuous-flow biofilter (CFB) and the other was operated as a sequencing batch biofilter (SBB). Both biofilters, inoculated with an identical starting culture and operated over a period lasting more than 300 days, received the same influent MEK concentration and same mass of MEK on a daily basis. The systems differed, however, in terms of the fraction of time during which contaminated air was supplied and the overall operating strategy employed. DGGE analysis indicated that microbial community structures differed as a function of height in each of the biofilters. The DGGE banding patterns also differed between the two biofilters, suggesting that operating strategies imposed on the biofilters imparted a sufficiently large selective pressure to influence microbial community structures. This may explain, in part, the superior performance of the SBB over the CFB during model transient loading conditions, and it may open new possibilities for purposely manipulating the microbial populations in biofilters treating gas-phase contaminants in a manner that leads to more favorable treatment performance.
Intrinsic bioremediability of an aromatic hydrocarbon-polluted groundwater: diversity of bacterial population and toluene monoxygenase genes by L. Cavalca; E. Dell’Amico; V. Andreoni (pp. 576-587).
The functional and phylogenetic biodiversity of bacterial communities in a benzene, toluene, ethylbenzene and xylene (BTEX)-polluted groundwater was analysed. To evaluate the feasibility of using an air sparging treatment to enhance bacterial degradative capabilities, the presence of degrading microorganisms was monitored. The amplification of gene fragments corresponding to toluene monooxygenase (tmo), catechol 1,2-dioxygenase, catechol 2,3-dioxygenase and toluene dioxygenase genes in DNA extracted directly from the groundwater samples was associated with the presence of indigenous degrading bacteria. Five months of air injection reduced species diversity in the cultivable community (as calculated by the Shannon-Weaver index), while little change was noted in the degree of biodiversity in the total bacterial community, as characterised by denaturing gradient gel electrophoresis (DGGE) analysis. BTEX-degrading strains belonged to the genera Pseudomonas, Microbacterium, Azoarcus, Mycobacterium and Bradyrhizobium. The degrading capacities of three strains in batch liquid cultures were also studied. In some of these microorganisms different pathways for toluene degradation seemed to operate simultaneously. Pseudomonas strains of the P24 operational taxonomic unit, able to grow only on catechol and not on BTEX, were the most abundant, and were present in the groundwater community at all stages of treatment, as evidenced both by cultivation approaches and by DGGE profiles. The presence of different tmo-like genes in phylogenetically distant strains of Pseudomonas, Mycobacterium and Bradyrhizobium suggested recent horizontal gene transfer in the groundwater.
Copper dissociation as a mechanism of fungal laccase denaturation by humic acid by Y.-S. Keum; Q. X. Li (pp. 588-592).
Effects of humic acid on removal of hydroxy polychlorobiphenyls (PCBs) with laccase from Trametes versicolor were studied. In the absence of humic acid, hydroxy PCBs were rapidly degraded by laccase. However, the rate constants decreased with increasing humic acid concentration, the reactions being completely inhibited at 150 mg l-1 of humic acid. Peroxidase from Arthromyces ramosus was not inhibited by the same treatment. The activity of humic acid-deactivated laccase was completely restored by copper ions (500 μM of Cu2+ in 150 mg l-1 of humic acid), but not by other metal ions (Zn2+, Fe2+ and Hg2+). Humic acid-deactivated laccase purified by gel permeation chromatography (GPC) showed no activity against 2,2′-azino-bis(3-ethylbenzthiazoline sulfonic acid) diammonium salt and 3,5-dichloro-4-hydroxybiphenyl, but its activity was restored by copper ion treatment. Humic acid-deactivated laccase showed similar properties, such as GPC retention time and copper ion requirements for activity, to those of laccase deactivated by nitrilotriacetic acid. The extent of humic acid inhibition, expressed as activity non-recoverable by copper ion treatment, increased over time more rapidly than that of the humic acid-free control. These results suggest that short-term inactivation of laccase, i.e., less than 1 day, is attributable to a depletion of copper ion.
Initial stages of microbiologically influenced tarnishing on titanium after 20 months of immersion in freshwater by D. A. Moreno; E. Cano; J. R. Ibars; J. L. Polo; F. Montero; J. M. Bastidas (pp. 593-598).
This paper studies the initial stages of iridescent tarnishes on titanium heat exchanger tubes in contact with running freshwater on the river Tagus in Spain for up to 20 months. Electrochemical impedance spectroscopy (EIS), scanning electron microscopy [(SEM with energy dispersive X-ray (EDX)] and X-ray photoelectron spectroscopy (XPS) in conjunction with argon-ion sputtering were the techniques used. The EIS data indicated a capacitive behavior, showing a semicircle that was better defined as the experimental time increased, indicating a decreasing tarnishing resistance of titanium. XPS and EDX results indicated that the main elements identified were calcium, phosphorus, nitrogen, and iron. The amount of these elements was higher on the tarnished titanium specimens than on the untarnished specimens. SEM analysis showed the presence of diatoms in the iridescent tarnishes on titanium tubes.
Chromium and aluminum biosorption on Chryseomonas luteola TEM05 by G. Ozdemir; S. H. Baysal (pp. 599-603).
Cr(VI) and Al(III) are environmental pollutants that are frequently encountered together in industrial wastewaters, e.g., from mining iron-steel, metal cleaning, plating, metal processing, automobile parts, and the manufacturing and dye industries. In this work, several variables that affect the capacity for chromium and aluminum biosorption by Chryseomonas luteola TEM05 were studied, particularly the effects of pH, metal concentration and contact time. Optimum adsorption pH values of Cr(VI) and Al(III) were determined as 4.0 and 5.0, respectively. The biosorption equilibrium was described by Freundlich and Langmuir adsorption isotherms. The value of Q o appears to be significantly higher for the Al(III) C. luteola TEM05 system. Langmuir parameters of C. luteola TEM05 also indicated a maximum adsorption capacity of 55.2 mg g−1 for Al(III) and 3.0 mg g−1 for Cr(VI).
Effect of redox potential on stationary-phase xylitol fermentations using Candida tropicalis
by J. R. Kastner; M. A. Eiteman; S. A. Lee (pp. 604-604).