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Applied Microbiology and Biotechnology (v.58, #6)
Inhibitors of fatty acid synthesis as antimicrobial chemotherapeutics by R. Heath; S. White; C. Rock (pp. 695-703).
Fatty acid biosynthesis is an emerging target for the development of novel antibacterial chemotherapeutics. The dissociated bacterial system is substantially different from the large, multifunctional protein of mammals, and many possibilities exist for type-selective drugs. Several compounds, both synthetic and natural, target bacterial fatty acid synthesis. Three compounds target the FabI enoyl-ACP reductase step; isoniazid, a clinically used antituberculosis drug, triclosan, a widely used consumer antimicrobial, and diazaborines. In addition, cerulenin and thiolactomycin, two fungal products, inhibit the FabH, FabB and FabF condensation enzymes. Finally, the synthetic reaction intermediates BP1 and decynoyl-N-acetyl cysteamine inhibit the acetyl-CoA carboxylase and dehydratase isomerase steps, respectively. The mechanisms of action of these compounds, as well as the potential development of new drugs targeted against this pathway, are discussed.
Biological conversion of cyclic alkanes and cyclic alcohols into dicarboxylic acids: biochemical and molecular basis by Q. Cheng; S. Thomas; P. Rouvière (pp. 704-711).
Biological oxidation of cyclic alkanes and cyclic alcohols normally results in formation of the corresponding dicarboxylic acids, which are further metabolized in the cell. The biochemical pathways for oxidative conversion of cyclic compounds are similar in various phylogenetically diverse bacteria. Significant progress has been made in the past 2 years in the isolation and characterization of genes involved in cyclic alkane oxidation pathways in several bacterial species. In this article, we review recent advancements in the field of cyclic alcohol oxidation with focus on the biochemical and genetic characterization of the gene functions. Phylogenetic relationships of the analogous enzymes in the pathways are analyzed. Potential biocatalysis applications of these enzymes are also discussed.
A continuous lactic acid production system using an immobilized packed bed of Lactobacillus helveticus by M. Tango; A. Ghaly (pp. 712-720).
A 5 l packed bed bioreactor was used to study the effect of initial lactose concentration and hydraulic retention time (HRT) on cell growth, lactose utilization and lactic acid production. Up to 95% of the initial lactose concentration was utilized at longer HRTs (30–36 h). The study showed that lactic acid production increased with increases in HRT (12–36 h) and initial lactose concentrations. The highest lactic acid production rate (3.90 g l–1 h–1) was obtained with an initial lactose concentration of 100 g/l and an HRT of 18 h, whereas the lowest lactic acid production rate (1.35 g l–1 h–1) was obtained with an initial lactose concentration of 50 g/l and an HRT of 36 h. This suggested that optimal lactic acid production can be achieved at an HRT of 18 h and initial lactose concentration of 100 g/l.
Process technological effects of deletion and amplification of hydrophobins I and II in transformants of Trichoderma reesei by M. Bailey; S. Askolin; N. Hörhammer; M. Tenkanen; M. Linder; M. Penttilä; T. Nakari-Setälä (pp. 721-727).
Transformants of the Trichoderma reesei strains QM9414 and Rut-C30 were constructed in which the genes for the two major hydrophobin proteins, hydrophobins I (HFBI) and II (HFBII), were deleted or amplified by molecular biological techniques. Growth parameters and foam production of the transformant strains were compared with the corresponding properties of the parent strains by cultivation in laboratory bioreactors under conditions of catabolite repression (glucose medium) or induction of cellulolytic enzymes and other secondary metabolites (cellulose and lactose media). All the transformed strains exhibited vegetative growth properties similar to those of their parent. The Δ hfb2 (but not the Δ hfb1) transformant showed reduced tendency to foam, whereas both strains overproducing hydrophobins foamed extensively, particularly in the case of HFBII. Enzyme production on cellulose medium was unaltered in the Δ hfb2 transformant VTT D-99676, but both the Δ hfb2 and HFBII-overproducing transformants exhibited somewhat decreased enzyme production properties on lactose medium. Production of HFBI by the multi-copy transformant VTT D-98692 was almost 3-fold that of the parent strain QM9414. Overproduction of HFBII by the transformant VTT D-99745, obtained by transformation with three additional copies of the hfb2 gene under the cbh1 promoter, was over 5-fold compared to production by the parent strain Rut-C30. The Δ hfb2 transformant VTT D-99676 produced a greatly increased number of spores on lactose medium compared with the parent strain, whereas the HFBII-overproducing transformant VTT D-99745 produced fewer spores.
Biocatalytic preparation of enantiopure (R)-ketoprofen from its racemic ester by a new yeast isolate Citeromyces matriensis CGMCC 0573 by P.-F. Gong; H.-Y. Wu; J.-H. Xu; D. Shen; Y.-Y. Liu (pp. 728-734).
The yeast strain CGMCC 0573 was identified as Citeromyces matriensis and shown to be capable of enantioselectively hydrolyzing ethyl ester of (R)-Ketoprofen (2-(3-benzoylphenyl)propionic acid). The strain was isolated for the first time from soil samples through a new and efficient screening procedure in which the probability of obtaining active strains was greatly increased by using ethanol and Tween-80 alternatively as additives during the enrichment culture. Studies of the culture conditions and catalytic performance of Citeromyces matriensis CGMCC 0573 showed that the enzyme occurs constitutively in the cells and its production is enhanced by feeding with Tween-80 during the early period of cultivation. Yeast extract was found to be beneficial both for growth and for esterase production. The optimal temperature and pH for the bioconversion were 40 °C and pH 8.0, respectively. Biotransformation using resting cells cultured in a flask with baffles and magnetic stirring and in the presence of 50 mM substrate resulted in the production of (R)-ketoprofen at 93% ee (enantiomeric excess) and at 42.6% conversion.
A theoretical analysis of the biosynthesis of actinorhodin in a hyper-producing Streptomyces lividans strain cultivated on various carbon sources by P. Bruheim; M. Butler; T. Ellingsen (pp. 735-742).
A stoichiometric equation for the biosynthesis of actinorhodin (ACT) was derived taking into consideration both the requirements of the carbon precursors (acetyl-CoA) and reducing power (NADPH). The estimate for reducing power was derived from a detailed molecular analysis of each step in the ACT biosynthetic pathway. Even though ACT is slightly more oxidized than most carbon substrates, e.g. glucose, reducing power (NADPH and NADH) is necessary due to reducing steps and to monooxygenase steps. The equation was used to evaluate, in a metabolic network context, the experimental results from batch fermentations with eight different carbon sources using a Streptomyces lividans 1326 derived strain containing the pathway-specific activator gene (actII-ORF4) on a multicopy plasmid (pIJ68). The yield of ACT on the various carbon sources ranged from 0.04 to 0.18 Cmol ACT/Cmol carbon source in the stationary phase. Glucose was the best carbon source and supported a yield of 25% of the maximum theoretical yield. There are no obvious constraints in the primary metabolic pathways that can explain why the various carbon sources allowed different levels of ACT production, because their potential for supplying acetyl-CoA and NADPH are far from fully utilized. For the observed ACT yields, there is an excess production of NADPH that has to be reoxidized either by a transhydrogenase or a NADPH oxidase. This study discusses the central metabolic pathways, focusing on providing precursors for ACT synthesis.
Production of canthaxanthin by Haloferax alexandrinus under non-aseptic conditions and a simple, rapid method for its extraction by D. Asker; Y. Ohta (pp. 743-750).
The production of carotenoids from Haloferax alexandrinus strain TMT was investigated at various concentrations of NaCl (10–25%) in culture media under non-aseptic conditions. PCR and dot blot hybridization assays were employed to monitor the growth of Hfx. alexandrinus in the culture under aseptic and non-aseptic conditions. The amplified PCR products of 16S rDNA from Hfx. alexandrinus grown under aseptic conditions were used as specific probes, which bound with amplified PCR products of 16S rDNA dots from both aseptic and non-aseptic conditions (20–25% NaCl). The results indicated that contamination of the culture was precluded at high NaCl concentrations (20–25%). Therefore, it is not necessary to perform asepsis during the biotechnological processes of carotenoid production by Hfx. alexandrinus. A 1-l-scale cultivation of the cells in flask cultures under non-aseptic conditions produced 3.12±0.5 g dry weight, 6.34±2.5 mg total carotenoids and 2,156.67±0.1 µg canthaxanthin. Further experiments in a batch fermenter, under non-aseptic conditions, also demonstrated increases in the biomass concentration and carotenoid production. When grown in a standard growth medium at 25% NaCl, the cells of Hfx. alexandrinus lysed spontaneously in fresh water and hence carotenoids could be extracted directly from the cells without any mechanical disintegration. These results demonstrate the feasibility and simplicity of commercial production of carotenoids using Hfx. alexandrinus.
Enhancement of entomopathogenic nematode production in in-vitro liquid culture of Heterorhabditis bacteriophora by fed-batch culture with glucose supplementation by G. Gil; H. Choo; R. Gaugler (pp. 751-755).
Nematode yield is a decisive factor for successful large-scale commercial production of entomopathogenic nematode. Various carbon sources were tested in in-vitro liquid culture to improve the yield of the entomopathogenic nematode Heterorhabditis bacteriophora. Canola oil was the optimal carbon source for nematode culture compared to carbohydrates when applied as a sole carbon source. However, when some of carbohydrates were applied together with canola oil, significant increases in nematode yield were observed. When 25 mg glucose ml–1 was supplemented to 25 mg oil-based liquid culture medium ml–1, the highest nematode yield, 3.62×105 infective juveniles, was achieved at 12 days, but nematode growth was suppressed at higher than 75 mg glucose ml–1. A fed-batch culture process was introduced in nematode liquid culture consisting of two growth phases: bacteria and nematode. In the oil fed-batch culture, in which only glucose was initially added and oil was fed to the culture after the bacterial growth phase concurrent with nematode inoculation, nematode yield increased up to 4.25×105 infective juveniles ml–1, while the batch culture resulted in 3.60×105 infective juveniles ml–1. These results indicate that glucose is a superior carbon source for the bacteria, whereas canola oil is optimal for the nematode. The application of fed-batch culture provides significant enhancement of nematode yield in in-vitro liquid culture.
Inclusion of solid particles in bacterial cellulose by G. Serafica; R. Mormino; H. Bungay (pp. 756-760).
Depending upon the strain and the method of cultivation, bacterial cellulose can be reticulated filaments, pellets, or a dense, tough gel called a pellicle. The pellicular form is commonly made by surface culture, but a rotating disk bioreactor is more efficient and reduces the time of a run to about 3.5 days instead of the usual 12–20 days. Particles added to the medium as the gel is forming are trapped to form a new class of composite materials. Particles enter the films that are forming on the disks at rates depending on the size and geometry of the particle, as well as the rotational speed and concentration of the suspension.
Xylanase production in solid state fermentation by Aspergillus niger mutant using statistical experimental designs by Y. Park; S. Kang; J. Lee; S. Hong; S. Kim (pp. 761-766).
The initial moisture content, cultivation time, inoculum size and concentration of basal medium were optimized in solid state fermentation (SSF) for the production of xylanase by an Aspergillus niger mutant using statistical experimental designs. The cultivation time and concentration of basal medium were the most important factors affecting xylanase activity. An inoculum size of 5×105 spores/g, initial moisture content of 65%, cultivation time of 5 days and 10 times concentration of basal medium containing 50 times concentration of corn steep liquor were optimum for xylanase production in SSF. Under the optimized conditions, the activity and productivity of xylanase obtained after 5 days of fermentation were 5,071 IU/g of rice straw and 14,790 IU l–1 h–1, respectively. The xylanase activity predicted by a polynomial model was 5,484 IU/g of rice straw.
Cloning, sequencing and overexpression of a Sinorhizobium meliloti M5N1CS carboxymethyl-cellulase gene by P. Michaud; A. Belaich; B. Courtois; J. Courtois (pp. 767-771).
The EndS encoding sequence was isolated from Sinorhizobium meliloti M5N1CS DNA. Comparisons between the deduced amino acid sequence of the mature EndS (337 amino acids, molecular mass 36,418 Da, isoelectric point 4.92) and those of published β-glycanases showed that this enzyme belongs to family 5 of the glycoside hydrolases. The protein was overproduced in Escherichia coli using a T7 expression system. When the purified overexpressed EndS protein was tested on cellulose-type components, the best substrate was CM-cellulose.
Gene cloning, overexpression and biochemical characterization of the peptide amidase from Stenotrophomonas maltophilia by S. Neumann; M.-R. Kula (pp. 772-780).
The peptide amidase (Pam) from the gram-negative bacterium Stenotrophomonas maltophilia catalyzes predominantly the hydrolysis of the C-terminal amide bond in peptide amides. Its gene (pam) was isolated by Southern hybridization using a DNA probe derived from the known N-terminal amino acid sequence. Pam is a member of the amidase signature family and was identified as a periplasmic protein by an N-terminal signal peptide found in the gene. The processed protein consists of 503 amino acids with a molecular mass of 53.5 kDa. The recombinant enzyme with a C-terminal His6 tag has a monomeric structure and its isoelectric point is 6.3. The dipeptide amide L-Ala-L-Phe-NH2 is hydrolyzed in the absence of cofactors to L-Ala-L-Phe-OH and ammonia with V max=194 U/mg and K m <0.5 mM. The natural function of Pam remains unclear. Chymostatin (K i<0.3 µM) and Pefabloc SC (K i not determined) were identified as inhibitors. When the gene was expressed in Escherichia coli on a 12-l scale, the specific activity in the crude extract was 60 U/mg, compared to 0.24 U/mg in S. maltophilia. In the expression system, Pam made up about 31% of the total soluble cell protein. From 75 g wet cells, 2.1 g of >95% pure enzyme was obtained, which corresponds to a total activity of 416,000 units.
Identification of two gene clusters involved in cyclohexanone oxidation in Brevibacterium epidermidis strain HCU by P. Brzostowicz; M. Blasko; P. Rouvière (pp. 781-789).
Brevibacterium epidermidis HCU can grow on cyclic ketones and alcohols as a sole carbon source. We have previously reported the identification of two cyclohexanone-induced Bayer-Villiger monooxygenase genes by mRNA differential display. Using the related technique of Out-PCR, we have amplified large DNA fragments flanking the two monooxygenase genes. Two large gene clusters were sequenced. Several ORFs in each gene cluster encoded proteins homologous to cyclohexanol and cyclohexanone oxidation enzymes from Acinetobacter. However, the structure of these two gene clusters differs significantly from that of Acinetobacter, where the complete pathway has been described. To assess activity of these genes, they were cloned and expressed in Escherichia coli. In vivo and in vitro assays enabled us to assign functions to the expressed ORFs. These ORFs included a cyclohexanol dehydrogenase, two different ε-caprolactone hydrolases and two 6-hydroxyhexanoate dehydrogenases belonging to different enzyme families. Because this environmental isolate is difficult to manipulate, we cannot determine at this time which cluster is involved in the degradation of cyclohexanone under physiological conditions. However, the original differential display experiments and some of the experiments reported here suggest the involvement of both gene clusters in the oxidation of cyclic ketones.
Enhanced expression of tandem multimers of the antimicrobial peptide buforin II in Escherichia coli by the DEAD-box protein and trxB mutant by J. Lee; M. Kim; J. Cho; S. Kim (pp. 790-796).
The tandem multimeric expression of various peptides has been explored by many researchers. However, expression levels have usually not been proportional to the degree of multimerization. To increase the expression level in Escherichia coli of tandem multimers of a cationic antimicrobial peptide, buforin II, fused to an anionic peptide, we studied the effect of the DEAD-box protein and the trxB mutant on the expression of tandem multimers. An expression vector with a tac promoter was more effective in directing multimeric expression than one with a T7 promoter. The expression level of large multimers was substantially increased with the tac promoter, possibly through stabilization of long transcripts by synchronization of transcription and translation. Coexpression of the DEAD-box protein, an RNA-binding protein, with the T7 expression system increased the expression level of multimers, especially large multimers, due to protection of the long RNA transcripts. In addition, the use of the trxB mutant also enhanced the expression level of tandem multimers, which contain two cysteine residues at both ends of the monomeric unit. It seems that disulfide bonds formed in the multimers in the trxB mutant might help efficient charge neutralization for inclusion body formation of the multimers, resulting in enhancement of expression. Our results show that the expression of multimers can be improved through the stabilization of the long transcripts by the DEAD-box protein or the expression, under an oxidizing environment, of the trxB mutant in which covalent cross-links through disulfide bonds facilitate inclusion body formation of the multimeric fusion peptide.
Single-step co-integration of multiple expressible heterologous genes into the ribosomal DNA of the methylotrophic yeast Hansenula polymorpha by J. Klabunde; A. Diesel; D. Waschk; G. Gellissen; C. Hollenberg; M. Suckow (pp. 797-805).
We have investigated the methylotrophic yeast Hansenula polymorpha as a host for the co-integration and expression of multiple heterologous genes using an rDNA integration approach. The ribosomal DNA (rDNA) of H. polymorpha was found to consist of a single rDNA cluster of about 50–60 repeats of an 8-kb unit located on chromosome II. A 2.4-kb segment of H. polymorpha rDNA encompassing parts of the 25S, the complete 5S and the non-transcribed spacer region between 25S and 18S rDNA was isolated and inserted into conventional integrative H. polymorpha plasmids harboring the Saccharomyces-cerevisiae-derived URA3 gene for selection. These rDNA plasmids integrated homologously into the rDNA repeats of a H. polymorpha (odc1) host as several independent clusters. Anticipating that this mode of multiple-cluster integration could be used for the simultaneous integration of several distinct rDNA plasmids, the host strain was co-transformed with a mixture of up to three different plasmids, all bearing the same URA3 selection marker. Transformations indeed resulted in mitotically stable strains harboring one, two, or all three plasmids integrated into the rDNA. The overall copy number of the plasmids integrated did not exceed the number of rDNA repeats present in the untransformed host strain, irrespective of the number of different plasmids involved. Strains harboring different plasmids co-expressed the introduced genes, resulting in functional proteins. Thus, this approach provides a new and attractive tool for the rapid generation of recombinant strains that simultaneously co-produce several proteins in desired stoichiometric ratios.
Screening of a molecule endowing Saccharomyces cerevisiae with n-nonane-tolerance from a combinatorial random protein library by W. Zou; M. Ueda; A. Tanaka (pp. 806-812).
A combinatorial random protein library was constructed from random DNA fragments generated by "DNA random priming", an improved method of "random-priming recombination" using random-sequence primers and template cDNA from the yeast Saccharomyces cerevisiae. In order to express this library on the yeast cell surface, a yeast multicopy cassette vector was constructed, in which the random-protein-encoding DNA fragments were fused to a gene encoding the C-terminal 320 amino acids of α-agglutinin. Fluorescent labeling of the immuno-reaction of RGS(His)6 epitope confirmed the surface display of random proteins. The surface display of heterologous random proteins on yeast cells will have a wide application. As an example, an n-nonane-tolerant yeast strain that could grow very well in nonane-overlaid culture medium was screened out from transformants displaying this combinatorial library. n-Nonane tolerance was dependent on the transformed plasmid, and the related protein was confirmed to localize on the cell surface by papain treatment and immunofluorescent labeling. Analysis of this displayed protein was also carried out. This strain is the first one to have been endowed artificially with organic solvent tolerance. This is a good example of creating cells exhibiting new phenotypes using a combinatorial protein library.
Integration of the information from gene expression and metabolic fluxes for the analysis of the regulatory mechanisms in Synechocystis by C. Yang; Q. Hua; K. Shimizu (pp. 813-822).
Synechocystis was grown under autotrophic, mixotrophic and heterotrophic conditions, and the gene expression patterns at the mRNA and protein levels were measured by using semi-quantitative RT-PCR and two-dimensional electrophoresis (2DE), respectively. Moreover, the intracellular metabolic flux distributions in Synechocystis grown under different trophic conditions were also determined using the carbon isotope labeling technique. By combining the information obtained from the transcript levels, protein abundance and metabolic fluxes, the regulatory mechanisms of some enzymes involved in the central metabolism of Synechocystis during growth in the different culture conditions were analyzed. It was found that depending on the energy source available to cyanobacterial cells, the enzymes required for central metabolism were differently regulated according to different mechanisms. The expression of several genes, such as rbcLS and gap2, was light-regulated transcriptionally, while the gene gnd was regulated in response to an apparent flux requirement but by an unknown mechanism. The expression of other genes was independent of the presence of light. The reactions catalyzed by G6PDH, Fbp, PfkA and FbaA were not regulated through enzyme synthesis but by a change in metabolite concentrations. The enzyme PrK was post-translationally regulated by light, probably through the operation of ferredoxin/thioredoxin system. For the enzyme RubisCO, both transcriptional and post-translational regulation was observed. These findings demonstrate that the information obtained from the analysis of mRNA expression, protein expression, and metabolic flux distribution is necessary to understand the regulatory events in complex cellular networks.
Reconstruction of the biomass history from carbon and nitrogen substrate consumption, ammonia release and proton transfer during solid cultures of Geotrichum candidum and Penicillium camembertii by M. Aldarf; A. Amrane; Y. Prigent (pp. 823-829).
Geotrichum candidum and Penicillium camembertii were cultivated on the surface of a gelified medium, simulating the composition of the aqueous phase of a Camembert cheese. The relation of their growth with substrate consumption (carbon or nitrogen), metabolite production (ammonia), or proton transfer (deduced from pH by means of the buffer capacity of the medium) was examined. The coefficients associated with cellular biosynthesis and resulting from cellular maintenance were determined. From these coefficients and the considered substrate utilization or metabolite production kinetics, the growth kinetics were reconstructed until the end of growth. The model allowed analysis of biosynthesis and cellular maintenance contributions to the considered kinetics. At the end of growth, almost all the peptone was used for G. candidum biosynthesis, while most of the lactic acid (62%) was used for cellular maintenance. P. camembertii metabolized fewer amino acids as carbon sources, resulting in use of peptone for maintenance (12%), and lactic acid (80%) for cell biosynthesis. For both microorganisms, ammonia production was growth-associated, since this production resulted from the deamination of carbon- and nitrogen-source amino acids, in close relation with peptone consumption.
Phototrophic transformation of phenol to 4-hydroxyphenylacetate by Rhodopseudomonas palustris by U. Noh; S. Heck; F. Giffhorn; G.-W. Kohring (pp. 830-835).
Newly isolated and culture collection strains of Rhodopseudomonas palustris were able to transform phenol to 4-hydroxyphenylacetate under phototrophic conditions in the presence of acetate, malate, benzoate, or cinnamate as growth substrates. The reaction was examined with uniformly 14C-labelled phenol and the product was identified by HPLC retention time, UV-scans, and 1H- and 13C-NMR analysis. The transformation reaction was detectable in cell-free extracts in the presence of NAD+ and acetyl-CoA. For further degradation of 4-hydroxyphenylacetate by R. palustris, low partial pressures of oxygen were essential, presumably for aerobic aromatic ring fission reactions by mono- and di-oxygenases.
Viability and release of complexing compounds during accumulation of heavy metals by a brewer's yeast by E. Soares; A. Duarte; R. Boaventura; H. Soares (pp. 836-841).
Saccharomyces cerevisiae NCYC 1190 cells accumulated (after 1 h) lead and cadmium at similar levels, and to a lesser degree also copper. During heavy metal accumulation, there was a considerable loss of viability of copper-treated cells (about 99% in the first 20 min of contact with the metal), and a less pronounced lethal effect on cadmium- and lead-treated cells (about 66% and 46% after 1 h of contact with cadmium or lead, respectively) was detected. During copper accumulation, a leakage of UV-absorbing compounds and inorganic phosphate was observed; this did not occur with lead, whereas with cadmium a small amount of leakage of inorganic phosphate was detected. The filtrates of copper-treated cells contained copper-binding molecules. The copper-binding capacity of the filtrates increased with time according to the release of inorganic phosphate and UV-absorbing compounds. These compounds can bind an appreciable quantity of metal ions, making them unavailable for cell uptake and thus reducing the efficiency of heavy metals removal by yeast cells.
Oxidative stress response of Kluyveromyces marxianus to hydrogen peroxide, paraquat and pressure by R. Pinheiro; I. Belo; M. Mota (pp. 842-847).
The aim of this work was to study the oxidative stress response of Kluyveromyces marxianus to hydrogen peroxide (50 mM), paraquat (1 mM), an increase in air pressure (120 kPa, 600 kPa) and pure oxygen pressure (120–600 kPa) in a pressurized bioreactor. The effect of these oxidants on metabolism and on the induction of antioxidant enzymes was investigated. The exposure for 1 h of K. marxianus at exponential growth phase with either H2O2 or paraquat, under air pressure of 120 kPa or 600 kPa, induced an increase in both superoxide dismutase (SOD) and glutathione reductase (GR) content. SOD induction by the chemical oxidants was independent of the air pressure values used. A 2-fold increase in SOD activity was observed after 1 h of exposure to H2O2 and a 3-fold increase was obtained by the presence of paraquat, with both air pressures studied. In contrast, GR activity was raised 1.7-fold by the exposure to both chemicals with 120 kPa, but a 2.4-fold GR induction was obtained with 600 kPa. As opposed to Saccharomyces cerevisiae, catalase was not induced and was even lower than the normal basal levels. This antioxidant enzyme seemed to be inhibited under increasing oxygen partial pressure. The cells showed a significant increase in SOD and GR activity levels, 4.7-fold and 4.4-fold, when exposed for 24 h to 120 kPa pure oxygen pressure. This behaviour was even more patent with 400 kPa. However, whenever cells were previously exposed to low air pressures, low enzymatic activity levels were measured after subsequent exposure to pure oxygen pressure.
Biodegradation of triazine herbicides on polyvinylalcohol gel plates by the soil yeast Lipomyces starkeyi by K. Nishimura; M. Yamamoto; T. Nakagomi; Y. Takiguchi; T. Naganuma; Y. Uzuka (pp. 848-852).
The soil yeast Lipomyces starkeyi was tested for its ability to degrade triazine herbicides. Polyvinylalcohol (PVA) was employed as a solid medium in culture plates instead of agar. The cell sizes of the control (without nitrogen source) on the PVA gel plate were much smaller than those on the agar gel plate. The difference between the diameters of the sample and control colonies on the PVA gel plate were almost twice those of the colonies on the agar gel plate (1.9 and 1.0 mm, respectively). Thus, the PVA gel plate is much better than the agar plate for evaluating the degree of utilization of a sole nitrogen source. The yeast grew well (more than 4 mm in diameter) with 1,3,5-triazine or cyanuric acid as nitrogen source. In addition, melamine and thiocyanuric acid inhibited growth of the yeast, and the sizes of colonies were smaller than those of the control. All triazine herbicides tested (simazine, atrazine, cyanazine, ametryn, and prometryn) could be degraded and assimilated by L. starkeyi.
Biodegradation of phenol in synthetic and industrial wastewater by Rhodococcus erythropolis UPV-1 immobilized in an air-stirred reactor with clarifier by M. Prieto; A. Hidalgo; C. Rodríguez-Fernández; J. Serra; M. Llama (pp. 853-860).
Phenol biodegradation by suspended and immobilized cells of Rhodococcus erythropolis UPV-1 was studied in discontinuous and continuous mode under optimum culture conditions. Phenol-acclimated cells were adsorbed on diatomaceous earth, where they grew actively forming a biofilm of short filaments. Immobilization protected cells against phenol and resulted in a remarkable enhancement of their respiratory activity and a shorter lag phase preceding active phenol degradation. Under optimum operation conditions in a laboratory-scale air-stirred reactor, the immobilized cells were able to completely degrade phenol in synthetic wastewater at a volumetric productivity of 11.5 kg phenol m–3 day–1. Phenol biodegradation was also tested in two different industrial wastewaters (WW1 and WW2) obtained from local resin manufacturing companies, which contained both phenols and formaldehyde. In this case, after wastewater conditioning (i.e., dilution, pH, nitrogen and phosphorous sources and micronutrient amendments) the immobilized cells were able to completely remove the formaldehyde present in both waters. Moreover, they biodegraded phenols completely at a rate of 0.5 kg phenol m–3 day–1 in the case of WW1 and partially (but at concentrations lower than 50 mg l–1) at 0.1 and 1.0 kg phenol m–3 day–1 in the cases of WW2 and WW1, respectively.