Forgot your password?
New user?
New Window Opens on the Secret Life of Microbes: Scientists Develop First Microbial Profiles of Ecosystems
CAS announces the release of SciFinder Scholar for Mac OS X
Press Releases
Press Releases
| Check out our New Publishers' Select for Free Articles |
Applied Microbiology and Biotechnology (v.61, #5-6)
Industrial production of β-lactam antibiotics by R. P. Elander (pp. 385-392).
The industrial production of β-lactam antibiotics by fermentation over the past 50 years is one of the outstanding examples of biotechnology. Today, the β-lactam antibiotics, particularly penicillins and cephalosporins, represent the world's major biotechnology products with worldwide dosage form sales of ~US$ 15 billion or ~65% of the total world market for antibiotics. Over the past five decades, major improvements in the productivity of the producer organisms, Penicillium chrysogenum and Acremonium chrysogenum (syn. Cephalosporium acremonium) and improved fermentation technology have culminated in enhanced productivity and substantial cost reduction. Major fermentation producers are now estimated to record harvest titers of 40–50 g/l for penicillin and 20–25 g/l for cephalosporin C. Recovery yields for penicillin G or penicillin V are now >90%. Chemical and enzymatic hydrolysis process technology for 6-aminopenicillanic acid or 7-aminocephalosporanic acid is also highly efficient (~80–90%) with new enzyme technology leading to major cost reductions over the past decade. Europe remains the dominant manufacturing area for both penicillins and cephalosporins. However, due to ever increasing labor, energy and raw material costs, more bulk manufacturing is moving to the Far East, with China, Korea and India becoming major production countries with dosage form filling becoming more dominant in Puerto Rico and in Ireland.
Catabolism of hydroxyacids and biotechnological production of lactones by Yarrowia lipolytica by Y. Waché; M. Aguedo; J.-M. Nicaud; J.-M. Belin (pp. 393-404).
The γ- and δ-lactones of less than 12 carbons constitute a group of compounds of great interest to the flavour industry. It is possible to produce some of these lactones through biotechnology. For instance, γ-decalactone can be obtained by biotransformation of methyl ricinoleate. Among the organisms used for this bioproduction, Yarrowia lipolytica is a yeast of choice. It is well adapted to growth on hydrophobic substrates, thanks to its efficient and numerous lipases, cytochrome P450, acyl-CoA oxidases and its ability to produce biosurfactants. Furthermore, genetic tools have been developed for its study. This review deals with the production of lactones by Y. lipolytica with special emphasis on the biotransformation of methyl ricinoleate to γ-decalactone. When appropriate, information from the lipid metabolism of other yeast species is presented.
Phytoremediation: an overview of metallic ion decontamination from soil by O. V. Singh; S. Labana; G. Pandey; R. Budhiraja; R. K. Jain (pp. 405-412).
In recent years, phytoremediation has emerged as a promising ecoremediation technology, particularly for soil and water cleanup of large volumes of contaminated sites. The exploitation of plants to remediate soils contaminated with trace elements could provide a cheap and sustainable technology for bioremediation. Many modern tools and analytical devices have provided insight into the selection and optimization of the remediation process by plant species. This review describes certain factors for the phytoremediation of metal ion decontamination and various aspects of plant metabolism during metallic decontamination. Metal-hyperaccumulating plants, desirable for heavily polluted environments, can be developed by the introduction of novel traits into high biomass plants in a transgenic approach, which is a promising strategy for the development of effective phytoremediation technology. The genetic manipulation of a phytoremediator plant needs a number of optimization processes, including mobilization of trace elements/metal ions, their uptake into the root, stem and other viable parts of the plant and their detoxification and allocation within the plant. This upcoming science is expanding as technology continues to offer new, low-cost remediation options.
Emerging water-borne pathogens by S. Sharma; P. Sachdeva; J. S. Virdi (pp. 424-428).
Emerging water-borne pathogens constitute a major health hazard in both developed and developing nations. A new dimension to the global epidemiology of cholera—an ancient scourge—was provided by the emergence of Vibrio cholerae O139. Also, water-borne enterohaemorrhagic Escherichia coli (E. coli O157:H7), although regarded as a problem of the industrialized west, has recently caused outbreaks in Africa. Outbreaks of chlorine-resistant Cryptosporidium have motivated water authorities to reassess the adequacy of current water-quality regulations. Of late, a host of other organisms, such as hepatitis viruses (including hepatitis E virus), Campylobacter jejuni, microsporidia, cyclospora, Yersinia enterocolitica, calciviruses and environmental bacteria like Mycobacterium spp, aeromonads, Legionella pneumophila and multidrug-resistant Pseudomonas aeruginosa have been associated with water-borne illnesses. This review critically examines the potential of these as emerging water-borne pathogens. It also examines the possible reasons, such as an increase in the number of immunocompromised individuals, urbanization and horizontal gene transfer, that may underlie their emergence. Further, measures required to face the challenge posed by these pathogens are also discussed.
Silica–alginate composites for microencapsulation by T. Coradin; N. Nassif; J. Livage (pp. 429-434).
Optimisation of membrane properties of alginate microcapsules is a key factor for the application of microencapsulation techniques to bioartificial organ elaboration. Coacervation and layer-by-layer processes involving additional biopolymers have been extensively studied. Recently, the use of silica as a membrane-forming agent was investigated. This approach was rendered possible by the development of biocompatible routes to silica formation. The composites exhibit enhanced mechanical and thermal stability as well as suitable diffusion properties. Moreover, encapsulated enzymes and cells retain their biological activities. Similarly, silica can be associated to many other biopolymers, opening a promising route for new biocomposites design and biotechnology applications.
Biotechnological solubilization of rock phosphate on media containing agro-industrial wastes by N. Vassilev; M. Vassileva (pp. 435-440).
Rock phosphate (RP) is an important natural material traditionally used for the production of phosphorus (P) fertilizers. Compared with chemical treatment, microbial solubilization of RP is an alternative environmentally mild approach. An overview of biotechnological techniques, mainly based on solubilization processes involving agro-industrial residues, is presented. Potential advantages of composting, solid-state fermentation, and liquid submerged fermentation employing free and immobilized microorganisms that produce organic acids and simultaneously solubilize RP are discussed. Subsequent introduction of the final fermented products into soil-plant systems promotes plant growth and P acquisition.
A novel process for the production of a veterinary rabies vaccine in BHK-21 cells grown on microcarriers in a 20-l bioreactor by H. Kallel; S. Rourou; S. Majoul; H. Loukil (pp. 441-446).
We studied BHK-21 cells growth in a 2-l bioreactor and investigated the effects of microcarrier concentration, type of growth medium, culture mode and serum concentration. The highest cell density reached was equal to 4×106 cells/ml and was achieved in minimum essential medium supplemented with Hanks' salts, non-essential amino acids and 5% fetal calf serum, using a perfusion culture mode and a microcarrier concentration of 4 g Cytodex 3/l. We studied rabies virus production (PV/BHK-21 strain) by BHK-21 cells grown at the optimal conditions determined previously. We analyzed the effects of multiplicity of infection (MOI) and type of medium used for virus multiplication in spinner-flasks and showed that the highest virus titer reached (when the cells were infected at a MOI of 0.3) in M199 medium supplemented with 0.2% of bovine serum albumin was equal to 8.2×107 Fluorescent Focus Units (FFU)/ml. When we grew the cells in a 2-l perfused bioreactor, we obtained a maximal virus titer of 3×108 FFU/ml. In addition, we scaled-up to a 20-l bioreactor and obtained similar results for cell density and virus titer. The experimental vaccine we developed meets WHO requirements for vaccine potency. Each run yielded about 40,000 doses of potent vaccine.
Effect of electrical stimulation on HIV-1-infected HeLa cells cultured on an electrode surface by M. Tominaga; E. Kumagai; S. Harada (pp. 447-450).
Acquired immunodeficiency syndrome (AIDS) is a disease caused by infection with the human immunodeficiency virus (HIV). Although drug therapy for AIDS is available, problems such as side effects associated with drug therapy and the appearance of resistant HIV strains have arisen. Therefore, therapies based on new principles other than drug treatment are required. In the present study, the effect of electrical stimulation on HIV-1LAI chronically infected HeLa (P6 HeLa/HIV-1LAI) cells cultured on an electrode surface was examined. The results indicated that sensitivity to electrical stimulation was much higher in P6 HeLa/HIV-1LAI cells than in uninfected p6 HeLa cells. When electrical stimulation was applied at 1.0 V (vs. Ag/AgCl) for 20 min, the proportion of damage to cell membrane among P6 HeLa/HIV-1LAI cells, as evaluated by Trypan blue staining, was approximately 4 times higher than that for uninfected P6 HeLa cells. Furthermore, in comparison with uninfected P6 HeLa cells, the proliferation of P6 HeLa/HIV-1LAI cells was significantly suppressed after electrical stimulation. This technique was proven to selectively kill P6 HeLa/HIV-1LAI cells, when compared with uninfected control cells.
Nutrient regulation of epothilone biosynthesis in heterologous and native production strains by R. Regentin; S. Frykman; J. Lau; H. Tsuruta; P. Licari (pp. 451-455).
Fermentation media with different initial concentrations of ammonium and phosphate salts were used to study the inhibitory effects of those ions on growth and production of epothilone in Sorangium cellulosum and Myxococcus xanthus. The native epothilone producer, S. cellulosum was more sensitive to ammonium and phosphate than the heterologous producer, M. xanthus. An ammonium concentration of 12 mM reduced epothilone titers by 90% in S. cellulosum but by only 40% in M. xanthus. When 5 mM phosphate was added to the medium, production in both strains was 60% lower. Higher phosphate concentrations had little additional effect on M. xanthus titers, but epothilone production with 17 mM extra-cellular phosphate in S. cellulosum was 95% lower than in the control condition. The effect of iron supplementation to the fermentation medium was also investigated. Both strains showed best production with 20 μM iron added to the medium.
Optimization of the extracellular production of a bacterial phytase with Escherichia coli by using different fed-batch fermentation strategies by S. Kleist; G. Miksch; B. Hitzmann; M. Arndt; K. Friehs; E. Flaschel (pp. 456-462).
The extracellular production of Escherichia coli phytase was studied in fed-batch fermentations. Two different feeding strategies were compared: control by keeping the glucose concentration constant, and control by keeping a low constant oxygen level in the medium. For the feeding control based on glucose concentration, a recently developed rapid glucose controlling system was tested for the first time in bacterial cultivations and used to establish the fermentative production of extracellular phytase with E. coli. High activity levels (120 U ml−1) at short cultivation times (14 h) were obtained. Even higher activity levels—albeit at longer cultivation times—were reached by applying a feeding control, the main characteristic of which was a constant low oxygen concentration. The optimum oxygen level for the production of phytase was in the range of 5–10% saturation.
Purification, characterization, and molecular cloning of a novel amine:pyruvate transaminase from Vibrio fluvialis JS17 by J.-S. Shin; H. Yun; J.-W. Jang; I. Park; B.-G. Kim (pp. 463-471).
A transaminase from Vibrio fluvialis JS17 showing activity toward chiral amines was purified to homogeneity and its enzymatic properties were characterized. The transaminase showed an apparent molecular mass of 100 kDa as determined by gel filtration chromatography and a subunit mass of 50 kDa by MALDI-TOF mass spectrometry, suggesting a dimeric structure. The enzyme had an isoelectric point of 5.4 and its absorption spectrum exhibited maxima at 320 and 405 nm. The optimal pH and temperature for enzyme activity were 9.2 and 37°C, respectively. Pyruvate and pyridoxal 5′-phosphate increased enzyme stability whereas (S)-α-methylbenzylamine reversibly inactivated the enzyme. The transaminase gene was cloned from a V. fluvialis JS17 genomic library. The deduced amino acid sequence (453 residues) showed significant homology with ω-amino acid:pyruvate transaminases (ω-APT) from various bacterial strains (80 identical residues with four ω-APTs). However, of 159 conserved residues in the four ω-APTs, 79 were not conserved in the transaminase from V. fluvialis JS17. Taken together with the sequence homology results, and the lack of activity toward β-alanine (a typical amino donor for the ω-APT), the results suggest that the transaminase is a novel amine:pyruvate transaminase that has not been reported to date.
Biochemical characterization and antifungal activity of an endo-1,3-β-glucanase of Paenibacillus sp. isolated from garden soil by T.-Y. Hong; M. Meng (pp. 472-478).
A 44-kDa 1,3-β-glucanase was purified from the culture medium of a Paenibacillus strain with a 28-fold increase in specific activity with 31% recovery. The purified enzyme preferentially catalyzes the hydrolysis of glucans with 1,3-β-linkage and has an endolytic mode of action. The enzyme also showed binding activity to various insoluble polysaccharides including unhydrolyzable substrates such as xylan and cellulose. The antifungal activity of this Paenibacillus enzyme and a previously purified 1,3-β-glucanase from Streptomyces sioyaensis were examined in this study. Both enzymes had the ability to damage the cell-wall structures of the growing mycelia of phytopathogenic fungi Pythium aphanidermatum and Rhizoctonic solani AG-4. Nonetheless, the Paenibacillus enzyme had a much stronger effect on inhibiting the growth of fungi tested.
Esterase EstE from Xanthomonas vesicatoria (Xv_EstE) is an outer membrane protein capable of hydrolyzing long-chain polar esters by D. Talker-Huiber; J. Jose; A. Glieder; M. Pressnig; G. Stubenrauch; H. Schwab (pp. 479-487).
A new esterase gene from Xanthomonas vesicatoria (formerly X. campestris) DSM 50861 was identified, cloned from a chromosomal gene library and overexpressed in Escherichia coli. The corresponding DNA fragment contains an ORF of 1,818 bp, encoding a hydrolase of the GDSL esterase family. A protein of about 67 kDa, named Xv_EstE, was expressed from this fragment. A N-terminal signal peptide was processed under low-expression conditions, yielding a 63-kDa mature protein. The predicted amino acid sequence showed distinct homology to esterases of the GDSL family. Based on homology, a catalytic triad Gly-Asp-Ser could be defined. Amino acid sequence alignments and computer-assisted structure prediction indicated the presence of a carboxyl-terminal β-barrel membrane domain which might facilitate binding of Xv_EstE to the outer membrane. This could be verified by differential cell fractionation experiments, in which Xv_EstE was exclusively found in the outer membrane fraction. Xv_EstE showed preferential hydrolytic activity on short chain (up to C8) and para-substituted nitrophenylesters as substrates. However, only long-chain 1-hydroxy-pyrene-3,6,8-trisulfonic acid (HPTS)-fatty acid esters were hydrolyzed. Xv_EstE was also found to be active on a series of substrates of industrial interest, such as 1-methylprop-2-ynyl acetate, for which an enantioselectivity up to 93% ee could be recognized.
Structure-function study of the amino-terminal stretch of the catalase subunit molecule in oligomerization, heme binding, and activity expression by M. Ueda; H. Kinoshita; S.-I. Maeda; W. Zou; A. Tanaka (pp. 488-494).
Analysis of the protein structure of bovine liver catalase suggested that the N-terminal region containing two α-helices may function as a linker binding to another subunit. The number of amino-acid residues in catalase from the n-alkane-assimilating yeast Candida tropicalis (CTC) is the lowest of any eukaryotic catalase molecule hitherto investigated, and only one helix, corresponding to the helix α2 in bovine liver catalase, is estimated to be present in the same region. In the present study, N-terminal-deleted mutants of CTC were characterized to evaluate the role of the α-helix structure in the N-terminal region. CTCΔ1–4 and CTCΔ1–24, whose N-terminal regions were shortened by four and 24 amino-acid residues, respectively, showed an 80% decrease in specific activity compared to wild-type CTC in spite of containing the same amount of heme as in the wild-type. Polyacrylamide gel electrophoresis under nondenaturing conditions revealed that the mutants contained large amounts of oligomeric forms with molecular masses less than 220 kDa (tetramer assembly). Although the smaller oligomers were found to be bound with heme, only the tetramer exhibited catalase activity in activity staining on nondenaturing gel. CTCΔ1–49, a mutant with deletion of the N-terminal 49 amino-acid residues which contain the conserved helix α2, showed no catalase activity and no heme binding. However, the CD spectrum profiles of CTCΔ1–49, CTCΔ1–4, and CTCΔ1–24 indicated that these mutant subunits could attain secondary conformations similar to that of wild-type CTC, regardless of their binding with heme. From these results, it was concluded that the N-terminal stretch of catalase is significant for complete assembly into active tetramer and that the conserved helix α2, although it has little effect on the formation of the subunit secondary structure, is indispensable not only in assembling tetramer but also in binding heme.
Medium and copy number effects on the secretion of human proinsulin in Escherichia coli using the universal stress promoters uspA and uspB by F. J. M. Mergulhão; G. A. Monteiro; G. Larsson; A. M. Sandén; A. Farewell; T. Nystrom; J. M. S. Cabral; M. A. Taipa (pp. 495-501).
The use of the uspA and uspB promoters (universal stress promoters) for heterologous protein production in Escherichia coli is described. Best results were obtained with a moderate copy number vector (15–60 copies) bearing the uspA promoter, reaching 4.6 mg/g dry cell weight (DCW) of ZZ-proinsulin secreted to the periplasm and 1.9 mg/g DCW secreted to the culture medium. These values are about 1.7-fold higher than those previously reported with the same ZZ fusion tag and the SpA leader peptide showing that these stress promoters are potentially valuable for recombinant protein secretion in E. coli. It is further demonstrated that the use of M9 minimal medium is advantageous for protein secretion as compared to LB rich medium.
Expression of the Aspergillus niger glucose oxidase gene in Saccharomyces cerevisiae and its potential applications in wine production by D. F. Malherbe; M. du Toit; R. R. Cordero Otero; P. van Rensburg; I. S. Pretorius (pp. 502-511).
There is a growing consumer demand for wines containing lower levels of alcohol and chemical preservatives. The objectives of this study were to express the Aspergillus niger gene encoding a glucose oxidase (GOX; β-d-glucose:oxygen oxidoreductase, EC 1.1.3.4) in Saccharomyces cerevisiae and to evaluate the transformants for lower alcohol production and inhibition of wine spoilage organisms, such as acetic acid bacteria and lactic acid bacteria, during fermentation. The A. niger structural glucose oxidase (gox) gene was cloned into an integration vector (YIp5) containing the yeast mating pheromone α-factor secretion signal (MFα1 S) and the phosphoglycerate-kinase-1 gene promoter (PGK1 P) and terminator (PGK1 T). The PGK1 P-MFα1 S-gox-PGK1 T cassette (designated GOX1) was introduced into a laboratory strain (Σ1278) of S. cerevisiae. Yeast transformants were analysed for the production of biologically active glucose oxidase on selective agar plates and in liquid assays. The results indicated that the recombinant glucose oxidase was active and was produced beginning early in the exponential growth phase, leading to a stable level in the stationary phase. The yeast transformants also displayed antimicrobial activity in a plate assay against lactic acid bacteria and acetic acid bacteria. This might be explained by the fact that a final product of the GOX enzymatic reaction is hydrogen peroxide, a known antimicrobial agent. Microvinification with the laboratory yeast transformants resulted in wines containing 1.8–2.0% less alcohol. This was probably due to the production of d-glucono-δ-lactone and gluconic acid from glucose by GOX. These results pave the way for the development of wine yeast starter culture strains for the production of wine with reduced levels of chemical preservatives and alcohol.
Deletion of scbA enhances antibiotic production in Streptomyces lividans by M. J. Butler; E. Takano; P. Bruheim; S. Jovetic; F. Marinelli; M. J. Bibb (pp. 512-516).
Antibiotic production in many streptomycetes is influenced by extracellular γ-butyrolactone signalling molecules. In this study, the gene scbA, which had been shown previously to be involved in the synthesis of the γ-butyrolactone SCB1 in Streptomyces coelicolor A3(2), was deleted from the chromosome of Streptomyces lividans 66. Deletion of scbA eliminated the production of the antibiotic stimulatory activity previously associated with SCB1 in S. coelicolor. When the S. lividans scbA mutant was transformed with a multi-copy plasmid carrying the gene encoding the pathway-specific activator for either actinorhodin or undecylprodigiosin biosynthesis, production of the corresponding antibiotic was elevated significantly compared to the corresponding scbA + strain carrying the same plasmid. Consequently, deletion of scbA may be useful in combination with other strategies to construct host strains capable of improved bioactive metabolite production.
Cloning and sequence analysis of the ces10 gene encoding a Sphingomonas paucimobilis esterase by P. A. Videira; A. M. Fialho; A. R. Marques; P. M. Coutinho; I. Sá-Correia (pp. 517-522).
The ces10 gene of the gellan gum-producing strain Sphingomonas paucimobilis ATCC 31461 was cloned and sequenced. Multi-sequence alignment of the deduced protein indicated that Ces10 belongs to the serine hydrolase family with a potential catalytic triad comprising Ser153 (within the G-X-S-X-G consensus sequence), His75 and Asp125. The mixed block results obtained following pattern search and the low identities detected in a BLAST analysis indicate that Ces10 is significantly different from other characterised bacterial esterases/lipases. Nevertheless, the Ces10 amino acid sequence showed 45% similarity with Rhodococcus sp. heroin esterase and 48% with Bacillus subtilis p-nitrobenzyl esterase. Ces10, with a predicted molecular mass of 30,641 Da, was overproduced in Escherichia coli and purified to homogeneity in a histidine-tagged form. Enzyme assays using p-nitrophenyl-esters (p-NP-esters) with different acyl chain-lengths as the substrate confirmed the anticipated esterase activity. Ces10 exhibited a marked preference for short-chain fatty acids, yielding the highest activity with p-NP-propionate (optimal pH 7.4, optimal temperature 37 °C).
Host-vector system for phenol-degrading Rhodococcus erythropolis based on Corynebacterium plasmids by M. Veselý; M. Pátek; J. Nešvera; A. Čejková; J. Masák; V. Jirků (pp. 523-527).
The strain Rhodococcus erythropolis CCM2595, which was shown to degrade phenol, was chosen for genetic studies. To facilitate strain improvement using the methods of gene manipulation, the technique of genetic transfer was introduced and cloning vectors were constructed. Using the plasmid pFAJ2574, an electrotransformation procedure yielding up to 7×104 transformants/μg DNA was optimized. Escherichia coli-R. erythropolis shuttle vectors were constructed using the replicons pSR1 and pGA1 from Corynebacterium glutamicum. The small vector pSRK21 (5.8 kb) provides six unique cloning sites and selection of recombinant clones using α-complementation of β-galactosidase in E. coli. This vector, exhibiting high segregational stability under non-selective conditions in R. erythropolis CCM2595, was applied to cloning and efficient expression of the gene coding for green fluorescent protein (gfpuv).
Functional analyses of genes involved in the metabolism of ferulic acid in Pseudomonas putida KT2440 by R. Plaggenborg; J. Overhage; A. Steinbüchel; H. Priefert (pp. 528-535).
Pseudomonas putida KT2440 is a physiologically extremely versatile non-pathogenic bacterium that is applied as a "biosafety strain" in biotechnological processes, as authorized by the USA National Institute of Health. Analysis of the P. putida KT2440 whole-genome sequence revealed the genetic organization of the genes fcs, ech, and vdh, which are essential for ferulic acid conversion to vanillic acid via vanillin. To confirm the physiological function of these structural genes as feruloyl-CoA synthetase (Fcs), enoyl-CoA hydratase/aldolase (Ech), and vanillin dehydrogenase (Vdh), respectively, they were cloned and expressed in Escherichia coli. Recombinant strains harboring fcs and ech were able to transform ferulic acid to vanillin. The enzyme activities of Fcs and Vdh were determined in protein extracts of these cells. The essential involvement of fcs, ech and vdh in the catabolism of ferulic acid in P. putida KT2440 was proven by separately inactivating each gene by insertion of Ω-elements. The corresponding mutant strains KT2440fcsΩKm, KT2440echΩKm, and KT2440vdhΩKm were not able to grow on ferulic acid. The potential application of P. putida KT2440 and the mutant strains in biotechnological vanillin production process is discussed.
Growth and magnetosome formation by microaerophilic Magnetospirillum strains in an oxygen-controlled fermentor by U. Heyen; D. Schüler (pp. 536-544).
Media and growth conditions were optimized for the microaerobic cultivation of Magnetospirillum gryphiswaldense in flasks and in a fermentor, resulting in significantly increased cell and magnetosome yields, compared with earlier studies. A reliable method was established for the automatic control of low dissolved oxygen tensions (pO2) in the fermentor (oxystat). Growth and magnetosome formation by M. gryphiswaldense, M. magnetotacticum and Magnetospirillum sp. AMB-1 were studied at various oxygen concentrations. Despite differences in their growth responses with respect to oxygen, we found a clear correlation between pO2 and magnetosome formation in all three Magnetospirillum strains. Magnetite biomineralization was induced only below a threshold value of 20 mbar O2 and optimum conditions for magnetosome formation were found at a pO2 of 0.25 mbar (1 bar = 105 Pa). A maximum yield of 6.3 mg magnetite l-1 day-1 was obtained with M. gryphiswaldense grown under oxystat conditions, which is the highest magnetosome productivity reported so far for a magnetotactic bacterium. In conclusion, the presented results provide the basis for large-scale cultivation of magnetospirilla under defined conditions.
Interactions between irradiance and nutrient availability during astaxanthin accumulation and degradation in Haematococcus pluvialis by J. Fábregas; A. Domínguez; A. Maseda; A. Otero (pp. 545-551).
Fully synchronised germination of Haematococcus pluvialis astaxanthin-replete aplanospores was induced by transfer to nitrogen-sufficient conditions under either high or low light intensities, and growth, pigment content and nitrogen consumption were monitored during the cell cycle. No germination of the aplanospores was achieved in the absence of nitrate, even when cells were transferred at low light intensities. On the other hand, cell density and chlorophyll concentration increased dramatically and astaxanthin concentration decreased in N-sufficient cultures due to the germination of 100% of the aplanospores, as demonstrated by flow cytometry. No significant effect of light intensity was observed on the degradation of astaxanthin during germination. In germinated cultures, nitrogen was depleted more rapidly under high light conditions, which resulted in earlier entry into the aplanospore stage and accumulation of astaxanthin. Germination of aplanospores accompanied by astaxanthin degradation could also be obtained in the dark in nutrient-sufficient conditions although at a much lower efficiency. The results demonstrate that nutrient availability is the main factor controlling the transition between red and green stages of H. pluvialis, with astaxanthin being accumulated only when cell division has ceased. High light levels accelerate the process by increasing the rate of nutrient depletion and providing more energy for astaxanthin synthesis.
The ability of Bipolaris sorokiniana to modify geraniol and (−)-alpha-bisabolol as exogenous substrates by R. P. Limberger; L. Ferreira; T. Castilhos; A. M. Aleixo; R. Z. Petersen; J. C. Germani; J. A. Zuanazzi; A. G. Fett-Neto; A. T. Henriques (pp. 552-555).
The biocatalytic potential of Bipolaris sorokiniana was investigated in its ability to modify the monoterpene geraniol and the sesquiterpene alpha-bisabolol as exogenous substrates, using phosphate buffer as reaction medium. The cultures showed a promising oxidative profile, with conversion of geraniol to 6-methyl-5-hepten-2-one (74.9% yield) in a 5-day incubation and alpha-bisabolol to bisabolol oxide B (84.2% yield), in a 7-day incubation.
Elemental compositions and characteristics of aerobic granules cultivated at different substrate N/C ratios by Y. Liu; S.-F. Yang; J.-H. Tay (pp. 556-561).
The effects of the substrate N/C ratios on the formation, elemental compositions and characteristics of aerobic granules were investigated in four sequencing batch reactors. Results showed that aerobic granules could form at substrate N/C ratios ranging from 5/100 to 30/100 and the substrate N/C ratio had a direct and profound effect on the elemental compositions and characteristics of the aerobic granules. Nitrifying populations in aerobic granules were enriched significantly with the increase in the substrate N/C ratio, while the respective ratio of cell oxygen, nitrogen and calcium to cell carbon were also determined by the substrate N/C ratio. It was found that cell hydrophobicity of aerobic granules was inversely related to the ratio of cell oxygen normalized to cell carbon. Since the cell calcium content in aerobic granules developed at different substrate N/C ratios was even lower than that in the seed sludge, it is reasonable to conclude that the cell calcium would not contribute to aerobic granulation. This study probably for the first time demonstrates that the elemental composition, microbial distribution and characteristics of aerobic granules are related to the substrate N/C ratio applied.
Predicting the effects of chlorine on the micro-organisms of filamentous bulking activated sludges by M. A. Séka; F. Hammes; W. Verstraete (pp. 562-568).
Rapid and definite assessment of the effect that a specific biocide has on a specific case of filamentous bulking sludge is a much-needed tool in activated sludge wastewater treatment. The Live/Dead stain (LIVE/DEAD BacLight) distinguishing "living" and "non-living" cells, a nitrifying activity (NA) test and the oxygen uptake rate (OUR) measurement were examined for their appropriateness to predict the effects of chlorine on filamentous bulking sludges. The study showed the live/dead stain to be relevant for revealing the specific effect of chlorine on the filamentous bacteria of a bulking sludge. However, using live/dead stain alone for the determination of the appropriate chlorine dose against bulking may lead to an underestimation of the damage caused by chlorine to the useful microorganisms in the flocs. Indeed, using the live/dead stain, it was not easy to distinguish dead cells caused by chlorination from those originally present in the flocs The NA test was the most sensitive in detecting damage caused by chlorine to the floc-forming microorganisms. Therefore, for a safer determination of the chlorine dose effective against bulking and protective of the microbial activity of the sludge, the results of this study suggest coupling of the live/dead stain with the NA test and/or the OUR test.