Check out our New Publishers' Select for Free Articles

Applied Microbiology and Biotechnology (v.47, #4)

Microbial linear plasmids by F. Meinhardt; R. Schaffrath; M. Larsen (pp. 329-336).

While plasmids were originally considered to be generally circular until almost two decades ago, linear elements were reported to exist as well. They are now known to be common genetic elements in both, pro- and eukaryotes. Two types of linear plasmids exist, the so-called hairpin plasmids with covalently closed ends and those with proteins bound to their 5′ termini. Hairpin plasmids are common in human-pathogenic Borrelia spirochetes, in which they are instrumental in escape from the immunological response; cryptic hairpin elements are present in mitochondria of the plant pathogenic fungus Rhizoctonia solani. Plasmids with 5′ attached proteins constitute the largest group. In actinomycetous bacteria they are conjugative and usually confer advantageous phenotypes, e.g. formation of antibiotics, degradation of xenobiotics, heavy-metal resistance and growth on hydrogen as the sole energy source. In contrast, the majority of linear plasmids from eukaryotes are cryptic, with only a few exceptions. In some yeasts a killer phenotype may be associated, the most thoroughly investigated elements being those from Kluyveromyces lactis killer strains. In Neurospora spp. and in Podospora anserina, senescence and longevity respectively are correlated with linear plasmids. This review focuses on the biology of linear plasmids, their environmental significance and their use as tools in molecular and applied microbiology.

Microbially influenced corrosion of glass by R. Drewello; R. Weissmann (pp. 337-346).

Microbially influenced corrosion of glass and countermeasures were studied by literature research and by an investigation of contaminated glass samples. Such corrosion is often linked to the growth of fungi. It is assumed that glass composition is not the decisive factor in biogenic contamination, but can encourage or retard the microbial activity significantly. It is suggested that a biochemically initiated ion-exchange reaction is most important for corrosion of glass exposed to the atmosphere. Future work will emphasize the biotechnological applications in the recovery of heavy metals from special glasses.

d-Lysine production from l-lysine by successive chemical racemization and microbial asymmetric degradation by E. Takahashi; M. Furui; H. Seko; T. Shibatani (pp. 347-351).

In order to develop a practical process for d-lysine production from l-lysine, successive chemical racemization and microbial asymmetric degradation were investigated. The racemization of l-lysine proceeded quantitatively at elevated temperatures. A sample␣of 1000 strains of bacteria, fungi, yeast and actinomyces were screened for the ability to degrade l-lysine asymmetrically. Microorganisms belonging to the Achromobacter, Agrobacterium, Candida, Comamonas, Flavobacterium, Proteus, Providencia, Pseudomonas and Yarrowia genera exhibited a high l-lysine-degrading activity. Comamonas testosteroni IAM 1048 was determined to be the best strain and used as a biocatalyst for eliminating the l isomer. The degradation rate of l-lysine with C. testosteroni IAM 1048 was influenced by pH, temperature and agitation speed. Under the optimal conditions, the l isomer in a 100-g/l mixture of racemic lysine was completely degraded within 72 h, with 47 g d-lysine/l left in the reaction mixture. Crystalline d-lysine, with a chemical purity greater than 99% and optical purity of 99.9% enantiomeric excess, was obtained at a yield of 38% from the reaction mixture by simple purification. An engineering analysis of l-lysine racemization and microbial degradation was carried out to establish the basis of process design for d-lysine production.

Immobilisation of whole bacterial cells for anaerobic biotransformations by S. Raihan; N. Ahmed; L. E. Macaskie; J. R. Lloyd (pp. 352-357).

Anaerobically grown cells of Escherichia coli were immobilised within a range of entrapment matrices and packed into a column under standard conditions, and the ability of the immobilised cells to reduce nitrite (0.5 mM) was measured at a range of flow rates using sodium formate (20 mM) as the electron donor for nitrite reduction. A flow-rate/activity plot was constructed for each flow-through reactor and RA_1/2 values (residence time corresponding to 50 % nitrite removal) calculated for each reactor type. Cells immobilised in flat and hollow-fibre membranes were the most effective (RA_1/2 = 0.35 h and 0.47 h respectively), with cells entrapped by dialysis membrane (1.53 h), alginate beads (1.93 h), Hypol foam (2.31 h) and polyacrylamide gel (50 % nitrite not removed at maximum residence time tested: 4.9 h) performing progressively less effectively. Cells grown as a biofilm on a range of support materials were also tested in comparable packed-bed reactors. Cell loss from these supports was extensive and contributed to poor performance of the reactors despite high initial biomass loadings (RA_1/2 values using raschig rings, coke and activated-carbon supports: 1.6 h, 2.3 h and 1.0 h respectively). Biofilms grown on Pharmacia microcarrier supports and used in packed and also fluidised beds were more stable and the performance of these reactors was superior to that of biofilm reactors using other supports, and comparable to that of the membrane reactors (RA_1/2 values for Cytoline 2, Cytopore 2 and Cytodex 3: 0.76 h, 0.56 h, 0.68 h respectively).

Application of response-surface methodology to evaluate the optimum environmental conditions for the enhanced production of surfactin by R. Sen; T. Swaminathan (pp. 358-363).

Response-surface methodology was applied to determine the effect of the fermentation process conditions, namely pH, temperature, rates of agitation and aeration, on surfactin production. The effects of the mutual interactions between these parameters were extensively studied to optimize the process conditions for the maximum production of surfactin. With a view to simultaneously reducing the number of experiments and obtaining the mutual interactions between the variables required for achieving the optimal experimental conditions, a 2⁴ full-factorial central composite design followed by multi-stage Monte-Carlo optimization was employed for experimental design and analysis of the results. The optimum process conditions for the enhanced production of surfactin were as follows: pH = 6.755, temperature = 37.4 °C, agitation = 140 rpm and aeration = 0.75 vvm. Relative surfactin concentrations were denoted by the reciprocal of the critical micelle concentrations.

Functional roles of protein domains on rice α-amylase activity by M. Terashima; M. Hosono; S. Katoh (pp. 364-367).

Characteristics of two rice α-amylases Amy1A and Amy3D, and those of two chimeric enzymes Amy1A/3D and Amy3D/1A, engineered from the two isozymes, were compared in the light of the functional roles of protein domains in α-amylase. The enzymes that have an Amy1A-type N-terminal domain, Amy1A and Amy1A/3D, showed high activity against soluble starch, while the enzymes that have an Amy3D-type barrel structure, Amy3D and Amy1A/3D, showed high activity in oligosaccharide hydrolysis. Rigidity of protein folding also significantly affected the enzyme activity in both soluble starch and oligosaccharide hydrolysis. Thus, the present work suggests that the structure of the N-terminal domain is important for stability and soluble starch hydrolysis, while the barrel structure that forms the active site significantly affects enzyme activities in oligosaccharide degradation.

Expression of a synthetic protein-based polymer (elastomer) gene in Aspergillus nidulans by R. W. Herzog; N. K. Singh; D. W. Urry; H. Daniell (pp. 368-372).

A gene for a synthetic protein-based polymer, G-(VPGVG)₁₁₉-VPGV, coding for the EG-120mer (elastomer), was cloned into a fungal expression vector to allow constitutive expression of the polymer controlled by the gpdA (glyceraldehyde-3-phosphate dehydrogenase) promoter sequence of Aspergillus nidulans. Stable transformants of A. nidulans showed plasmid integration with varying copy number when analyzed by Southern-blot hybridization. Expression of the synthetic gene was demonstrated by Northern-blot hybridization. However, the translational efficiency for production of the polymer polypeptide was low, presumably because of certain codons in the polymer gene (CCG and GUA) that are rarely used by A. nidulans. Partial purification by reversible phase transition followed by sodium dodecyl sulfate/polyacrylamide gel electrophoresis revealed the presence of polymer protein in a transformant that contained multiple copies of the polymer gene. This study represents the first attempt to express a synthetic gene (with no natural analog) in a fungus.

Localization and characterization of inclusion bodies in recombinant Escherichia coli cells overproducing penicillin G acylase by N. Sriubolmas; W. Panbangred; S. Sriurairatana; V. Meevootisom (pp. 373-378).

Various concentrations of isopropyl β-d-thiogalactopyranoside (IPTG) were used to induce production of the enzyme penicillin G acylase by recom binant Escherichia coli harboring plasmid pQEA11. The plasmid pQEA11 carries a wild-type pga gene, which is under the control of the tac promoter and lacI ^q. At low IPTG concentrations (0.025 – 0.1 mM), enzyme activity increased with increasing IPTG concentrations. At higher IPTG concentrations (0.2 and 0.5 mM), enzyme activity declined progressively. Examination of induced recombinant E. coli cells by transmission electron microscopy showed the presence of only periplasmic inclusion bodies at low IPTG concentrations (up to 0.1 mM) and both periplasmic and cytoplasmic inclusion bodies at high IPTG concentrations (0.2 mM and 0.5 mM). Results from sodium dodecyl sulfate/polyacrylamide gel electrophoresis and immunoblots of whole-cell proteins, membrane proteins and inclusion body proteins in these cells indicated that cytoplasmic inclusion bodies constituted an accumulation of preproenzyme (i.e., precursor polypeptide containing a signal peptide) and that periplasmic inclusion bodies constituted an accumulation of proenzyme (i.e., precursor polypeptide lacking a signal peptide).

Cloning and expression of the Bacillus sphaericus 2362 mosquitocidal genes in a non-toxic unicellular cyanobacterium, Synechococcus PCC6301 by K. Sangthongpitag; R. J. Penfold; S. F. Delaney; P. L. Rogers (pp. 379-384).

Genes encoding the mosquitocidal binary toxin of Bacillus sphaericus 2362 were introduced into Synechococcus PCC6301, a cyanobacterium that can tolerate a number of potential variations in the mosquito breeding environment, and can serve as a food source for mosquito larvae. The toxin genes, preceded by a Synechococcus rbcL promoter, were located on a mobilizable Escherichia coli Synechococcus shuttle vector, which was introduced into Synechococcus PCC6301 at frequencies of 10⁻⁵–10⁻⁷ exconjugants/recipient, depending on the selective conditions used. Recombinant Synechococcus exhibited significant toxicity against 2-day-old and 6-day-old Culex quinquefasciatus larvae, the concentration required to kill 50 % of larvae (LC₅₀) being 2.1 × 10⁵ and 1.3 × 10⁵ cells/ml respectively. Mosquitocidal activity decreased tenfold after 20 generations of non-selective growth.

The Propionibacterium freudenreichii hemYHBXRL gene cluster, which encodes enzymes and a regulator involved in the biosynthetic pathway from glutamate to protoheme by Y. Hashimoto; M. Yamashita; Y. Murooka (pp. 385-392).

A clone that can complement both Escherichia coli hemB and hemL mutations was found among plasmids containing the Propionibacterium freudenreichii hemB gene, which encodes δ-aminolevulinic acid dehydratase. The regions upstream and downstream of the hemB gene were sequenced. Two open-reading frames (ORF1 and -2), which were similar to the hemY gene encoding protoporphyrinogen oxidase and the hemH gene encoding ferrochelatase from Bacillus subtilis, were found upstream of the hemB gene. ORF1 and -2 complemented the E. coli hemG mutation, defective in protoporphyrinogen oxidase, and the hemH gene respectively. Since ORF1 had no homology to hemG, the gene was designated hemY. The hemYHB genes appeared to be within the same transcription unit. Downstream from the hemB gene, three open-reading frames were found. One of these, transcribed in the same direction as the hemB gene, was identical to be the hemL gene, which encodes glutamate-1-semialdehyde 2,1-aminomutase. The other two open-reading frames, located between the hemYHB and hemL genes, were transcribed divergently, and their deduced amino acid sequences showed similarities to a membrane-bound transport protein and a transcriptional regulatory protein respectively. The two genes may thus be involved in hem transport and the regulation of hem gene expression respectively, and were tentatively named hemX and hemR. Although hemX and hemL are unlikely to be part of the same operon, hemYHBXRL␣are clustered on the P. freudenreichii chromosome.

An attempt to channel the transformation of vanillic acid into vanillin by controlling methoxyhydroquinone formation in Pycnoporus cinnabarinus with cellobiose by L. Lesage-Meessen; M. Haon; M. Delattre; J.-F. Thibault; B. Colonna Ceccaldi; M. Asther (pp. 393-397).

The effects of adding cellobiose on the transformation of vanillic acid to vanillin by two strains of Pycnoporus cinnabarinus MUCL39532 and MUCL38467 were studied. When maltose was used as the carbon source in the culture medium, very high levels of methoxyhydroquinone were formed from vanillic acid. When cellobiose was used as the carbon source and/or added to the culture medium of P. cinnabarinus strains on day 3 just before vanillic acid was added, it channelled the vanillic acid metabolism via the reductive route leading to vanillin. Adding 3.5 g l⁻¹ cellobiose to 3-day-old maltose cultures of P. cinnabarinus MUCL39532 and 2.5 g l⁻¹ cellobiose to 3-day-old cellobiose cultures of P. cinnabarinus MUCL38467, yielded 510 mg l⁻¹ and 560 mg l⁻¹vanillin with a molar yield of 50.2 % and 51.7 % respectively. Cellobiose may either have acted as an easily metabolizable carbon source, required for the reductive pathway to occur, or as an inducer of cellobiose:quinone oxidoreductase, which is known to inhibit vanillic acid decarboxylation.

Isolation of isoflavones from soy-based fermentations of the erythromycin-producing bacterium Saccharopolyspora erythraea by P. E. Hessler; P. E. Larsen; A. I. Constantinou; K. H. Schram; J. M. Weber (pp. 398-404).

A search for an abundant and economical source of isoflavones, particularly genistein, led to the discovery that the erythromycin-producing organism Saccharopolyspora erythraea also produces this promising new cancer-prevention agent. Erythromycin fermentation is a large-scale, soybean-based process used world-wide for the commercial production of this medically important antibiotic. Results from this study indicate that genistin (the glucoside form of genistein), which is added to the fermentation in the soybean media, was converted to genistein through the action of a β-glucosidase produced by the organism. Genistein was co-extracted with erythromycin from the fermentation broth, then separated from erythromycin during the second step of the purification process for the production of erythromycin.

Isolation of freeze-tolerant laboratory strains of Saccharomyces cerevisiae from proline-analogue-resistant mutants by H. Takagi; F. Iwamoto; S. Nakamori (pp. 405-411).

Since some amino acids, polyols and sugars in cells are thought to be osmoprotectants, we expected that several amino acids might also contribute to enhancing freeze tolerance in yeast cells. In fact, proline and charged amino acids such as glutamate, arginine and lysine showed a marked cryoprotective activity nearly equivalent to that of glycerol or trehalose, both known as major cryoprotectants for Saccharomyces cerevisiae. To investigate the cryoprotective effect of proline on the freezing stress of yeast, we isolated proline-analogue-resistant mutants derived from a proline-non-utilizing strain of S. cerevisiae. When cultured in liquid minimal medium, many mutants showed a prominent increase, two- to approximately tenfold, in cell viability compared to the parent after freezing in the medium at −20 °C for 1 week. Some of the freeze-tolerant mutants were found to accumulate a higher amount of proline, as well as of glutamate and arginine which are involved in proline metabolism. It was also observed that proline-non-utilizer and the freeze-tolerant mutants were able to grow against osmotic stress. These results suggest that the increased flux in the meta-bolic pathway of specific amino acids such as proline is effective for breeding novel freeze-tolerant yeasts.

Patterns of ligninolytic enzymes in Trametes versicolor. Distribution of extra- and intracellular enzyme activities during cultivation on glucose, wheat straw and beech wood by D. Schlosser; R. Grey; W. Fritsche (pp. 412-418).

Trametes versicolor was shown to produce extracellular laccase during surface cultivation on glucose, wheat straw and beech wood. Growth on both wheat straw and beech wood led to an increase as high as 3.5-fold in extracellular laccase activity, in comparison with growth on glucose. The corresponding yields in fungal biomass reached only about 20% of the value obtained on glucose. Manganese peroxidase activity␣appeared during growth on wheat straw and beech wood. Mycelia grown on glucose, wheat straw and beech wood also showed intracellular laccase activities, monitored with 2,6-dimethoxyphenol, 2,2′-azino-bis(3-ethylbenzothiazoline-6-sulphonic acid), 4-hydroxy-3,5-dimethoxybenzaldehyde azine (syringaldazine) and 3,4-dihydroxyphenylalanine (l-DOPA). Assaying intracellular laccase with 2,6-dimethoxyphenol, syringaldazine and l-DOPA showed the maximum oxidation rates to be at pH values different from those producing maximum oxidation rates with extracellular laccase. In each case most of the total laccase activity was recovered from the culture filtrates. Growth on wheat straw and beech wood led to increased values for both extra- and intracellular laccase activities, based on fungal dry weight, in comparison with growth on glucose.

Depolymerization of low-rank coal by extracellular fungal enzyme systems. II. The ligninolytic enzymes of the coal-humic-acid-depolymerizing fungus Nematoloma frowardii b19 by M. Hofrichter; W. Fritsche (pp. 419-424).

The production of ligninolytic enzymes was studied in surface cultures of the South American white-rot fungus Nematoloma frowardii b19 and four other strains of this ecophysiological group (Clitocybula dusenii b11, Auricularia sp. m37a, wood isolates u39 and u45), which are able to depolymerize low-rank-coal-derived humic acids with the formation of fulvic-acid-like compounds. The fungi produced the three crucial enzymes of lignin degradation – lignin peroxidase, manganese peroxidase and laccase. In the case of N. frowardii b19, laccase and the two peroxidases could be stimulated by veratryl alcohol. Manganese (II) ions (Mn²⁺) caused a rapid increase of Mn peroxidase activity accompanied by the complete repression of lignin peroxidase. Under nitrogen-limited conditions the growth as well as the production of ligninolytic enzymes was partly repressed. During the depolymerization process of coal humic acids using solid agar media, gradients of ligninolytic enzyme activities toward 2,2′-azinobis(3-ethylbenzthiazoline-6-sulphonate) and syringaldazine were detectable inside the agar medium.

Growth conditions of Aspergillus sp. ATHUM-3482 for polygalacturonase production by M. Galiotou-Panayotou; M. Kapantai; O. Kalantzi (pp. 425-429).

A wild type of Aspergillus sp. ATHUM-3482 produced extracellular polygalacturonase when grown in liquid medium containing citrus pectin as sole carbon source. A number of factors affecting enzyme activity were investigated. Polygalacturonase activities as high as␣4.3 U␣ml⁻¹(reducing-group-releasing activity) and 17␣U␣ml⁻¹ (viscosity-diminishing activity) were obtained under optimum growth conditions. With sugar-beet as sole carbon source the respective activities were 6.5 U␣ml⁻¹ and 40 U ml⁻¹, the highest achieved in this work. Under these conditions no pectin lyase or pectinesterase activity was detected. The above yields of polygalacturonase activity compare favourably with those reported for fungi grown under similar growth conditions.

Elucidation of anaplerotic pathways in Corynebacterium glutamicum via ¹³C-NMR spectroscopy and GC-MS by S. M. Park; C. Shaw-Reid; A. J. Sinskey; G. Stephanopoulos (pp. 430-440).

We have obtained direct evidence indicating the presence of pyruvate-carboxylating activity in Corynebacterium glutamicum, a lysine-overproducing bacterium. This evidence was obtained through the use of ¹³C nuclear magnetic resonance (NMR) spectroscopy and gas chromatography/mass spectrometry (GC-MS) of secreted metabolites in a lysine fermentation. The distribution of ¹³C label after multiple turns in the tricarboxylic acid cycle was accounted for properly to obtain predictions for [¹³C] metabolite enrichments that were employed in the interpretation of ¹³C-NMR and GC-MS data. Of critical importance in arriving at the conclusions was the use of C. glutamicum mutants with deletions of the pyruvate kinase and/or phosphoenolpyruvate carboxylase enzymes. Our results demonstrate the presence of pyruvate-carboxylating pathway(s) in C.␣glutamicum operating simultaneously with phosphoenolpyruvate carboxylase, with the latter enzyme contributing approximately 10 % of the total oxaloacetate synthesis during the lysine-production phase with pyruvate and gluconate as carbon sources. These findings are important for developing strategies to increase the total carbon flux for synthesis of amino acids of the aspartate family through metabolic engineering.

Propionic acid fermentation from glycerol: comparison with conventional substrates by F. Barbirato; D. Chedaille; A. Bories (pp. 441-446).

Instead of the conventional carbon sources used for propionic acid biosynthesis, the utilization of glycerol is considered here, since the metabolic pathway involved in the conversion of glycerol to propionic acid is redox-neutral and energetic. Three strains, Propionibacterium acidipropionici, Propionibacterium acnes and Clostridium propionicum were tested for their ability to convert glycerol to propionic acid during batch fermentation with initially 20 g/l glycerol. P. acidipropionici showed higher efficiency in terms of fermentation time and conversion yield than did the other strains. The fermentation profile of this bacterium consisted in propionic acid as the major product (0.844 mol/mol), and in minimal by-products: succinic (0.055 mol/mol), acetic (0.023 mol/mol) and formic (0.020 mol/mol) acids and n-propanol (0.036 mol/mol). The overall propionic acid productivity was 0.18 g l⁻¹h⁻¹. A comparative study with glucose and lactic acid as carbon sources showed both less diversity in end-product composition and a 17% and 13% lower propionic acid conversion yield respectively than with glycerol. Increasing the initial glycerol concentration resulted in an enhanced productivity up to 0.36 g l⁻¹h⁻¹ and in a maximal propionic acid concentration of 42 g/l, while a slight decrease of the conversion yield was noticed. Such a propionic acid production rate was similar or higher than the values obtained with lactic acid (0.35 g l⁻¹h⁻¹) or glucose (0.28 g l⁻¹h⁻¹). These results demonstrated that glycerol is a carbon source of interest for propionic acid production.

Effect of xylitol and trehalose on dry resistance of yeasts by I. Krallish; H. Jeppsson; A. Rapoport; B. Hahn-Hägerdal (pp. 447-451).

The effects of dehydration/rehydration on two strains of Saccharomyces cerevisiae: S600, a metabolically engineered xylose-utilising strain, and H158, the non-xylose-utilising host strain; and on the naturally xylose-utilising yeast Pachysolen tannophilus CBS 4044, were compared after glucose and xylose utilisation respectively. The yeast strains differed in their ability to excrete and accumulate intracellular xylitol. A high intracellular xylitol content before and after dehydration coincided with a higher viability after a dehydration/rehydration cycle. The intracellular trehalose content increased during dehydration in all three yeast strains, but this did not correspond to enhanced cell viability after dehydration/rehydration. The results are discussed in relation to the ability of xylitol and trehalose to structure water.

Screening for fungi intensively mineralizing 2,4,6-trinitrotoluene by K. Scheibner; M. Hofrichter; A. Herre; J. Michels; W. Fritsche (pp. 452-457).

Within a screening program, 91 fungal strains belonging to 32 genera of different ecological and taxonomic groups (wood- and litter-decaying basidiomycetes, saprophytic micromycetes) were tested for their ability to metabolize and mineralize 2,4,6-trinitrotoluene (TNT). All these strains metabolized TNT rapidly by forming monoaminodinitrotoluenes (AmDNT). Micromycetes produced higher amounts of AmDNT than did wood- and litter-decaying basidiomycetes. A significant mineralization of [¹⁴C]TNT was only observed for certain wood- and litter-decaying basidiomycetes. The most active strains, Clitocybula dusenii TMb12 and Stropharia rugosa-annulata DSM11372 mineralized 42 % and 36 % respectively of the initial added [¹⁴C]TNT (100 μM corresponding to 4.75 μCi/l) to ¹⁴CO₂ within 64 days. Micromycetes (deuteromycetes, ascomycetes, zygomycetes) proved to be unable to mineralize [¹⁴C]TNT significantly.

Isolation and characterization of Rhodococcus rhodochrous for the degradation of the wastewater component 2-hydroxybenzothiazole by H. De Wever; S. De Cort; I. Noots; H. Verachtert (pp. 458-461).

2-Hydroxybenzothiazole (OBT) is present in wastewaters from the industrial production of the rubber vulcanization accelerator 2-mercaptobenzothiazole (MBT). We have achieved the first isolation of axenic bacterial cultures capable of the degradation of OBT and growth on this substrate as the sole source of carbon, nitrogen and energy. All isolates had similar characteristics corresponding to one particular isolate, which was studied in more detail and identified as Rhodococcus rhodochrous. The strains were also capable of degrading benzothiazole (BT) but not MBT or benzothiazole-2-sulphonate (BTSO₃). OBT was degraded at a concentration of up to 600 mg · l⁻¹. BT was toxic above 300 mg · l⁻¹. MBT inhibited OBT degradation. Growth on OBT was not significantly different at pH values of between 6.3 and 7.9 or salt concentrations between 1 % and 3 %. In shake flasks the cells clumped together, which resulted in a lower rate of oxygen transfer and slower degradation as compared to cells grown on OBT in a stirred reactor.

Bioremediation of diesel-oil-contaminated alpine soils at low temperatures by R. Margesin; F. Schinner (pp. 462-468).

Bioremediation of two diesel-oil-contaminated alpine subsoils, differing in soil type and bedrock, was investigated in laboratory experiments at 10 °C after supplementation with an inorganic fertilizer. Initial diesel oil contamination of 4000 mg kg⁻¹ soil dry matter (dm) was reduced to 380–400 mg kg⁻¹ dm after 155 days of incubation. In both soils, about 30 % of the diesel oil contamination (1200 mg kg⁻¹ dm) was eliminated by abiotic processes. The residual decontamination (60 %–65 %) could be attributed to microbial degradation activities. In both soils, the addition of a cold-adapted diesel-oil-degrading inoculum enhanced biodegradation rates only slightly and temporarily. From C/N and N/P ratios (determined by measuring the contents of total hydrocarbons, NH₄ ⁺ N, NO₃ ⁻ N and PO₄ ³⁻ P) of soils␣it could be deduced that there was no nutrient deficiency during the whole incubation period. Soil biological activities (basal respiration and dehydrogenase activity) corresponded to the course of biodegradation activities in the soils.

Sections

Personal tools

Applied Microbiology and Biotechnology (v.47, #4)

Sections

Personal tools

Local resources

Applied Microbiology and Biotechnology (v.47, #4)