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Applied Microbiology and Biotechnology (v.79, #2)

An overview of mannan structure and mannan-degrading enzyme systems by L. R. S. Moreira; E. X. F. Filho (pp. 165-178).

Hemicellulose is a complex group of heterogeneous polymers and represents one of the major sources of renewable organic matter. Mannan is one of the major constituent groups of hemicellulose in the wall of higher plants. It comprises linear or branched polymers derived from sugars such as d-mannose, d-galactose, and d-glucose. The principal component of softwood hemicellulose is glucomannan. Structural studies revealed that the galactosyl side chain hydrogen interacts to the mannan backbone intramolecularly and provides structural stability. Differences in the distribution of d-galactosyl units along the mannan structure are found in galactomannans from different sources. Acetyl groups were identified and distributed irregularly in glucomannan. Some of the mannosyl units of galactoglucomannan are partially substituted by O-acetyl groups. Some unusual structures are found in the mannan family from seaweed, showing a complex system of sulfated structure. Endohydrolases and exohydrolases are involved in the breakdown of the mannan backbone to oligosaccharides or fermentable sugars. The main-chain mannan-degrading enzymes include β-mannanase, β-glucosidase, and β-mannosidase. Additional enzymes such as acetyl mannan esterase and α-galactosidase are required to remove side-chain substituents that are attached at various points on mannan, creating more sites for subsequent enzymatic hydrolysis. Mannan-degrading enzymes have found applications in the pharmaceutical, food, feed, and pulp and paper industries. This review reports the structure of mannans and some biochemical properties and applications of mannan-degrading enzymes.

Keywords: Hemicellulose; Mannan; β-Mannanase; Biotechnology application

Lovastatin biosynthetic genes of Aspergillus terreus are expressed differentially in solid-state and in liquid submerged fermentation by J. Barrios-González; J. G. Baños; A. A. Covarrubias; A. Garay-Arroyo (pp. 179-186).

Molecular studies were performed to establish the causes of the superior lovastatin productivity of a novel solid-state fermentation (SSF) process, in relation with liquid submerged fermentation (SmF; 20 mg/g vs. 0.65 mg/ml). In SSF, biosynthetic genes lovE and lovF transcripts accumulated to high levels from day 1 to day 7. In this period, lovE transcript showed 4.6-fold higher accumulation levels (transcription) than the highest level detected in SmF (day 5). lovF transcript showed two-fold higher expression than the highest point in SmF. In SmF, the expression was only detected clearly on day 5 and, showing a 50% decrease, on day 7. These results show that the higher lovastatin production in SSF is related to a more intense transcription of these biosynthetic genes. A strong expression of gldB gene in lovastatin SSF indicated that Aspergillus terreus senses osmotic stress during the course of SSF, but not in SmF. However, when a liquid medium of identical concentration was used in SmF, lovastatin production decreased in 50%, while lovE and lovF transcripts accumulation was 20 and six-fold lower than in SSF; showing that physiology is different in SSF, and that osmotic stress alone is not responsible for the higher gene expression in SSF.

Keywords: Solid-state fermentation; Submerged fermentation; Lovastatin biosynthesis gene expression

Quantifying the surface characteristics and flocculability of Ralstonia eutropha by Xiao-Meng Liu; Guo-Ping Sheng; Jin Wang; Han-Qing Yu (pp. 187-194).

The microbial surface and flocculability were qualitatively characterized through the combination of the surface thermodynamic and the extended DLVO approaches, with Ralstonia eutropha, a polyhydroxybutyrate-producing bacterium, as an example. The negativity of the ζ potential of R. eutropha decreased from the initial −19.5 to −11 mV in its cultivation with the consumption of glucose. The total interfacial free energy (ΔG _adh) was changed from −80 to 28.5 mJ m⁻² in its entire growth process. This suggests that the bacterial surface changed from hydrophobic into hydrophilic, resulting in an alteration of its surface characteristics and flocculability in its different growth phases. As a result, the stability ratio of suspensions increased with the increasing cultivation time, indicating that the cell particles became more repulsive with each other and led to a more stable suspension of R. eutropha in its cultivation. The obtained information in this work might be useful for better understanding the surface characteristics and the flocculability and even manipulating its flocculability in the microbial growth process.

Keywords: Extended DLVO theory; Flocculation; Polyhydroxybutyrate (PHB); Ralstonia eutropha ; Surface characteristics; Thermodynamics

Improvement of thermostability of recombinant collagen-like protein by incorporating a foldon sequence by Chunling Du; Mingqi Wang; Jinying Liu; Mingli Pan; Yurong Cai; Juming Yao (pp. 195-202).

Collagen is a popular biomaterial in many specific biological interactions as well as a structural element. In this work, the recombinant collagen-like proteins were synthesized using Escherichia coli expression system. A foldon sequence, GYIPEAPRDGQAYVRKDGEWVLLSTFL, derived from the native T4 phage fibritin was incorporated at the C-terminal of collagen-like protein molecules to stabilize the triple helix formed in the proteins. The differential scanning calorimetry and thermogravimetric analysis measurements showed that the thermostability of the recombinant collagen-like proteins was significantly improved when compared with those without the foldon sequence at the C-terminal. Fourier transform infrared and scanning electron microscopy observations indicated that the collagen-like proteins forms the triple helix structure and prefer to aggregate as fibrils, same as the native collagen. Moreover, the mice fibroblasts L929 cells could attach and grew very well on the recombinant collage-like proteins. 3-(4,5-Dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide assay showed that the cell biocompatibility of collagen-like proteins produced in this work was even better than that of native collagen, suggesting that the collagen-like proteins may be a satisfactory candidate for the future applications as a biomaterial.

Keywords: Collagen; Recombinant protein; Fibritin; Foldon; Thermostability; Cell biocompatibility

Construction of a stress-induced system in Escherichia coli for efficient polyhydroxyalkanoates production by Zhen Kang; Qian Wang; Haojun Zhang; Qingsheng Qi (pp. 203-208).

In the application of engineered Escherichia coli in industrial polyhydroxybutyrate production process, one of the major concerns is the induction of the metabolic pathway. In this study, we developed a stress-induced system by which the PHB biosynthesis pathways can be induced under stress conditions. Fermentation results showed that recombinant E. coli DH5α (pQKZ103) harboring this system was able to accumulate polyhydroxybutyrate up to 85.8% of cell dry weight in minimal glucose medium without adding any inducer. Growth experiment with GFP as a reporter indicated that the induction of this system happened at the late exponential phase and was sensitive to stressed environment. This system can also be applied in many other biotechnological processes.

Keywords: Metabolic engineering; PHB; Promoter; Biosynthesis; Escherichia coli

Bioconversion of lovastatin to a novel statin by Amycolatopsis sp. by Bin Zhuge; Hui Ying Fang; Hai Yu; Zhi Ming Rao; Wei Shen; Jian Song; Jian Zhuge (pp. 209-216).

3-Hydroxy-3-methylglutaryl–coenzyme A (HMG–CoA) reductase catalyzes the conversion of HMG–CoA to mevalonic acid, which plays a significant role in cholesterol synthesis. Several statins, inhibitors of HMG–CoA reductase, can be synthesized and converted by microorganisms. Among 700 strains obtained from culture collections, one strain could convert lovastatin to a novel statin, wuxistatin. The strain was identified as a member of the genus Amycolatopsis based on 16S rRNA gene sequence, morphology analysis, and chemotaxonomic properties. Wuxistatin, a novel HMG–CoA reductase inhibitor, was purified by chromatography, and the structure was determined by electrospray ionization mass and nuclear magnetic resonance spectroscopy. The results show that wuxistatin was butanoic acid, 2-methyl-,1,2,3,5,8,8a-hexahydro-5-hydroxy-7-methyl-8-[2-(tetrahydro-4-hydroxy-6-oxo-2H-pyran-2-yl) ethy]-1-naphthalenyl ester. An additional hydroxyl group was added to lovastatin at the 5-position to yield wuxistatin. This modification enhanced the intrinsic inhibitory activity (IC50) of wuxistatin (41 ± 5 nM) for fourfold compared with lovastatin (160 ± 10 nM). A stoichiometric conversion of lovastatin to wuxistatin occurred.

Keywords: Amycolatopsis sp.; HMG–CoA reductase; Structure; Wuxistatin

Cloning and characterization of a new laccase from Bacillus licheniformis catalyzing dimerization of phenolic acids by Katja Koschorreck; Sven M. Richter; Augusta B. Ene; Emil Roduner; Rolf D. Schmid; Vlada B. Urlacher (pp. 217-224).

A new laccase gene (cotA) was cloned from Bacillus licheniformis and expressed in Escherichia coli. The recombinant protein CotA was purified and showed spectroscopic properties, typical for blue multi-copper oxidases. The enzyme has a molecular weight of ~65 kDa and demonstrates activity towards canonical laccase substrates 2,2′-azino-bis(3-ethylbenzothiazoline-6-sulphonic acid) (ABTS), syringaldazine (SGZ) and 2,6-dimethoxyphenol (2,6-DMP). Kinetic constants K _M and k _cat for ABTS were of 6.5 ± 0.2 μM and 83 s⁻¹, for SGZ of 4.3 ± 0.2 μM and 100 s⁻¹, and for 2,6-DMP of 56.7 ± 1.0 μM and 28 s⁻¹. Highest oxidizing activity towards ABTS was obtained at 85°C. However, after 1 h incubation of CotA at 70°C and 80°C, a residual activity of 43% and 8%, respectively, was measured. Furthermore, oxidation of several phenolic acids and one non-phenolic acid by CotA was investigated. CotA failed to oxidize coumaric acid, cinnamic acid, and vanillic acid, while syringic acid was oxidized to 2,6-dimethoxy-1,4-benzoquinone. Additionally, dimerization of sinapic acid, caffeic acid, and ferulic acid by CotA was observed, and highest activity of CotA was found towards sinapic acid.

Keywords: Laccase; Phenol oxidation; Dimerization

Cloning of a rumen fungal xylanase gene and purification of the recombinant enzyme via artificial oil bodies by Je-Ruei Liu; Chung-Hang Duan; Xin Zhao; Jason T. C. Tzen; Kuo-Joan Cheng; Cheng-Kang Pai (pp. 225-233).

A gene encoding a xylanase, named xynS20, was cloned from the ruminal fungus Neocallimastix patriciarum. The DNA sequence of xynS20 revealed that the gene was 1,008 bp in size and encoded amino acid sequences with a predicted molecular weight of 36 kDa. The amino acid sequence alignment showed that the highest sequence identity (28.4%) is with insect gut xylanase XYL6805. According to the sequence-based classification, a putative conserved domain of glycosyl hydrolase family 11 was detected at the N-terminus of XynS20 and a putative conserved domain of family 1 carbohydrate-binding module (CBM) was observed at the C-terminus of XynS20. An Asn-rich linker sequence was found between the N-terminal catalytic domain and the C-terminal CBM of XynS20. To examine the activity of the gene product, xynS20 gene was cloned as an oleosin-fused protein, expressed in Escherichia coli, affinity-purified by formation of artificial oil bodies, released from oleosin by intein-mediated peptide cleavage, and finally harvested by concentration of the supernatant. The specific activity of purified XynS20 toward oat spelt xylan was 1,982.8 U mg⁻¹. The recombinant XynS20 was stable in the mild acid pH range from 5.0 to 6.0, and the optimum pH was 6.0. The optimal reaction temperature of XynS20 was 45°C; at temperatures below 30 and above 55°C, enzyme activity was less than 50% of that at the optimal temperature.

Keywords: Rumen; Neocallimastix patriciarum ; Xylanase; Artificial oil body

Multi-copy expression and fed-batch production of Rhodotorula araucariae epoxide hydrolase in Yarrowia lipolytica by Dheepak Maharajh; Robyn Roth; Rajesh Lalloo; Clinton Simpson; Robin Mitra; Johann Görgens; Santosh Ramchuran (pp. 235-244).

Epoxide hydrolases (EHs) of fungal origin have the ability to catalyze the enantioselective hydrolysis of epoxides to their corresponding diols. However, wild type fungal EHs are limited in substrate range and enantioselectivity. Additionally, the production of fungal epoxide hydrolase (EH) by wild-type strains is typically very low. In the present study, the EH-encoding gene from Rhodotorula araucariae was functionally expressed in Yarrowia lipolytica, under the control of a growth phase inducible hp4d promoter, in a multi-copy expression cassette. The transformation experiments yielded a positive transformant, with a final EH activity of 220 U/g dw in shake-flask cultures. Evaluation of this transformant in batch fermentations resulted in ~ 7-fold improvement in EH activity over the flask scale. Different constant specific feed rates were tested in fed-batch fermentations, resulting in an EH activity of 1,750 U/g dw at a specific feed rate of ~ 0.1 g/g/h, in comparison to enzyme production levels of 0.3 U/g dw for the wild type R. araucariae and 52 U/g dw for an Escherichia coli recombinant strain expressing the same gene. The expression of EH in Y. lipolytica using a multi-copy cassette demonstrates potential for commercial application.

Keywords: Epoxide hydrolases; Fed-batch fermentation; Yarrowia lipolytica ; Rhodotorula araucariae

Cloning, characterization and functional expression of an alkalitolerant type C feruloyl esterase from Fusarium oxysporum by Maria Moukouli; Evangelos Topakas; Paul Christakopoulos (pp. 245-254).

A hypothetical protein FoFaeC-12213 of Fusarium oxysporum was found to have high amino acid sequence identity with known type C feruloyl esterases (FAEs) containing a 13-amino acid conserved region flanking the characteristic G-X-S-X-G motif of a serine esterase. The putative FAE from the genomic DNA was successfully cloned in frame with the Saccharomyces cerevisiae α-factor secretion signal under the transcriptional control of the alcohol oxidase (AOX1) promoter and integrated in Pichia pastoris X-33 to confirm that the enzyme exhibits FAE activity. The molecular weight (62 kDa) and pI (6.8) were in agreement with the theoretical calculated values indicating the correct processing of the secretion signal in P. pastoris. The recombinant FAE was purified to its homogeneity and subsequently characterized using a series of model substrates including methyl esters of hydroxycinnamates, alkyl ferulates and monoferuloylated 4-nitrophenyl glycosides. The substrate specificity profiling reveals that the enzyme is a type C FAE showing broad hydrolytic activity against the four methyl esters of hydroxycinnamic acids and strong preference for the hydrolysis of n-propyl ferulate. Ferulic acid (FA) was efficiently released from destarched wheat bran when the esterase was incubated together with xylanase from Trichoderma longibrachiatum (a maximum of 67% total FA released after 1-h incubation). The esterase showed broad pH stability making it an important candidate for alkaline applications such as pulp treatment in the paper industry.

Keywords: Alkalitolerant; Expression; Fusarium oxysporum ; Feruloyl esterase; Gene cloning; Pichia pastoris

Heterologous hyper-expression of a glucansucrase-type glycosyltransferase gene by Anna Maria Swistowska; Sabine Wittrock; Wera Collisi; Bernd Hofer (pp. 255-261).

Heterologous expression of the large glucansucrase-type glycosyltransferases genes is still a challenge, and typically yields are poor. Therefore, a number of different Escherichia coli systems for the expression of such a gene, encoding the glycosyltransferase R (GtfR) from Streptococcus oralis, were constructed and evaluated. We thereby obtained a strain producing the highest molar yields described so far for this class of enzymes. Cloning of a 5′-terminally truncated version of the gene in the expression vector pET33b(+) yielded, in dissolved form, about 2 μmol (300 mg) of enzyme per liter of culture of an optical density at 600 nm of four. Problems frequently encountered in the heterologous biosynthesis of this class of enzymes, such as formation of a high fraction of insoluble aggregates and/or proteolytic degradation, were not observed in the described system. The over-produced enzyme, devoid of almost its entire variable region, retained its characteristic activities.

Keywords: Glucosyltransferase; Glucansucrase; High level expression; Truncation; Escherichia coli

Development of chemically defined medium for Mannheimia succiniciproducens based on its genome sequence by Hyohak Song; Tae Yong Kim; Bo-Kyeong Choi; Seong Jun Choi; Lars K. Nielsen; Ho Nam Chang; Sang Yup Lee (pp. 263-272).

This study presents a novel methodology for the development of a chemically defined medium (CDM) using genome-scale metabolic network and flux balance analysis. The genome-based in silico analysis identified two amino acids and four vitamins as non-substitutable essential compounds to be supplemented to a minimal medium for the sustainable growth of Mannheimia succiniciproducens, while no substitutable essential compounds were identified. The in silico predictions were verified by cultivating the cells on a CDM containing the six non-substitutable essential compounds, and it was further demonstrated by observing no cell growth on the CDM lacking any one of the non-substitutable essentials. An optimal CDM for the enhancement of cell growth and succinic acid production, as a target product, was formulated with a single-addition technique. The fermentation on the optimal CDM increased the succinic acid productivity by 36%, the final succinic acid concentration by 17%, and the succinic acid yield on glucose by 15% compared to the cultivation using a complex medium. The optimal CDM also lowered the sum of the amounts of by-products (acetic, formic, and lactic acids) by 30%. The strategy reported in this paper should be generally applicable to the development of CDMs for other organisms, whose genome sequences are available.

Keywords: Chemically defined medium; Mannheimia succiniciproducens ; Metabolic network; Flux balance analysis; Succinic acid

Gene expression profiles and intracellular contents of stress protectants in Saccharomyces cerevisiae under ethanol and sorbitol stresses by Tomohiro Kaino; Hiroshi Takagi (pp. 273-283).

In response to osmotic stress, proline is accumulated in many bacterial and plant cells. During various stresses, the yeast Saccharomyces cerevisiae induces glycerol or trehalose synthesis, but the fluctuations in gene expression and intracellular levels of proline in yeast are not yet well understood. We previously found that proline protects yeast cells from damage by freezing, oxidative, or ethanol stress. In this study, we examined the relationships between the gene expression profiles and intracellular contents of glycerol, trehalose, and proline under stress conditions. When yeast cells were exposed to 1 M sorbitol stress, the expression of GPD1 encoding glycerol-3-phosphate dehydrogenase is induced, leading to glycerol accumulation. In contrast, in the presence of 9% ethanol, the rapid induction of TPS2 encoding trehalose-6-phosphate phosphatase resulted in trehalose accumulation. We found that intracellular proline levels did not increase immediately after addition of sorbitol or ethanol. However, the expressions of genes involved in proline synthesis and degradation did not change during exposure to these stresses. It appears that the elevated proline levels are due primarily to an increase in proline uptake from a nutrient medium caused by the induction of PUT4. These results suggest that S. cerevisiae cells do not accumulate proline in response to sorbitol or ethanol stress different from other organisms.

Keywords: Saccharomyces cerevisiae ; Stress response; Proline; Gene; Expression; Glycerol; Trehalose

Bacterial community composition of a wastewater treatment system reliant on N₂ fixation by Nicola M. Reid; Tracey H. Bowers; Gareth Lloyd-Jones (pp. 285-292).

The temporal stability and change of the dominant phylogenetic groups of the domain bacteria were studied in a model plant-based industrial wastewater treatment system showing high levels of organic carbon removal supported by high levels of N₂ fixation. Community profiles were obtained through terminal restriction fragment length polymorphism analysis and cloning of 16S rRNA amplicons followed by sequencing. Bacterial community profiles showed that ten common terminal restriction fragments made up approximately 50% of the measured bacterial community. As much as 42% of the measured bacterial community could be monitored by using quantitative PCR and primers that targeted three dominant operational taxonomic units. Despite changes in wastewater composition and dissolved oxygen levels, the bacterial community composition appeared stable and was dominated by α-Proteobacteria and β-Proteobacteria, with a lesser amount of the highly diverse bacterial phylum Bacteroidetes. A short period of considerable change in the bacterial community composition did not appear to affect treatment performance indicating functional redundancy in this treatment system.

Keywords: Biorefinery; Wastewater; Nitrogen fixation; T-RFLP; qPCR; 16S

Investigating the interaction mechanism between zinc and Saccharomyces cerevisiae using combined SEM-EDX and XAFS by Chen Can; Wang Jianlong (pp. 293-299).

The interaction mechanism between zinc and the intact yeast cells of Saccharomyces cerevisiae was investigated by using the scanning electron microscopy with energy-dispersive X-ray analysis, as well as X-ray absorption fine structure spectroscopy (XAFS). Displacement of H⁺, K⁺, Mg²⁺, and Na⁺ during zinc uptake confirmed the existence of both covalent interactions and ionic interactions between Zn²⁺ and the microbe. Ion exchange mechanism played a role in zinc uptake. The local environment of Zn accumulated in the intact yeast cells was determined by XAFS, which suggests that the nearest neighboring atom of the bound zinc ion on the biomass is oxygen atom. The adsorbed zinc ion on the intact cells of S. cerevisiae is a tetrahedron structure, with the Zn–O bond length of 1.97 Å, and the coordination number is only 3.2 of Zn–O structure in the first shell.

Keywords: Zn²⁺ ; Saccharomyces cerevisiae ; Interaction; XAFS; Mechanism

Biodegradation and kinetics of aerobic granules under high organic loading rates in sequencing batch reactor by Yao Chen; Wenju Jiang; David Tee Liang; Joo Hwa Tay (pp. 301-308).

Biodegradation, kinetics, and microbial diversity of aerobic granules were investigated under a high range of organic loading rate 6.0 to 12.0 kg chemical oxygen demand (COD) m⁻³ day⁻¹ in a sequencing batch reactor. The selection and enriching of different bacterial species under different organic loading rates had an important effect on the characteristics and performance of the mature aerobic granules and caused the difference on granular biodegradation and kinetic behaviors. Good granular characteristics and performance were presented at steady state under various organic loading rates. Larger and denser aerobic granules were developed and stabilized at relatively higher organic loading rates with decreased bioactivity in terms of specific oxygen utilization rate and specific growth rate (μ _overall) or solid retention time. The decrease of bioactivity was helpful to maintain granule stability under high organic loading rates and improve reactor operation. The corresponding biokinetic coefficients of endogenous decay rate (k _d), observed yield (Y _obs), and theoretical yield (Y) were measured and calculated in this study. As the increase of organic loading rate, a decreased net sludge production (Y _obs) is associated with an increased solid retention time, while k _d and Y changed insignificantly and can be regarded as constants under different organic loading rates.

Keywords: Aerobic granule; Sequencing batch reactor; PCR-DGGE; Biokinetics; Specific oxygen utilization rate; Solid retention time

Molecular microbial and chemical investigation of the bioremediation of two-phase olive mill waste using laboratory-scale bioreactors by J. A. Morillo; M. Aguilera; B. Antízar-Ladislao; S. Fuentes; A. Ramos-Cormenzana; N. J. Russell; M. Monteoliva-Sánchez (pp. 309-317).

Two-phase olive mill waste (TPOMW) is a semi-solid effluent that is rich in contaminating polyphenols and is produced in large amounts by the industry of olive oil production. Laboratory-scale bioreactors were used to investigate the biodegradation of TPOMW by its indigenous microbiota. The effect of nutrient addition (inorganic N and P) and aeration of the bioreactors was studied. Microbial changes were investigated by PCR-temperature time gradient electrophoresis (TTGE) and following the dynamics of polar lipid fatty acids (PLFA). The greatest decrease in the polyphenolic and organic matter contents of bioreactors was concomitant with an increase in the PLFA fungal/bacterial ratio. Amplicon sequences of nuclear ribosomal internal transcribed spacer region (ITS) and16S rDNA allowed identification of fungal and bacterial types, respectively, by comparative DNA sequence analyses. Predominant fungi identified included members of the genera Penicillium, Candida, Geotrichum, Pichia, Cladosporium, and Aschochyta. A total of 14 bacterial genera were detected, with a dominance of organisms that have previously been associated with plant material. Overall, this work highlights that indigenous microbiota within the bioreactors through stimulation of the fungal fraction, is able to degrade the polyphenolic content without the inoculation of specific microorganisms.

Keywords: Bioremediation; Microbial diversity; Olive mill waste

Influence of synthetic packing materials on the gas dispersion and biodegradation kinetics in fungal air biofilters by Francesc X. Prenafeta-Boldú; Josep Illa; Johan W. van Groenestijn; Xavier Flotats (pp. 319-327).

The biodegradation of toluene was studied in two lab-scale air biofilters operated in parallel, packed respectively with perlite granules (PEG) and polyurethane foam cubes (PUC) and inoculated with the same toluene-degrading fungus. Differences on the material pore size, from micrometres in PEG to millimetres in PUC, were responsible for distinct biomass growth patterns. A compact biofilm was formed around PEG, being the interstitial spaces progressively filled with biomass. Microbial growth concentrated at the core of PUC and the excess of biomass was washed-off, remaining the gas pressure drop comparatively low. Air dispersion in the bed was characterised by tracer studies and modelled as a series of completely stirred tanks (CSTR). The obtained number of CSTR (n) in the PEG packing increased from 33 to 86 along with the applied gas flow (equivalent to empty bed retention times from 48 to 12 s) and with operation time (up to 6 months). In the PUC bed, n varied between 9 and 13, indicating that a stronger and steadier gas dispersion was achieved. Michaelis–Menten half saturation constant (k _m) estimates ranged 71–113 mg m⁻³, depending on the experimental conditions, but such differences were not significant at a 95% confidence interval. The maximum volumetric elimination rate (r _m) varied from 23 to 50 g m⁻³ h⁻¹. Comparison between volumetric and biomass specific biodegradation activities indicated that toluene mass transfer was slower with PEG than with PUC as a consequence of a smaller biofilm surface and to the presence of larger zones of stagnant air.

Keywords: Air biofiltration; Packing materials; Biodegradation kinetics; Dispersion dynamics; Fungi; Toluene abatement

The state of the art in the analysis of two-dimensional gel electrophoresis images by Matthias Berth; Frank Michael Moser; Markus Kolbe; Jörg Bernhardt (pp. 329-329).

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Applied Microbiology and Biotechnology (v.79, #2)

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Applied Microbiology and Biotechnology (v.79, #2)