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Applied Microbiology and Biotechnology (v.83, #3)

Sponge spicules as blueprints for the biofabrication of inorganic–organic composites and biomaterials by Werner E. G. Müller; Xiaohong Wang; Fu-Zhai Cui; Klaus Peter Jochum; Wolfgang Tremel; Joachim Bill; Heinz C. Schröder; Filipe Natalio; Ute Schloßmacher; Matthias Wiens (pp. 397-413).

While most forms of multicellular life have developed a calcium-based skeleton, a few specialized organisms complement their body plan with silica. However, of all recent animals, only sponges (phylum Porifera) are able to polymerize silica enzymatically mediated in order to generate massive siliceous skeletal elements (spicules) during a unique reaction, at ambient temperature and pressure. During this biomineralization process (i.e., biosilicification) hydrated, amorphous silica is deposited within highly specialized sponge cells, ultimately resulting in structures that range in size from micrometers to meters. Spicules lend structural stability to the sponge body, deter predators, and transmit light similar to optic fibers. This peculiar phenomenon has been comprehensively studied in recent years and in several approaches, the molecular background was explored to create tools that might be employed for novel bioinspired biotechnological and biomedical applications. Thus, it was discovered that spiculogenesis is mediated by the enzyme silicatein and starts intracellularly. The resulting silica nanoparticles fuse and subsequently form concentric lamellar layers around a central protein filament, consisting of silicatein and the scaffold protein silintaphin-1. Once the growing spicule is extruded into the extracellular space, it obtains final size and shape. Again, this process is mediated by silicatein and silintaphin-1, in combination with other molecules such as galectin and collagen. The molecular toolbox generated so far allows the fabrication of novel micro- and nanostructured composites, contributing to the economical and sustainable synthesis of biomaterials with unique characteristics. In this context, first bioinspired approaches implement recombinant silicatein and silintaphin-1 for applications in the field of biomedicine (biosilica-mediated regeneration of tooth and bone defects) or micro-optics (in vitro synthesis of light waveguides) with promising results.

Keywords: Biosilica; Silicatein; Silintaphin-1; Biomaterials; Porifera; Sponges; Biomedicine; Biotechnology

Recent progress on industrial fermentative production of acetone–butanol–ethanol by Clostridium acetobutylicum in China by Ye Ni; Zhihao Sun (pp. 415-423).

China is one of the few countries, which maintained the fermentative acetone–butanol–ethanol (ABE) production for several decades. Until the end of the last century, the ABE fermentation from grain was operated in a few industrial scale plants. Due to the strong competition from the petrochemical industries, the fermentative ABE production lost its position in the 1990s, when all the solvent fermentation plants in China were closed. Under the current circumstances of concern about energy limitations and environmental pollution, new opportunities have emerged for the traditional ABE fermentation industry since it could again be potentially competitive with chemical synthesis. From 2006, several ABE fermentation plants in China have resumed production. The total solvent (acetone, butanol, and ethanol) production capacity from ten plants reached 210,000 tons, and the total solvent production is expected to be extended to 1,000,000 tons (based on the available data as of Sept. 2008). This article reviews current work in strain development, the continuous fermentation process, solvent recovery, and economic evaluation of ABE process in China. Challenges for an economically competitive ABE process in the future are also discussed.

Keywords: Acetone butanol ethanol (ABE); Fermentation; Clostridium acetobutylicum ; China

Production of oligosaccharides and cellobionic acid by Fibrobacter succinogenes S85 growing on sugars, cellulose and wheat straw by Régis Nouaille; Maria Matulova; Vladimír Pätoprstý; Anne-Marie Delort; Evelyne Forano (pp. 425-433).

Extracellular culture fluid of Fibrobacter succinogenes S85 grown on glucose, cellobiose, cellulose or wheat straw was analysed by 2D-NMR spectroscopy. Cellodextrins did not accumulate in the culture medium of cells grown on cellulose or straw. Maltodextrins and maltodextrin-1P were identified in the culture medium of glucose, cellobiose and cellulose grown cells. New glucose derivatives were identified in the culture fluid under all the substrate conditions. In particular, a compound identified as cellobionic acid accumulated at high levels in the medium of F. succinogenes S85 cultures. The production of cellobionic acid (and cellobionolactone also identified) was very surprising in an anaerobic bacterium. The results suggest metabolic shifts when cells were growing on solid substrate cellulose or straw compared to soluble sugars.

Keywords: Rumen; Fibrobacter succinogenes ; Cellobionate; NMR; Oligosaccharides

Optimization and production of novel antimicrobial agents from sponge associated marine actinomycetes Nocardiopsis dassonvillei MAD08 by Joseph Selvin; S. Shanmughapriya; R. Gandhimathi; G. Seghal Kiran; T. Rajeetha Ravji; K. Natarajaseenivasan; T. A. Hema (pp. 435-445).

The sponge-associated actinomycetes were isolated from the marine sponge Dendrilla nigra, collected from the southwest coast of India. Eleven actinomycetes were isolated depending upon the heterogeneity and stability in subculturing. Among these, Nocardiopsis dassonvillei MAD08 showed 100% activity against the multidrug resistant pathogens tested. The culture conditions of N. dassonvillei MAD08 was optimized under submerged fermentation conditions for enhanced antimicrobial production. The unique feature of MAD08 includes extracellular amylase, cellulase, lipase, and protease production. These enzymes ultimately increase the scope of optimization using broad range of raw materials which might be efficiently utilized. The extraction of the cell free supernatant with ethyl acetate yielded bioactive crude extract that displayed activity against a panel of pathogens tested. Analysis of the active thin layer chromatography fraction by Fourier transform infrared and gas chromatography-mass spectrometry evidenced 11 compounds with antimicrobial activity. The ammonium sulfate precipitation of the culture supernatant at 80% saturation yielded an anticandidal protein of molecular weight 87.12 kDa. This is the first strain that produces both organic solvent and water soluble antimicrobial compounds. The active extract was non-hemolytic and showed surface active property envisaging its probable role in inhibiting the attachment of pathogens to host tissues, thus, blocking host–pathogen interaction at an earlier stage of pathogenesis.

Keywords: Marine-Actinomycetes; Nocardiopsis ; Antimicrobial agents; Anticandidal protein; Optimization

Identification and characterization of fermentation inhibitors formed during hydrothermal treatment and following SSF of wheat straw by Mette Hedegaard Thomsen; Anders Thygesen; Anne Belinda Thomsen (pp. 447-455).

A pilot plant for hydrothermal treatment of wheat straw was compared in reactor systems of two steps (first, 80°C; second, 190–205°C) and of three steps (first, 80°C; second, 170–180°C; third, 195°C). Fermentation (SSF) with Sacharomyces cerevisiae of the pretreated fibers and hydrolysate from the two-step system gave higher ethanol yield (64–75%) than that obtained from the three-step system (61–65%), due to higher enzymatic cellulose convertibility. At the optimal conditions (two steps, 195°C for 6 min), 69% of available C6-sugar could be fermented into ethanol with a high hemicellulose recovery (65%). The concentration of furfural obtained during the pretreatment process increased versus temperature from 50 mg/l at 190°C to 1,200 mg/l at 205°C as a result of xylose degradation. S. cerevisiae detoxified the hydrolysates by degradation of several toxic compounds such as 90–99% furfural and 80–100% phenolic aldehydes, which extended the lag phase to 5 h. Acetic acid concentration increased by 0.2–1 g/l during enzymatic hydrolysis and 0–3.4 g/l during fermentation due to hydrolysis of acetyl groups and minor xylose degradation. Formic acid concentration increased by 0.5–1.5 g/l probably due to degradation of furfural. Phenolic aldehydes were oxidized to the corresponding acids during fermentation reducing the inhibition level.

Keywords: Pilot scale pretreatment; Lignocellulose; Furans; Phenols; Simultaneous saccharification and fermentation; Sacharomyces cerevisiae

Synthesis of a mesoporous functional copolymer bead carrier and its properties for glucoamylase immobilization by Yongxiao Bai; Yanfeng Li; Lin Lei (pp. 457-464).

A series of mesoporous and hydrophilic novel bead carriers containing epoxy groups were synthesized by modified inverse suspension polymerization. Glycidyl methacrylate and acryloyloxyethyl trimethyl ammonium chloride were used as the monomers, and divinyl benzene, allyl methacrylate, and ethylene glycol dimethacrylate as crosslinking agents, respectively. The resulting carriers were employed in the immobilization of glucoamylase (Glu) with covalent bond between epoxy groups and enzymes. The activity recovery of the three series of immobilized Glus could reach 76%, 79%, and 86%, respectively. The immobilized Glus exhibit excellent stability and reusability than that of the free ones.

Keywords: Mesoporous bead carrier; Functional copolymer; Inverse suspension polymerization; Immobilized glucoamylase; Enzymatic reaction

Characterization of a ring-hydroxylating dioxygenase from phenanthrene-degrading Sphingomonas sp. strain LH128 able to oxidize benz[a]anthracene by Luc Schuler; Yves Jouanneau; Sinéad M. Ní Chadhain; Christine Meyer; Maria Pouli; Gerben J. Zylstra; Pascal Hols; Spiros N. Agathos (pp. 465-475).

Sphingomonas sp. strain LH128 was isolated from a polycyclic aromatic hydrocarbon (PAH)-contaminated soil using phenanthrene as the sole source of carbon and energy. A dioxygenase complex, phnA1fA2f, encoding the α and β subunit of a terminal dioxygenase responsible for the initial attack on PAHs, was identified and isolated from this strain. PhnA1f showed 98%, 78%, and 78% identity to the α subunit of PAH dioxygenase from Novosphingobium aromaticivorans strain F199, Sphingomonas sp. strain CHY-1, and Sphingobium yanoikuyae strain B1, respectively. When overexpressed in Escherichia coli, PhnA1fA2f was able to oxidize low-molecular-weight PAHs, chlorinated biphenyls, dibenzo-p-dioxin, and the high-molecular-weight PAHs benz[a]anthracene, chrysene, and pyrene. The action of PhnA1fA2f on benz[a]anthracene produced two benz[a]anthracene dihydrodiols.

Keywords: Bioremediation; Meta-cleavage operon genes; Indigo formation; Rieske nonheme iron oxygenase

Gene cloning, expression, and characterization of a novel trehalose synthase from Arthrobacter aurescens by Wu Xiuli; Ding Hongbiao; Yue Ming; Qiao Yu (pp. 477-482).

Trehalose synthase (TreS) is an intramolecular transglycosylase. It specially catalyzes the conversion of maltose and trehalose. In this study, a novel treS gene, which had a length of 1,797 bp and encoded 598 amino acids, was cloned from Arthrobacter aurescens CGMCC 1.1892 and expressed in Escherichia coli. Thin layer chromatography results indicated that it could catalyze the conversion between maltose and trehalose in one step. However, the ion chromatography results showed that, as a byproduct, about 13% glucose was also produced. The purified recombinant enzyme had a molecular weight of 68 kDa and showed its optimal activity at 35 °C and pH 6.5. This enzyme was not thermostable, and its activity was increased by 1 mM Mg²⁺, Mn²⁺, and Ca²⁺ while strongly inhibited by 5 mM Cu²⁺ and SDS.

Keywords: Trehalose synthase; Trehalose; Arthrobacter aurescens ; Escherichia coli

Mutations at subsite −3 in cyclodextrin glycosyltransferase from Paenibacillus macerans enhancing α-cyclodextrin specificity by Zhaofeng Li; Jiayu Zhang; Miao Wang; Zhengbiao Gu; Guocheng Du; Jianke Li; Jing Wu; Jian Chen (pp. 483-490).

A major disadvantage of cyclodextrin production is the limited cyclodextrin product specificity of cyclodextrin glycosyltransferase (CGTase). Here, we described mutations of Asp372 and Tyr89 at subsite −3 in the CGTase from Paenibacillus macerans strain JFB05-01. The results showed that Asp372 and Tyr89 played important roles in cyclodextrin product specificity of CGTase. The replacement of Asp372 by lysine and Tyr89 by aspartic acid, asparagine, lysine, and arginine resulted in a shift in specificity towards the production of α-cyclodextrin, which was most apparent for the mutants D372K and Y89R. Furthermore, the changes in cyclodextrin product specificity for the single mutants D372K and Y89R could be combined in the double mutant D372K/Y89R, which displayed a 1.5-fold increase in the production of α-cyclodextrin, with a concomitant 43% decrease in the production of β-cyclodextrin when compared to the wild-type CGTase. Thus, the D372K and Y89R single and double mutants were much more suitable for the industrial production of α-cyclodextrin than the wild-type enzyme. The enhanced α-cyclodextrin specificity of these mutants might be a result of stabilizing the bent conformation of the intermediate in the cyclization reaction.

Keywords: Cyclodextrin glycosyltransferase; Cyclodextrin; Product specificity; Paenibacillus macerans ; Mutation; Subsite −3

A novel family VIII carboxylesterase derived from a leachate metagenome library exhibits promiscuous β-lactamase activity on nitrocefin by Konanani Rashamuse; Victoria Magomani; Tina Ronneburg; Dean Brady (pp. 491-500).

The realization that majority of microbes are not amenable to cultivation as isolates under laboratory conditions has led to the culture-independent metagenomic approach as a novel technique for novel biocatalyst discovery. A leachate fosmid shotgun metagenome library was constructed and subsequently screened for esterolytic activities on a tributyrin agar medium. Nucleotide sequencing and translational analysis of an esterase-positive fosmid clone led to the identification of a 1,281 bp esterase gene (estC) encoding a protein (EstC) of 427 aa with translated molecular weight of 46.3 kDa. The EstC primary structure contained a signal leader peptide (29 aa), which could be cleaved to form a mature protein of 398 aa with molecular weight 43.3 kDa. Homology searches revealed that EstC belonged to the family VIII esterases, which exploit a serine residue within the S-x-x-K motif as a catalytic nucleophile. Substrate specificity studies showed that EstC prefers short to medium acyl chain length of p-nitrophenyl esters, a characteristic typical of “true” carboxylesterases. Moreover, EstC represents the first member of the family VIII esterases with a leader peptide and a detectable promiscuous β-lactam hydrolytic activity. Site-directed mutagenesis studies also revealed that in addition to Ser103 and Lys106 residues, the Tyr219 residue also plays a catalytic role in EstC. The organic solvent stability and the specificity towards esters of tertiary alcohols linalyl acetate (3,7-dimethyl-1,6-octadien-3-yl acetate) make EstC potentially useful in biocatalysis.

Keywords: Metagenome library; Carboxylesterases; Promiscuous β-lactamase activity; Family VIII esterases

Molecular characterization of an atoxigenic Aspergillus flavus strain AF051 by Jinhua Jiang; Leiyan Yan; Zhonghua Ma (pp. 501-505).

An atoxigenic Aspergillus flavus strain AF051 collected from a peanut field in Jiangsu province, P. R. China was characterized by analysis of aflatoxin gene cluster in this study. By using a thermal asymmetric interlaced PCR (TAIL-PCR) and conventional PCR techniques, an 89.59-kb deletion was found in the cluster, and this deletion was replaced by a 3.83-kb insert, which was located at 300-bp upstream ver1 gene and 2594-bp downstream a putative gluconolactone oxidase gene. Based on the DNA sequence at the breakpoint, a nested-PCR method was developed for the rapid and sensitive detection of AF051 strain in soil and peanut samples once the strain is used as a biological agent.

Keywords: Aspergillus flavus ; Atoxigenic strain; Aflatoxin gene cluster; Insert

Generation of high-yield rapamycin-producing strains through protoplasts-related techniques by Xiyang Chen; Peilian Wei; Limei Fan; Dong Yang; Xiangchen Zhu; Wenhe Shen; Zhinan Xu; Peilin Cen (pp. 507-512).

Rapamycin is a 31-member ring macrolide produced by Streptomyces hygroscopicus and has many applications in clinical medicine. In the present work, several protoplasts-related techniques including protoplasts mutation, intraspecies and interspecies protoplasts fusion were tried to improve the rapamycin productivity in S. hygroscopicus. Although mutation and fusion of different protoplasts of S. hygroscopicus did not improve the productivity of rapamycin significantly, the interspecies fusion of protoplasts of S. hygroscopicus D7-804 and Streptomyces erythreus ZJU325 could have brought about one high-yield (345 mg/L) rapamycin producer with 23.6% higher than that of the parental strain. Then, with seven mutants of S. hygroscopicus with different features and rapamycin productivities as the parental strains, only one-round genome shuffling has generated a high-yield rapamycin-producing strain with an outstanding yield of 445 mg/L. The systematic research of protoplast-related techniques has established an applicable way to generate high-yield strains from original microorganisms which can only produce low amount of expected natural products, without information of target gene clusters and gene sequences.

Keywords: Protoplast fusion; Streptomyces hygroscopicus ; Rapamycin; Genome shuffling

Microbial production of 3-hydroxydodecanoic acid by pha operon and fadBA knockout mutant of Pseudomonas putida KT2442 harboring tesB gene by Ahleum Chung; Qian Liu; Shao-Ping Ouyang; Qiong Wu; Guo-Qiang Chen (pp. 513-519).

To produce extracellular chiral 3-hydroxyacyl acids (3HA) by fermentation, a novel pathway was constructed by expressing tesB gene encoding thioesterase II into Pseudomonas putida KTOY01, which was a polyhydroxyalkanoate (PHA) synthesis operon knockout mutant. 3HA mixtures of 0.35 g/l consisting of 3-hydroxyhexanoate, 3-hydroxyoctanoate, 3-hydroxydecanoate, and 3-hydroxydodecanoate (3HDD) were produced in shake-flask study using dodecanoate as a sole carbon source. Additional knockout of fadB and fadA genes encoding 3-ketoacyl-CoA thiolase and 3-hydroxyacyl-CoA dehydrogenase in P. putida KTOY01 led to the weakening of the β-oxidation pathway. The fadBA and PHA synthesis operon knockout mutant P. putida KTOY07 expressing tesB gene produced 2.44 g/l 3HA, significantly more than that of the β-oxidation intact mutant. The 3HA mixture contained 90 mol% 3HDD as a dominant component. A fed-batch fermentation process carried out in a 6-l automatic fermentor produced 7.27 g/l extracellular 3HA containing 96 mol% fraction of 3HDD after 28 h of growth. For the first time, it became possible to produce 3HDD-dominant 3HA monomers.

Keywords: Polyhydroxyalkanoates; PHA; 3-hydroxyalkanoic acid; 3HA; 3-hydroxydodecanoic acid; 3HDD; Pseudomonas putida ; 3-Ketoacyl-CoA thiolase; 3-Hydroxyacyl-CoA dehydrogenase; Thioesterase II; TesB; fadBA

Characterisation of a new thermoalkaliphilic bacterium for the production of high-quality hemp fibres, Geobacillus thermoglucosidasius strain PB94A by A. G. Valladares Juárez; J. Dreyer; P. K. Göpel; N. Koschke; D. Frank; H. Märkl; R. Müller (pp. 521-527).

Novel thermophilic and alkaliphilic bacteria for the processing of bast fibres were isolated using hemp pectin as substrate. The strain PB94A, which showed the highest growth rate (µ = 0.5/h) was identified as Geobacillus thermoglucosidasius (DSM 21625). The strain grew optimally at 60°C and pH 8.5. During growth on citrus pectin, the strain produced pectinolytic lyases, which were excreted into the medium. In contrast to the commercially available pectinase Bioprep 3000 L, the enzymes from G. thermoglucosidasius PB94A converted pectin isolated from hemp fibres. In addition to hemp pectin, the culture supernatant also degraded citrus, sugar beet and apple pectin and polygalacturonic acid. When hemp fibres were incubated with the cell-free fermentation broth of G. thermoglucosidasius PB94A, the fineness of the fibres increased. The strain did not produce any cellulases, which is important in order to avoid damaging the fibres during incubation. Therefore, these bacteria or their enzymes can be used to produce fine high-quality hemp fibres.

Keywords: Geobacillus thermoglucosidasius ; Hemp; Pectin degradation; Fibre retting

Importance of malate synthase in the glyoxylate cycle of Ashbya gossypii for the efficient production of riboflavin by Takashi Sugimoto; Shin Kanamasa; Tatsuya Kato; Enoch Y. Park (pp. 529-539).

The glyoxylate cycle is an anabolic pathway that is necessary for growth on nonfermentable carbon sources such as vegetable oils and is important for riboflavin production by the filamentous fungus Ashbya gossypii. The aim of this study was to identify malate synthase in the glyoxylate cycle of A. gossypii and to investigate its importance in riboflavin production from rapeseed oil. The ACR268C gene was identified as the malate synthase gene that encoded functional malate synthase in the glyoxylate cycle. The ACR268C gene knockout mutant lost malate synthase activity, and its riboflavin production and oil consumption were 10- and 2-fold lower, respectively, than the values of the wild-type strain. In contrast, the ACR268C gene-overexpressing strain showed a 1.6-fold increase in the malate synthase activity and 1.7-fold higher riboflavin production than the control strain. These results demonstrate that the malate synthase in the glyoxylate cycle has an important role not only in riboflavin production but also in oil consumption.

Keywords: Riboflavin; Ashbya gossypii ; Malate synthase; Gene disruptant; Gene-targeting disruption; Glyoxylate cycle

Anti-adhesion activity of two biosurfactants produced by Bacillus spp. prevents biofilm formation of human bacterial pathogens by F. Rivardo; R. J. Turner; G. Allegrone; H. Ceri; M. G. Martinotti (pp. 541-553).

In this work, two biosurfactant-producing strains, Bacillus subtilis and Bacillus licheniformis, have been characterized. Both strains were able to grow at high salinity conditions and produce biosurfactants up to 10% NaCl. Both extracted-enriched biosurfactants showed good surface tension reduction of water, from 72 to 26–30 mN/m, low critical micelle concentration, and high resistance to pH and salinity. The potential of the two lipopeptide biosurfactants at inhibiting biofilm adhesion of pathogenic bacteria was demonstrated by using the MBEC device. The two biosurfactants showed interesting specific anti-adhesion activity being able to inhibit selectively biofilm formation of two pathogenic strains. In particular, Escherichia coli CFT073 and Staphylococcus aureus ATCC 29213 biofilm formation was decreased of 97% and 90%, respectively. The V9T14 biosurfactant active on the Gram-negative strain was ineffective against the Gram-positive and the opposite for the V19T21. This activity was observed either by coating the polystyrene surface or by adding the biosurfactant to the inoculum. Two fractions from each purified biosurfactant, obtained by flash chromatography, fractions (I) and (II), showed that fraction (II), belonging to fengycin-like family, was responsible for the anti-adhesion activity against biofilm of both strains.

Keywords: Bacillus ; Biosurfactant; Biofilm; Anti-adhesion; Escherichia coli CFT073; Staphylococcus aureus ATCC 29213

Physiological and taxonomic description of the novel autotrophic, metal oxidizing bacterium, Pseudogulbenkiania sp. strain 2002 by Karrie A. Weber; David B. Hedrick; Aaron D. Peacock; J. Cameron Thrash; David C. White; Laurie A. Achenbach; John D. Coates (pp. 555-565).

A lithoautotrophic, Fe(II) oxidizing, nitrate-reducing bacterium, strain 2002 (ATCC BAA-1479; =DSM 18807), was isolated as part of a study on nitrate-dependent Fe(II) oxidation in freshwater lake sediments. Here we provide an in-depth phenotypic and phylogenetic description of the isolate. Strain 2002 is a gram-negative, non-spore forming, motile, rod-shaped bacterium which tested positive for oxidase, catalase, and urease. Analysis of the complete 16S rRNA gene sequence placed strain 2002 in a clade within the family Neisseriaceae in the order Nessieriales of the Betaproteobacteria 99.3% similar to Pseudogulbenkiania subflava. Similar to P. sublfava, predominant whole cell fatty acids were identified as 16:17c, 42.4%, and 16:0, 34.1%. Whole cell difference spectra of the Fe(II) reduced minus nitrate oxidized cyctochrome content revealed a possible role of c-type cytochromes in nitrate-dependent Fe(II) oxidation. Strain 2002 was unable to oxidize aqueous or solid-phase Mn(II) with nitrate as the electron acceptor. In addition to lithotrophic growth with Fe(II), strain 2002 could alternatively grow heterotrophically with long-chain fatty acids, simple organic acids, carbohydrates, yeast extract, or casamino acids. Nitrate, nitrite, nitrous oxide, and oxygen also served as terminal electron acceptors with acetate as the electron donor.

Keywords: Fe(II) oxidation; Anaerobic; Nitrate; Bioremediation; Uranium

Biosorption of Cr(VI) from aqueous solution using A. hydrophila in up-flow column: optimization of process variables by S. H. Hasan; P. Srivastava; D. Ranjan; M. Talat (pp. 567-577).

In the present study, continuous up-flow fixed-bed column study was carried out using immobilized dead biomass of Aeromonas hydrophila for the removal of Cr(VI) from aqueous solution. Different polymeric matrices were used to immobilized biomass and polysulfone-immobilized biomass has shown to give maximum removal. The sorption capacity of immobilized biomass for the removal of Cr(VI) evaluating the breakthrough curves obtained at different flow rate and bed height. A maximum of 78.58% Cr(VI) removal was obtained at bed height of 19 cm and flow rate of 2 mL/min. Bed depth service time model provides a good description of experimental results with high correlation coefficient (>0.996). An attempt has been made to investigate the individual as well as cumulative effect of the process variables and to optimize the process conditions for the maximum removal of chromium from water by two-level two-factor full-factorial central composite design with the help of Minitab ® version 15 statistical software. The predicted results are having a good agreement (R ² = 98.19%) with the result obtained. Sorption–desorption studies revealed that polysulfone-immobilized biomass could be reused up to 11 cycles and bed was completely exhausted after 28 cycles.

Keywords: Aeromonas hydrophila ; Cr(VI); Sorption; Bed depth service time; Desorption; Central composite design

Inhibition of microbiological sulfide oxidation by methanethiol and dimethyl polysulfides at natron-alkaline conditions by Pim L. F. van den Bosch; Marco de Graaff; Marc Fortuny-Picornell; Robin C. van Leerdam; Albert J. H. Janssen (pp. 579-587).

To avoid problems related to the discharge of sulfidic spent caustics, a biotechnological process is developed for the treatment of gases containing both hydrogen sulfide and methanethiol. The process operates at natron-alkaline conditions (>1 mol L⁻¹ of sodium- and potassium carbonates and a pH of 8.5–10) to enable the treatment of gases with a high partial CO₂ pressure. In the process, methanethiol reacts with biologically produced sulfur particles to form a complex mixture predominantly consisting of inorganic polysulfides, dimethyl disulfide (DMDS), and dimethyl trisulfide (DMTS). The effect of these organic sulfur compounds on the biological oxidation of sulfide to elemental sulfur was studied with natron-alkaliphilic bacteria belonging to the genus Thioalkalivibrio. Biological oxidation rates were reduced by 50% at 0.05 mM methanethiol, while for DMDS and DMTS, this was estimated to occur at 1.5 and 1.0 mM, respectively. The inhibiting effect of methanethiol on biological sulfide oxidation diminished due to its reaction with biologically produced sulfur particles. This reaction increases the feasibility of biotechnological treatment of gases containing both hydrogen sulfide and methanethiol at natron-alkaline conditions.

Keywords: Methanethiol; Polysulfide; Sulfide oxidation; Spent caustics; Thioalkalivibrio

Use of cyclodextrin and its derivatives for increased transformation efficiency of competent bacterial cells by Finn Lillelund Aachmann; Trond Erik Vee Aune (pp. 589-596).

Methodologies for introduction of DNA into cells are essential in molecular genetics and vital for applications such as genetic engineering and gene therapy. The use of cyclodextrins (CyDs) for increased efficiency of introducing DNA into eukaryotic cells (transfection) has been reported, but CyDs’ effect on the introduction of DNA into bacterial cells (transformation) is unknown. Here, we have investigated the potential of using CyDs in the transformation of chemically competent in-house, commercially available, and, on non-competent bacterial cells, with plasmid DNA of two different sizes. Possible interactions between CyDs and DNA were studied with nuclear magnetic resonance (NMR) spectroscopy. The presence of CyDs resulted in an up to fourfold increment of the transformation rate for in-house cells, with β-CyD and derivates giving the strongest effect. For commercial cells and transformation with megaplasmids, a more moderate effect around 1.4-fold was obtained. However, CyDs have little or no effect on DNA uptake by noncompetent cells. Results obtained from NMR spectroscopy show no interactions between CyDs and DNA-like molecules, which indicated that the CyDs’ effect is related to the bacterial cell wall.

Keywords: Cyclodextrins; DNA; Plasmid; Bacteria; Competent cell; Transformation

Use of cyclodextrin and its derivatives for increased transformation efficiency of competent bacterial cells by Finn Lillelund Aachmann; Trond Erik Vee Aune (pp. 589-596).

Keywords: Cyclodextrins; DNA; Plasmid; Bacteria; Competent cell; Transformation

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Applied Microbiology and Biotechnology (v.83, #3)

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Applied Microbiology and Biotechnology (v.83, #3)