Check out our New Publishers' Select for Free Articles

Applied Microbiology and Biotechnology (v.92, #6)

Microbial degradation of furanic compounds: biochemistry, genetics, and impact by Nick Wierckx; Frank Koopman; Harald J. Ruijssenaars; Johannes H. de Winde (pp. 1095-1105).

Microbial metabolism of furanic compounds, especially furfural and 5-hydroxymethylfurfural (HMF), is rapidly gaining interest in the scientific community. This interest can largely be attributed to the occurrence of toxic furanic aldehydes in lignocellulosic hydrolysates. However, these compounds are also widespread in nature and in human processed foods, and are produced in industry. Although several microorganisms are known to degrade furanic compounds, the variety of species is limited mostly to Gram-negative aerobic bacteria, with a few notable exceptions. Furanic aldehydes are highly toxic to microorganisms, which have evolved a wide variety of defense mechanisms, such as the oxidation and/or reduction to the furanic alcohol and acid forms. These oxidation/reduction reactions constitute the initial steps of the biological pathways for furfural and HMF degradation. Furfural degradation proceeds via 2-furoic acid, which is metabolized to the primary intermediate 2-oxoglutarate. HMF is converted, via 2,5-furandicarboxylic acid, into 2-furoic acid. The enzymes in these HMF/furfural degradation pathways are encoded by eight hmf genes, organized in two distinct clusters in Cupriavidus basilensis HMF14. The organization of the five genes of the furfural degradation cluster is highly conserved among microorganisms capable of degrading furfural, while the three genes constituting the initial HMF degradation route are organized in a highly diverse manner. The genetic and biochemical characterization of the microbial metabolism of furanic compounds holds great promises for industrial applications such as the biodetoxifcation of lignocellulosic hydrolysates and the production of value-added compounds such as 2,5-furandicarboxylic acid.

Keywords: Furfural; Hydroxymethylfurfural; Lignocellulosic hydrolysate; Metabolic pathway; Detoxification

Bacteria-mediated disease therapy by Hao Yu (pp. 1107-1113).

Laboratory bacteria have been model systems for studying gene function or developing molecular biotechnologies; industrial bacteria have been used to produce drugs, foods, fuel etc.; while pathogenic bacteria have been the subject of infectious diseases studies with aim of controlling them. Recently, with our increasing knowledge in molecular biology, bacterial genetics, and immunology, bacteria have gained increased interest in therapeutic applications. This review will summarize recent advances toward applying bacteria in treatment of diseases, such as inflammatory disease, cancer, and virus infection. Probiotics have long been appreciated for their immunomodulatory effect, which are discussed in the anti-inflammatory section. Anaerobic bacteria have been applied for destructing tumor cells or used as a magic bullet to specifically deliver therapeutic agents to tumor tissue. Examples and strategies of applying those tumor-targeting bacteria are discussed in the antitumor section. Finally, the pioneer study of applying Salmonella in delivering RNase P that was specifically engineered to target essential mRNAs of virus is summarized.

Keywords: Probiotics; Anti-inflammatory; Antitumor; Antivirus; Oncolytic; Bacteriolytic; Gene therapy

Bioluminescence and its application in the monitoring of antimicrobial photodynamic therapy by Eliana Alves; Liliana Costa; Ângela Cunha; Maria Amparo F. Faustino; Maria Graça P. M. S. Neves; Adelaide Almeida (pp. 1115-1128).

Light output from bioluminescent microorganisms is a highly sensitive reporter of their metabolic activity and therefore can be used to monitor in real time the effects of antimicrobials. Antimicrobial photodynamic therapy (aPDT) is receiving considerable attention for its potentialities as a new antimicrobial treatment modality. This therapy combines oxygen, a nontoxic photoactive photosensitizer, and visible light to generate reactive oxygen species (singlet oxygen and free radicals) that efficiently destroy microorganisms. To monitor this photoinactivation process, faster methods are required instead of laborious conventional plating and overnight incubation procedures. The bioluminescence method is a very interesting approach to achieve this goal. This review covers recent developments on the use of microbial bioluminescence in aPDT in the clinical and environmental areas.

Keywords: Bioluminescence; Biotechnology; Antimicrobial photodynamic therapy; Biomedical research; Environmental microbiology; Tetrapyrrolic macrocycles; Drug monitoring

Peculiarities of Pycnoporus species for applications in biotechnology by Anne Lomascolo; Eva Uzan-Boukhris; Isabelle Herpoël-Gimbert; Jean-Claude Sigoillot; Laurence Lesage-Meessen (pp. 1129-1149).

The genus Pycnoporus forms a cosmopolitan group of four species belonging to the polyporoid white-rot fungi, the most representative group of homobasidiomycetes causing wood decay. Pycnoporus fungi are listed as food- and cosmetic-grade microorganisms and emerged in the early 1990s as a genus whose biochemistry, biodegradation and biotechnological properties have since been progressively detailed. First highlighted for their original metabolic pathways involved in the functionalization of plant cell wall aromatic compounds to yield high-value molecules, e.g. aromas and antioxidants, the Pycnoporus species were later explored for their potential to produce various enzymes of industrial interest, such as hydrolases and oxidases. However, the most noteworthy feature of the genus Pycnoporus is its ability to overproduce high redox potential laccase—a multi-copper extracellular phenoloxidase—as the predominant ligninolytic enzyme. A major potential use of the Pycnoporus fungi is thus to harness their laccases for various applications such as the bioconversion of agricultural by-products and raw plant materials into valuable products, the biopulping and biobleaching of paper pulp and the biodegradation of organopollutants, xenobiotics and industrial contaminants. All the studies performed in the last decade show the genus Pycnoporus to be a strong contender for white biotechnology. In this review, we describe the properties of Pycnoporus fungi in relation to their biotechnological applications and potential.

Keywords: Pycnoporus ; Biotechnology; Enzyme; Laccase; Flavour; Application

Peptide derived from anti-idiotypic single-chain antibody is a potent antifungal agent compared to its parent fungicide HM-1 killer toxin peptide by M. Enamul Kabir; Nurul Karim; Senthilkumar Krishnaswamy; Dakshnamurthy Selvakumar; Masahiko Miyamoto; Yasuhiro Furuichi; Tadazumi Komiyama (pp. 1151-1160).

Based on anti-idiotypic network theory in light of the need for new antifungal drugs, we attempted to identify biologically active fragments from HM-1 yeast killer toxin and its anti-idiotypic antibody and to compare their potency as an antifungal agent. Thirteen overlapping peptides from HM-1 killer toxin and six peptides from its anti-idiotypic single-chain variable fragment (scFv) antibodies representing the complementarity determining regions were synthesized. The binding affinities of these peptides were investigated and measured by Dot blot and surface plasmon resonance analysis and finally their antifungal activities were investigated by inhibition of growth, colony forming unit assay. Peptide P6, containing the potential active site of HM-1 was highly capable of inhibiting the growth of Saccharomyces cerevisiae but was less effective on pathogenic fungi. However, peptide fragments derived from scFv antibody exerted remarkable inhibitory effect on the growth of pathogenic strains of Candida and Cryptococcus species in vitro. One scFv-derived decapeptide (SP6) was selected as the strongest killer peptide for its high binding affinity and antifungal abilities on both Candida and Cryptococcus species with IC₅₀ values from 2.33 × 10⁻⁷ M to 36.0 × 10⁻⁷ M. SP6 peptide activity was neutralized by laminarin, a β-1,3-glucan molecule, indicating this peptide derived from scFv anti-idiotypic antibody retains antifungal activity through interaction with cell wall β-glucan of their target fungal cells. Experimental evidence strongly suggested the possibility of development of anti-idiotypic scFv peptide-based antifungal agents which may lead to improve therapeutics for the management of varieties of fungal infections.

Keywords: HM-1 yeast killer toxin; Recombinant anti-idiotypic antibody; Antifungal peptides; Complementarity determining regions; β-1; 3-glucan

Cell growth and P(3HB) accumulation from CO₂ of a carbon monoxide-tolerant hydrogen-oxidizing bacterium, Ideonella sp. O-1 by Kenji Tanaka; Kenta Miyawaki; Akane Yamaguchi; Kianoush Khosravi-Darani; Hiromi Matsusaki (pp. 1161-1169).

Cell growth and accumulation of polyhydroxybutyric acid, P(3HB), from CO₂ in autotrophic condition of a newly isolated hydrogen-oxidizing bacterium, the strain O-1, was investigated. The bacterium, which was deposited in the Japan Collection of Microorganisms as JCM17105, autotrophically grows by assimilating H₂, O₂, and CO₂ as substrate. 16S rRNA gene sequence of the bacterium was the closest to Ideonella dechloratans (99%). Specific growth rate of the strain O-1 was faster than a hydrogen-oxidizing bacterium, Ralstonia eutropha, which is well-known P(3HB)-producing microorganism. The strain O-1 is tolerant to high O₂ concentration and it can grow above 30% (v/v) O₂, while the growth of R. eutropha and Alcaligenes latus was seriously inhibited. In culture medium containing 1 g/L (NH₄)₂SO₄, cell concentration of the strain O-1 and P(3HB) increased to 6.75 and 5.26 g/L, respectively. The content of P(3HB) in the cells was 77.9% (w/w). The strain O-1 was very tolerant to carbon monoxide (CO) and it grew even at 70% (v/v) CO, while the growth of R. eutropha and A. latus were seriously inhibited at 5% (v/v) CO. From these results, it is expected that the strain O-1 will be useful in the manufacture of P(3HB) because the industrial exhaust gas containing CO₂, H₂, and CO can be directly used as the substrate in the fermentation process.

Keywords: Hydrogen-oxidizing bacteria; Ideonella ; PHB; CO₂ ; CO

Synthesis and properties of a novel biosuperabsorbent from alkali soluble Rhizomucor pusillus proteins by Sara Majdejabbari; Hamidreza Barghi; Mohammad J. Taherzadeh (pp. 1171-1177).

A novel biosuperabsorbent protein hydrogel was prepared from protein-rich alcoholic–alkali soluble parts of zygomycete Rhizomucor pusillus biomass. The fungal protein content was 46.8%, and the lipid content was 13.1%. Extraction of protein from this microorganism through the method applied prevents protein decomposition, resulting in maximum yield. After alcoholic–alkaline extraction, the proteins from the biomass were acylated using ethylenediaminetetraacetic dianhydride and subsequently treated with glutaraldehyde as a crosslinker for further experiments. Thermal consistency was investigated by means of two different methods: thermal denaturation via differential scanning calorimetry and thermal decomposition study via thermogravimetric analysis. The swelling behaviour of the crosslinked hydrogel was measured in deionised water, 0.9% NaCl solution and synthetic urine, which were 87.6, 43 and 38.6 g/g water after 24 h, respectively. Moreover, the isoelectric point (pI) of the hydrogel was determined as pH = 8 by studying swelling behaviour at different pHs. In addition, the dependencies of the swelling behaviour with regard to the chemical modification, the ionic strength, the degree of crosslinking, as well as water absorbency with or without load were studied.

Keywords: Biosuperabsorbent; Chemical modification; Protein; Rhizomucor pusillus ; Zygomycetes

Characterization of two β-xylosidases from Bifidobacterium adolescentis and their contribution to the hydrolysis of prebiotic xylooligosaccharides by Stijn Lagaert; Annick Pollet; Jan A. Delcour; Rob Lavigne; Christophe M. Courtin; Guido Volckaert (pp. 1179-1185).

Xylooligosaccharides have strong bifidogenic properties and are increasingly used as a prebiotic. Nonetheless, little is known about the degradation of these substrates by bifidobacteria. We characterized two recombinant β-xylosidases, XylB and XylC, with different substrate specificities from Bifidobacterium adolescentis. XylB is a novel β-xylosidase that belongs to the recently introduced glycoside hydrolase family 120. In contrast to most reported β-xylosidases, it shows only weak activity on xylobiose and prefers xylooligosaccharides with a degree of polymerization above two. The remaining xylobiose is efficiently hydrolyzed by the second B. adolescentis β-xylosidase, XylC, a glycoside hydrolase of family 43. Furthermore, XylB releases more xylose from arabinose-substituted xylooligosaccharides than XylC (30% and 20%, respectively). The different specificities of XylB, XylC, and the recently described reducing-end xylose-releasing exo-oligoxylanase RexA show how B. adolescentis can efficiently degrade prebiotic xylooligosaccharides.

Keywords: Bifidobacterium adolescentis ; Xylooligosaccharides; Prebiotic; Betaxylosidase

Characterization of a recombinant cellobiose 2-epimerase from Caldicellulosiruptor saccharolyticus and its application in the production of mannose from glucose by Chang-Su Park; Jung-Eun Kim; Jin-Geun Choi; Deok-Kun Oh (pp. 1187-1196).

A putative N-acyl-d-glucosamine 2-epimerase from Caldicellulosiruptor saccharolyticus was cloned and expressed in Escherichia coli. The recombinant enzyme was identified as a cellobiose 2-epimerase by the analysis of the activity for substrates, acid-hydrolyzed products, and amino acid sequence. The cellobiose 2-epimerase was purified with a specific activity of 35 nmol min^–1 mg^–1 for d-glucose with a 47-kDa monomer. The epimerization activity for d-glucose was maximal at pH 7.5 and 75°C. The half-lives of the enzyme at 60°C, 65°C, 70°C, 75°C, and 80°C were 142, 71, 35, 18, and 4.6 h, respectively. The enzyme catalyzed the epimerization reactions of the aldoses harboring hydroxyl groups oriented in the right-hand configuration at the C2 position and the left-hand configuration at the C3 position, such as d-glucose, d-xylose, l-altrose, l-idose, and l-arabinose, to their C2 epimers, such as d-mannose, d-lyxose, l-allose, l-gulose, and l-ribose, respectively. The enzyme catalyzed also the isomerization reactions. The enzyme exhibited the highest activity for mannose among monosaccharides. Thus, mannose at 75 g l^–1 and fructose at 47.5 g l^–1 were produced from 500 g l^–1 glucose at pH 7.5 and 75°C over 3 h by the enzyme.

Keywords: Mannose production; Epimerization; Isomerization; Thermostable enzyme; Cellobiose 2-epimerase; Caldicellulosiruptor saccharolyticus

A carrier fusion significantly induces unfolded protein response in heterologous protein production by Aspergillus oryzae by Ayako Ohno; Jun-ichi Maruyama; Takashi Nemoto; Manabu Arioka; Katsuhiko Kitamoto (pp. 1197-1206).

In heterologous protein production by filamentous fungi, target proteins are expressed as fusions with homologous secretory proteins, called carriers, for higher production yields. Although carrier fusion is thought to overcome the bottleneck in transcriptional and (post)translational processes during heterologous protein production, there is limited knowledge of its physiological effects on the host strain. In this study, we performed DNA microarray analysis by comparing gene expression patterns of two Aspergillus oryzae strains expressing either carrier- or non-carrier-fused bovine chymosin (CHY). When CHY was expressed as a fusion with α-amylase (AmyB), the production level increased by approximately 2-fold as compared with the non-carrier-fused CHY. DNA microarray analysis revealed that the carrier fusion significantly up-regulated many genes involved in endoplasmic reticulum (ER) protein-folding and secretion. Consistently, hacA transcripts were efficiently spliced in the strain expressing the carrier-fused CHY, indicating an unfolded protein response (UPR). The carrier-fused CHY was detected intracellularly without processing at the Kex2 cleavage site, which is likely recognized in the Golgi, and the carrier fusion delayed extracellular CHY production in the early growth phase as compared with the non-carrier-fused expression. Taken together, our data suggest a proposal that the carrier fusion temporarily accumulates the carrier-fused CHY in the ER and significantly induces UPR.

Keywords: Aspergillus oryzae ; Heterologous protein production; Carrier; UPR; ER

Expression of a lipid-inducible, self-regulating form of Yarrowia lipolytica lipase LIP2 in Saccharomyces cerevisiae by Jay Shockey; Dorselyn Chapital; Satinder Gidda; Catherine Mason; Gaynelle Davis; K. Thomas Klasson; Heping Cao; Robert Mullen; John Dyer (pp. 1207-1217).

Saccharomyces cerevisiae is frequently used as a bioreactor for conversion of exogenously acquired metabolites into value-added products, but has not been utilized for bioconversion of low-cost lipids such as triacylglycerols (TAGs) because the cells are typically unable to acquire these lipid substrates from the growth media. To help circumvent this limitation, the Yarrowia lipolytica lipase 2 (LIP2) gene was cloned into S. cerevisiae expression vectors and used to generate S. cerevisiae strains that secrete active Lip2 lipase (Lip2p) enzyme into the growth media. Specifically, LIP2 expression was driven by the S. cerevisiae PEX11 promoter, which maintains basal transgene expression levels in the presence of sugars in the culture medium but is rapidly upregulated by fatty acids. Northern blotting, lipase enzyme activity assays, and gas chromatographic measurements of cellular fatty acid composition after lipid feeding all confirmed that cells transformed with the PEX11 promoter–LIP2 construct were responsive to lipids in the media, i.e., cells expressing LIP2 responded rapidly to either free fatty acids or TAGs and accumulated high levels of the corresponding fatty acids in intracellular lipids. These data provided evidence of the creation of a self-regulating positive control feedback loop that allows the cells to upregulate Lip2p production only when lipids are present in the media. Regulated, autonomous production of extracellular lipase activity is a necessary step towards the generation of yeast strains that can serve as biocatalysts for conversion of low-value lipids to value-added TAGs and other novel lipid products.

Keywords: Saccharomyces cerevisiae ; Lipase; Lipid; Bioconversion; PEX11

The P_II protein GlnK is a pleiotropic regulator for morphological differentiation and secondary metabolism in Streptomyces coelicolor by Eva Waldvogel; Alexander Herbig; Florian Battke; Rafat Amin; Merle Nentwich; Kay Nieselt; Trond E. Ellingsen; Alexander Wentzel; David A. Hodgson; Wolfgang Wohlleben; Yvonne Mast (pp. 1219-1236).

GlnK is an important nitrogen sensor protein in Streptomyces coelicolor. Deletion of glnK results in a medium-dependent failure of aerial mycelium and spore formation and loss of antibiotic production. Thus, GlnK is not only a regulator of nitrogen metabolism but also of morphological differentiation and secondary metabolite production. Through a comparative transcriptomic approach between the S. coelicolor wild-type and a S. coelicolor glnK mutant strain, 142 genes were identified that are differentially regulated in both strains. Among these are genes of the ram and rag operon, which are involved in S. coelicolor morphogenesis, as well as genes involved in gas vesicle biosynthesis and ectoine biosynthesis. Surprisingly, no relevant nitrogen genes were found to be differentially regulated, revealing that GlnK is not an important nitrogen sensor under the tested conditions.

Keywords: Actinomycetes; P_II protein; GlnK; Transcriptome; Glutamate

RNA-Seq of the xylose-fermenting yeast Scheffersomyces stipitis cultivated in glucose or xylose by Tiezheng Yuan; Yan Ren; Kun Meng; Yun Feng; Peilong Yang; Shaojing Wang; Pengjun Shi; Lei Wang; Daoxin Xie; Bin Yao (pp. 1237-1249).

Xylose is the second most abundant lignocellulosic component besides glucose, but it cannot be fermented by the widely used ethanol-producing yeast Saccharomyces cerevisiae. The yeast Scheffersomyces stipitis, however, is well known for its high native capacity to ferment xylose. Here, we applied next-generation sequencing technology for RNA (RNA-Seq) to generate two high-resolution transcriptional maps of the S. stipitis genome when this yeast was grown using glucose or xylose as the sole carbon source. RNA-Seq revealed that 5,176 of 5,816 annotated open reading frames had a uniform transcription and that 214 open reading frames were differentially transcribed. Differential expression analysis showed that, compared with other biological processes, carbohydrate metabolism and oxidation-reduction reactions were highly enhanced in yeast grown on xylose. Measurement of metabolic indicators of fermentation showed that, in yeast grown on xylose, the concentrations of cysteine and ornithine were twofold higher and the concentrations of unsaturated fatty acids were also increased. Analysis of metabolic profiles coincided with analysis of certain differentially expressed genes involved in metabolisms of amino acid and fatty acid. In addition, we predicted protein–protein interactions of S. stipitis through integration of gene orthology and gene expression. Further analysis of metabolic and protein–protein interactions networks through integration of transcriptional and metabolic profiles predicted correlations of genes involved in glycolysis, the tricarboxylic acid cycle, gluconeogenesis, sugar uptake, amino acid metabolism, and fatty acid β-oxidation. Our study reveals potential target genes for xylose fermentation improvement and provides insights into the mechanisms underlying xylose fermentation in S. stipitis.

Keywords: Scheffersomyces stipitis ; Xylose fermentation; Transcriptome; RNA-Seq; Metabolic networks; Protein–protein interactions

B cells are required for tumor-targeting Salmonella in host by Che-Hsin Lee; Jeng-Long Hsieh; Chao-Liang Wu; Hui-Chun Hsu; Ai-Li Shiau (pp. 1251-1260).

Systemic administration of Salmonella to tumor-bearing mice leads to the preferential accumulation within tumor sites and retardation of the tumor growth. Host factors including innate and adaptive immune responses influence Salmonella-induced antitumor activity. Antitumor activities of Salmonella are not only determined by the tumor regression but also by the host immune response. Herein, we demonstrated that B cells play an important role in the antitumor activity mediated by Salmonella. Body weight and survival of B cell-deficient mice were decreased compared with wild-type, CD8⁺ cell-deficient, or CD4⁺ cell-deficient mice after Salmonella administration. Although Salmonella accumulated within the tumors in B cell-deficient mice, the bacterial loads of healthy organs were higher than those in wild-type mice. The inflammation cytokine and bacteremia were found in B cell-deficient mice after Salmonella treatment. When Salmonella accumulated within the tumor, B cells inhibited the dissemination of Salmonella to other healthy organs. The depletion of host B cells resulted in a noticeably higher total number of Salmonella in the tumor and inhibited tumor growth. Meanwhile, B cell-depletive and B cell-adoptive transfer of serum experiments demonstrated that the natural antibody produced by B cell takes part in the control of Salmonella dissemination in tumor-bearing mice. In this study, we want to address the mechanisms of incorporating host immunoresponse as a way to augment the antitumor activities of Salmonella.

Keywords: B cell; Salmonella ; Tumor targeting; Natural antibody

Evaluation of cell damage caused by cold sampling and quenching for metabolome analysis by Friederike Schädel; Florian David; Ezequiel Franco-Lara (pp. 1261-1274).

Cell damage during sampling and quenching for metabolome analysis have been investigated at whole sample level using an OD-based method and ATP loss investigation, and at single cell level by means of flow cytometry. Escherichia coli was cultivated in shake flasks and sampled into several cold quenching solutions during exponential growth phase varying quenching solution composition and sampling temperature. For single cell analysis, the samples were incubated with selective propidium iodide dye and analysed via flow cytometry to differentiate between intact and damaged cells. It was found that every combination of quenching solution, temperature, or cooling rate tested influenced the E. coli cell membrane integrity indicating rupture which will not only let the dye in, but also intracellular ATP out of the cells, which is not desired in in vivo metabolome analysis.

Keywords: Cell leakage; Quenching; Flow cytometry; Propidium iodide; Membrane integrity

Optimized compatible set of BioBrick™ vectors for metabolic pathway engineering by Jacob E. Vick; Ethan T. Johnson; Swati Choudhary; Sarah E. Bloch; Fernando Lopez-Gallego; Poonam Srivastava; Ilya B. Tikh; Grayson T. Wawrzyn; Claudia Schmidt-Dannert (pp. 1275-1286).

The BioBrick™ paradigm for the assembly of enzymatic pathways is being adopted and becoming a standard practice in microbial engineering. We present a strategy to adapt the BioBrick™ paradigm to allow the quick assembly of multi-gene pathways into a number of vectors as well as for the quick mobilization of any cloned gene into vectors with different features for gene expression and protein purification. A primary BioBrick™ (BB-eGFP) was developed where the promoter/RBS, multiple cloning sites, optional protein purification affinity tags and reporter gene were all separated into discrete regions by additional restriction enzymes. This primary BB-eGFP then served as the template for additional BioBrick™ vectors with different origins of replication, antibiotic resistances, inducible promoters (arabinose, IPTG or anhydrotetracycline), N- or C-terminal Histidine tags with thrombin cleavage, a LacZα reporter gene and an additional origin of mobility (oriT). All developed BioBricks™ and BioBrick™ compatible vectors were shown to be functional by measuring reporter gene expression. Lastly, a C₃₀ carotenoid pathway was assembled as a model enzymatic pathway to demonstrate in vivo functionality and compatibility of this engineered vector system.

Keywords: BioBrick™; Synthetic biology; Pathway engineering; Vector system; Escherichia coli ; Carotenoid; Metabolic engineering

Validation of the H₂S method to detect bacteria of fecal origin by cultured and molecular methods by Lanakila McMahan; Anthony A. Devine; Amy M. Grunden; Mark D. Sobsey (pp. 1287-1295).

Using biochemical and molecular methods, this research determined whether or not the H₂S test did correctly identify sewage-contaminated waters by being the first to use culturing and molecular methods to identify the types and numbers of fecal indicator organisms, pathogens, and other microbes present in sewage samples with positive H₂S test results. For the culture-based method, samples were analyzed for the presence of fecal bacteria by spread plating the sewage sample onto differential and selective media for Aeromonas spp., Escherichia coli, sulfite-reducing clostridia, H₂S-producing bacteria, and Salmonella/Shigella spp. The isolates were then: (1) tested to determine whether they were H₂S-producing organisms and (2) identified to the genus and species level using biochemical methods. The molecular method used to characterize the microbial populations of select samples was terminal restriction fragment length polymorphisms. These experiments on sewage provided evidence that positive H₂S tests consistently contained fecal bacteria and pathogens. There were strong relationships of agreement between the organisms identified by both methods tested. This study is an important advance in microbial water quality detection since it is focused on the evaluation of a novel, low-cost, water microbiology test that has the potential to provide millions of people worldwide access to water quality detection technology. Of prime consideration in evaluating water quality tests is the determination of the test’s accuracy and specificity, and this article is a fundamental step in providing that information.

Keywords: H₂S test; TRFLP; Microbial water quality

Selectively inducing the synthesis of a key structural exopolysaccharide in aerobic granules by enriching for Candidatus “Competibacter phosphatis” by Thomas William Seviour; Lynette K. Lambert; Maite Pijuan; Zhiguo Yuan (pp. 1297-1305).

A gel-forming exopolysaccharide was previously shown to play an important structural role in aerobic granules treating nutrient-rich industrial wastewater. To identify whether this exopolysaccharide performs a similar role in other granular biomass and if conditions favouring its production can be more precisely elucidated, extracellular polymeric substances (EPS) were extracted from granules grown under four different operating conditions. ¹H nuclear magnetic resonance (NMR) spectroscopy of their EPS indicated that the gel-forming exopolysaccharide was expressed in two granular sludges both enriched in Candidatus “Competibacter phosphatis”. In contrast, it was not expressed in granules performing denitrification with methanol as a carbon source and nitrate as the electron acceptor or granules enriched in Candidatus “Accumulibacter phosphatis” performing enhanced biological phosphorus removal from synthetic wastewater. In one of the first two sludges, the exopolysaccharide contained in the seeding granular sludge continued to be a major component of the granule EPS while Competibacter was being enriched. In the second sludge, a floccular sludge not containing the gel-forming exopolysaccharide initially was also enriched for Competibacter. In this sludge, an increase in particle size was detected coinciding with a yield increase of EPS. NMR spectroscopy confirmed its yield increase to be attributable to the production of this structural gel-forming exopolysaccharide. The results show that (1) the particular gel-forming exopolysaccharide previously identified is not necessarily a key structural exopolysaccharide for all granule types, and (2) synthesis of this exopolysaccharide is induced under conditions favouring the selective enrichment of Competibacter. This indicates that Competibacter may be involved in its production.

Keywords: Aerobic sludge granules; Exopolysaccharides; EPS; NMR; Competibacter

Population dynamics and current-generation mechanisms in cassette-electrode microbial fuel cells by Kazuya Watanabe; Morio Miyahara; Takefumi Shimoyama; Kazuhito Hashimoto (pp. 1307-1314).

Cassette-electrode microbial fuel cells (CE-MFCs) have been demonstrated useful to treat biomass wastes and recover electric energy from them. In order to reveal electricity-generation mechanisms in CE-MFCs, the present study operated a bench-scale reactor (1 l in capacity; approximately 1,000 cm² in anode and cathode areas) for treating a high-strength model organic wastewater (comprised of starch, peptone, and fish extract). Approximately 1 month was needed for the bench reactor to attain a stable performance, after which volumetric maximum power densities persisted between 120 and 150 mW/l throughout the experiment (for over 2 months). Temporal increases in the external resistance were found to induce subsequent increases in power outputs. After electric output became stable, electrolyte and anode were sampled from the reactor for evaluating their current-generation abilities; it was estimated that most of current (over 80%) was generated by microbes in the electrolyte. Cyclic voltammetry of an electrolyte supernatant detected several electron shuttles with different standard redox potentials at high concentrations (equivalent to or more than 100 μM 5-hydroxy-1,4-naphthoquinone). Denaturing gradient gel electrophoresis and quantitative real-time PCR of 16S ribosomal RNA gene fragments showed that bacteria related to the genus Dysgonomonas occurred abundantly in association with the increases in power outputs. These results suggest that mediated electron transfer was the main mechanism for electricity generation in CE-MFC, where high-concentration electron shuttles and Dysgonomonas bacteria played important roles.

Keywords: Waste treatment; Electricity; Extracellular electron transfer; Electron shuttle; Phylogeny

Erratum to: Transcriptome profiling of degU expression reveals unexpected regulatory patterns in Bacillus megaterium and discloses new targets for optimizing expression by Claudia Borgmeier; Rebekka Biedendieck; Kristina Hoffmann; Dieter Jahn; Friedhelm Meinhardt (pp. 1315-1316).

Sections

Personal tools

Applied Microbiology and Biotechnology (v.92, #6)

Sections

Personal tools

Local resources

Applied Microbiology and Biotechnology (v.92, #6)