Check out our New Publishers' Select for Free Articles

Applied Microbiology and Biotechnology (v.91, #2)

Flavonoids biotransformation by bacterial non-heme dioxygenases, biphenyl and naphthalene dioxygenase by Jiyoung Seo; Su-Il Kang; Mihyang Kim; Jaehong Han; Hor-Gil Hur (pp. 219-228).

This review details recent progresses in the flavonoid biotransformation by bacterial non-heme dioxygenases, biphenyl dioxygenase (BDO), and naphthalene dioxygenase (NDO), which can initially activate biphenyl and naphthalene with insertion of dioxygen in stereospecfic and regiospecific manners. Flavone, isoflavone, flavanone, and isoflavanol were biotransformed by BDO from Pseudomonas pseudoalcaligenes KF707 and NDO from Pseudomonas sp. strain NCIB9816-4, respectively. In general, BDO showed wide range of substrate spectrum and produced the oxidized products, whereas NDO only metabolized flat two-dimensional substrates of flavone and isoflavone. Furthermore, biotransformation of B-ring skewed substrates, flavanone and isoflavanol, by BDO produced the epoxide products, instead of dihydrodiols. These results support the idea that substrate-driven reactivity alteration of the Fe-oxo active species may occur in the active site of non-heme dioxygenases. The study of flavonoid biotransformation by structurally-well defined BDO and NDO will provide the substrate structure and reactivity relationships and eventually establish the production of non-plant-originated flavonoids by means of microbial biotechnology.

Keywords: Biotransformation; Biphenyl dioxygenase; Naphthalene dioxygenase; Flavonoid; Polyphenol

Microbial metabolism and biotechnological production of d-allose by Yu-Ri Lim; Deok-Kun Oh (pp. 229-235).

d-Allose has attracted a great deal of attention in recent years due to its many pharmaceutical activities, which include anti-cancer, anti-tumor, anti-inflammatory, anti-oxidative, anti-hypertensive, cryoprotective, and immunosuppressant activities. d-Allose has been produced from d-psicose using d-allose-producing enzymes, including l-rhamnose isomerase, ribose-5-phosphate isomerase, and galactose-6-phosphate isomerase. In this article, the properties, applications, and metabolism of d-allose are described, and the biochemical properties of d-allose-producing enzymes and their d-allose production are reviewed and compared. Moreover, several methods for effective d-allose production are suggested herein.

Keywords: d-Allose; l-Rhamnose isomerase; Ribose-5-phosphate isomerase; Galactose-6-phosphate isomerase; Biotransformation; Metabolism

Advantages and challenges of increased antimicrobial copper use and copper mining by Jutta Elguindi; Xiuli Hao; Yanbing Lin; Hend A. Alwathnani; Gehong Wei; Christopher Rensing (pp. 237-249).

Copper is a highly utilized metal for electrical, automotive, household objects, and more recently as an effective antimicrobial surface. Copper-containing solutions applied to fruits and vegetables can prevent bacterial and fungal infections. Bacteria, such as Salmonellae and Cronobacter sakazakii, often found in food contamination, are rapidly killed on contact with copper alloys. The antimicrobial effectiveness of copper alloys in the healthcare environment against bacteria causing hospital-acquired infections such as methicillin-resistant Staphylococcus aureus (MRSA), Escherichia coli O157:H7, and Clostridium difficile has been described recently. The use of copper and copper-containing materials will continue to expand and may lead to an increase in copper mining and production. However, the copper mining and manufacturing industry and the consumer do not necessarily enjoy a favorable relationship. Open pit mining, copper mine tailings, leaching products, and deposits of toxic metals in the environment often raises concerns and sometimes public outrage. In addition, consumers may fear that copper alloys utilized as antimicrobial surfaces in food production will lead to copper toxicity in humans. Therefore, there is a need to mitigate some of the negative effects of increased copper use and copper mining. More thermo-tolerant, copper ion-resistant microorganisms could improve copper leaching and lessen copper groundwater contamination. Copper ion-resistant bacteria associated with plants might be useful in biostabilization and phytoremediation of copper-contaminated environments. In this review, recent progress in microbiological and biotechnological aspects of microorganisms in contact with copper will be presented and discussed, exploring their role in the improvement for the industries involved as well as providing better environmental outcomes.

Keywords: Antimicrobial copper; Copper mining; Phytoremediation; Microbial copper resistance

Regulatory and metabolic network of rhamnolipid biosynthesis: Traditional and advanced engineering towards biotechnological production by Markus Michael Müller; Rudolf Hausmann (pp. 251-264).

During the last decade, the demand for economical and sustainable bioprocesses replacing petrochemical-derived products has significantly increased. Rhamnolipids are interesting biosurfactants that might possess a broad industrial application range. However, despite of 60 years of research in the area of rhamnolipid production, the economic feasibility of these glycolipids is pending. Although the biosynthesis and regulatory network are in a big part known, the actual incidents on the cellular and process level during bioreactor cultivation are not mastered. Traditional engineering by random and targeted genetic alteration, process design, and recombinant strategies did not succeed by now. For enhanced process development, there is an urgent need of in-depth information about the rhamnolipid production regulation during bioreactor cultivation to design knowledge-based genetic and process engineering strategies. Rhamnolipids are structurally comparable, simple secondary metabolites and thus have the potential to become instrumental in future secondary metabolite engineering by systems biotechnology. This review summarizes current knowledge about the regulatory and metabolic network of rhamnolipid synthesis and discusses traditional and advanced engineering strategies performed for rhamnolipid production improvement focusing on Pseudomonas aeruginosa. Finally, the opportunities of applying the systems biotechnology toolbox on the whole-cell biocatalyst and bioprocess level for further rhamnolipid production optimization are discussed.

Keywords: Rhamnolipid; Systems biotechnology; Secondary metabolite; Process optimization; Biosurfactant; Glycolipid

Progress on plague vaccine development by Jason A. Rosenzweig; Olufisayo Jejelowo; Jian Sha; Tatiana E. Erova; Sheri M. Brackman; Michelle L. Kirtley; Cristina J. van Lier; Ashok K. Chopra (pp. 265-286).

Yersinia pestis (YP), the gram-negative plague bacterium, has shaped human history unlike any other pathogen known to mankind. YP (transmitted by the bite of an infected flea) diverged only recently from the related enteric pathogen Yersinia pseudotuberculosis but causes radically different diseases. Three forms of plague exist in humans: bubonic (swollen lymph nodes or bubos), septicemic (spread of YP through the lymphatics or bloodstream from the bubos to other organs), and contagious, pneumonic plague which can be communicated via YP-charged respiratory droplets resulting in person–person transmission and rapid death if left untreated (50–90% mortality). Despite the potential threat of weaponized YP being employed in bioterrorism and YP infections remaining prevalent in endemic regions of the world where rodent populations are high (including the four corner regions of the USA), an efficacious vaccine that confers immunoprotection has yet to be developed. This review article will describe the current vaccine candidates being evaluated in various model systems and provide an overall summary on the progress of this important endeavor.

Keywords: Plague; Vaccine; Yersinia pestis ; Bubonic; Septicemic; Pneumonic plague

Characterization of a novel dextran produced by Gluconobacter oxydans DSM 2003 by Shu Wang; Xiangzhao Mao; Hualei Wang; Jinping Lin; Fuli Li; Dongzhi Wei (pp. 287-294).

A novel water-soluble dextran was synthesized from maltodextrin by cell-free extract of Gluconobacter oxydans DSM 2003. The dextran was purified by size exclusion chromatography, and the structure was determined by Fourier transform infrared spectroscopy, nuclear magnetic resonance, and gas chromatography–mass spectrometer. Based on the spectral data, we found that the dextran contained only d-glucose residues. The ratio of nonreducing end glucopyranosyl (Glcp) to 6-linked Glcp to 4,6-linked Glcp was estimated to be 8.62:78.79:12.59 by methylation analysis. This result indicated the existence of a small proportion of α(1,4) branches in α(1,6) glucosyl linear chains. Here, we reported the first time a novel dextran was synthesized by G. oxydans DSM 2003.

Keywords: Dextran; Gluconobacter oxydans ; Monosaccharide composition; Structure analysis

Continuous production of poly([R]-3-hydroxybutyrate) by Cupriavidus necator in a multistage bioreactor cascade by Aid Atlić; Martin Koller; Dietrich Scherzer; Christoph Kutschera; Elizabeth Grillo-Fernandes; Predrag Horvat; Emo Chiellini; Gerhart Braunegg (pp. 295-304).

Poly(hydroxyalkanoates) (PHAs) constitute biodegradable polyesters and are considered among the most promising candidates to replace common petrochemical plastics in various applications. To date, all commercial processes for PHA production employ microbial discontinuous fed-batch fermentations. These processes feature drawbacks such as varying product quality and the inevitable periods of downtime for preparation and post-treatment of the bioreactor equipment. An unprecedented approach to PHA production was chosen in the presented work using a multistage system consisting of five continuous stirred tank reactors in series (5-SCR), which can be considered as a process engineering substitute of a continuous tubular plug flow reactor. The first stage of the reactor cascade is the site of balanced bacterial growth; thereafter, the fermentation broth is continuously fed from the first into the subsequent reactors, where PHA accumulation takes place under nitrogen-limiting conditions. Cupriavidus necator was used as production strain. The focus of the experimental work was devoted to the development of a PHA production process characterized by high productivity and high intracellular polymer content. The results of the experimental work with the reactor cascade demonstrated its potential in terms of volumetric and specific productivity (1.85 g L⁻¹ h⁻¹ and 0.100 g g⁻¹ h⁻¹, respectively), polymer content (77%, w/w) and polymer properties (M _w = 665 kg/mol, PDI = 2.6). Thus, implementing the technology for 5-SCR production of PHB results in an economically viable process. The study compares the outcome of the work with literature data from continuous two-stage PHA production and industrial PHA production in fed-batch mode.

Keywords: Bioreactor cascade; Continuous production process; Cupriavidus necator ; Multistage fermentation; Poly([R]-3-hydroxybutyrate)

Effects of culture temperature and pH on flag-tagged COMP angiopoietin-1 (FCA1) production from recombinant CHO cells: FCA1 aggregation by Su-Jeong Hwang; Sung Kwan Yoon; Gou Young Koh; Gyun Min Lee (pp. 305-315).

To maximize the production of flag-tagged cartilage oligomeric matrix protein angiopoietin-1 (FCA1) from Chinese hamster ovary (CHO) cells, the effects of culture pH and temperature on cell growth and FCA1 production were investigated. Cells were cultivated in a bioreactor at different culture pH (6.7, 6.9, 7.2, and 7.5) and temperatures (33 and 37 °C). Lowering the culture temperature suppressed cell growth while allowing maintenance of high cell viability for a longer culture period. The specific FCA1 productivity (q _FCA1) was increased at low culture temperature. Accordingly, the highest FCA1 concentration was obtained at pH 7.2 and 33 °C, and was approximately 4.0-fold higher than that at pH 7.2 and 37 °C. However, aggregates and a monomeric form of FCA1, which are undesirable due to reduced biological activity or immunogenicity, were significant at pH 7.2 and 33 °C. It was also found that the expression pattern of FCA1 was affected more significantly by culture pH than by the culture temperature. FCA1 aggregation dramatically decreased at culture pH 7.5 regardless of the culture temperature. Furthermore, the monomeric form of FCA1 was not observed. Taken together, optimization of culture temperature and culture pH (33 °C and pH 7.5) significantly improves the production of biologically active FCA1 with tetrameric or pentameric forms from CHO cells.

Keywords: COMP Angiopoietin-1; Chinese hamster ovary (CHO) cells; Culture pH; Culture temperature

Enzymatic synthesis of nucleoside analogues using immobilized 2′-deoxyribosyltransferase from Lactobacillus reuteri by Jesús Fernández-Lucas; Alba Fresco-Taboada; Carmen Acebal; Isabel de la Mata; Miguel Arroyo (pp. 317-327).

Covalent attachment of recombinant Lactobacillus reuteri 2′-deoxyribosyltransferase to Sepabeads EC-EP303 leads to the immobilized biocatalyst SLrNDT4, which displayed an enzymatic activity of 65.4 IU/g of wet biocatalyst in 2′-deoxyadenosine synthesis from 2′-deoxyuridine and adenine at 40°C and pH 6.5. Response surface methodology was employed for the optimization of SLrNDT4 activity. Optimal conditions for SLrNDT4 highest activity were observed at 40°C and pH 6.5. Immobilized biocatalyst retained 50% of its maximal activity after 17.9 h at 60°C, whereas 96% activity was observed after storage at 40°C for 110 h. This novel immobilized biocatalyst has been successfully employed in the enzymatic synthesis of different natural and therapeutic nucleosides effective against cancer and viral diseases. Among these last products, enzymatic synthesis of therapeutic nucleosides such as 5-ethyl-2′-deoxyuridine and 5-trifluorothymidine has been carried out for the first time. Importantly for its potential application, SLrNDT4 could be recycled for 26 consecutive batch reactions in the synthesis of 2,6-diaminopurine-2′-deoxyriboside with negligible loss of catalytic activity.

Keywords: 2′-Deoxyribosyltransferase; Nucleoside synthesis; Lactobacillus reuteri ; Immobilization; Sepabeads

Truncation of N- and C-terminal regions of Streptococcus mutans dextranase enhances catalytic activity by Young-Min Kim; Ryoko Shimizu; Hiroyuki Nakai; Haruhide Mori; Masayuki Okuyama; Min-Sun Kang; Zui Fujimoto; Kazumi Funane; Doman Kim; Atsuo Kimura (pp. 329-339).

Multiple forms of native and recombinant endo-dextranases (Dexs) of the glycoside hydrolase family (GH) 66 exist. The GH 66 Dex gene from Streptococcus mutans ATCC 25175 (SmDex) was expressed in Escherichia coli. The recombinant full-size (95.4 kDa) SmDex protein was digested to form an 89.8 kDa isoform (SmDex90). The purified SmDex90 was proteolytically degraded to more than seven polypeptides (23–70 kDa) during long storage. The protease-insensitive protein was desirable for the biochemical analysis and utilization of SmDex. GH 66 Dex was predicted to comprise four regions from the N- to C-termini: N-terminal variable region (N-VR), conserved region (CR), glucan-binding site (GBS), and C-terminal variable region (C-VR). Five truncated SmDexs were generated by deleting N-VR, GBS, and/or C-VR. Two truncation-mutant enzymes devoid of C-VR (TM-NCGΔ) or N-VR/C-VR (TM-ΔCGΔ) were catalytically active, thereby indicating that N-VR and C-VR were not essential for the catalytic activity. TM-ΔCGΔ did not accept any further protease-degradation during long storage. TM-NCGΔ and TM-ΔCGΔ enhanced substrate hydrolysis, suggesting that N-VR and C-VR induce hindered substrate binding to the active site.

Keywords: Endo-dextranase; Glycoside hydrolase family 66; Limited proteolysis; Truncation

Enhancement of carotenoids biosynthesis in Chlamydomonas reinhardtii by nuclear transformation using a phytoene synthase gene isolated from Chlorella zofingiensis by Baldo F. Cordero; Inmaculada Couso; Rosa León; Herminia Rodríguez; M. Ángeles Vargas (pp. 341-351).

The isolation and characterization of the phytoene synthase gene from the green microalga Chlorella zofingiensis (CzPSY), involved in the first step of the carotenoids biosynthetic pathway, have been performed. CzPSY gene encodes a polypeptide of 420 amino acids. A single copy of CzPSY has been found in C. zofingiensis by Southern blot analysis. Heterologous genetic complementation in Escherichia coli showed the ability of the predicted protein to catalyze the condensation of two molecules of geranylgeranyl pyrophosphate (GGPP) to form phytoene. Phylogenetic analysis has shown that the deduced protein forms a cluster with the rest of the phytoene synthases (PSY) of the chlorophycean microalgae studied, being very closely related to PSY of plants. This new isolated gene has been adequately inserted in a vector and expressed in Chlamydomonas reinhardtii. The overexpression of CzPSY in C. reinhardtii, by nuclear transformation, has led to an increase in the corresponding CzPSY transcript level as well as in the content of the carotenoids violaxanthin and lutein which were 2.0- and 2.2-fold higher than in untransformed cells. This is an example of manipulation of the carotenogenic pathway in eukaryotic microalgae, which can open up the possibility of enhancing the productivity of commercial carotenoids by molecular engineering.

Keywords: Carotenoids; Chlorella zofingiensis ; Phytoene synthase; Transgenic microalgae; Chlamydomonas reinhardtii

Roles of Hfq in the stress adaptation and virulence in fish pathogen Vibrio alginolyticus and its potential application as a target for live attenuated vaccine by Huan Liu; Qiyao Wang; Qin Liu; Xiaodan Cao; Cunbin Shi; Yuanxing Zhang (pp. 353-364).

Vibrio alginolyticus has brought about severe economic damage to the mariculture industry by causing vibriosis in various fish species in South China. The virulent determinants of this bacterium have not been well characterized except the exotoxin alkaline serine protease, Asp. In addition, the mechanism of virulence regulation in V. alginolyticus remains largely unknown apart from a Vibrio harveyi-like quorum sensing (QS) system which is established to manipulate the expression of various virulence-related genes. Hfq, an sRNA chaperone, is an important post-transcriptional regulator in a variety of bacteria. Here, the roles of Hfq were characterized in regulating the stress resistance and pathogenesis in V. alginolyticus. We demonstrated that the hfq deletion mutant became more sensitive to several environmental stresses, including osmotic stress, ethanol, temperature shift, and iron starvation. The deletion of hfq abrogated the motility and biofilm formation in this bacterium. Hfq negatively regulated the expression of main virulence factor, Asp, through QS system. The results also indicated that Hfq modulated the survival and multiplication of V. alginolyticus in fish. Hfq thus appears to be a new pleiotropic regulator of pathogenesis in V. alginolyticus. Moreover, high immunoprotective rate was achieved with a single dose of injection or immersion vaccination with live hfq mutant, suggesting the mutant’s merits as a valuable vaccine candidate against V. alginolyticus.

Keywords: Hfq; Quorum sensing; Stress resistance; Extracellular protease; Vibrio alginolyticus

Impacts of variations in elemental nutrient concentration of Chardonnay musts on Saccharomyces cerevisiae fermentation kinetics and wine composition by Simon A. Schmidt; Simon Dillon; Radka Kolouchova; Paul A. Henschke; Paul J. Chambers (pp. 365-375).

Chardonnay, being the predominant white wine-grape cultivar in the Australian wine sector, is subject to widely varying winemaking processes with the aim of producing a variety of wine styles. Therefore, juice composition might not always be ideal for optimal fermentation outcomes. Our aim was to better understand the composition of Chardonnay juice and how compositional parameters impact on fermentation outcomes. This was achieved through a survey of 96 commercially prepared Chardonnay juices during the 2009 vintage. Common juice variables were estimated using near infrared spectroscopy, and elemental composition was determined using radial view inductively coupled plasma optical emission spectrometry. The influence of elemental composition on fermentation outcomes was assessed by fermentation of a defined medium formulated to reflect the composition and range of concentrations as determined by the juice survey. Yeast (Saccharomyces cerevisiae) strain effects were also assessed. Key parameters influencing fermentation outcomes were verified by laboratory scale fermentation of Chardonnay juice. This exploration of Chardonnay juice identified interactions between juice pH and potassium concentration as key factors impacting on fermentation performance and wine quality. Outcomes differed depending on yeast strain.

Keywords: Fermentation performance; Elemental composition; Saccharomyces cerevisiae ; Chardonnay; Acetic acid; Stuck fermentation; Potassium

Role of the photosynthetic electron transfer chain in electrogenic activity of cyanobacteria by John M. Pisciotta; YongJin Zou; Ilia V. Baskakov (pp. 377-385).

Certain anaerobic bacteria, termed electrogens, produce an electric current when electrons from oxidized organic molecules are deposited to extracellular metal oxide acceptors. In these heterotrophic “metal breathers”, the respiratory electron transport chain (R-ETC) works in concert with membrane-bound cytochrome oxidases to transfer electrons to the extracellular acceptors. The diversity of bacteria able to generate an electric current appears more widespread than previously thought, and aerobic phototrophs, including cyanobacteria, possess electrogenic activity. However, unlike heterotrophs, cyanobacteria electrogenic activity is light dependent, which suggests that a novel pathway could exist. To elucidate the electrogenic mechanism of cyanobacteria, the current studies used site-specific inhibitors to target components of the photosynthetic electron transport chain (P-ETC) and cytochrome oxidases. Here, we show that (1) P-ETC and, particularly, water photolysed by photosystem II (PSII) is the source of electrons discharged to the environment by illuminated cyanobacteria, and (2) water-derived electrons are transmitted from PSII to extracellular electron acceptors via plastoquinone and cytochrome bd quinol oxidase. Two cyanobacterial genera (Lyngbya and Nostoc) displayed very similar electrogenic responses when treated with P-ETC site-specific inhibitors, suggesting a conserved electrogenic pathway. We propose that in cyanobacteria, electrogenic activity may represent a form of overflow metabolism to protect cells under high-intensity light. This study offers insight into electron transfer between phototrophic microorganisms and the environment and expands our knowledge into biologically based mechanisms for harnessing solar energy.

Keywords: Cyanobacteria; Electrogen; Electron transfer; Microbial fuel cells; Photosynthetic

Regulation of pentose utilisation by AraR, but not XlnR, differs in Aspergillus nidulans and Aspergillus niger by Evy Battaglia; Sara Fasmer Hansen; Anne Leendertse; Susan Madrid; Harm Mulder; Igor Nikolaev; Ronald P. de Vries (pp. 387-397).

Filamentous fungi are important producers of plant polysaccharide degrading enzymes that are used in many industrial applications. These enzymes are produced by the fungus to liberate monomeric sugars that are used as carbon source. Two of the main components of plant polysaccharides are l-arabinose and d-xylose, which are metabolized through the pentose catabolic pathway (PCP) in these fungi. In Aspergillus niger, the regulation of pentose release from polysaccharides and the PCP involves the transcriptional activators AraR and XlnR, which are also present in other Aspergilli such as Aspergillus nidulans. The comparative analysis revealed that the regulation of the PCP by AraR differs in A. nidulans and A. niger, whereas the regulation of the PCP by XlnR was similar in both species. This was demonstrated by the growth differences on l-arabinose between disruptant strains for araR and xlnR in A. nidulans and A. niger. In addition, the expression profiles of genes encoding l-arabinose reductase (larA), l-arabitol dehydrogenase (ladA) and xylitol dehydrogenase (xdhA) differed in these strains. This data suggests evolutionary changes in these two species that affect pentose utilisation. This study also implies that manipulating regulatory systems to improve the production of polysaccharide degrading enzymes, may give different results in different industrial fungi.

Keywords: Aspergillus nidulans ; Aspergillus niger ; Regulation; Pentose catabolic pathway

Separation of ionic liquid [Mmim][DMP] and glucose from enzymatic hydrolysis mixture of cellulose using alumina column chromatography by Dexin Feng; Liangzhi Li; Fang Yang; Weiqiang Tan; Guoming Zhao; Huibin Zou; Mo Xian; Yingwei Zhang (pp. 399-405).

Pretreatment of cellulose with ionic liquids (ILs) can improve the efficiency of the hydrolysis by increasing the surface area of the substrates accessible to solvents and cellulases. However, the IL methods are facing challenges to separate the hydrolyzed sugar products as well as the renewable ILs from the complex hydrolysis mixtures. In this study, an alumina column chromatography (ACC) method was developed for the separation of hydrophilic IL N-methyl-N-methylimidazolium dimethyl phosphate ([Mmim][DMP]) and glucose, which was the main ingredient of the monosaccharide hydrolyzate. The processing parameters involved in ACC separation were investigated in detail. Our results showed that the recovery yields of [Mmim][DMP] and glucose can reach up to 93.38% and 90.14%, respectively, under the optimized parameters: the sampling ratio of 1:20 between the applied sample volume and the bed volume of the column; a gradient elution using methanol (100%, 150 ml) and then water (170 ml) as eluents with 1 ml/min flow rate. The recovered [Mmim][DMP] showed qualified property and was effective in a new hydrolysis reaction. In addition, scale-up ACC separations were successfully done with satisfied separation performance. The results indicated that the ACC is one of the available methods for the separation of ILs and monosaccharides from the hydrolysis mixtures.

Keywords: Ionic liquids; Hydrophilic; Recycle; Alumina column chromatography; Monosaccharide

Degradation of chlorobenzene by strain Ralstonia pickettii L2 isolated from a biotrickling filter treating a chlorobenzene-contaminated gas stream by Li Li Zhang; Shou Qin Leng; Run Ye Zhu; Jian Meng Chen (pp. 407-415).

A Ralstonia pickettii species able to degrade chlorobenzene (CB) as the sole source of carbon and energy was isolated from a biotrickling filter used for the removal of CB from waste gases. This organism, strain L2, could degrade CB as high as 220 mg/L completely. Following CB consumption, stoichiometric amounts of chloride were released, and CO₂ production rate up to 80.2% proved that the loss of CB was mainly via mineralization and incorporation into cell material. The Haldane modification of the Monod equation adequately described the relationship between the specific growth rate and substrate concentration. The maximum specific growth rate and yield coefficient were 0.26 h⁻¹ and 0.26 mg of biomass produced/mg of CB consumed, respectively. The pathways for CB degradation were proposed by the identification of metabolites and assay of ring cleavage enzymes in cell extracts. CB was degraded predominantly via 2-chlorophenol to 3-chlorocatechol and also partially via phenol to catechol with subsequent ortho ring cleavage, suggesting partially new pathways for CB-utilizing bacteria.

Keywords: Ralstonia pickettii ; Chlorobenzene; Biodegradation; Metabolite; Pathway

Decolorization of azo dyes by Shewanella oneidensis MR-1 in the presence of humic acids by Guangfei Liu; Jiti Zhou; Jing Wang; Xiujuan Wang; Ruofei Jin; Hong Lv (pp. 417-424).

The effects of humic acid (HA) on azo dye decolorization by Shewanella oneidensis MR-1 were studied. It was found that HA species isolated from different sources could all accelerate the decolorization of Acid Red 27 (AR27). Anoxic and anaerobic conditions were required for the enhancement of azo dye decolorization by HA. In the presence of 50 mg DOC L⁻¹ Aldrich HA, 15–29% increases in decolorization efficiencies of azo dyes with different structures were achieved in 11 h. The enhancing effects increased with the increase of HA concentrations ranging from 25 to 150 mg DOC L⁻¹, and the decolorization rates were directly proportional to the HA concentrations when they were below 100 mg DOC L⁻¹. Lactate and formate were good electron donors for AR27 decolorization in the presence of HA. Both nitrate (0.1–3.0 mM) and nitrite (0.3–1.2 mM) inhibited AR27 decolorization in the presence of HA, and negligible decolorization was observed before their removal. Soluble FeCl₃ could accelerate the decolorization process in the presence of HA, whereas insoluble hematite could not. These findings may affect the understanding of bioremediation of azo dye-polluted environments and help improve the treatment of azo dye wastewaters.

Keywords: Azo dye; Decolorization; Humic acid; Shewanella oneidensis MR-1

A diverse bacterial community in an anoxic quinoline-degrading bioreactor determined by using pyrosequencing and clone library analysis by Xiaojun Zhang; Siqing Yue; Huihui Zhong; Weiying Hua; Ruijia Chen; Youfang Cao; Liping Zhao (pp. 425-434).

There is a concern of whether the structure and diversity of a microbial community can be effectively revealed by short-length pyrosequencing reads. In this study, we performed a microbial community analysis on a sample from a high-efficiency denitrifying quinoline-degrading bioreactor and compared the results generated by pyrosequencing with those generated by clone library technology. By both technologies, 16S rRNA gene analysis indicated that the bacteria in the sample were closely related to, for example, Proteobacteria, Actinobacteria, and Bacteroidetes. The sequences belonging to Rhodococcus were the most predominant, and Pseudomonas, Sphingomonas, Acidovorax, and Zoogloea were also abundant. Both methods revealed a similar overall bacterial community structure. However, the 622 pyrosequencing reads of the hypervariable V3 region of the 16S rRNA gene revealed much higher bacterial diversity than the 130 sequences from the full-length 16S rRNA gene clone library. The 92 operational taxonomic unit (OTUs) detected using pyrosequencing belonged to 45 families, whereas the 37 OTUs found in the clone library belonged to 25 families. Most sequences obtained from the clone library had equivalents in the pyrosequencing reads. However, 64 OTUs detected by pyrosequencing were not represented in the clone library. Our results demonstrate that pyrosequencing of the V3 region of the 16S rRNA gene is not only a powerful tool for discovering low-abundance bacterial populations but is also reliable for dissecting the bacterial community structure in a wastewater environment.

Keywords: Quinoline degradation; Microbial community; Pyrosequencing; Clone library; 16S rRNA gene

Bacterial production of free fatty acids from freshwater macroalgal cellulose by Spencer W. Hoover; Wesley D. Marner II; Amy K. Brownson; Rebecca M. Lennen; Tyler M. Wittkopp; Jun Yoshitani; Shahrizim Zulkifly; Linda E. Graham; Sheena D. Chaston; Katherine D. McMahon; Brian F. Pfleger (pp. 435-446).

The predominant strategy for using algae to produce biofuels relies on the overproduction of lipids in microalgae with subsequent conversion to biodiesel (methyl-esters) or green diesel (alkanes). Conditions that both optimize algal growth and lipid accumulation rarely overlap, and differences in growth rates can lead to wild species outcompeting the desired lipid-rich strains. Here, we demonstrate an alternative strategy in which cellulose contained in the cell walls of multicellular algae is used as a feedstock for cultivating biofuel-producing microorganisms. Cellulose was extracted from an environmental sample of Cladophora glomerata-dominated periphyton that was collected from Lake Mendota, WI, USA. The resulting cellulose cake was hydrolyzed by commercial enzymes to release fermentable glucose. The hydrolysis mixture was used to formulate an undefined medium that was able to support the growth, without supplementation, of a free fatty acid (FFA)-overproducing strain of Escherichia coli (Lennen et. al 2010). To maximize free fatty acid production from glucose, an isopropyl β-d-1-thiogalactopyranoside (IPTG)-inducible vector was constructed to express the Umbellularia californica acyl–acyl carrier protein (ACP) thioesterase. Thioesterase expression was optimized by inducing cultures with 50 μM IPTG. Cell density and FFA titers from cultures grown on algae-based media reached 50% of those (∼90 μg/mL FFA) cultures grown on rich Luria–Bertani broth supplemented with 0.2% glucose. In comparison, cultures grown in two media based on AFEX-pretreated corn stover generated tenfold less FFA than cultures grown in algae-based media. This study demonstrates that macroalgal cellulose is a potential carbon source for the production of biofuels or other microbially synthesized compounds.

Keywords: Biofuel; Algae; Fatty acid; Escherichia coli ; Thioesterase

Sections

Personal tools

Applied Microbiology and Biotechnology (v.91, #2)

Sections

Personal tools

Local resources

Applied Microbiology and Biotechnology (v.91, #2)