1,720,957 research outputs found
No-culture strategy for tracking AAB and yeasts in low-acidic and high polyphenolic niches
No full textCommunity of acetic acid bacteria (AAB) and yeasts inhabitslow acidic and high polyphenolic niches such as fermentedbeverages. In this work, we selected kombucha asmodel to optimize a no-culture strategy for tracking thedynamics of AAB and yeasts. The strategy consisted of: i)Genomic DNA extraction optimization, ii) PCR/DGGEsetup and iii) Validation of the assay. For gDNA extractionoptimization, we evaluated the suitability of the followinggDNA preparations for a standard PCR-DGGE assay: 1)CTAB/AAB; 2) CTAB/vinegar; 3) Freeze/bead/CTAB1; 4)Freeze/bead/CTAB2 methods. Different extraction methodsaffected not only the quantity and purity of DNA but alsothe complexity of PCR/DGGE profiling. Method 4 allowedus to obtain suitable DNA for PCR assays, as well as thehighest level of complexity in PCR/DGGE band patternsboth for AAB and yeasts. Moreover changes from exopolysaccharidicto liquid phases did not affect the suitability ofthis method. PCR/DGGE setup was performed consideringthe following variables: DNA template concentration, PCRconditions and specificity, effect of GC-clamp and nestedPCR. For AAB, primers pair WBAC1/WBAC2 enabled tostudy AAB dynamics as well other bacterial groups, whereas341f/518r permitted the detection of members of theGluconacetobacter genus. For yeasts, primers pair U1/U2was more efficient then NL1/LS2 in community profiling ofthe majority of kombucha samples. GC-clamp added toforward primers negatively affected gDNA suitability and anested re-PCR for yeasts and AAB was required. Finally,validation of the assay was carried out during kombuchafermentation following AAB and yeasts dynamics from theinoculum to 12 days of incubation. Within AAB species,Gluconacetobacter xylinus responsible for the exopolysaccharidicnetwork matrix, was mainly detected, whereasZygosaccharomyces spp, Dekkera spp, Pichia spp andSchizosaccharomyces pombe in the case of yeasts
Acetic Acid Bacteria: Physiology and Carbon Sources Oxidation
No full textAcetic acid bacteria (AAB) are obligately aerobic bacteria within the family Acetobacteraceae, widespread in sugary, acidic and alcoholic niches. They are known for their ability to partially oxidise a variety of carbohydrates and to release the corresponding metabolites (aldehydes, ketones and organic acids) into the media. Since a long time they are used to perform specific oxidation reactions through processes called “oxidative fermentations”, especially in vinegar production. In the last decades physiology of AAB have been widely studied because of their role in food production, where they act as beneficial or spoiling organisms, and in biotechnological industry, where their oxidation machinery is exploited to produce a number of compounds such as l-ascorbic acid, dihydroxyacetone, gluconic acid and cellulose. The present review aims to provide an overview of AAB physiology focusing carbon sources oxidation and main products of their metabolism
Evaluation and optimisation of bacterial genomic DNA extraction forno-culture techniques applied to vinegars
No full textDirect genomic DNA extraction from vinegars was set up and suitability for PCR assaysperformed by PCR/DGGE and sequencing of 16S rRNA gene. The method was tested on 12intermediary products of special vinegars, fruit vinegars and condiments produced from different rawmaterials and procedures. DNAs extraction was performed on pellets by chemical, enzymatic, resinmediated methods and their modifications. Suitable yield and DNA purity were obtained bymodification of a method based on the use of PVP/CTAB to remove polyphenolic components andesopolysaccharides. By sequencing of bands from DGGE gel, Ga. europaeus, A. malorum/cerevisiae andA. orleanensis were detected as main species in samples having more than 4% of acetic acid content.From samples having no acetic acid content, sequences retrieved from excised bands revealed highsimilarity with prokaryotes with no function on vinegar fermentation: Burkholderia spp, Cupriavidusspp., Lactococcus lactis and Leuconostoc mesenteroides. The method was suitable to be applied for noculturestudy of vinegars containing polyphenols and esopolysaccharides allowing a more completeassessment of vinegar bacteria
Acetobacter pasteurianus strain AB0220: cultivability andphenotypic stability over 9 years of preservation
No full textAcetobacter species are members of the a-subclassof Proteobacteria, which harbors a large number of bacteriarecalcitrant to cultivation. Strain AB0220 was isolatedfrom a superficial acetification system and preserved for9 years by short and long time methods. Under short timepreservation it was estimated that 540.54 number of generationsoccurred, whereas in long time preservation conditionsthe number of generations was 17.40. Ethanoloxidation to acetic acid was stable and confirmed, as wellas acetate assimilation during long time preservation.Cultivability checks showed persistence of phenotypictraits (growth on ethanol and methanol, growth on differentcarbon sources and cellulose production) over the extendedpreservation time. 16S rRNA gene sequences analysisshowed 100 % of similarity with A. pasteurianus (Accessionnumber GQ240636). Stability of subcultures related tothe culture age and subcultures frequency, tested by ERIC/PCR, confirmed the suitability of long term preservationat least over a period of 9 years
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Variations on the Author
Full text link“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Appropriate Similarity Measures for Author Cocitation Analysis
Full text linkWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
Kombucha Tea as a Reservoir of Cellulose Producing Bacteria: Assessing Diversity among Komagataeibacter Isolates
Full text linkBacterial cellulose (BC) is receiving a great deal of attention due to its unique properties such as high purity, water retention capacity, high mechanical strength, and biocompatibility. However, the production of BC has been limited because of the associated high costs and low productivity. In light of this, the isolation of new BC producing bacteria and the selection of highly productive strains has become a prominent issue. Kombucha tea is a fermented beverage in which the bacteria fraction of the microbial community is composed mostly of strains belonging to the genus Komagataeibacter. In this study, Kombucha tea production trials were performed starting from a previous batch, and bacterial isolation was conducted along cultivation time. From the whole microbial pool, 46 isolates were tested for their ability to produce BC. The obtained BC yield ranged from 0.59 g/L, for the isolate K2G36, to 23 g/L for K2G30—which used as the reference strain. The genetic intraspecific diversity of the 46 isolates was investigated using two repetitive-sequence-based PCR typing methods: the enterobacterial repetitive intergenic consensus (ERIC) elements and the (GTG)5 sequences, respectively. The results obtained using the two different approaches revealed the suitability of the fingerprint techniques, showing a discrimination power, calculated as the D index, of 0.94 for (GTG)5 rep-PCR and 0.95 for ERIC rep-PCR. In order to improve the sensitivity of the applied method, a combined model for the two genotyping experiments was performed, allowing for the ability to discriminate among strains
Dispelling the Myths Behind First-author Citation Counts
Full text linkWe conducted a full-scale evaluative citation analysis study of scholars in the XML research field to explore just how different from each other author rankings resulting from different citation counting methods actually are, and to demonstrate the capability of emerging data and tools on the Web in supporting more realistic citation counting methods. Our results contest some common arguments for the continued
use of first-author citation counts in the evaluation of scholars, such as high correlations between author rankings by first-author citation counts and other citation
counting methods, and high costs of using more realistic citation counting methods that are not well-supported by the ISI databases. It is argued that increasingly available digital full text research papers make it possible for citation analysis studies to go beyond what the ISI databases have directly supported and to employ more
sophisticated methods
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