1,721,015 research outputs found
Beneficial microorganisms for honey bees: problems and progresses
No full textNowadays, honey bees are stressed by a number of biotic and abiotic factors which may compromise to some extent the pollination service and the hive productivity. The EU ban of antibiotics as therapeutic agents against bee pathogens has stimulated the search for natural alternatives. The increasing knowledge on the composition and functions of the bee gut microbiota and the link between a balanced gut microbiota and health status have encouraged the research on the use of gut microorganisms to improve bee health. Somehow, we are assisting to the transfer of the “probiotic concept” into the bee science. In this review, we examine the role of the honey bee gut microbiota in bee health and critically describe the available applications of beneficial microorganisms as pest control agents and health support. Most of the strains, mainly belonging to the genera Lactobacillus, Bifidobacterium and Bacillus, are isolated from honey bee crop or gut, but some applications involve environmental strains or formulation for animal and human consumption. Overall, the obtained results show the favourable effect of applied microbial strains on bee health and productivity, in particular if strains of bee origin are used. However, it is actually not yet possible to conclude whether this strategy will ever work. In particular, many aspects regarding the overall setup of the experiments, the dose, the timing and the duration of the treatment need to be optimized, also considering the microbiological safety of the hive products (i.e. pollen and honey). In addition, a deep investigation about the effect on host immunity and physiology is envisaged. Lastly, the final users of the formulations, i.e. beekeepers, should be taken into account for the achievement of high-quality, cost-effective and easy-to-use products
ISOLATION AND CHARACTERIZATION OF AN ENDO- PHYTE FROM ACTINIDIA SP. SHOWING A STRONG ANTAGONISTIC ACTIVITY AGAINST PSEUDOMONAS SYRINGAE PV. ACTINIDIAE
No full textThe bacterial canker of kiwifruit is the most destructive disease
of cultivated Actinidia spp. The causal agent is the Gram negative bacterium Pseudomonas syringae pv. actinidiae (Psa).
The pathogen grows inside the trunk, vines and leaves of its host
plants, causing wilting and formation of cankers, with subsequent
death of the plant. During the past three years, samples have been
collected from various parts of asymptomatic Actinidia spp. within
infected kiwi orchards and many endophytic bacteria have been
isolated. Among them, a few isolates were identified and proved
to be able to strongly inhibit Psa namely an isolate of Pantoea agglomerans,
two pseudomonads belonging to the fluorescens/putida
group, and one novel Pseudomonas sp., which proved to be highly
effective in inhibiting, in vitro, several important phytopathogenic
bacteria. This last isolate was chosen for further studies. Concentrated
supernatant of its liquid culture in LB medium could
inhibit Psa, indicating that the active compound produced by the
antagonist is excreted from the cell into the environment. The
nature of that biotoxin is not proteic, and its size is smaller than
3 kDa, as a result of its partial purification. Moreover, a bank of
mutants deficient in their antagonistic activity has been constructed
by triparental mating, in order to search and identify genes
involved in antagonism against Psa. Fifty six prospective mutants
have been already obtained: twenty two of them were subject to
Southern blotting to verify a single transposon insertion. Gene
identification is under way
Antimicrobial activity of Melia azedarach fruit extracts for control of bacteria in inoculated in-vitro shoots of ‘MRS 2/5’ plum hybrid and calla lily and extract influence on the shoot cultures
No full textThe study aimed to investigate the antibacterial activity of Melia azedarach fruit extracts in plant shoot culture. Unripe fruits were collected in different periods and the extracts were obtained through homogenization in an ethanol (EtOH) solution (40 g fresh weight in 100 ml 50 % EtOH) followed by EtOH evaporation. Their activity was tested against isolates of several bacterial species (Bacillus spp., Pseudomonas spp.) of agronomic interest, and on shoots of ‘MRS 2/5’ (Prunus cerasifera x Prunus spinosa) and calla lily (Zantedeschia aethiopica) inoculated (bacterized) with Microbacterium oleivorans (Mo), Bacillus subtilis (A17), Sphingomonas meloni (Sm) and Bacillus nealsonii (Bn). Shoot number and fresh weight of explants of ‘MRS 2/5’ on the proliferation medium and shoot length on the rooting medium were reduced in cultures derived from shoots bacterized with Mo and A17. Moreover, rooting frequency and root number decreased in A17-bacterized shoots. In calla lily, the number of rooted shoots was strongly reduced also by Sm. The extracts had a bactericidal activity against Mo, A17, Bn and most other Bacillus spp. isolates within 2-year trials. This activity remained unchanged against most of the tested bacterial strains after autoclave-sterilization (20 min at 120 °C). The filter-sterilized (0.22-μm Millipore membrane) extract generally reduced shoot elongation, and caused the death of some ‘MRS 2/5’shoots at a 20 % level in the proliferation medium, while all calla lily shoots survived the treatment. It strongly reduced Mo and Bn spread in both plant genotypes, and was even bactericidal against Mo in’MRS 2/5’, without showing any negative effect on growth of survived shoots already at the second subculture on standard medium. The HPTLC analysis revealed the prevalence of polyphenols in the extracts from fruits collected in two successive periods; this was consistent with their antimicrobial activity
Molecular characterisation of an endophyte showing a strong antagonistic activity against Pseudomonas syringae pv. actinidiae
No full textAbstract
Background and aims
Endophytic bacteria have been often studied as biological control agents of plant pathogens and many of their secondary metabolites involved in antagonism are Non Ribosomal Peptides (NRPs). In this study, the molecular basis of the biocontrol properties of the endophyte Pseudomonas synxantha, isolated from Actinidia chinensis, against Pseudomonas syringae pv. actinidiae (Psa), the causal agent of bacterial kiwi canker, has been investigated.
Methods
Antagonism-deficient mutants of P. synxantha strain DLS65 were generated by insertion of minitransposon mTn5-GNm in its genome. Southern blot analysis allowed the selection of single transposon insertion-mutants. Amplification of the transposon flanking regions by means of arbitrary and single primer PCR in selected mutants was perfomed to obtain amplicons for sequencing purposes.
Results
Sequencing results of the amplicons obtained from three antagonism-deficient mutants led to the localization of the transposonin three genes, which implies their involvement in the antagonism of P. synxantha: an acyl-homoserine lactone acylase gene (pvdQ), a glucose-6-phosphate dehydrogenase gene (zwf) and an mbtH-like gene were identified. It is known from the literature that these three genes are involved directly or indirectly in NRPs synthesis.
Conclusions
We suggest that a molecule with antibiotic properties, produced by NRP synthetases, contributes to the antagonistic activity of P. synxantha.
Keyword
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
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
- …
