Characterization of the Microbial Community Involved in the Suppression of Pythium aphanidermatum in Cucumber Grown on Rockwool

ABSTRACT The root pathogen Pythium aphanidermatum induced lower levels of disease in cucumber (Cucumis sativus) plants on unsterilized, re-used rockwool slabs than on heat-sterilized, re-used rockwool. Several recolonization treatments of the sterilized rockwool enhanced the suppressiveness of the rockwool. Microbial community structures in the different rockwool treatments were investigated by plate counts on selective media. Disease suppressiveness in the different rockwool treatments showed the highest correlation with the culturable number of filamentous actinomycetes in both experiments (r = 0.79 and 0.94), whereas the numbers of Trichoderma spp. correlated with suppression only in the first experiment (0.86). The numbers of total culturable bacteria, fluorescent pseudomonads, Bacillus spores, and fungi all showed lower correlations with disease suppressiveness. The filamentous actinomycetes enumerated with the plate counts were mainly Streptomyces spp., of which 10% were antagonistic toward P. aphanidermatum in dual culture. The composition of the bacterial and actinomycete populations was studied with polymerase chain reaction (PCR)-denaturing gradient gel electrophoresis (DGGE). Multivariate analyses of these patterns with canonical correspondence analysis showed significant correlations between the microbial composition and the disease suppressiveness. However, none of the bands in PCR-DGGE patterns occurred exclusively in the treatments that had enhanced disease suppressiveness. Bands extracted from the actinomycete-specific DGGE gels showed closest similarity with members of several actinomycete genera, i.e., Streptomyces, Mycobacterium, Microbacterium, Rhodococcus, Curtobacterium, and Tsukamurella. The possible mechanism of disease suppressiveness in used rockwool slabs, based on the results obtained with culture-dependent and culture-independent detection methods, is discussed.     

Perfrin,a novel bacteriocin associated with netB positive Clostridium perfringens strains from broilers with necrotic enteritis

Necrotic enteritis in broiler chickens is associated with netB positive Clostridium perfringens type A strains. It is known that C. perfringens strains isolated from outbreaks of necrotic enteritis are more capable of secreting factors inhibiting growth of other C. perfringens strains than strains isolated from the gut of healthy chickens. This characteristic could lead to extensive and selective presence of a strain that contains the genetic make-up enabling to secrete toxins that cause gut lesions. This report describes the discovery, purification, characterization and recombinant expression of a novel bacteriocin, referred to as perfrin, produced by a necrotic enteritis-associated netB-positive C. perfringens strain. Perfrin is a 11.5 kDa C-terminal fragment of a 22.9 kDa protein and showed no sequence homology to any currently known bacteriocin. The 11.5 kDa fragment can be cloned into Escherichia coli, and expression yielded an active peptide. PCR detection of the gene showed its presence in 10 netB-positive C. perfringens strains of broiler origin, and not in other C. perfringens strains tested (isolated from broilers, cattle, sheep, pigs, and humans). Perfrin and NetB are not located on the same genetic element since NetB is plasmid-encoded and perfrin is not. The bacteriocin has bactericidal activity over a wide pH-range but is thermolabile and sensitive to proteolytic digestion (trypsin, proteinase K). C. perfringens bacteriocins, such as perfrin, can be considered as an additional factor involved in the pathogenesis of necrotic enteritis in broilers.     

An entomopathogenic fungus for control of adult African malaria mosquitoes

Biological control of malaria mosquitoes in Africa has rarely been used in vector control programs. Recent developments in this field show that certain fungi are virulent to adult Anopheles mosquitoes. Practical delivery of an entomopathogenic fungus that infected and killed adult Anopheles gambiae, Africa's main malaria vector, was achieved in rural African village houses. An entomological inoculation rate model suggests that implementation of this vector control method, even at the observed moderate coverage during a field study in Tanzania, would significantly reduce malaria transmission intensity.     

Noncanonical TGFβ signaling contributes to aortic aneurysm progression in Marfan syndrome mice

Transforming growth factor-β (TGFβ) signaling drives aneurysm progression in multiple disorders, including Marfan syndrome (MFS), and therapies that inhibit this signaling cascade are in clinical trials. TGFβ can stimulate multiple intracellular signaling pathways, but it is unclear which of these pathways drives aortic disease and, when inhibited, which result in disease amelioration. Here we show that extracellular signal-regulated kinase (ERK) 1 and 2 and Smad2 are activated in a mouse model of MFS, and both are inhibited by therapies directed against TGFβ. Whereas selective inhibition of ERK1/2 activation ameliorated aortic growth, Smad4 deficiency exacerbated aortic disease and caused premature death in MFS mice. Smad4-deficient MFS mice uniquely showed activation of Jun N-terminal kinase-1 (JNK1), and a JNK antagonist ameliorated aortic growth in MFS mice that lacked or retained full Smad4 expression. Thus, noncanonical (Smad-independent) TGFβ signaling is a prominent driver of aortic disease in MFS mice, and inhibition of the ERK1/2 or JNK1 pathways is a potential therapeutic strategy for the disease.     

Furfuryl ethyl ether: important aging flavor and a new marker for the storage conditions of beer

Recently, it was reported that furfuryl ethyl ether is an important flavor compound indicative of beer storage and aging conditions. A study of the reaction mechanism indicates that furfuryl ethyl ether is most likely formed by protonation of furfuryl alcohol or furfuryl acetate followed by S(N)2-substitution of the leaving group by the nucleophilic ethanol. For the reaction in beer, a pseudo-first-order reaction kinetics was derived. A close correlation was found between the values predicted by the kinetic model and the actual furfuryl ethyl ether concentration evolution during storage of beer. Furthermore, 10 commercial beers of different types, aged during 4 years in natural conditions, were analyzed, and it was found that the furfuryl ethyl ether flavor threshold was largely exceeded in each type of beer. In these natural aging conditions, lower pH, darker color, and higher alcohol content were factors that enhanced furfuryl ethyl ether formation. On the other hand, sulfite clearly reduced furfuryl ethyl ether formation. All results show that the furfuryl ethyl ether concentration is an excellent time-temperature integrator for beer storage.     

Temperature compensation for near infrared reflectance measurement of apple fruit soluble solids contents

Near infrared reflectance (NIR) spectroscopy has been used successfully to measure soluble solids in apple fruit. However, for practical implementation, the technique needs to be able to compensate for fruit temperature fluctuations, as it was observed that the sample temperature affects the near infrared reflectance spectrum in a non-linear way. Temperature fluctuations may occur in practice because of varying weather conditions or improper conditioning of the fruit immediately after harvest. Two techniques were found well suited to control the accuracy of the calibration models for soluble solids with respect to temperature fluctuations. The first, and most practical one, consisted of developing a global robust calibration model to cover the temperature range expected in the future. The second method involved the development of a range of temperature dedicated calibration models. The drawback of the latter approach is that the required data collection is very large. When no precautions are taken, the error on the soluble solids content reading may be as large as 4%brix.     

Transient gene expression in transformed banana (Musa cv. Bluggoe) protoplasts and embryogenic cell suspensions

Summary In order to introduce currently-available genes with agronomical value into banana, two genetic transformation protocols have been optimized.Firstly, regenerable protoplasts isolated from embryogenic cell suspensions of the cultivar Bluggoe have been used for the introduction of several chimaeric uidA gene constructs by electroporation. With the inclusion of polyethylene glycol and heat shock, the frequency of transiently expressing protoplasts reached 1.8% as shown by an in situ -glucuronidase assay. A duplicated 35S promoter with an alfalfa mosaic virus leader sequence (pBI-426) induced the highest expression rate among the constructs tested.Embryogenic cell suspensions of cv. Bluggoe have also been bombarded with accelerated particles coated with a high expression uidA gene construct (pEmuGN) using a biolistic gun. After a partial optimization of the procedure, transient GUS assays reproducibly demonstrated the presence of 400 blue foci in 30 l of settled cell volume (approximately 25 mg cells). Selection and characterization of antibiotic-resistant transformed cultures is in progress.Abbreviations AMV alfalfa mosaic virus - GUS -glucuronidase - TGE transient GUS expression - uidA gene for -glucuronidase