Water disinfection by ozonation has advantages over UV irradiation in a brackish water recirculation aquaculture system for Pacific white shrimp (Litopenaeus vannamei)

By keeping tropical shrimp, like Litopenaeus vannamei, in recirculating aquaculture systems (RAS), valuable food for human consumption can be produced sustainable. L. vannamei tolerates low salinities, and therefore, the systems can operate under brackish water conditions. The stabilization of the microbial community in RAS might be difficult under high organic loads, and therefore, water treatment measures like UV irradiation or ozone application are commonly used for bacterial reduction. To investigate the impact of these measures, the effects of UV irradiation and ozone application were studied in small-scale brackish water RAS with a salinity of 15‰ stocked with L. vannamei. UV reactors with 7 and 9 W were used, and by ozonizers with a power of 5–50 mg/hr, the redox potential in the water was adjusted to 350 mV. Ozone had a stabilizing effect on the microbial composition in the water and on biofilms of tank surfaces and shrimp carapaces, prevented an increase of nitrite and accelerated the degradation of nitrate in the water. UV irradiation led to changes in the microbial composition and was less effective in optimizing the chemical water quality. Thus, the use of ozone could be recommended for water treatment in brackish water RAS for shrimp.     

Inhibition of two family 18 chitinases by various allosamidin derivatives

The inhibitory activities of several allosamidin derivatives on two family 18 chitinases, an insect enzyme from the epithelial cell line from Chironomus tentans, and a bacterial enzyme, chitinase A from Serratia marcescens, were evaluated. The following structural requirements are necessary for inhibition of the Chironomus enzyme: 1. One N-acetylallosamine residue can be omitted without impairment of enzyme inhibition. 2. At least one N-acetylallosamine sugar must be present. 3. Glucosamine can replace the allosamine moiety without a negative effect on the inhibitory activity. 4. The spatial arrangement of the allosamizoline moiety is important for inhibition. 5. If one sugar is omitted and the arrangement of the cyclitol residue is changed, the inhibitory effect is diminished further. For purified chitinase A from Serratia marcescens the arrangement of the aglycone moiety is equally important, but recognition of the sugar is different: 1. Omission of one allosamine residue decreases the inhibitory activity considerably. 2. Inhibition is improved if the remaining N-acetylallosamine is replaced by the epimer N-acetylglucosamine. Only endochitinase activity is affected, since chitin formation (up to 10^-4 M ) and N-acetylglucosaminidase activity (up to 10^-3 M ) are not impaired, at least in Chironomus cells. © 1998 SCI.     

Flow cytometric analysis of mitogen-induced activation of rainbow trout (Oncorhynchus mykiss) peripheral blood leucocytes

Proliferation of rainbow trout peripheral blood leucocytes in vitro is usually assessed by measuring incorporated tritiated thymidine. In this report we monitored the in vitro proliferative response to the mitogen Concanavalin A (Con A) by means of flow cytometry (FCM) and 3H-thymidine incorporation. When analysed by FCM, blood leucocytes displayed two main cell populations with distinct forward and side scatter (FSC/SSC) characteristics: lymphocytes with low FSC/SSC values and non-lymphoid leucocytes (NLL) with increased FSC/SSC values. The nature of these cell types were confirmed by microscopy. Interestingly, the FSC/SSC pattern of lymphocytes remained unchanged after in vitro stimulation with Con A, whereas cells from the NLL population showed a marked shift towards increased FSC values. In stimulated cultures, the increase of FSC values of the NLL population significantly correlated with contemporarily measured 3H-thymidine incorporation (r = 0.7, P < 0.001). The mitogenic response of blood leucocytes originating from different individual fish varied over wide ranges. It was found to be related to the numbers of NLL present in the leucocyte sample. The present results show that qualitative and quantitative FCM analysis of morphological parameters (FSC/SSC) of blood leucocytes makes it possible to discriminate between leucocyte populations of the rainbow trout and to monitor cell proliferation experiments.     

Characterization of shiga toxin-producing Escherichia coli strains isolated from calves in Poland

Fecal samples from 67 3–5-months-old calves with diarrhea were screened for the presence of shiga toxin-producing Escherichia coli (STEC). Several accessory virulence factors genes were also tested. Among 192 E.coli isolates tested, 15 (7.6%) were found to harbour the shiga toxin 1 or 2 (stx1 or stx2) genes. The stx2-carrying samples were further subtyped by PCR for the stx2c, stx2d, and stx2e toxin variants. It was shown that stx2-positive bacteria mainly possessed the stx2c shiga toxin type gene. The enterohemolysin (hlyA) and intimin (eae) genes were found in seven (46.7%) STEC strains whereas the cytotoxic necrotizin factor 1 and 2 or the P fimbrial genes were detected in two isolates only. This study confirmed that calves are a reservoir of STEC strains (with all pathogenicity genes) that may be virulent for humans.     

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.     

Introduction of electronics into milking technology

In countries, like the former German Democratic Republic (GDR), where ‘industrialized’ milk production in large herds was the goal to be reached, research on automation of machine milking was started more than 30 years ago. Initially, the main goal was to mechanize operations at the end of the milking process. This work finally resulted in milking devices that do not apply uniform parameters to all cows, but operate according to the milk flow obtained from the cow actually to be milked. This evolution towards ‘controlled milking’ would not have been possible without application of electricity and electronic components for sensors and control units. Also depending on the technical evolution of electronic control systems are devices for recording milk yield and for taking samples for milk analysis, which were available around the year 1980. At that time initial projects for automatic milk recording were evaluated, which had an obvious influence on further development of milk meters. The most demanding step of application of electronic control systems up to now was the introduction of automatic milking systems. Here not only application of teat cups has to be executed, it also is necessary to enable automatic checks of udder condition, milk quality and other operations which may be challenging even for trained human operators. Further evolution of electronic measurement procedures may be important for the milk-producing farmer too, especially when on-line milk analysis is to be introduced within the near future.     

Evidence from numerical experiments for a feedback dynamo generating Mercury's magnetic field

The observed weakness of Mercury's magnetic field poses a long-standing puzzle to dynamo theory. Using numerical dynamo simulations, we show that it could be explained by a negative feedback between the magnetospheric and the internal magnetic fields. Without feedback, a small internal field was amplified by the dynamo process up to Earth-like values. With feedback, the field strength saturated at a much lower level, compatible with the observations at Mercury. The classical saturation mechanism via the Lorentz force was replaced by the external field impact. The resulting surface field was dominated by uneven harmonic components. This will allow the feedback model to be distinguished from other models once a more accurate field model is constructed from MErcury Surface, Space ENvironment, GEochemistry, and Ranging (MESSENGER) and BepiColombo data.