Bacterial Rot of Dieffenbachia maculata (Lodd.) G. Don. Caused by Erwinia chrysanthemi

Five bacterial isolates were obtained in a nursery near Gent (Belgium) from diseased Dieffenbachia maculata (Lodd.) G., Don. cv. Compacta, cv. Camillo and cv. Veerle plants. They were identified by API 20E, API 50 CHE and API ZYM systems as Erwinia chrysanthemi. These strains and seven collection strains were pathogenic to all three D. maculata cultivars tested: cv. Camillo, cv. Compacta and cv. Tropic Snow. Inoculation in the stem or petiole was the only effective method for obtaining systemic infection. The petiole appeared to be the part of the plant in which disease developed most readily. Wounding was required for the induction of the disease. Temperatures between 25° and 30° C, a relative air humidity of 75 % or more and low light intensity (0.5 ft-c) favoured the disease, whereas high inoculum sizes (10⁶ or more cells) accelerated and increased it. Histological studies showed tissue degradation in infected areas. Petioles were most severely affected. Transport of bacteria seemed to occur after vessel infection in stem or petiole tissues.     

Effects of location of food delivery and social status on foraging-site selection by juvenile Atlantic salmon

Synopsis Experiments were conducted to investigate the response of juvenile Atlantic salmon,Salmo salar, to changes in the location at which food entered a stream tank. Experience with the location of food input into the system significantly influenced foraging-site selection by the dominant fish. Dominant fish changed location of their foraging site in response to a change in the location of food input, and occupied, aggressively defending, sites just downstream of the location of food introduction. In contrast, subordinate fish occupied foraging sites at the downstream end of the stream tank, regardless of location of food input. As a result of both site selection and social status, dominant fish captured significantly more prey than subordinates. Our results support the contention that salmonids choose foraging sites to maximize foraging opportunities. Our results also provide a possible explanation for the use of atypical foraging sites by individual fish within their home range over the course of a single day, as observed in a number of salmonid species in the field.     

Biodiversity of microorganisms that degrade bacterial and synthetic polyesters

The biodiversity and occurrence in nature of bioplastic-degrading microorganisms are exemplified by the identification of 695 strains, isolated from different environments, such as soils, composts, natural waters, and sludge, that are able to degrade the bacterial polyester poly(3-hydroxybutyrate)in vitro. These microorganisms belong to at least 57 different taxa, including Gram-negative and Gram-positive bacteria, streptomycetes, and moulds. The literature on the biodiversity of poly(3-hydroxybutyrate)-degrading microorganisms is reviewed. The degrading abilities of 171 streptomycete strains were investigated on four different bacterial poly(3-hydroxyalkanoates), and the synthetic polyesters poly(-caprolactone) and BIONOLLE, and most of these strains degraded at least three different polymers.     

Modulation of 3-hydroxy-3-methylglutaryl coenyzyme a (HMG-CoA) reductase activity with intracellular fractions of hamster adrenals

Hamster adrenal HMG-CoA reductase activity was enhanced with rat liver cytosolic phosphorylase phosphatase as well as with similarly isolated beef and hamster adrenal cytosolic preparations. HMG-CoA reductase was inactivated when microsomes were incubated in an EDTA-free medium but containing MgCl₂ and ATP. The reductase activity of microsomes isolated from adrenals of hamsters sacrificed at 1100 h and 1900 h were (mean ± SEM, pmo1/mg protein/min.) 299.6±62.3 and 588.3 ± 96.6 respectively and could be enhanced by a factor of four when preincubated in the presence of liver phosphatase.     

Differences in susceptibility of Listeria monocytogenes strains to sakacin P,sakacin A,pediocin PA-1, and nisin

Two hundred strains of Listeria monocytogenes collected from food and the food industry were analyzed for susceptibility to the class IIa bacteriocins sakacin P, sakacin A, and pediocin PA-1 and the class I bacteriocin nisin. The individual 50% inhibitory concentrations (IC(50)) were determined in a microtiter assay and expressed in nanograms per milliliter. The IC(50) of sakacin P ranged from 0.01 to 0.61 ng ml(-1). The corresponding values for pediocin PA-1, sakacin A, and nisin were 0.10 to 7.34, 0.16 to 44.2, and 2.2 to 781 ng ml(-1), respectively. The use of a large number of strains and the accuracy of the IC(50) determination revealed patterns not previously described, and for the first time it was shown that the IC(50) of sakacin P divided the L. monocytogenes strains into two distinct groups. Ten strains from each group were analyzed by sodium dodecyl sulfate-polyacrylamide gel electrophoresis of whole-cell proteins and amplified fragment length polymorphism. The results from these studies essentially confirmed the grouping based on the IC(50) of sakacin P. A high correlation was found between the IC(50) of sakacin P and that of pediocin PA-1 for the 200 strains. Surprisingly, the correlation between the IC(50) of the two class IIa bacteriocins sakacin A and sakacin P was lower than the correlation between the IC(50) of sakacin A and the class I bacteriocin nisin.     

Culture-independent analysis of probiotic products by denaturing gradient gel electrophoresis

In order to obtain functional and safe probiotic products for human consumption, fast and reliable quality control of these products is crucial. Currently, analysis of most probiotics is still based on culture-dependent methods involving the use of specific isolation media and identification of a limited number of isolates, which makes this approach relatively insensitive, laborious, and time-consuming. In this study, a collection of 10 probiotic products, including four dairy products, one fruit drink, and five freeze-dried products, were subjected to microbial analysis by using a culture-independent approach, and the results were compared with the results of a conventional culture-dependent analysis. The culture-independent approach involved extraction of total bacterial DNA directly from the product, PCR amplification of the V3 region of the 16S ribosomal DNA, and separation of the amplicons on a denaturing gradient gel. Digital capturing and processing of denaturing gradient gel electrophoresis (DGGE) band patterns allowed direct identification of the amplicons at the species level. This whole culture-independent approach can be performed in less than 30 h. Compared with culture-dependent analysis, the DGGE approach was found to have a much higher sensitivity for detection of microbial strains in probiotic products in a fast, reliable, and reproducible manner. Unfortunately, as reported in previous studies in which the culture-dependent approach was used, a rather high percentage of probiotic products suffered from incorrect labeling and yielded low bacterial counts, which may decrease their probiotic potential.     

Stepping stones towards a new prokaryotic taxonomy

Technological developments provide new insights into prokaryotic evolution and diversity and provoke a continuous need to update taxonomy and revise classification schemes. Our present species concept and definition are being challenged by the growing amount of whole genomic information, which should allow improvements in the natural species definition. The continuous quest for an objective and stable method for sorting strains into coherent homogeneous groups is inherent to prokaryotic systematics and nomenclature. Morphological, biochemical, physiological, phenotypic and chemotaxonomic criteria have been complemented by molecular data and pragmatic, purpose built, species definitions are being replaced by more natural ones based on evolutionary insights. It is imperative to give due consideration to both fundamental and applied aspects of future species concepts and definitions. The present paper discusses the present practice in prokaryotic taxonomy of how this system developed and how it may evolve in the future.