In vivo adherence of Pseudomonas aeruginosa to rat bladder epithelium

To date, the study of bacterial adherence to uroepithelial cells has utilized considerable variation in methodology, resulting in highly divergent conclusions. In an attempt to standardize methodology, a modified method is described to more accurately measure the in vivo bacterial adherence to rat bladder uroepithelium utilizing Pseudomonas species labeled with 2-[3H]adenine. Two isolates of P. aeruginosa were selected for more intensive study; one showed consistently good adherence; the second strain always adhered poorly, thus providing a negative control. Maximum adherence was detected after 60 min of incubation. Neither of the two Pseudomonas isolates when examined by transmission electron microscopy showed evidence of pili formation. The morphological features of Pseudomonas adherence to bladder mucosa as studied by scanning electron microscopy are described.     

Evaluation of isozyme systems in Citrus to facilitate identification of fusion products

Summary Ten isozymes were analyzed in nucellar calli of nine Citrus species and cultivars and roots of the corresponding apomictic seedlings. The zymograms obtained can be divided into three groups: a) isozyme patterns similar in both calli and roots, b) isozyme patterns similar in calli but variable in roots, and c) isozyme patterns variable in both calli and roots. Analysis of these ten isozyme systems may facilitate identification of fusion products in Citrus.Contribution from the Agricultural Research Organization, The Volcani Center, Bet Dagan, Israel. No. 354-E, 1982 series     

Identification, phylogenetic relationships and a new maximum size of two rudd populations (Scardinius, Cyprinidae) from the Adriatic Sea drainage, Croatia

In order to determine an unknown fish population from the Vrana Lake, mitochondrial cytochrome b gene and non-coding nuclear region Cyfun P were investigated. Stabile population of Bulldog rudd, Scardinius dergle Heckel & Kner, the endemic Croatian freshwater fish in the Krka River, was genetically characterized with the same markers in order to compare it with the material from the Vrana Lake. Genetic markers were sequenced and aligned with the similar ones obtained from the GenBank in order to determine taxonomic and phylogenetic position of these two species. A significant discrepancy between nuclear genetic markers of our specimens and the sequence from the GenBank was found. Phylogenetic analysis suggested that the specimens from the Vrana Lake belong to the species S. hesperidicus. Morphometric characteristics, the maximum length and body mass showed new maximum values for both S. dergle and S. hesperidicus.     

Limnological and ecophysiological aspects of Aphanizomenon ovalisporum bloom in Lake Kinneret, Israel

The first appearance of Aphanizomenon ovalisporum in Lake Kinneret in August 1994 was apparently boosted by relatively high concentrations of total dissolved phosphorus (12 g P l^-1 as compared to an average of 8 g P l^-1). The increasing Aphanizomenon biomass in a lake in which phytoplankton are generally phosphate limited in summer and autumn was accompanied by high enzymatic activity of alkaline phosphatase, reaching values of 2830 nmol MU l^-1 h^-1, suggesting a great demand for phosphorus. In addition, the nitrogen requirement of the developing population of Aphanizomenon was partly provided by nitrogen fixation, as indicated by a high percentage of heterocysts. Laboratory experiments demonstrated that filtrate from an old Peridinium gatunense culture enhanced Aphanizomenon growth. Thus, it is postulated that the degradation of the massive Peridinium bloom in spring and early summer supported the development of A.ovalisporum. The high pH and alkalinity during the bloom of Aphanizomenon indicate that A.ovalisporum is probably a HCO3^- user. After 1994, akinetes of A.ovalisporum were left in sediments and the water column, and could be a source for the next year's bloom. This possibility was demonstrated by inoculation of lake water and sediments into nitrogen-depleted BG-11 medium, resulting in the dominance of A.ovalisporum.      

Synchronization of cell death in a dinoflagellate population is mediated by an excreted thiol protease

Regulated programmed cell death (PCD) processes have been documented in several phytoplankton species and are hypothesized to play a role in population dynamics. However, the mechanisms leading to the coordinated collapse of phytoplankton blooms are poorly understood. We showed that the collapse of the annual bloom of Peridinium gatunense, an abundant dinoflagellate in Lake Kinneret, Israel, is initiated by CO2 limitation followed by oxidative stress that triggers a PCD-like cascade. We provide evidences that a protease excreted by senescing P. gatunense cells sensitizes younger cells to oxidative stress and may consequently trigger synchronized cell death of the population. Ageing of the P. gatunense cultures was characterized by a remarkable rise in DNA fragmentation and enhanced sensitivity to H2O2. Exposure of logarithmic phase (young) cultures to conditioning media from stationary phase (old) cells sensitized them to H2O2 and led to premature massive cell death. We detected the induction of specific extracellular protease activity, leupeptin-sensitive, in ageing cultures and in lake waters during the succession of the P. gatunense bloom. Partial purification of the conditioned media revealed that this protease activity is responsible for the higher susceptibility of young cells to oxidative stress. Inhibition of the protease activity lowered the sensitivity to oxidative stress, whereas application of papain to logarithmic phase P. gatunense cultures mimicked the effect of the spent media and enhanced cell death. We propose a novel mechanistic framework by which a population of unicellular phytoplankton orchestrates a coordinated response to stress, thereby determine the fate of its individuals.     

Precise temporal modulation in the response of the SOS DNA repair network in individual bacteria

The SOS genetic network is responsible for the repair/bypass of DNA damage in bacterial cells. While the initial stages of the response have been well characterized, less is known about the dynamics of the response after induction and its shutoff. To address this, we followed the response of the SOS network in living individual Escherichia coli cells. The promoter activity (PA) of SOS genes was monitored using fluorescent protein-promoter fusions, with high temporal resolution, after ultraviolet irradiation activation. We find a temporal pattern of discrete activity peaks masked in studies of cell populations. The number of peaks increases, while their amplitude reaches saturation, as the damage level is increased. Peak timing is highly precise from cell to cell and is independent of the stage in the cell cycle at the time of damage. Evidence is presented for the involvement of the umuDC operon in maintaining the pattern of PA and its temporal precision, providing further evidence for the role UmuD cleavage plays in effecting a timed pause during the SOS response, as previously proposed. The modulations in PA we observe share many features in common with the oscillatory behavior recently observed in a mammalian DNA damage response. Our results, which reveal a hitherto unknown modulation of the SOS response, underscore the importance of carrying out dynamic measurements at the level of individual living cells in order to unravel how a natural genetic network operates at the systems level.