Structural and Functional Impact of SRP54 Mutations Causing Severe Congenital Neutropenia

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A locus involved in kanamycin, chloramphenicol and L-serine resistance is located in the bglY-galU region of the Escherichia coli K12 chromosome

Summary Spontaneous mutants of Escherichia coli K12 displaying an increased level of the kanamycin resistance conferred by plasmid pGR71 were selected. Several mutants obtained in this way apparently carry large chromosomal deletions extending into galU and/or bglY (27 min). This positive selection of deletions allowed detection of a new locus located between galU and bglY. Deletions of this locus are responsible for increased resistance to kanamycin (Irk), decreased resistance to l-serine in minimal medium (Drs) and decreased resistance to chloramphenicol (Drc) when a cat gene is present in the bacteria.     

Isolation and characterization of nonheterocystous tropical cyanobacteria growing on nitrogen-free medium

Summary Fourteen non-heterocystous cyanobacteria were selected from a continuous waterlogged biotope on a mineral medium free of combined nitrogen. Following morphological characterization, four, nine and one of the strains respectively, were assigned to sections I, II and III of a new cyanobacterial classification. Their phenotypic properties, including growth rates, photoheterotrophy, phycobiliprotein content, antibiotic resistance and toxin production were determined. Three strains were found to harbour one to three plasmids of low molecular weight.

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Resumen Mediante un medio mineral sin nitrogéno combinado se seleccionaron catorce cepas de cianobacterias no heterocísticas a partir de un biotopo permanentemente inundado. Apartir de sus carácterísticas morfológicas cuatro, nueve y una de las cepas fueron asignadas respectivamente a las secciones I, II y III de un nuevo sistema para la clasificación de cianobacterias. Se determinaron sus principales características fenotípicas, incluyendo tasas de crecimiento, fotoheterotrofia, contenido en ficobiliproteína, resistencia a antibióticos y producción de toxinas. Tres de las cepas contenían de uno a tres plásmidos de bajo peso molecular.

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Résumé Quatorze souches de cyanobactéries non-hétérocystées ont été isolées d'un biotope inondé sur un milieu minéral dépourvu d'azote combiné. Après détermination de leurs caractères morphologiques, respectivement quatre, neuf et une des souches ont été assignées aux sections I, II et III de la classification des cyanobactéries. Leurs propriétés phénotypiques telles que taux de croissance, photohétérotrophie, contenu en phycobiliprotéines, résistance aux antibiotiques et la production de toxine ont été déterminées. Trois des souches contiennent de un à trois plasmides de faible masse moléculaire.

     

Environmental vibrio phage–bacteria interaction networks reflect the genetic structure of host populations

Phages depend on their bacterial hosts to replicate. The habitat, density and genetic diversity of host populations are therefore key factors in phage ecology, but our ability to explore their biology depends on the isolation of a diverse and representative collection of phages from different sources. Here, we compared two populations of marine bacterial hosts and their phages collected during a time series sampling program in an oyster farm. The population of Vibrio crassostreae, a species associated specifically to oysters, was genetically structured into clades of near clonal strains, leading to the isolation of closely related phages forming large modules in phage–bacterial infection networks. For Vibrio chagasii, which blooms in the water column, a lower number of closely related hosts and a higher diversity of isolated phages resulted in small modules in the phage–bacterial infection network. Over time, phage load was correlated with V. chagasii abundance, indicating a role of host blooms in driving phage abundance. Genetic experiments further demonstrated that these phage blooms can generate epigenetic and genetic variability that can counteract host defence systems. These results highlight the importance of considering both the environmental dynamics and the genetic structure of the host when interpreting phage–bacteria networks.     

Escherichia coli Heat Shock Protein DnaK: Production and Consequences in Terms of Monitoring Cooking

Through use of commercially available DnaK proteins and anti-DnaK monoclonal antibodies, a competitive enzyme-linked immunosorbent assay was developed to quantify this heat shock protein in Escherichia coli ATCC 25922 subjected to various heating regimens. For a given process lethality (F₇₀¹⁰ of 1, 3, and 5 min), the intracellular concentration of DnaK in E. coli varied with the heating temperature (50 or 55°C). In fact, the highest DnaK concentrations were found after treatments at the lower temperature (50°C) applied for a longer time. Residual DnaK after heating was found to be necessary for cell recovery, and additional DnaK was produced during the recovery process. Overall, higher intracellular concentrations of DnaK tended to enhance cell resistance to a subsequent lethal stress. Indeed, E. coli cells that had undergone a sublethal heat shock (105 min at 55°C, F₇₀¹⁰ = 3 min) accompanied by a 12-h recovery (containing 76,786 ± 25,230 molecules/cell) resisted better than exponentially growing cells (38,500 ± 6,056 molecules/cell) when later heated to 60°C for 50 min (F₇₀¹⁰ = 5 min). Results reported here suggest that using stress protein to determine cell adaptation and survival, rather than cell counts alone, may lead to more efficient heat treatment.