Structural and Functional Impact of SRP54 Mutations Causing Severe Congenital Neutropenia

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Down syndrome with duplication of a region of chromosome 21 containing the CuZn superoxide dismutase gene without detectable karyotypic abnormality

Summary We report the case of an 18-month-old boy with many typical Down syndrome features but a normal cytogenetic analysis. High-resolution banding techniques on lymphocytes and fibroblasts of the propositus and his parents did not show any detectable abnormality including that of trisomy 21 mosaicism. However, CuZn superoxide dismutase (CuZn SOD) in the patient's red cells was increased as in trisomy 21. DNA analysis (Southern blots) using a human CuZn SOD probe showed that the genotype of the propositus contained three CuZn SOD genes. In situ hybridization on metaphase chromosomes with the same probe confirmed the gene location in a segment enclosing the distal part of 21q21 and 21q22.1. There was no significant labeling on other chromosomes of the patient. These results indicate that the Down syndrome phenotype of this patient is due to microduplication of a chromosome 21 fragment containing the CuZn SOD gene.     

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.     

Variability of Xanthomonas Campestris pv. vasculorum From Sugarcane and Other Gramineae in Reunion Island. Characterization of a Different Xanthomonad

Stains presumed to be of Xanthomonas campestris pv. vasculorum (Cobb.) Dye, obtained from sugarcane and other gramineae in Réunion Island, were compared in terms of cultural aspects, pathogenic and physiological reactions, fatty acid profiles and restriction fragment length polymorphism (RFLP) of genomic DNA. The strains could be divided into two separate groups (G1 and G2). The G1 strains were identical to strains described as X. campestris pv. vasculorum; they showedan important variability in their cultural characteristics and in their aggressiveness. The G2 strains did not induce the usual symptoms of gumming disease on sugarcane cultivars infected under natural conditions or inoculated in the greenhouse. The G2 strains grew faster on agar medium, their colonies were more pigmented and less fluidal and had a different morphology on agar slant. Unlike the G1 strains, G2 strains hydrolyzed starch weakly and casein strongly; they utilized L-fucose and, to a lesser extent, melibioze. The fatty acid and genomic DNA profiles differed between the groups. Differences seemed large enough to support separation of G1 and G2 strains into distinct taxonomic entities, namely G1 as Xanthomonas campestris pv. vasculorum and G2 as a different pathovar of X. campestris. The taxonomic position of G2 strains is discussed.     

Characterization of Xanthomonas campestris Pathovars by rRNA Gene Restriction Patterns

Genomic DNA of 191 strains of the family Pseudomonadaceae, including 187 strains of the genus Xanthomonas, was cleaved by EcoRI endonuclease. After hybridization of Southern transfer blots with 2-acetylamino-fluorene-labelled Escherichia coli 16+23S rRNA probe, 27 different patterns were obtained. The strains are clearly distinguishable at the genus, species, and pathovar levels. The variability of the rRNA gene restriction patterns was determined for four pathovars of Xanthomonas campestris species. The 16 strains of X. campestris pv. begoniae analyzed gave only one pattern. The variability of rRNA gene restriction patterns of X. campestris pv. manihotis strains could be related to ecotypes. In contrast, the variability of patterns observed for X. campestris pv. malvacearum was not correlated with pathogenicity or with the geographical origins of the strains. The highest degree of variability of DNA fingerprints was observed within X. campestris pv. dieffenbachiae, which is pathogenic to several hosts of the Araceae family. In this case, variability was related to both host plant and pathogenicity.     

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.