Antonie van Leeuwenhoek

Each of four conserved glutamate residues of Bacillus stearothermophilus leucine aminopeptidase II (BsLAPII) was replaced with aspartate, lysine, and leucine respectively by site-directed mutagenesis. The over-expressed wild-type and mutant enzymes were purified to homogeneity by nickel-chelate chromatography and the molecular mass of the subunit was determined to be 44.5 kDa by SDS-PAGE. The specific activity for the Glu-316 and Glu-340 mutants was completely abolished, while Glu-249 mutants showed comparable activity to that of the wild-type BsLAPII. Compared with the wild-type enzyme, the E250D and E250L mutant enzymes retained less than 18% of the enzyme activity and exhibited a dramatic decrease in the value of k cat/K m. These observations indicate that Glu-250, Glu-316, and Glu-340 residues are critical for the catalytic activity of BsLAPII.

Các đặc tính của 166 chủng vi khuẩn môi trường thuộc bảy loài enterococcus đã được nghiên cứu. Enterococcus chủ yếu xuất phát từ nước bề mặt và nước thải. Chúng đã được kiểm tra sự hiện diện của enterocin, các yếu tố virulence và kháng sinh. Sự hiện diện của các gen enterocin khác nhau (entA, entB, entP, ent31, entL50AB) thường được quan sát thấy ở các chủng enterococcus của chúng tôi, 109 chủng chứa ít nhất một gen enterocin. Sự phân bố của các gen enterocin thay đổi theo loài, các gen này chủ yếu có mặt trong E. hirae và E. faecium. Qua thử nghiệm spot enterocin, 10 chủng đã ức chế sự phát triển của các chủng Listeria. Để đánh giá khả năng gây bệnh của các chủng, sự phân bố của các gen virulence chọn lọc (cylA, gelE và esp) đã được điều tra, mười một chủng dương tính với một số trong các gen này, năm trong số đó thuộc về E. faecalis. Về kháng sinh của các chủng, chỉ có hai chủng kháng đa thuốc và hai chủng (E. hirae và E. casseliflavus) kháng lại vancomycin.

Eubacteria of the genus Rhodococcus are a diverse group of microorganisms commonly found in many environmental niches from soils to seawaters and as plant and animal pathogens. They exhibit a remarkable ability to degrade many organic compounds and their economic importance is becoming increasingly apparent. Although their genetic organisation is still far from understood, there have been many advances in recent years. Reviewed here is the current knowledge of rhodococci relating to gene transfer, recombination, plasmid replication and functions, cloning vectors and reporter genes, gene expression and its control, bacteriophages, insertion sequences and genomic rearrangements. Further fundamental studies of Rhodococcus genetics and the application of genetic techniques to the these bacteria will be needed for their continued biotechnological exploitation.

Les travaux expérimentaux réalisés dans notre laboratoire ont démontré la présence d'une absorption lors de la filtration du virus poliomyélitique sur filtres Seitz. Cette absorption est maximale dans les premières fractions filtrées. Lorsque la filtration est effectuée avec un milieu de culture riche en acides aminés (3‰), contenant du Tween 80 (60 mg‰) à raison de 250 cm3 par cm2 de surface, la récupération du virus filtré est quasi totale. Ces conditions de filtration du virus poliomyélitique permettent d'appliquer rigoureusement les mesures de sécurité au cours de la fabrication du vaccin antipoliomyélitique (double filtration sur filtre Seitz S1) sans crainte d'une perte d'efficacité du produit final.

A Gram-strain positive, aerobic, endospore-forming bacterial strain (JJ-246T) was isolated from the rhizosphere of Zea mays. The 16S rRNA gene sequence similarity comparisons showed a most closely relationship to Paenibacillus oenotherae DT7-4T (98.4%) and Paenibacillus xanthinolyticus 11N27T (98.0%). The pairwise average nucleotide identity and digital DNA-DNA hybridisation values of the JJ-246T genome assembly against publicly available Paenibacillus type strain genomes were below 82% and 33%, respectively. The draft genome of JJ-246T shared many putative plant-beneficial functions contributing (PBFC) genes, related to plant root colonisation, oxidative stress protection, degradation of aromatic compounds, plant growth-promoting traits, disease resistance, drug and heavy metal resistance, and nutrient acquisition. The quinone system of strain JJ-246T, the polar lipid profile and the major fatty acids were congruent with those reported for members of the genus Paenibacillus. JJ-246T was shown to represent a novel species of the genus Paenibacillus, for which the name Paenibacillus plantiphilus sp. nov. is proposed, with JJ-246T (= LMG 32093T = CCM 9089T = CIP 111893T) as the type strain.

From a „Froschlaich” formed in a sugar-factory, the responsible organism was isolated. This organism could be identified with the dextran-forming, heterofermentative, rod-shaped lactic acid bacterium,Betabacterium vermiforme, a bacterium first described byWard as one of the constituents of the „ginger-beer plant” and recently recognized byMayer (18) as being also one of the components of the „tibi”-consortium. Thus it has been shown that the formation of the „Froschlaich” in sugar factories is not always due toLeuconostoc mesenterioides or toBacillus vulgatus, but can also be caused byBetabacterium vermiforme. A hitherto unknown species of the genusStreptobacterium, was found to be an accompanying organism. This rod-shaped, homofermentative, dextran-forming bacterium has been described in detail as the speciesStreptobacterium dextranicum nov. spec.

In this study, the nitrogen fixing Astragalus glycyphyllos symbionts were characterized by phenotypic properties, restriction fragment length polymorphism (RFLP), and sequences of 16S rDNA. The generation time of A. glycyphyllos rhizobia in yeast extract mannitol medium was in the range 4–6 h. The studied isolates exhibited a low resistance to antibiotics, a moderate tolerance to NaCl, assimilated di- and trisaccharides, and produced acid in medium containing mannitol as a sole carbon source. In the cluster analysis, based on 86 phenotypic properties of A. glycyphyllos symbionts and the reference rhizobia, examined isolates and the genus Mesorhizobium strains were placed on a single branch, clearly distinct from other lineages of rhizobial genera. By the comparative analysis of 16S rRNA gene sequences and 16S rDNA–RFLP, A. glycyphyllos nodulators were also identified as the members of the genus Mesorhizobium. On the 16S rDNA sequence phylogram, the representatives of A. glycyphyllos nodule isolates formed a robust, monophyletic cluster together with the Mesorhizobium species at 16S rDNA sequence similarity of these bacteria between 95 and 99 %. Similarly, the cluster analysis of the combined RFLP–16S rDNA patterns, obtained with seven restriction endonucleases, showed that A. glycyphyllos rhizobia are closely related to the genus Mesorhizobium bacteria. The taxonomic approaches used in this paper allowed us to classify the studied bacteria into the genus Mesorhizobium.

Two strictly anaerobic nitrogen-fixing strains, designated RG17T and RG53T, were isolated from paddy soils in China. Strains RG17T and RG53T showed the highest 16S rRNA gene sequence similarities to the type strain Geomonas paludis (97.9–98.4%). Phylogenetic tree based on 16S rRNA gene sequences showed that two strains clustered with members of the genus Geomonas. Growth of strain RG17T was observed at 20–42 °C, pH 5.5–8.5 and 0–0.3% (w/v) NaCl while strain RG53T growth was observed at 20–42 °C, pH 5.5–9.5 and 0–0.7% (w/v) NaCl. Strains RG17T and RG53T contained MK-8 as main menaquinone and C15:1 ω6c, iso-C15:0, and Summed Feature 3 as the major fatty acids. The genomic DNA G + C content of strains RG17T and RG53T were 61.6 and 60.7%, respectively. The digital DNA–DNA hybridization (dDDH) and average nucleotide identity (ANI) values between the isolated strains and the closely related Geomonas species were lower than the cut-off value (dDDH 70% and ANI 95–96%) for prokaryotic species delineation. Both strains possessed nif genes nifHDK and nitrogenase activities. Based on the above results, the two strains represent two novel species of the genus Geomonas, for which the names Geomonas fuzhouensis sp. nov. and Geomonas agri sp. nov., are proposed. The type strains are RG17T (= GDMCC 1.2687T = KCTC 25332T) and RG53T (= GDMCC 1.2630T = KCTC 25331T), respectively.