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Archives of Microbiology (v.181, #5)
Rhizobium etli maize populations and their competitiveness for root colonization by Mónica Rosenblueth; Esperanza Martínez-Romero (pp. 337-344).
Rhizobium etli, which normally forms nitrogen-fixing nodules on Phaseolus vulgaris (common bean), is a natural maize endophyte. The genetic diversity of R. etli strains from bulk soil, bean nodules, the maize rhizosphere, the maize root, and inside stem tissue in traditional fields where maize is intercropped with P. vulgaris-beans was analyzed. Based on plasmid profiles and alloenzymes, it was determined that several R. etli types were preferentially encountered as putative maize endophytes. Some of these strains from maize were more competitive maize-root colonizers than other R. etli strains from the rhizosphere or from bean nodules. The dominant and highly competitive strain Ch24-10 was the most tolerant to 6-methoxy-2-benzoxazolinone (MBOA), a maize antimicrobial compound that is inhibitory to some bacteria and fungi. The R. tropici strain CIAT899, successfully used as inoculant of P. vulgaris, was also found to be a competitive maize endophyte in inoculation experiments.
Temperature and nutrient availability control growth rate and fatty acid composition of facultatively psychrophilic Cobetia marina strain L-2 by Isao Yumoto; Kikue Hirota; Hideaki Iwata; Masatoshi Akutsu; Keita Kusumoto; Naoki Morita; Yoshio Ezura; Hidetoshi Okuyama; Hidetoshi Matsuyama (pp. 345-351).
A facultative psychrophilic bacterium, strain L-2, that grows at 0 and 5°C as minimum growth temperatures in complex and defined media, respectively, was isolated. On the basis of taxonomic studies, strain L-2 was identified as Cobetia marina. The adaptability of strain L-2 to cold temperature was higher than that of the type strain and of other reported strains of the same species. When the bacterium was grown at 5–15°C in a defined medium, it produced a high amount of trans-unsaturated fatty acids. By contrast, in a complex medium in the same temperature range it produced a low amount of trans-unsaturated fatty acids. In the complex medium at 5°C, the bacterium exhibited a three-fold higher growth rate than that obtained in the defined medium. Following a temperature shift from 11 to 5°C, strain L-2 grew better in complex than in defined medium. Furthermore, when the growth temperature was shifted from 0 to 5°C both the growth rate and the yield of strain L-2 growing in complex medium was markedly enhanced. These phenomena suggest that an upshift of the growth temperature had a positive effect on metabolism. The effects of adding complex medium components to the defined medium on bacterial growth rate and fatty acid composition at 5°C were also studied. The addition of yeast extract followed by peptone was effective in promoting rapid growth, while glutamate addition was less effective, resulting in a cis-unsaturated fatty acid ratio similar to that of cells grown in the complex medium. These results suggest that the rapid growth of strain L-2 at low temperatures requires a high content of various amino acids rather than the presence of a high ratio of cis-unsaturated fatty acids in the cell membrane.
Keywords: Facultative psychrophile; Cobetia marina ; cis-Unsaturated fatty acid; trans-Unsaturated fatty acid; Cold adaptation
Phylogenetic analysis of the lux operon distinguishes two evolutionarily distinct clades of Photobacterium leiognathi by Jennifer C. Ast; Paul V. Dunlap (pp. 352-361).
The luminous marine bacterium Photobacterium mandapamensis was synonymized several years ago with Photobacterium leiognathi based on a high degree of phenotypic and genetic similarity. To test the possibility that P. leiognathi as now formulated, however, actually contains two distinct bacterial groups reflecting the earlier identification of P. mandapamensis and P. leiognathi as separate species, we compared P. leiognathi strains isolated from light-organ symbiosis with leiognathid fishes (i.e., ATCC 25521T, ATCC 25587, lequu.1.1 and lleuc.1.1) with strains from seawater originally described as P. mandapamensis and later synonymized as P. leiognathi (i.e., ATCC 27561T and ATCC 33981) and certain strains initially identified as P. leiognathi (i.e., PL-721, PL-741, 554). Analysis of the 16S rRNA and gyrB genes did not resolve distinct clades, affirming a close relationship among these strains. However, strains ATCC 27561T, ATCC 33981, PL-721, PL-741 and 554 were found to bear a luxF gene in the lux operon (luxABFE), whereas ATCC 25521T, ATCC 25587, lequu.1.1 and lleuc.1.1 lack this gene (luxABE). Phylogenetic analysis of the luxAB(F)E region confirmed this distinction. Furthermore, ATCC 27561T, ATCC 33981, PL-721, PL-741 and 554 all produced a higher level of luminescence on high-salt medium, as previously described for PL-721, whereas ATCC 25521T, ATCC 25587, lequu.1.1 and lleuc.1.1 all produced a higher level of luminescence on low-salt medium, a characteristic of P. leiognathi from leiognathid fish light organs. These results demonstrate that P. leiognathi contains two evolutionarily and phenotypically distinct clades, P. leiognathi subsp. leiognathi (strains ATCC 25521T, ATCC 25587, lequu.1.1 and lleuc.1.1), and P. leiognathi subsp. mandapamensis (strains ATCC 27561T, ATCC 33981, PL-721, PL-741 and 554).
Keywords: Photobacterium leiognathi ; Photobacterium mandapamensis ; 16S rRNA gene; gyrB ; lux operon; luxF ; Vibrionaceae
Novel transcriptional regulators of Legionella pneumophila that affect replication in Acanthamoeba castellanii by Ilya Lebeau; Elke Lammertyn; Emmy De Buck; Liesbeth Maes; Nick Geukens; Lieve Van Mellaert; Jozef Anné (pp. 362-370).
Legionella pneumophila is commonly found in freshwater environments and is able to invade and replicate within amoebae and ciliated protozoa. Moreover, this bacterium is also able to replicate within human alveolar macrophages causing a severe form of pneumonia, designated Legionnaires’ disease. L. pneumophila pathogenesis is not yet completely understood, but the genes responsible for infection and intracellular replication are becoming known. Nonetheless, knowledge as to how these genes are controlled is still very limited. The partially sequenced genome of L. pneumophila was searched for open reading frames encoding proteins with sequence similarity to members of the LuxR family of transcriptional regulators. These were designated LpnR1, LpnR2, LpnR3, and LpnR4. Although these proteins could not be identified as true LuxR proteins, they do act as regulators, as illustrated in this report. LpnR1 negatively affected rpoS expression, whereas LpnR2 and LpnR3 positively affected flagellin expression. Furthermore, LpnR2 proved to be necessary for efficient invasion of Acanthamoeba castellanii and LpnR3 for intracellular replication in this protozoan host. LpnR4 was recently identified as LetA.
Keywords: Legionella pneumophila ; Regulation; FlaA; Acanthamoeba castellanii ; Legionnaires’ disease; Pneumonia
Identification of thermostable glyoxalase I in the fission yeast Schizosaccharomyces pombe by Yoshifumi Takatsume; Shingo Izawa; Yoshiharu Inoue (pp. 371-377).
Glyoxalase I is a ubiquitous enzyme that detoxifies methylglyoxal, which is derived from glycolysis but inhibits the growth of cells from microorganisms to mammals. Here, the structural gene for glyoxalase I (glo1 +) from the fission yeast Schizosaccharomyces pombe was identified. Disruption of glo1 + enhanced susceptibility to methylglyoxal, while expression of glo1 + in a Δglo1 mutant of Saccharomyces cerevisiae restored tolerance to this aldehyde. The glo1 + gene product was purified. The glyoxalase I of S. pombe was a monomeric enzyme with a molecular weight of 34,000 and the k cat/K m value for methylglyoxal was 4.3×107 M−1 min−1. Treatment of purified enzyme with EDTA in imidazole buffer completely abolished enzyme activity, whereas the EDTA-treated enzyme was reactivated by several divalent metal ions, such as Zn2+, Co2+, Ni2+ and Mn2+. The glyoxalase I of S. pombe exhibited fairly high thermal stability, and almost 100% activity was retained after incubating the enzyme at 60°C for 4 h.
Keywords: Glyoxalase I; Methylglyoxal; Glutathione; Metalloenzyme; Thermo tolerance
Deletion of the Aspergillus fumigatus lysine biosynthesis gene lysF encoding homoaconitase leads to attenuated virulence in a low-dose mouse infection model of invasive aspergillosis by Burghard Liebmann; Thomas W. Mühleisen; Meike Müller; Matthias Hecht; Gerhard Weidner; Armin Braun; Matthias Brock; Axel A. Brakhage (pp. 378-383).
Aspergillus fumigatus is an important pathogen of the immunocompromised host, causing pneumonia and invasive disseminated disease with high mortality. In order to determine the importance of lysine biosynthesis for growth and pathogenicity, the A. fumigatus lysF gene, encoding a homologue of the A. nidulans homoaconitase LysF, was cloned and characterized. Cosmid cosGTM encoding lysF complemented a lysF mutant of Aspergillus nidulans. A. fumigatus lysF was deleted, resulting in a lysine-auxotroph. This phenotype was complemented to the wild-type by supplementation of the medium with both L-lysine and α-aminoadipic acid, or transformation using cosmid cosGTM. To study the virulence of the lysF deletion mutant of A. fumigatus, a low-dose intranasal mouse infection model of invasive aspergillosis was optimized for immunosuppressed BALB/c mice, allowing the application of an infection dose as low as 5×103 conidia per mouse. In this murine model, the ΔlysF mutant was avirulent, suggesting that lysine biosynthesis, or at least a functional homoaconitase, is important for survival of A. fumigatus in vivo and a potential target for antifungal drugs.
Keywords: Aspergillus fumigatus ; Lysine biosynthesis; Homoaconitase; Animal model; Invasive aspergillosis; Antifungal drug target
Differential production of two antibiotics of Streptomyces coelicolor A3(2), actinorhodin and undecylprodigiosin, upon salt stress conditions by Beatrica Sevcikova; Jan Kormanec (pp. 384-389).
Production of two pigmented antibiotics, actinorhodin and undecylprodigiosin, is differentially affected in Streptomyces coelicolor A3(2) at high salt concentration, with actinorhodin being inhibited and undecylprodigiosin activated. Analysis of expression of two genes coding for pathway-specific transcriptional regulators of actinorhodin and undecylprodigiosin synthesis, actII-ORF4 and redD, revealed that their expression is similarly differentially affected. Thus, the effect of high salt concentration on actinorhodin and undecylprodigiosin production is mediated at the transcriptional level by the differential expression of genes encoding corresponding pathway-specific transcriptional regulators.
Keywords: Actinorhodin; Antibiotics; Gene expression; Promoter; Salt stress; Streptomyces coelicolor A3(2); Undecylprodigiosin
New genes involved in chromate resistance in Ralstonia metallidurans strain CH34
by Susanne Juhnke; Nicola Peitzsch; Nicole Hübener; Cornelia Große; Dietrich H. Nies (pp. 390-390).