<i>Alteromonas stellipolaris</i> sp. nov., a novel, budding, prosthecate bacterium from Antarctic seas, and emended description of the genus <i>Alteromonas</i>

Seven novel, cold-adapted, strictly aerobic, facultatively oligotrophic strains, isolated from Antarctic sea water, were investigated by using a polyphasic taxonomic approach. The isolates were Gram-negative, chemoheterotrophic, motile, rod-shaped cells that were psychrotolerant and moderately halophilic. Buds were produced on mother and daughter cells and on prosthecae. Prostheca formation was peritrichous and prosthecae could be branched. Phylogenetic analysis based on 16S rRNA gene sequences indicated that these strains belong to the γ-Proteobacteria and are related to the genus Alteromonas, with 98·3 % sequence similarity to Alteromonas macleodii and 98·0 % to Alteromonas marina, their nearest phylogenetic neighbours. Whole-cell fatty acid profiles of the isolates were very similar and included C16 : 0, C16 : 1 ω7c, C17 : 1 ω8c and C18 : 1 ω8c as the major fatty acid components. These results support the affiliation of these isolates to the genus Alteromonas. DNA–DNA hybridization results and differences in phenotypic characteristics show that the strains represent a novel species with a DNA G+C content of 43–45 mol%. The name Alteromonas stellipolaris sp. nov. is proposed for this novel species; the type strain is ANT 69aT (=LMG 21861T=DSM 15691T). An emended description of the genus Alteromonas is given

Protection of Sinorhizobium against Host Cysteine-Rich Antimicrobial Peptides Is Critical for Symbiosis

A bacterial membrane protein, BacA, protects Sinorhizobium meliloti against the antimicrobial activity of host peptides, enabling the peptides to induce bacterial persistence rather than bacterial death

Partial complementation of Sinorhizobium meliloti bacA mutant phenotypes by the Mycobacterium tuberculosis BacA protein

The Sinorhizobium meliloti BacA ABC transporter protein plays an important role in its nodulating symbiosis with the legume alfalfa (Medicago sativa). The Mycobacterium tuberculosis BacA homolog was found to be important for the maintenance of chronic murine infections, yet its in vivo function is unknown. In the legume plant as well as in the mammalian host, bacteria encounter host antimicrobial peptides (AMPs). We found that the M. tuberculosis BacA protein was able to partially complement the symbiotic defect of an S. meliloti BacA-deficient mutant on alfalfa plants and to protect this mutant in vitro from the antimicrobial activity of a synthetic legume peptide, NCR247, and a recombinant human \u3b2-defensin 2 (HBD2). This finding was also confirmed using an M. tuberculosis insertion mutant. Furthermore, M. tuberculosis BacA-mediated protection of the legume symbiont S. meliloti against legume defensins as well as HBD2 is dependent on its attached ATPase domain. In addition, we show that M. tuberculosis BacA mediates peptide uptake of the truncated bovine AMP, Bac71-16. This process required a functional ATPase domain. We therefore suggest that M. tuberculosis BacA is important for the transport of peptides across the cytoplasmic membrane and is part of a complete ABC transporter. Hence, BacA-mediated protection against host AMPs might be important for the maintenance of latent infections

In Situ Identification of Plant-Invasive Bacteria with MALDI-TOF Mass Spectrometry

Rhizobia form a disparate collection of soil bacteria capable of reducing atmospheric nitrogen in symbiosis with legumes. The study of rhizobial populations in nature involves the collection of large numbers of nodules found on roots or stems of legumes, and the subsequent typing of nodule bacteria. To avoid the time-consuming steps of isolating and cultivating nodule bacteria prior to genotyping, a protocol of strain identification based on the comparison of MALDI-TOF MS spectra was established. In this procedure, plant nodules were considered as natural bioreactors that amplify clonal populations of nitrogen-fixing bacteroids. Following a simple isolation procedure, bacteroids were fingerprinted by analysing biomarker cellular proteins of 3 to 13 kDa using Matrix Assisted Laser Desorption/Ionization Time of Flight (MALDI-TOF) mass spectrometry. In total, bacteroids of more than 1,200 nodules collected from roots of three legumes of the Phaseoleae tribe (cowpea, soybean or siratro) were examined. Plants were inoculated with pure cultures of a slow-growing Bradyrhizobium japonicum strain G49, or either of two closely related and fast-growing Sinorhizobium fredii strains NGR234 and USDA257, or with mixed inoculants. In the fully automatic mode, correct identification of bacteroids was obtained for >97% of the nodules, and reached 100% with a minimal manual input in processing of spectra. These results showed that MALDI-TOF MS is a powerful tool for the identification of intracellular bacteria taken directly from plant tissues

We're in this Together: Sensation of the Host Cell Environment by Endosymbiotic Bacteria

Bacteria inhabit diverse environments, including the inside of eukaryotic cells. While a bacterial invader may initially act as a parasite or pathogen, a subsequent mutualistic relationship can emerge in which the endosymbiotic bacteria and their host share metabolites. While the environment of the host cell provides improved stability when compared to an extracellular environment, the endosymbiont population must still cope with changing conditions, including variable nutrient concentrations, the host cell cycle, host developmental programs, and host genetic variation. Furthermore, the eukaryotic host can deploy mechanisms actively preventing a bacterial return to a pathogenic state. Many endosymbionts are likely to use two-component systems (TCSs) to sense their surroundings, and expanded genomic studies of endosymbionts should reveal how TCSs may promote bacterial integration with a host cell. We suggest that studying TCS maintenance or loss may be informative about the evolutionary pathway taken toward endosymbiosis, or even toward endosymbiont-to-organelle conversion.Peer reviewe

The nodulation gene nolK of Azorhizobium caulinodans is involved in the formation of GDP-fucose from GDP-mannose

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