Forgot your password?
New user?
New Window Opens on the Secret Life of Microbes: Scientists Develop First Microbial Profiles of Ecosystems
CAS announces the release of SciFinder Scholar for Mac OS X
Press Releases
Press Releases
| Check out our New Publishers' Select for Free Articles |
Archives of Microbiology (v.193, #6)
Characterization of root-nodulating bacteria associated to Prosopis farcta growing in the arid regions of Tunisia by A. Fterich; M. Mahdhi; M. A. Caviedes; E. Pajuelo; R. Rivas; I. D. Rodriguez-Llorente; M. Mars (pp. 385-397).
Diversity of 50 bacterial isolates recovered from root nodules of Prosopis farcta grown in different arid soils in Tunisia, was investigated. Characterization of isolates was assessed using a polyphasic approach including phenotypic characteristics, 16S rRNA gene PCR–RFLP and sequencing, nodA gene sequencing and MLSA. It was found that most of isolates are tolerant to high temperature (40°C) and salinity (3%). Genetic characterization emphasizes that isolates were assigned to the genus Ensifer (80%), Mesorhizobium (4%) and non-nodulating endophytic bacteria (16%). Forty isolates belonging to the genus Ensifer were affiliated to Ensifer meliloti, Ensifer xinjiangense/Ensifer fredii and Ensifer numidicus species. Two isolates belonged to the genus Mesorhizobium. Eight isolates failing to renodulate their host plant were endophytic bacteria and belonged to Bacillus, Paenibacillus and Acinetobacter genera. Symbiotic properties of nodulating isolates showed a diversity in their capacity to infect their host plant and fix atmospheric nitrogen. Isolate PG29 identified as Ensifer meliloti was the most effective one. Ability of Prosopis farcta to establish symbiosis with rhizobial species confers an important advantage for this species to be used in reforestation programs. This study offered the first systematic information about the diversity of microsymbionts nodulating Prosopis farcta in the arid regions of Tunisia.
Keywords: Prosopis farcta ; Arid soils; 16S rRNA gene; nodA gene; MLSA; Rhizobia
Inducible expression of choline sulfatase and its regulator BetR in Pseudomonas sp. ATCC19151 by Branko Jovcic; Vittorio Venturi; Ljubisa Topisirovic; Milan Kojic (pp. 399-405).
Pseudomonas sp. strain ATCC19151 is a natural isolate from sewage with the ability to degrade detergents. Genes encoding potential choline sulfatase (betC), substrate-binding ABC transporter protein (betD), sulfate transporter (betE), and divergent putative transcriptional regulator (betR) were cloned and characterized from strain ATCC19151. In silico analysis revealed that (1) the BetC protein belongs to alkPPc superfamily and shares CXPXR sequence with the cysteine sulfatases of group I, (2) BetR belongs to the LysR family of transcriptional regulators, (3) BetD is part of the PBPb superfamily of periplasmic and membrane-associated proteins, and (4) BetE is a permease and contains STAS domain. Insertional mutagenesis and genetic complementation show that betC gene encodes a functional choline sulfatase. Analysis of the betC (P betC ) and betR (P betR ) promoters revealed that they are inducible. BetR activates betC and betR transcription in the presence of choline sulfate, whilst in the absence of choline sulfate, BetR represses its own transcription. It was further established that BetR directly binds to betC–betR intergenic region in vitro, with higher affinity in the presence of choline sulfate as cofactor. Transcription of betC and betR was not induced in the presence of high concentration of NaCl.
Keywords: Pseudomonas ; Choline sulfatase; Transcriptional regulation of gene expression; Osmoprotection
Facultative methylotrophs from the human oral cavity and methylotrophy in strains of Gordonia, Leifsonia, and Microbacterium by Wei-Lian Hung; William G. Wade; Rich Boden; Donovan P. Kelly; Ann P. Wood (pp. 407-417).
We show that bacteria with methylotrophic potential are ubiquitous in the human mouth microbiota. Numerous strains of Actinobacteria (Brevibacterium, Gordonia, Leifsonia, Microbacterium, Micrococcus, Rhodococcus) and Proteobacteria (Achromobacter, Klebsiella, Methylobacterium, Pseudomonas, Ralstonia) were isolated, and one strain of each of the eleven genera was studied in detail. These strains expressed enzymes associated with methylotrophic metabolism (methanol, methylamine, and formate dehydrogenases), and the assimilation of one-carbon compounds by the serine pathway (hydroxypyruvate reductase). Methylotrophic growth of the strains was enhanced by the addition of glass beads to cultures, suggesting that they may naturally occur in biofilms in the mouth. This is the first report of Gordonia, Leifsonia, and Rhodococcus being present in the mouth and of the unequivocal demonstration for the first time of the methylotrophic potential of strains of Gordonia, Leifsonia, and Microbacterium.
Keywords: Gordonia ; Microbacterium ; Leifsonia ; Rhodococcus ; Serine pathway; Oral microbiota
Delineation of the translocation of colicin E7 across the inner membrane of Escherichia coli by Yuh-Ren Chen; Tsung-Yeh Yang; Guang-Sheng Lei; Lung-JR Lin; Kin-Fu Chak (pp. 419-428).
The lysis protein of the colicinogenic operon is essential for colicin release and its main function is to activate the outer membrane phospholipase A (OMPLA) for the traverse of colicin across the cell envelope. However, little is known about the involvement of the lysis protein in the translocation of colicin across the inner membrane into the periplasm. The introduction of specific point mutations into the lipobox or sorting signal sequence of the lysE7 gene resulted in the production of various forms of lysis proteins. Our experimental results indicated that cells with wild-type mature LysE7 protein exhibited higher efficiency of colicin E7 translocation across the inner membrane into the periplasm than those with premature LysE7 protein. Moreover, the degree of permeability of the inner membrane induced by the mature LysE7 protein was significantly increased as compared to the unmodified LysE7 precursor. These results suggest that the efficiency of colicin movement into the periplasm is correlated with the increase in inner membrane permeability induced by the LysE7 protein. Thus, we propose that mature LysE7 protein has two critical roles: firstly mediating the translocation of colicin E7 across the inner membrane into the periplasm, and secondly activating the OMPLA to allow colicin release.
Keywords: Colicin E7; LysE7 protein; Colicin release; OMPLA
Oxygen uptake rates in the hyperthermophilic anaerobe Thermotoga maritima grown in a bioreactor under controlled oxygen exposure: clues to its defence strategy against oxidative stress by Raja Lakhal; Richard Auria; Sylvain Davidson; Bernard Ollivier; Marie-Claire Durand; Alain Dolla; Moktar Hamdi; Yannick Combet-Blanc (pp. 429-438).
A 2.3-L bioreactor was specially adapted to grow hyperthermophilic microorganisms under controlled conditions of temperature, pH, redox potential and dissolved O2. Using this bioreactor regulated at 80°C and pH 7.0, we demonstrated that Thermotoga maritima recovered its growth despite being exposed to oxygen for a short time (30 min with a maximum concentration of 23 μM of dissolved oxygen). Under these conditions, we demonstrated that O2 uptake rate, estimated at 73.6 μmoles O2 min−1 g proteins−1 for dissolved oxygen, was optimal and constant, when dissolved oxygen was present in a range of 22–5 μM. Transcription analyses revealed that during short oxygen exposure, T. maritima expressed genes coding for enzymes to deal with O2 and reactive oxygen species (ROS) such as peroxides. Thus, genes encoding ROS-scavenging systems, alkyl hydroperoxide reductase (ahp), thioredoxin-dependent thiol peroxidase (bcp 2) and to a lesser extent neelaredoxin (nlr) and rubrerythrin (rbr), were found to be upregulated during oxygen exposure. The oxygen reductase FprA, homologous to the rubredoxin-oxygen oxidoreductase (ROO) found in Desulfovibrio species, is proposed as a primary consumer of O2 in T. maritima. Moreover, the expression of frpA was shown to depend on the redox (Eh) level of the culture medium.
Keywords: Thermotoga maritima ; Oxidative stress; Oxygen
Characteristics of a phylogenetically ambiguous, arsenic-oxidizing Thiomonas sp., Thiomonas arsenitoxydans strain 3AsT sp. nov by Djamila Slyemi; Danielle Moinier; Céline Brochier-Armanet; Violaine Bonnefoy; D. Barrie Johnson (pp. 439-449).
A moderately acidophilic, facultative chemoautotrophic, As(III)-oxidizing Thiomonas sp. (strain 3AsT) was previously shown, on the basis of comparative 16S rRNA gene sequences, to be closely related to both Tm. perometabolis DSM 18570T and Tm. intermedia DSM 18155T. While it had shared many physiological traits with Tm. intermedia T, a mean DNA–DNA hybridization value (DDHV) of 47.2% confirmed that strain 3AsT was not a strain of Tm. intermedia, though the situation with regard to Tm. perometabolis (DDHV previously determined as 72%) was more ambiguous. A comparative physiological and chemotaxonomic study of strain 3AsT and Tm. perometabolis T was therefore carried out, together with multilocus sequence analysis (MLSA) of all three bacteria. Differences in fatty acid profiles and utilization of organic substrates supported the view that strain 3AsT and Tm. perometabolis are distinct species, while MLSA showed a closer relationship between strain 3AsT and Tm. intermedia T than between strain 3AsT and Tm. perometabolis T. These apparent contradictory conclusions were explained by differences in genome of these three bacteria, which are known to be highly flexible in Thiomonas spp. A novel species designation Thiomonas arsenitoxydans is proposed for strain 3AsT (DSM 22701T, CIP 110005T), which is nominated as the type strain of this species.
Keywords: Thiomonas ; Thiomonas arsenitoxydans ; Arsenic; DNA–DNA hybridization; Multilocus sequence analysis
A CtrA homolog affects swarming motility and encystment in Rhodospirillum centenum by Terry H. Bird; Allison MacKrell (pp. 451-459).
The α-proteobacterium, Rhodospirillum centenum, has a complex life cycle that allows adaptation to different environments. Transitions between vegetative swim cell and swarmer cell types depend on whether the organism is growing in liquid surroundings or on a solid substrate. Moreover, starvation can induce vegetative cells to differentiate into quiescent cysts. This paper describes the results of our investigation into the role of a putative DNA-binding response regulator that is homologous to CtrA, the cell cycle regulator from Caulobacter crescentus. Deletion of ctrA from the R. centenum genome resulted in a viable strain with impaired swarming motility coupled with an increased tendency to form cysts. Conversely, overexpression of wild type CtrA or a phosphomimetic allele, CtrAD51E, suppressed cyst cell formation, whereas overexpression of a CtrAD51A allele failed to suppress encystment but did prevent swarming motility. Thus, we propose that CtrA participates within a two-component signal transduction pathway that promotes swarming motility while contributing to the suppression of cyst cell formation.
Keywords: Signal transduction; Prokaryotic development; Encystment
Erratum to: Extracellular monoenzyme deglycosylation system of 7-O-linked flavonoid β-rutinosides and its disaccharide transglycosylation activity from Stilbella fimetaria
by Laura Mazzaferro; Lucrecia Piñuel; Marisol Minig; Javier D. Breccia (pp. 461-461).