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Archives of Microbiology (v.192, #10)
Unicellular cyanobacteria with a new mode of life: the lack of photosynthetic oxygen evolution allows nitrogen fixation to proceed by Hermann Bothe; H. James Tripp; Jonathan P. Zehr (pp. 783-790).
Some unicellular N2-fixing cyanobacteria have recently been found to lack a functional photosystem II of photosynthesis. Such organisms, provisionally termed UCYN-A, of the oceanic picoplanktion are major contributors to the global marine N-input by N2-fixation. Since their photosystem II is inactive, they can perform N2-fixation during the day. UCYN-A organisms cannot be cultivated as yet. Their genomic analysis indicates that they lack genes coding for enzymes of the Calvin cycle, the tricarboxylic acid cycle and for the biosynthesis of several amino acids. The carbon source in the ocean that allows them to thrive in such high abundance has not been identified. Their genomic analysis implies that they metabolize organic carbon by a new mode of life. These unicellular N2-fixing cyanobacteria of the oceanic picoplankton are evolutionarily related to spheroid bodies present in diatoms of the family Epithemiaceae, such as Rhopalodia gibba. More recently, spheroid bodies were ultimately proven to be related to cyanobacteria and to express nitrogenase. They have been reported to be completely inactive in all photosynthetic reactions despite the presence of thylakoids. Sequence data show that R. gibba and its spheroid bodies are an evolutionarily young symbiosis that might serve as a model system to unravel early events in the evolution of chloroplasts. The cell metabolism of UCYN-A and the spheroid bodies may be related to that of the acetate photoassimilating green alga Chlamydobotrys.
Keywords: Unicellular cyanobacteria without photosystem II; Spheroid bodies of diatoms; Symbiotic nitrogen fixation; Marine nitrogen-fixing cyanobacteria; Rhopalodia gibba ; Chlamydobotrys ; UCYN-A cyanobacteria
Characterization of the substrate-binding PotD subunit in Synechocystis sp. strain PCC 6803 by Anna-Maria Brandt; Wuttinun Raksajit; Panutda Yodsang; Paula Mulo; Aran Incharoensakdi; Tiina A. Salminen; Pirkko Mäenpää (pp. 791-801).
The potD gene encodes the bacterial substrate-binding subunit of the polyamine transport system. The uptake system, which belongs to the ABC transporters, has been characterized in Escherichia coli, but it has not been previously studied in cyanobacteria. Although the overall sequence identity between Synechocystis sp. strain PCC 6803 (hereafter Synechocystis) PotD and Escherichia coli PotD is 24%, the ligand-binding site in the constructed homology model of Synechocystis PotD is well conserved. The conservation of the five polyamine-binding residues (Asp206, Glu209, Trp267, Trp293, and Asp295 in Synechocystis PotD) between these two species indicated polyamine-binding capacity for Synechocystis PotD. The Synechocystis potD gene is functional and its expression is under environmental regulation at transcriptional as well as post-transcriptional levels. Furthermore, an in vitro binding assay with the purified recombinant PotD protein demonstrated that the Synechocystis PotD protein is able to bind polyamines and favors spermidine over putrescine. Finally, we confirmed that Synechocystis PotD plays a physiological role in the uptake of polyamines in vivo using a constructed Synechocystis potD-disruption mutant.
Keywords: Polyamine transport; PotD; ABC transporter; Homology modeling; Regulation of expression
Phenotypic and genotypic characterization of tetracycline and minocycline resistance in Clostridium perfringens by Miseon Park; Alejandro P. Rooney; David W. Hecht; Jihong Li; Bruce A. McClane; Rajesh Nayak; Donald D. Paine; Fatemeh Rafii (pp. 803-810).
The aim of this study was to determine the incidence of tetracycline resistance and the prevalence of tetracycline-resistance genes in strains of Clostridium perfringens isolated from different sources between 1994 and 2005. Susceptibility to tetracycline and minocycline in strains from humans (35 isolates), chickens (15 isolates), food (21 isolates), soil (16 isolates) and veterinary sources (6 isolates) was determined, and tetracycline-resistance genes were detected. Resistance was most common in strains isolated from chickens, followed by those from soils, clinical samples and foods. The most highly resistant strains were found among clinical and food isolates. tetA(P) was the most common resistance gene, and along with tetB(P) was found in all resistant strains and some sensitive strains. One tetracycline-resistant food isolate had an intact tet(M) gene. However, PCR fragments of 0.4 or 0.8 kb with high degrees of identity to parts of the tet(M) sequences of other bacteria were found, mainly in clinical isolates, and often in isolates with tetB(P). No correlation between level of sensitivity to tetracycline or minocycline and the presence of tetA(P), tetB(P) or part of tet(M) was found. The presence of part of tet(M) in some strains of C. perfringens containing tetB(P) may have occurred by recent gene transfer.
Keywords: Clostridium perfringens ; Tetracycline; Resistance
Kosmotoga arenicorallina sp. nov. a thermophilic and obligately anaerobic heterotroph isolated from a shallow hydrothermal system occurring within a coral reef, southern part of the Yaeyama Archipelago, Japan, reclassification of Thermococcoides shengliensis as Kosmotoga shengliensis comb. nov., and emended description of the genus Kosmotoga by Takuro Nunoura; Miho Hirai; Hiroyuki Imachi; Masayuki Miyazaki; Hiroko Makita; Hisako Hirayama; Yasuo Furushima; Hiroyuki Yamamoto; Ken Takai (pp. 811-819).
A novel thermophilic and sulfur-reducing bacterium, strain S304T, was isolated from the Taketomi submarine hot spring shallow hydrothermal field located at southern part of the Yaeyama Archipelago, Japan. The cells were non-motile short thick rods or oval cocci 1.1–2.7 μm in length and 1.1–1.9 μm in width. Strain S304T was an obligately anaerobic heterotroph and sulfur reduction stimulates growth. Growth was observed between 50–65°C (optimum 60°C), pH 6.2–8.0 (optimum pH 7.1), 1.0–6.0% NaCl concentration (optimum 3.0%). The fatty acid composition was C16:0 (71.4%), C18:0 (20.9%) and C18:1 (7.7%). The G + C content of genomic DNA was 40.8 mol%. The 16S rRNA gene sequence analysis indicated that strain S304T belonged to the genus Kosmotoga. Based on physiological and phylogenetic features of a new isolate, we propose new species in the genus Kosmotoga: the type strain of Kosmotoga arenicorallina sp. nov is S304T (=JCM 15790T = DSM22549T). Thermococcoides shengliensis 2SM-2T is phylogenetically associated with Kosmotoga olearia 14.5.1T. Based on the phylogenetic relationship between Thermococcoides shengliensis 2SM-2T and Kosmotoga olearia 14.5.1T, we propose the reclassification of Thermococcoides shengliensis as Kosmotoga shengliensis comb. nov. (type strain 2SM-2T). In addition, an emended description of the genus Kosmotoga is proposed.
Keywords: Kosmotoga ; Thermococcoides ; Thermotogales ; Hydrothermal; Thermophile; Anaerobe
Diverse pathways for salicin utilization in Shigella sonnei and Escherichia coli carrying an impaired bgl operon by Stuti K. Desai; Krithi Nandimath; S. Mahadevan (pp. 821-833).
Utilization of the aryl-β-glucosides salicin or arbutin in most wild-type strains of E. coli is achieved by a single-step mutational activation of the bgl operon. Shigella sonnei, a branch of the diverse E. coli strain tree, requires two sequential mutational steps for achieving salicin utilization as the bglB gene, encoding the phospho-β-glucosidase B, harbors an inactivating insertion. We show that in a natural isolate of S. sonnei, transcriptional activation of the gene SSO1595, encoding a phospho-β-glucosidase, enables salicin utilization with the permease function being provided by the activated bgl operon. SSO1595 is absent in most commensal strains of E. coli, but is present in extra-intestinal pathogens as bgcA, a component of the bgc operon that enables β-glucoside utilization at low temperature. Salicin utilization in an E. coli bglB laboratory strain also requires a two-step activation process leading to expression of BglF, the PTS-associated permease encoded by the bgl operon and AscB, the phospho-β-glucosidase B encoded by the silent asc operon. BglF function is needed since AscF is unable to transport β-glucosides as it lacks the IIA domain involved in phopho-relay. Activation of the asc operon in the Sal+ mutant is by a promoter-up mutation and the activated operon is subject to induction. The pathway to achieve salicin utilization is therefore diverse in these two evolutionarily related organisms; however, both show cooperation between two silent genetic systems to achieve a new metabolic capability under selection.
Keywords: Silent genes; Beta-glucosides; Transcriptional activation
Antioxidant pathways are up-regulated during biological nitrogen fixation to prevent ROS-induced nitrogenase inhibition in Gluconacetobacter diazotrophicus by Sylvia M. C. Alquéres; Jose Henrique M. Oliveira; Eduardo M. Nogueira; Helma V. Guedes; Pedro L. Oliveira; Fernando Câmara; Jose I. Baldani; Orlando B. Martins (pp. 835-841).
Gluconacetobacter diazotrophicus, an endophyte isolated from sugarcane, is a strict aerobe that fixates N2. This process is catalyzed by nitrogenase and requires copious amounts of ATP. Nitrogenase activity is extremely sensitive to inhibition by oxygen and reactive oxygen species (ROS). However, the elevated oxidative metabolic rates required to sustain biological nitrogen fixation (BNF) may favor an increased production of ROS. Here, we explored this paradox and observed that ROS levels are, in fact, decreased in nitrogen-fixing cells due to the up-regulation of transcript levels of six ROS-detoxifying genes. A cluster analyses based on common expression patterns revealed the existence of a stable cluster with 99.8% similarity made up of the genes encoding the α-subunit of nitrogenase Mo–Fe protein (nifD), superoxide dismutase (sodA) and catalase type E (katE). Finally, nitrogenase activity was inhibited in a dose-dependent manner by paraquat, a redox cycler that increases cellular ROS levels. Our data revealed that ROS can strongly inhibit nitrogenase activity, and G. diazotrophicus alters its redox metabolism during BNF by increasing antioxidant transcript levels resulting in a lower ROS generation. We suggest that careful controlled ROS production during this critical phase is an adaptive mechanism to allow nitrogen fixation.
Keywords: Gluconacetobacter diazotrophicus ; Biological nitrogen fixation; Reactive oxygen species; Nitrogenase
The in vitro antibiofilm activity of selected marine bacterial culture supernatants against Vibrio spp. by Chari Nithya; Shunmugiah Karutha Pandian (pp. 843-854).
The aim of the work is to investigate the effect of marine bacterial culture supernatants on biofilm formation of Vibrio spp., a major menace in aquaculture industries. Vibrio spp. biofilm cause life-threatening infections in humans and animals. Forty-three marine bacterial culture supernatants were screened against the hydrophobicity index, initial attachment and biofilm formation in Vibrio spp. Twelve culture supernatants showed antibiofilm activity. The bacterial culture supernatants S8-07 (Bacillus pumilus) and S6-01 (B. indicus) inhibited the initial attachment, biofilm formation and dispersed the mature biofilm at 5% v/v concentration without inhibiting the growth. Analysis by light microscopy and confocal laser scanning microscopy showed that the architecture of the biofilm was destroyed by bacterial supernatants when compared to the control. The bacterial supernatants also reduce the surface hydrophobicity of Vibrio spp. which is one of the important requirements for biofilm formation. Further characterization of antibiofilm activity in S8-07 culture supernatant confirmed that it is an enzymatic activity and the size is more than 10 kDa and in S6-01, it is a heat-stable, non-protein compound. Furthermore, both the supernatants failed to show any biosurfactant activity. The culture supernatants of S8-07 and S6-01 with promising antibiofilm property have potential for application in medicine and marine aquaculture.
Keywords: Biofilm disruptors; Vibrio biofilm; Bacillus pumilus ; Bacillus indicus ; Biocontrol
Evidence from the structure and function of cytochromes c2 that nonsulfur purple bacterial photosynthesis followed the evolution of oxygen respiration by Terry Meyer; Gonzalez Van Driessche; Richard Ambler; John Kyndt; Bart Devreese; Jozef Van Beeumen; Michael Cusanovich (pp. 855-865).
Cytochromes c2 are the nearest bacterial homologs of mitochondrial cytochrome c. The sequences of the known cytochromes c2 can be placed in two subfamilies based upon insertions and deletions, one subfamily is most like mitochondrial cytochrome c (the small C2s, without significant insertions and deletions), and the other, designated large C2, shares 3- and 8-residue insertions as well as a single-residue deletion. C2s generally function between cytochrome bc1 and cytochrome oxidase in respiration (ca 80 examples known to date) and between cytochrome bc1 and the reaction center in nonsulfur purple bacterial photosynthesis (ca 21 examples). However, members of the large C2 subfamily are almost always involved in photosynthesis (12 of 14 examples). In addition, the gene for the large C2 (cycA) is associated with those for the photosynthetic reaction center (pufBALM). We hypothesize that the insertions in the large C2s, which were already functioning in photosynthesis, allowed them to replace the membrane-bound tetraheme cytochrome, PufC, that otherwise mediates between the small C2 or other redox proteins and photosynthetic reaction centers. Based upon our analysis, we propose that the involvement of C2 in nonsulfur purple bacterial photosynthesis was a metabolic feature subsequent to the evolution of oxygen respiration.
Keywords: Nonsulfur purple Bacteria; Photosynthesis; Evolution; Cytochrome c2
Effect of osmotic stress on plant growth promoting Pseudomonas spp. by V. Sandhya; Sk. Z. Ali; B. Venkateswarlu; Gopal Reddy; Minakshi Grover (pp. 867-876).
In this study we isolated and screened drought tolerant Pseudomonas isolates from arid and semi arid crop production systems of India. Five isolates could tolerate osmotic stress up to −0.73 MPa and possessed multiple PGP properties such as P-solubilization, production of phytohormones (IAA, GA and cytokinin), siderophores, ammonia and HCN however under osmotic stress expression of PGP traits was low compared to non-stressed conditions. The strains were identified as Pseudomonas entomophila, Pseudomonas stutzeri, Pseudomonas putida, Pseudomonas syringae and Pseudomonas monteilli respectively on the basis of 16S rRNA gene sequence analysis. Osmotic stress affected growth pattern of all the isolates as indicated by increased mean generation time. An increase level of intracellular free amino acids, proline, total soluble sugars and exopolysaccharides was observed under osmotic stress suggesting bacterial response to applied stress. Further, strains GAP-P45 and GRFHYTP52 showing higher levels of EPS and osmolytes (amino acids and proline) accumulation under stress as compared to non-stress conditions, also exhibited higher expression of PGP traits under stress indicating a relationship between stress response and expression of PGP traits. We conclude that isolation and screening of indigenous, stress adaptable strains possessing PGP traits can be a method for selection of efficient stress tolerant PGPR strains.
Keywords: Pseudomonas spp.; Drought stress; Osmolytes; PGP traits; 16S rDNA
Influence of Legionella pneumophila and other water bacteria on the survival and growth of Acanthamoeba polyphaga by I. Anacarso; E. Guerrieri; M. Bondi; S. de Niederhäusern; R. Iseppi; C. Sabia; M. Contri; P. Borella; P. Messi (pp. 877-882).
We investigated in solid medium, in water microcosm co-cultures and by light and transmission electron microscopy the influence of Legionella pneumophila Lp-1, Pseudomonas aeruginosa ATCC 27853, Burkholderia cepacia ATCC 25416 and Pseudomonas fluorescens SSD35 on the growth and survival of Acanthamoeba polyphaga. The infection with L. pneumophila was microscopically characterized by the presence of few bacteria inside protozoa at 4th h, and by the beginning of disruptive effects in late phase of trial. In water microcosm studies, performed at different temperature, the more significant interactions were observed at 30°C. In these conditions, L. pneumophila caused a marked reduction in trophozoite and cyst counts from the 4th day until the end of incubation (11 days). B. cepacia showed, by microscopic observation, few and generally single rods within protozoan phagosomes and caused a light reduction of trophozoite viability and cyst formation in co-cultures. A more invasive type of endocytosis, characterized by an early invasion with the presence of a high bacteria number inside amoebae, was observed for Pseudomonas strains. P. fluorescens produced a violent lysis of the host, whereas P. aeruginosa did not cause lysis or suffering. These results underline that water bacteria other than legionella are capable of intracellular survival in Acanthamoeba, influencing the protozoa viable cycle.
Keywords: Acanthamoeba polyphaga ; Legionella pneumophila ; Pseudomonas ; Water bacteria