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Archives of Microbiology (v.177, #5)
No Title by Raeid M. Abed; Ferran Garcia-Pichel; Mariona Hernández-Mariné (pp. 361-370).
A new genus of moderately halophilic, moderately halotolerant and moderately thermophilic cyanobacteria with very thin trichomes is described. The four strains included in this genus were isolated from benthic microbial mats in a man-made hypersaline pond. Trichomes were around 1 µm thick, with small constrictions at the cross-walls and diffluent colorless sheaths. Thylakoids were parallel to the cell wall, but thylakoids and nucleoid were often excentrically arranged within the cytoplasm with respect to the main trichome axis. Strains grew at between 3.2 and 12–15% (w/v) salinity with optima between 3.2 and 12%. They showed lower temperature limits around 20 °C and upper limits between 45 and 50 °C, with optima between 28 and 45–50 °C. Carotenoid and mycosporine amino-acid complements were identical among strains. Phylogenetic analyses based on 16S rRNA gene sequence showed that all strains were closely related (99% or higher similarity) and distantly related to other cyanobacteria (91% or lower similarity). We propose the new genus and species Halomicronema excentricum for these strains. The type strain is TFEP1.
Keywords: Microbial mats Hypersaline environments Phormidium, Leptolyngbya Polyphasic taxonomy Halotolerance 16S rRNA Phylogeny Halomicronema Carotenoids Thermotolerance
No Title by Martin Krehenbrink; Fred-Bernd Oppermann-Sanio; Alexander Steinbüchel (pp. 371-380).
All publicly accessible microbial genome databases were searched for the occurrence of genes encoding proteins homologous to the cyanophycin synthetase (CphA) of Synechocystis sp. strain PCC 6803 in order to reveal the capability of microorganisms not belonging to the cyanobacteria to synthesize cyanophycin. Among 65 genome sequences, genes homologous to cphA were found in Acinetobacter sp. strain ADP1 (encoding a protein homologous to CphA with 40% amino acid identity), Bordetella bronchiseptica strain RB50 (39%), Bordetella pertussis strain Tohama I (39%), Bordetella parapertussis strain 12822 (39%), Clostridium botulinum strain ATCC 3502 (39%), Desulfitobacterium hafniense strain DCB-2 (38%) and Nitrosomonas europaea strain ATCC 25978 (37%). The gene homologous to cphA from Acinetobacter sp. strain DSM 587 was amplified by PCR, ligated to the vector pBluescript SK– downstream of the lac promoter and introduced into Escherichia coli. The recombinant strain of E. coli expressed CphA activity at up to 1.2 U/mg protein and accumulated cyanophycin to up to 7.5% of the cellular dry matter, indicating that CphA of Acinetobacter sp. strain DSM 587 is functionally active. In Acinetobacter sp. strain DSM 587 itself, cyanophycin accumulated to up to 1.4% of the total protein under phosphate-limited conditions, and cyanophycin synthetase activity was detected, which indicated the function of cyanophycin as a storage compound in this strain.
Keywords: Biopolymer Cyanophycin Cyanophycin synthetase Cyanophycinase CphA CphB Acinetobacter Bordetella bronchiseptica Bordetella pertussis Bordetella parapertussis Clostridium botulinum Desulfitobacterium hafniense Nitrosomonas europaea Ralstonia metallidurans Genome sequences
No Title by Bernhard Schink; Volker Thiemann; Heike Laue; Michael W. Friedrich (pp. 381-391).
A new sulfate-reducing bacterium was isolated from marine sediment with phosphite as sole electron donor and CO2 as the only carbon source. Strain FiPS-3 grew slowly, with doubling times of 3–4 days, and oxidized phosphite, hydrogen, formate, acetate, fumarate, pyruvate, glycine, glutamate, and other substrates nearly completely, with concomitant reduction of sulfate to sulfide. Acetate was formed as a side product to a small extent. Glucose, arabinose, and proline were partly oxidized and partly fermented to acetate plus propionate. Growth with phosphite, hydrogen, or formate was autotrophic. Also, in the presence of sulfate, CO dehydrogenase was present, and added acetate did not increase growth rates or growth yields. In the absence of sulfate, phosphite oxidation was coupled to homoacetogenic acetate formation, with growth yields similar to those in the presence of sulfate. Cells were small rods, 0.6–0.8×2–4 µm in size, and gram-negative, with a G+C content of 53.9 mol%. They contained desulforubidin, but no desulfoviridin. Based on sequence analysis of the 16S rRNA gene and the sulfite reductase genes dsrAB, strain FiPS-3 was found to be closely related to Desulfotignum balticum. However, physiological properties differed in many points from those of D. balticum. These findings justify the establishment of a new species, Desulfotignum phosphitoxidans.
Keywords: Phosphite oxidation Sulfate reduction Energy metabolism Homoacetogenic fermentation Desulfotignum sp.
No Title by Scott R. Miller; Miriam Martin; Janeene Touchton; Richard W. Castenholz (pp. 392-400).
Because pigments of phototrophs can be involved either in photosynthesis or photoprotection, pigmentation changes in response to nutrient availability can affect how cells interact with their solar environment. We investigated the impact of nitrogen availability both on pigmentation of the cyanobacterium Synechococcus sp. strain SH-94–5 and on carbon assimilation by this strain in the presence or absence of UV radiation. Pigmentation changes in strain SH-94–5 due to ammonium exhaustion included phycobiliprotein degradation, an exponential decline in chlorophyll a content, and a net increase in β-carotene. Following its replenishment, ammonium stimulated non-photosynthetic carbon assimilation for several hours prior to the resumption of photosynthesis and growth. Carbon fixation during this lag phase was concurrent with the metabolism of glycogen reserves, and it is likely that inorganic carbon was incorporated into glycogen-derived carbon skeletons primarily for amino acid synthesis. In contrast, carbon fixation was almost exclusively photosynthetic during exponential growth. UV-A radiation (320–400 nm) inhibited photosynthetic but not non-photosynthetic carbon assimilation. Only growing cells were inhibited, and the disappearance of inhibition following nitrogen depletion appeared to result from the reduction of cellular photosensitizing targets below a threshold level rather than from the inactivation of photosynthesis.
Keywords: Chlorophyll Cyanobacteria Nitrogen starvation Pigmentation-photosynthesis Synechococcus UV radiation
No Title by Thomas Hansen; Meike Musfeldt; Peter Schönheit (pp. 401-409).
The ATP-dependent 6-phosphofructokinase (ATP-PFK) of the hyperthermophilic bacterium Thermotoga maritima was purified 730-fold to homogeneity. The enzyme is a 140-kDa homotetramer composed of 34 kDa subunits. Kinetic constants were determined for all substrates in both reaction directions at pH 7 and at 75 °C. Rate dependence (forward reaction) on fructose 6-phosphate (F-6-P) showed sigmoidal kinetics with a half-maximal saturation constant (S 0.5) of 0.7 mM and a Hill coefficient of 2.2. The apparent K m for ATP was 0.2 mM and the apparent V max value was about 360 U/mg. The enzyme also catalyzed in vitro the reverse reaction with an apparent K m for fructose 1,6-bisphosphate and ADP of 7.6 mM and 1.4 mM, respectively, and an apparent V max of about 13 U/mg. Divalent cations were required for maximal activity; Mg2+, which was most effective, could partially be replaced by Mn2+ and Fe2+. Enzyme activity was allosterically regulated by classical effectors of ATP-PFKs of Eukarya and Bacteria; it was activated by ADP and inhibited by PEP. The enzyme had a temperature optimum of 93 °C and showed a significant thermostability up to 100 °C. Using the N-terminal amino acid sequence of the subunit, the pfk gene coding for ATP-PFK was identified and functionally overexpressed in Escherichia coli. The purified recombinant ATP-PFK had identical kinetic and allosteric properties as the native enzyme purified from T. maritima. The deduced amino acid sequence showed high sequence similarity to members of the PFK-A family. In accordance with its allosteric properties, ATP-PFK of T. maritima contained the conserved allosteric effector-binding sites for ADP and PEP.
Keywords: Thermotoga maritma Hyperthermophilic bacteria ATP-dependent 6-phosphofructokinase PFK-A family Allosteric regulation Thermostability Embden-Meyerhof pathway Evolution
No Title by Andreas Brinkkötter; Ansiah Shakeri-Garakani; Joseph W. Lengeler (pp. 410-419).
Escherichia coli, Salmonella enterica, Klebsiella pneumoniae and Klebsiella oxytoca were found to contain two D-tagatose 1,6-bisphosphate (TagBP)-specific aldolases involved in catabolism of galactitol (genes gatY gatZ) and of N-acetyl-galactosamine and D-galactosamine (genes kbaY kbaZ, also called agaY agaZ). The two aldolases were closely related (≥53.8% identical amino acids) and could substitute for each other in vivo. The catalytic subunits GatY or KbaY alone were sufficient to show aldolase activity. Although substantially shorter than other aldolases (285 amino acids, instead of 358 and 349 amino acids), these subunits contained most or all of the residues that have been identified as essential in substrate/product recognition and catalysis for class II aldolases. In contrast to these, both aldolases required subunits GatZ or KbaZ (420 amino acids) for full activity and for good in vivo and in vitro stability. The Z subunits alone did not show any aldolase activity. Close relatives of these new TagBP aldolases were found in several gram-negative and gram-positive bacteria, e.g., Streptomyces coelicolor.
Keywords: D-Tagatose 1,6-bisphosphate aldolases Class II aldolases Enteric bacteria
No Title by Anke Neumann; Anke Siebert; Tina Trescher; Simone Reinhardt; Gert Wohlfarth; Gabriele Diekert (pp. 420-426).
The substrate specificity of the tetrachloroethene reductive dehalogenase of Dehalospirillum multivorans and its corrinoid cofactor were studied. Besides reduced methyl viologen, titanium(III) citrate could serve as electron donor for reductive dehalogenation of tetrachloroethene (PCE) and trichloroethene to cis-1,2-dichloroethene. In addition to chlorinated ethenes, chlorinated propenes were reductively dechlorinated solely by the native enzyme. trans-1,3-Dichloropropene, 1,1,3-trichloropropene and 2,3-dichloropropene were reduced to a mixture of mono-chloropropenes, 1,1-dichloropropene, and 2-chloropropene, respectively. Other halogenated compounds that were rapidly reduced by the enzyme were also dehalogenated abiotically by the heat-inactivated enzyme and by commercially available cyanocobalamin. The rate of this abiotic reaction was dependent on the number and type of halogen substituents and on the type of catalyst. The corrinoid cofactor purified from the tetrachloroethene dehalogenase of D. multivorans exhibited an activity about 50-fold higher than that of cyanocobalamin (vitamin B12) with trichloroacetate as electron acceptor, indicating that the corrinoid cofactor of the PCE dehalogenase is not cyanocobalamin. Corrinoids catalyzed the rapid dehalogenation of trichloroacetic acid. The rate was proportional to the amount of, e.g. cyanocobalamin; therefore, the reductive dehalogenation assay can be used for the sensitive and rapid quantification of this cofactor.
Keywords: Dehalospirillum multivorans Tetrachloroethene reductive dehalogenase Reductive dehalogenation Chloropropene Cyanocobalamin Vitamin B12 Corrinoid Corrinoid assay Tetrachloroethene Trichloroacetate Alkyl halide
No Title by Carolyn Cousin; Jean Grant; Freddie Dixon; Desta Beyene; Peter van Berkum (pp. 427-430).
The interaction of biosolids compost application to soil and bradyrhizobial genotypes recovered from nodules was examined. Among 170 isolates, seven genotypes were recovered from soils receiving either no biosolids application or rates of 73 or 146 Mg/ha for three successive years. With the exception of one genotype, the distribution of the bacterial genotypes recovered from nodules was interrelated with the level of biosolids. Two of the genotypes nodulated both soybean and cowpea. Because soybean-nodulating bradyrhizobia were not recovered from control plots, it is possible that they had been introduced together with the biosolids compost application.
Keywords: Biosolids compost Cowpea, Soybean Nodulation, Nitrogen fixation Bradyrhizobium Genotype Symbiosis Plant-microbe interaction