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Archives of Microbiology (v.174, #4)
No Title by Juan Carlos Argüelles (pp. 217-224).
The disaccharide trehalose is widely distributed in nature and can be found in many organisms, including bacteria, fungi, plants, invertebrates and mammals. Due to its particular physical features, trehalose is able to protect the integrity of the cell against a variety of environmental injuries and nutritional limitations. In addition, data available on several species of bacteria and yeast suggest specific functions for trehalose in these organisms. Bacteria can use exogenous trehalose as the sole source of carbon and energy as well as synthesize enormous amounts of the disaccharide as compatible solute. This ability to accumulate trehalose is the result of an elaborate genetic system, which is regulated by osmolarity. Some mycobacteria contain sterified trehalose as a structural component of the cell wall, whereas yeast cells are largely unable to grow on trehalose as carbon source. In these lower eukaryotes, trehalose appears to play a dual function: as a reserve compound, mainly stored in vegetative resting cells and reproductive structures, and as a stress metabolite. Recent findings also point to important biotechnological applications for trehalose.
Keywords: Trehalose Bacteria Yeast Carbon source Compatible solute Stress metabolite Reserve carbohydrate
No Title by Christina Afting; Elisabeth Kremmer; Claudia Brucker; Andreas Hochheimer; Rudolf K. Thauer (pp. 225-232).
Recently it was found that the specific activity of H2-forming methylenetetrahydromethanopterin dehydrogenase (Hmd) in Methanothermobacter marburgensis (formerly Methanobacterium thermoautotrophicum strain Marburg) increased six-fold when the hydrogenotrophic archaeon was grown in chemostat culture under nickel-limited conditions. We report here that the increase is due, at least in part, to increased expression of the hmd gene. This was demonstrated by Northern and Western blot analysis. These techniques were also used to show that hmd expression in growing M. marburgensis is not under the control of the H2 concentration. Studies with monoclonal antibodies on the effect of growth conditions on the expression of hmdII and hmdIII, which have been proposed to encode Hmd isoenzymes, were also carried out. The results indicate that the expression of these two genes is regulated by H2 rather than by nickel, and that HmdII and HmdIII most probably do not exhibit Hmd activity.
Keywords: Hydrogenase Methanogenic archaea Nickel Transcriptional regulation Methanobacterium thermoautotrophicum Tetrahydromethanopterin
No Title by Annemieke Ultee; Edwin P.W. Kets; Mark Alberda; Folkert A. Hoekstra; Eddy J. Smid (pp. 233-238).
Carvacrol, a natural antimicrobial compound present in the essential oil fraction of oregano and thyme, is bactericidal towards Bacillus cereus. A decrease of the sensitivity of B. cereus towards carvacrol was observed after growth in the presence of non-lethal carvacrol concentrations. A decrease of the melting temperature (T m) of membranes from 20.5 °C to 12.6 °C was the immediate effect of the addition of carvacrol. Cells adapted to 0.4 mM carvacrol showed a lower membrane fluidity than non-adapted cells. Adaptation of 0.4 mM carvacrol increased the T m from 20.5 °C to 28.3 °C. The addition of carvacrol to cell suspensions of adapted B. cereus cells decreased T m again to 19.5 °C, approximately the same value as for the non-adapted cells in the absence of carvacrol. During adaptation, changes in the fatty acid composition were observed. The relative amount of iso-C13:0, C14:0 and iso-C15:0 increased and cis-C16:1 and C18:0 decreased. The head-group composition also changed, two additional phospholipids were formed and one phospholipid was lacking in the adapted cells. It could be concluded that B. cereus adapts to carvacrol when present at non-lethal concentrations in the growth medium by lowering its membrane fluidity by changing the fatty acid and head-group composition.
Keywords: Bacillus cereus Carvacrol Adaptation Membranes Gel-to-liquid-crystalline transition temperature Fatty acid composition Head-group composition Membrane fluidity
No Title by Hanno Biebl; Hildegard Schwab-Hanisch; Cathrin Spröer; Heinrich Lünsdorf (pp. 239-247).
Anaerobic enrichment cultures, with erythritol as substrate, resulted in the isolation of a strain with properties not yet found in an existing genus in this combination. The strain, FKBS1, was strictly anaerobic, stained gram-negative and formed spores. Cells were small motile vibrios with flagella inserted at the concave side of the cell. Spores were located terminally and caused only slight swelling of the cells if compared to related spore-forming genera. FKBS1 fermented fructose, mannitol, sorbitol, xylitol and erythritol to propionic acid, acetic acid, CO2 and small amounts of H2 to balance the difference in the oxidation-reduction value between substrate and cell mass. The 16S rDNA sequence revealed relationship to the Sporomusa-Pectinatus-Selenomonas group. However, the phylogenetic distance to any of its members was too great to allow it to be placed in one of the existing genera. Morphologically the strain resembled Sporomusa, which, however, performs an acetogenic type of fermentation. The propionic-acid-forming genera of the group are either not spore-formers or, in the case of Dendrosporobacter quercicolus (syn. Clostridium quercicolum), morphologically different. It is therefore proposed to classify strain FKBS1 as a new genus and species, Propionispora vibrioides.
Keywords: Propionispora vibrioides gen. nov., sp. nov. Polyols fermentation Propionic acid fermentation Spore formation Sporomusa-Pectinatus-Selenomonas phyletic group
No Title by Tuan-Nghia Phan; Jeffrey S. Reidmiller; Robert E. Marquis (pp. 248-255).
Fluoride and other weak acids, such as benzoate, indomethacin, salicylate and sorbate, were found to be sensitizers for acid killing of cells of Actinomyces naeslundii ATCC 19246 and Streptococcus sanguis NCTC 10904 in suspensions or in mono-organism biofilms on glass slides. These bacteria are among the more acid-sensitive organisms from dental plaque and were killed when acidified to pH values between 3.5 and 4.0. Biofilm cells were more resistant than cells in suspensions, especially in terms of the fraction of the initial population surviving acidification. The mechanism for sensitization to acid killing by fluoride and the other weak acids involved enhanced transmembrane transport of protons, reflected by increases in measured proton permeabilities of the cells. Thus, the weak acids thwarted the functions of F(H+)-ATPases in extruding protons and protecting cells against acid damage. Fluoride sensitization of biofilms or cells in suspensions to acid damage occurred rapidly. There was a delay in sensitization of biofilms by indomethacin and higher molecular weight acids which was interpreted in terms of diffusion limitation of sensitizer penetration. Overall, it seemed that weak-acid sensitization to acid killing is a general phenomenon that occurs not just for oral bacteria but also for organisms in food, soil, and other acidified environments.
Keywords: Acid damage Oral bacteria Weak-acid sensitizers
No Title by Lili Rosana Mesak; Michael K. Dahl (pp. 256-264).
Phosphoglucomutases catalyze the reversible conversion of D-glucose 1-phosphate to D-glucose 6-phosphate, a key metabolic step in all cells. Two classes of phosphoglucomutases have been described so far, using either the α- or β-forms of the phosphorylated sugars. The pgcM gene of Bacillus subtilis was cloned and used to construct a plasmid-based overexpression system for PgcM in Bacillus megaterium. The obtained protein was purified and its enzymatic activities were characterized. PgcM exhibits β-phosphoglucomutase activity, transforming mainly β-glucose 1-phosphate to β-glucose 6-phosphate via the intermediate glucose 1,6-bisphosphate. Nevertheless, α-glucose 1-phosphate can also serve as a substrate, but with a seven-fold lower affinity than that observed for the β-form. Additionally, PgcM exhibits a glucose-1-phosphate phosphodismutase activity using the α- and β-forms as substrates, with affinities comparable to those observed for the phosphoglucomutase activity. Conformational changes of PgcM triggered by cofactors (MgCl2, glucose 1,6-bisphosphate) and substrate (glucose 1-phosphate) were detected by fluorescence spectra. Insertional mutagenesis of pgcM resulted in an inactivation of β-phosphoglucomutase activity in B. subtilis. These mutants showed growth deficiency on minimal medium containing starch or maltodextrins (maltose to maltoheptaose) compared either to the wild-type or to growth on minimal medium containing glucose.
Keywords: Bacillus subtilis Dextrins Disaccharides Enzymology Metabolism Protein purification Structure-function relation
No Title by Shinji Takenaka; Shuichiro Murakami; Young-Ju Kim; Kenji Aoki (pp. 265-272).
A 13.9-kb region, which contained the 2-aminophenol 1,6-dioxygenase genes (amnBA) reported before, was cloned from the 2-aminophenol-assimilating bacterium Pseudomonas sp. AP-3. The complete nucleotide sequence of this region was determined and six genes were found downstream of amnBA. The eight genes together were designated amnBACFEDHG. Each gene was similar to the corresponding gene operating in the meta-cleavage pathway, except for amnB, amnA, and amnD. The four 2-aminophenol-metabolizing enzymes, 2-aminomuconic 6-semialdehyde dehydrogenase, 2-aminomuconate deaminase, 4-oxalocrotonate decarboxylase, and 2-oxopent-4-enoate hydratase, were purified and characterized. NH2-terminal amino acid sequences of each purified enzyme agreed with those deduced from amnC, amnF, amnE, and amnD, respectively. These genes were therefore assigned as the genes encoding these respective proteins. The tight clustering of the amn genes, which were all transcribed in the same direction, raised the possibility that these genes formed a single operon. The organization of the amn genes was entirely different from that of the atd, dmp, and xyl genes reported in the meta-cleavage pathway, although these latter genes clustered similarly.
Keywords: Pseudomonas sp. AP-3 2-Aminophenol metabolism Modified meta-cleavage pathway Amn genes Single operon 2-Aminophenol 1,6-dioxygenase 2-Aminomuconic 6-semialdehyde dehydrogenase 2-Aminomuconate deaminase 4-Oxalocrotonate decarboxylase 2-Oxopent-4-enoate hydratase
No Title by Stefan Mikkat; Martin Hagemann (pp. 273-282).
Genes encoding a substrate-binding protein (ggtB) and two integral membrane proteins (ggtC and ggtD) of the binding-protein-dependent ABC transporter for glucosylglycerol were identified in the genome of Synechocystis sp. strain PCC6803. These genes are clustered on the chromosome about 220 kb away from the previously identified ggtA gene, which encodes the ATP-binding protein of this transport system. The deduced amino acid sequences show significant similarities to corresponding subunits of ABC transporters mediating uptake of maltose and other di- and oligosaccharides in bacteria and archaea. Mutants were constructed by inserting an aphII gene cassette into the coding region of the ggtB, ggtC and ggtD genes. These mutants lost the ability to take up glucosylglycerol, sucrose and trehalose, proving that these compounds are transported by the same system. A truncated ggtB gene lacking the putative signal-peptide-encoding sequence was expressed in Escherichia coli yielding a histidine-tagged soluble protein. The recombinant GgtB protein bound glucosylglycerol with a K D of 0.45 µM and exhibited a somewhat lower affinity towards sucrose and a substantially lower affinity towards trehalose. Transcript analysis by RT-PCR indicated that the genes of the ggtBCD gene cluster form an operon. The transcript level estimated by RNA slot blot analysis using a ggtC-specific probe was very low in cells grown in basal medium but increased significantly after a salt shock.
Keywords: ABC transporter Glucosylglycerol Osmoregulation Salt adaptation Synechocystis sp. strain PCC6803 Sucrose Transport Trehalose
No Title by Irina A. Bryantseva; Vladimir M. Gorlenko; Elena. I. Kompantseva; Tatyana P. Tourova; Boris B. Kuznetsov; Georgii A. Osipov (pp. 283-291).
A rod-shaped heliobacterium motile by peritrichous flagella, designated strain OS-H1, was isolated from a sample of shoreline soil of the soda lake Ostozhe (pH 9.2, total salt content 0.22%) located in the steppe of south-east Siberia. In the first few transfers, the isolate produced heat-resistant endospores. Like other heliobacteria, strain OS-H1 contained bacteriochlorophyll g and lacked intracytoplasmic membranes. The new isolate was a strict anaerobe and photoheterotroph. In the light and in the presence of organic compounds, strain OS-H1 oxidized sulfide to elemental sulfur and polysulfides, but was not capable of photoautotrophic growth. The isolate was an obligate alkaliphile able to grow at pH 8–10.2. The best growth was observed at pH 8.5–9.5, a temperature of 30 °C and at 5–10 g sodium carbonate l–1. Biotin was required as a growth factor. The G+C content of strain OS-H1 was 45.0 mol%. Comparison of the 16S rRNA gene sequence to that of phototrophic bacteria showed strain OS-H1 to group within gram-positive bacteria of the family Heliobacteriaceae with the closest relationship to Heliorestis daurensis (95.6% similarity). Based on physiological, genetic and chemotaxonomic characteristics, the new heliobacterium is described as a new species of the genus Heliorestis, Heliorestis baculata.
Keywords: Anoxygenic phototrophic bacteria Heliobacteriaceae Heliorestis baculata sp. nov. Alkaliphiles
No Title by Wolfgang R. Streit; Kai Hofmann; Wolfgang Liebl (pp. 292-295).
The Sinorhizobium meliloti nlpD gene consists of 1,539 nucleotides and codes for 512 amino acids. Expression of the nlpD gene as a histidine-tagged protein in Escherichia coli resulted in the production of a 57-kDa protein. The deduced polypeptide sequence of NlpD contains one unusual hexamer repeat (KVQRGQ), one tetramer (TVTV) and two direct and inverted trimer repeats (KAA, AAK). The N-terminal amino acid residues displayed similarity with signal peptides of secreted bacterial lipoproteins. Mutations of the S. meliloti nlpD gene caused decreased survival of cells in the stationary phase.
Keywords: Sinorhizobium meliloti Survival Stationary growth phase bioS Stress Alfalfa Root colonization nlpD