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Archives of Microbiology (v.177, #6)
No Title by Jörg Stülke (pp. 433-440).
During the past few years, our knowledge of gene regulation by RNA-binding proteins has greatly increased. RNA-binding proteins are involved in processes such as protection of RNAs from RNase degradation, prevention of ribosome binding to mRNA, control of formation of secondary structures of the mRNA that permit or prevent translation initiation, and termination/antitermination of transcription in response to external signals. Modulation of transcription termination by RNA-binding proteins involves the formation of alternative structures. One of the structures can act as a transcriptional terminator, while adoption of the alternative structure prevents formation of the terminator and does thus result in transcript elongation. Which of the two structures prevails under a given condition depends on two factors: the intrinsic stability of the alternative structures and the stabilization of one of both by an RNA-binding regulatory protein. Binding of a protein to the nascent mRNA may result in transcript elongation, as is the case for cold-shock proteins or in several catabolic operons. The RNA-binding ability of the RNA-binding proteins is modulated by direct interaction with the inducer, by protein-protein interactions with sensor proteins or by protein phosphorylation. In contrast, in the pyrimidine or tryptophan biosynthetic operons of Bacillus subtilis, the transcriptional terminators are stabilized by RNA-binding proteins resulting in the absence of expression of these operons.
No Title by Ming-Ren Yen; Yi-Hsiung Tseng; Erin H. Nguyen; Long-Fe Wu; Milton H. Saier (pp. 441-450).
Twin-arginine targeting (Tat) protein secretion systems consist of two protein types, members of the TatA and TatC families. Homologues of these proteins are found in many archaea, bacteria, chloroplasts and mitochondria. Every prokaryotic organism with a fully sequenced genome exhibits either neither family member, or between one and three paralogues of these two family members. The Arabidopsis thaliana genome encodes three of each. Although many mitochondrially encoded TatC homologues have been identified, corresponding TatA homologues have not been found in this organelle. Phylogenetic analyses reveal that most prokaryotic Tat systems consist of one TatC homologue and two sequence-divergent TatA homologues (TatA and TatB). When only one TatA homologue is present, TatB is missing, and when three TatA homologues are present, the third one arose by duplication of TatA, not TatB. Further, homologues most resembling TatB are more sequence-divergent than those more closely resembling TatA. In contrast to the TatA family, the TatC family shows phylogenetic clustering in strict accordance with organismal type. These results are discussed in terms of their probable structural, functional and evolutionary significance.
Keywords: Twin-arginine targeting Protein secretion Evolution Phylogeny
No Title by Tadao Hasegawa; Keizo Torii; Shinnosuke Hashikawa; Yoshitsugu Iinuma; Michio Ohta (pp. 451-456).
The proteins in the culture supernatant (exoproteins) from Streptococcus pyogenes serotype M1 were separated by two-dimensional gel electrophoresis, and their N-terminal amino acid sequences were determined. The amino acid sequences were compared to sequences in the S. pyogenes genome database. The coding sequence showed similarity to sequences of two genes, mf2-v (mf2 variant) and mf3, which had sequence similarity to genes encoding mitogenic factor (MF); MF has DNase activity. The recombinant genes were expressed in Escherichia coli and the proteins were synthesized. Mf2-v and Mf3 had DNase activity. The activity of Mf2-v was localized to the C-terminal half of the protein. The mf3 gene was shown to be present in most clinically isolated strains of S. pyogenes tested, and the mf2 gene was detected in 20% of the isolates. The products of the mf2 and mf3 genes in clinically isolated S. pyogenes strains were thus shown to be DNases.
Keywords: Streptococcus pyogenes Exoprotein DNase Two-dimensional gel electrophoresis Recombinant protein Mitogenic factor
No Title by Kirsi Peltoniemi; Erkki Vesanto; Airi Palva (pp. 457-467).
The operon of the putative lactobacillar oligopeptide transport system (Opp) from Lactobacillus delbrueckii subsp. bulgaricus B14 was cloned and characterized. The opp operon was found to consist of five genes, oppD, oppF, oppB, oppC and oppA 1 . In addition, an oppA 1 homolog, oppA 2 , was found downstream of the operon. Sequence comparisons of the L. delbrueckii subsp. bulgaricus Opp system with other bacterial transport systems revealed the highest similarity to the oligopeptide transport system of Lactococcus lactis. Northern analyses of opp mRNAs revealed 6.1-kb and 2.1-kb transcripts, confirming that, in addition to the operon structure oppDFBCA 1 , the oppA 1 gene was also expressed as a monocistronic transcript. The oppA 2 gene was expressed as a separate 2.1-kb monocistronic transcript with a low expression level. Primer-extension mapping of the 5′end of oppDFBCA 1 mRNA revealed two adjacent transcriptional start sites, and primer extension analyses of oppA 1 and oppA 2 mRNAs confirmed the location of the predicted promoters of these genes. For complementation analysis, oppA 1 alone and the operon constructs oppDFBCA 1 and oppDFBCA 2 were fused with the nisA promoter and expressed in Lactococcus lactis NZ9000ΔoppA strain. Only the L. delbrueckii subsp. bulgaricus oppDFBCA 1 genes were able to complement the L. lactis oppA mutation.
Keywords: Opp Transport Bacteria Lactobacillus bulgaricus
No Title by Andrea Sass; Heike Rütters; Heribert Cypionka; Henrik Sass (pp. 468-474).
A new sulfate-reducing bacterium, strain 86FS1, was isolated from a deep-sea sediment in the western Mediterranean Sea with sodium lactate as electron and carbon source. Cells were ovoid, gram-negative and motile. Strain 86FS1 contained b- and c-type cytochromes. The organism was able to utilize propionate, pyruvate, lactate, succinate, fumarate, malate, alanine, primary alcohols (C2–C5), and mono- and disaccharides (glucose, fructose, galactose, ribose, sucrose, cellobiose, lactose) as electron donors for the reduction of sulfate, sulfite or thiosulfate. The major products of carbon metabolism were acetate and CO2, with exception of n-butanol and n-pentanol, which were oxidized only to the corresponding fatty acids. The growth yield with sulfate and glucose or lactate was 8.3 and 15 g dry mass, respectively, per mol sulfate. The temperature limits for growth were 10 °C and 30 °C with an optimum at 25 °C. Growth was observed at salinities ranging from 10 to 70 g NaCl l–1. Sulfide concentrations above 4 mmol l–1 inhibited growth. The fatty acid pattern of strain 86FS1 resembled that of Desulfobulbus propionicus with n-14:0, n-16:1ω7, n-16:1 ω5, n-17:1 ω6 and n-18:1 ω7 as dominant fatty acids. On the basis of its phylogenetic position and its phenotypic properties, strain 86FS1 affiliates with the genus Desulfobulbus and is described as a new species, Desulfobulbus mediterraneus sp. nov.
Keywords: Deep sea Carbohydrates Sulfide toxicity Oxygen sensitivity Growth yield Fatty acid pattern
No Title by Jens Glaeser; Lluis Bañeras; Heike Rütters; Jörg Overmann (pp. 475-485).
The relative composition of bacteriochlorophyll (BChl) homologs in five different strains of brown-colored green sulfur bacteria was investigated by HPLC-MS/MS and NMR analyses. In addition, the effect of incubation light intensities on homolog distribution was studied in one of the strains (strain Dagow III). A total of 23 different BChl e structures were detected and comprise four homologous porphyrin ring systems and eight different esterifying alcohols. Several BChl e structures are novel. These include a C-8 ethyl, C-12 methyl [E, M] BChl e F homolog which was identified by 1H-NMR analyses of the isolated, main farnesyl homologs (BChl e F). In addition, five previously unknown homolog series with dodecanol, pentadecenol, tetradecanol, hexadecenol and phytol as the esterifying alcohols were detected. The composition of BChl e homologs from the five strains of green sulfur bacteria differed with respect to the relative abundance of the homologs (BChl e F : 25.6–67.0% of total BChl e content in stationary cultures). In strain Dagow III, the abundance of BChl e F homologs decreased upon entry into the stationary phase. In all free-living strains, the abundance of BChl e F was increased when the relative carotenoid content was low. The present results provide a detailed picture of pigment composition in chlorosomes and thus will help to elucidate their structure and function. Furthermore, the newly discovered BChl e molecules are valuable biomarkers for the study of the occurrence and metabolism of green sulfur bacteria in past and present ecosystems.
Keywords: Green sulfur bacteria Phototrophic consortia "Pelochromatium roseum" Bacteriochlorophyll Isorenieratene Chlorosomes Low-light adaptation Lipid biomarkers
No Title by Jean J. Huang; Nancy H. Kolodny; Jennifer T. Redfearn; Mary M. Allen (pp. 486-493).
The cyanobacterium Synechocystis sp. strain PCC 6308 has been shown to exhibit predictable physiological responses to acid stress. Originally isolated from a Wisconsin lake, this cyanobacterium grows optimally under alkaline conditions in the laboratory. After acid stress at a pH of between 4.4 and 7.7, cells return to exponential growth following a lag phase. The organism's response to this tolerable acid stress involves cell concentration-dependent neutralization of the external medium to pH 6 or above within 5 min, maintenance of a transmembrane pH gradient, and maintenance of photosystem II efficiency. Lethal acid stress, at a pH below 4.4, results in the formation of aggregates of denatured proteins observed as granules near the cell periphery, the disruption of the transmembrane pH gradient, cell color change to blue, and damage to photosystem II.
Keywords: Cyanobacteria Acid stress pH effects
No Title by Yolanda Pedreño; Jose V. Gimeno-Alcañiz; Emilia Matallana; Juan-Carlos Argüelles (pp. 494-499).
The role of trehalose as cell protector against oxidative stress induced by H2O2 has been studied in Saccharomyces cerevisiae mutants in which the two trehalase genes ATH1 and NTH1 are deleted. The addition of low H2O2 concentrations to proliferating cultures of either strain did not harm cell viability and induced a marked activity to Nth1p, but with no significant level of trehalose accumulation. This pattern was reversed after a more severe H2O2 treatment that caused drastic cell killing. The most severe phenotype corresponded to the Δnth1 mutant. Under these conditions, the increase in Nth1p was abolished and a three-fold rise in trehalose content was recorded concomitant with activation of the trehalose synthase complex. The behavior of the double-disruptant Δath1Δnth1 mutant was identical to that of wild-type cells, although in exponential cultures Ath1p activity was virtually undetectable upon exposure to H2O2. Furthermore, these strains displayed an adaptive response to oxidative stress that was independent of intracellular trehalose synthesis. Our data strongly suggest that trehalose storage in budding yeasts is not an essential protectant in cell defense against oxidative challenge.
Keywords: H2O2 Oxidative stress Trehalose Trehalase Yeasts
No Title by Christopher N. Kästner; Karin Schneider; Peter Dimroth; Klaas M. Pos (pp. 500-506).
The genome of Klebsiella pneumoniae contains at least three different genes encoding citrate transporters. Recently, a third and hitherto unknown gene encoding a citrate transport system (citW) was identified. Escherichia coli transformed with a plasmid expressing citW was able to grow on citrate as sole carbon and energy source, identifying CitW as a citrate carrier. In this report, we provide evidence that further specifies CitW as a Na+-independent citrate/citrate and citrate/acetate exchanger. Kinetic analysis of citrate uptake at different pH values identified Hcitrate2– as the transported citrate species, with a K m of 25 µM. Since citW is expressed under anoxic conditions and acetate is the main end-product of citrate fermentation in K. pneumoniae, citrate/acetate exchange might be its in vivo function. Sequence similarity searches identified CitW (454 amino acids, 48.15 kDa) as a member of the 2-hydroxycarboxylate transporter family (TC 2.A.24). The substrate specificity seems to partially contradict this phylogenetic classification, but appears logical with respect to the putative functional role of CitW in the citrate fermentation pathway of K. pneumoniae.
Keywords: citW gene CitW citrate carrier Substrate/product exchange Klebsiella pneumoniae