• The delta subunit of RNA polymerase, RpoE, is a global modulator of Streptococcus mutans environmental adaptation.

      Xue, Xiaoli; Tomasch, Jürgen; Sztajer, Helena; Wagner-Döbler, Irene; Research Group Microbial Communication, Division of Cell Biology, Helmholtz-Centre for Infection Research, Inhoffenstr. 7, D-38124 Braunschweig, Germany. (2010-10)
      The delta subunit of RNA polymerase, RpoE, is widespread in low-G+C Gram-positive bacteria and is thought to play a role in enhancing transcriptional specificity by blocking RNA polymerase binding at weak promoter sites and stimulating RNA synthesis by accelerating core enzyme recycling. Despite the well-studied biochemical properties of RpoE, a role for this protein in vivo has not been defined in depth. In this study, we show that inactivation of rpoE in the human dental caries pathogen Streptococcus mutans causes impaired growth and loss of important virulence traits, including biofilm formation, resistance to antibiotics, and tolerance to environmental stresses. Complementation of the mutant with rpoE expressed in trans restored its phenotype to wild type. The luciferase fusion reporter showed that rpoE was highly transcribed throughout growth and that acid and hydrogen peroxide stresses repressed rpoE expression. Transcriptome profiling of wild-type and ΔrpoE cells in the exponential and early stationary phase of growth, under acid and hydrogen peroxide stress and under both stresses combined, revealed that genes involved in histidine synthesis, malolactic fermentation, biofilm formation, and antibiotic resistance were downregulated in the ΔrpoE mutant under all conditions. Moreover, the loss of RpoE resulted in dramatic changes in transport and metabolism of carbohydrates and amino acids. Interestingly, differential expression, mostly upregulation, of 330 noncoding regions was found. In conclusion, this study demonstrates that RpoE is an important global modulator of gene expression in S. mutans which is required for optimal growth and environmental adaptation.
    • Description of Labrenzia alexandrii gen. nov., sp. nov., a novel alphaproteobacterium containing bacteriochlorophyll a, and a proposal for reclassification of Stappia aggregata as Labrenzia aggregata comb. nov., of Stappia marina as Labrenzia marina comb. nov. and of Stappia alba as Labrenzia alba comb. nov., and emended descriptions of the genera Pannonibacter, Stappia and Roseibium, and of the species Roseibium denhamense and Roseibium hamelinense.

      Biebl, Hanno; Pukall, Rüdiger; Lünsdorf, Heinrich; Schulz, Stefan; Allgaier, Martin; Tindall, Brian J; Wagner-Döbler, Irene; Helmholtz Centre for Infection Research HZI, Braunschweig, Germany. (2007-05)
      A slightly pink-coloured strain, strain DFL-11(T), was isolated from single cells of the marine dinoflagellate Alexandrium lusitanicum and was found to contain the genes encoding two proteins of the photosynthetic reaction centre, pufL and pufM. 16S rRNA gene sequence analysis revealed that the novel strain belonged to the alpha-2 subgroup of the Proteobacteria and was most closely related to Stappia aggregata (97.7 % similarity), Stappia alba (98.0 %) and Stappia marina (98.0 %). Dark-grown cells of strain DFL-11(T) contained small amounts of bacteriochlorophyll a (bchl a) and a carotenoid. Cells of strain DFL-11(T) were rods, 0.5-0.7 x 0.9-3.0 microm in size and motile by means of a single, subpolarly inserted flagellum. The novel strain was strictly aerobic and utilized a wide range of organic carbon sources, including fatty acids, tricarboxylic acid cycle intermediates and sugars. Biotin and thiamine were required as growth factors. Growth was obtained at sea salt concentrations of between 1 and 10 % (w/v), at a pH between 6 and 9.2 and at a temperature of up to 33 degrees C (optimum, 26 degrees C). Nitrate was not reduced and indole was not produced from tryptophan. Strain DFL11(T) was resistant to potassium tellurite and transformed it to elemental tellurium. The major respiratory lipoquinone was ubiquinone 10 (Q10). The polar lipids comprised phosphatidylglycerol, diphosphatidylglycerol, phosphatidylethanolamine, phosphatidylmonomethylethanolamine, phosphatidylcholine, an unidentified aminolipid and the glycolipid sulphoquinovosyldiacylglyceride. The fatty acids comprised 16 : 1 omega7c, 16 : 0, 18 : 1 omega7c, 18 : 0, 11-methyl 18 : 1 omega6t, 11-methyl 20 : 1 omega6t, 20 : 1 omega7c, 22 : 0, 22 : 1 and the hydroxy fatty acids 3-OH 14 : 0, 3-OH 16 : 0 (ester-linked), 3-OH 18 : 0, 3-OH 20 : 1 and 3-OH 20 : 0, all of which are amide-linked. The DNA G+C value was 56 mol%. Comparative analysis of alpha-2 subgroup 16S rRNA gene sequences showed that the type species of the genus Stappia, Stappia stellulata, is only distantly related to S. aggregata (95.3 % sequence similarity). Based on the combination of the 16S rRNA gene sequence data, a detailed chemotaxonomic study and the biochemical and physiological properties of members of the genera Stappia, Pannonibacter and Roseibium, it is proposed that S. aggregata, S. alba, S. marina are transferred to a new genus, Labrenzia gen. nov., as Labrenzia aggregata comb. nov., Labrenzia alba comb. nov. and Labrenzia marina comb. nov. The type species of the new genus is Labrenzia alexandrii sp. nov., with strain DFL-11(T) (=DSM 17067(T)=NCIMB 14079(T)) as the type strain. The pufLM genes of the photosynthesis reaction centre were shown to be present in some, but not all, species of the new genus Labrenzia and they were identified for the first time in S. stellulata. In accordance with the new data collected in this study, emended descriptions are provided for the genera Pannonibacter, Roseibium and Stappia.
    • Genetic variability of mutans streptococci revealed by wide whole-genome sequencing.

      Song, Lifu; Wang, Wei; Conrads, Georg; Rheinberg, Anke; Sztajer, Helena; Reck, Michael; Wagner-Döbler, Irene; Zeng, An-Ping; Institute of Bioprocess and Biosystems, Technical University Hamburg Harburg, Hamburg Harburg, Germany. (2013)
      Mutans streptococci are a group of bacteria significantly contributing to tooth decay. Their genetic variability is however still not well understood.
    • A genome-wide study of two-component signal transduction systems in eight newly sequenced mutans streptococci strains.

      Song, Lifu; Sudhakar, Padhmanand; Wang, Wei; Conrads, Georg; Brock, Anke; Sun, Jibin; Wagner-Döbler, Irene; Zeng, An-Ping; Helmholtz Centre for infection research, Inhoffenstr. 7, D-38124 Braunschweig, Germany. (2012)
      Mutans streptococci are a group of gram-positive bacteria including the primary cariogenic dental pathogen Streptococcus mutans and closely related species. Two component systems (TCSs) composed of a signal sensing histidine kinase (HK) and a response regulator (RR) play key roles in pathogenicity, but have not been comparatively studied for these oral bacterial pathogens.
    • Potential for luxS related signalling in marine bacteria and production of autoinducer-2 in the genus Shewanella.

      Bodor, Agnes; Elxnat, Bettina; Thiel, Verena; Schulz, Stefan; Wagner-Döbler, Irene; Helmholtz-Center for Infection Research, Group Microbial Communication, Division of Cell Biology, Inhoffenstr, 7, 38124 Braunschweig, Germany. agb@gbf.de (2008)
      BACKGROUND: The autoinducer-2 (AI-2) group of signalling molecules are produced by both Gram positive and Gram negative bacteria as the by-product of a metabolic transformation carried out by the LuxS enzyme. They are the only non species-specific quorum sensing compounds presently known in bacteria. The luxS gene coding for the AI-2 synthase enzyme was found in many important pathogens. Here, we surveyed its occurrence in a collection of 165 marine isolates belonging to abundant marine phyla using conserved degenerated PCR primers and sequencing of selected positive bands to determine if the presence of the luxS gene is phylogenetically conserved or dependent on the habitat. RESULTS: The luxS gene was not present in any of the Alphaproteobacteria (n = 71) and Bacteroidetes strains (n = 29) tested; by contrast, these bacteria harboured the sahH gene, coding for an alternative enzyme for the detoxification of S-adenosylhomocysteine (SAH) in the activated methyl cycle. Within the Gammaproteobacteria (n = 76), luxS was found in all Shewanella, Vibrio and Alteromonas isolates and some Pseudoalteromonas and Halomonas species, while sahH was detected in Psychrobacter strains. A number of Gammaproteobacteria (n = 27) appeared to have neither the luxS nor the sahH gene. We then studied the production of AI-2 in the genus Shewanella using the Vibrio harveyi bioassay. All ten species of Shewanella tested produced a pronounced peak of AI-2 towards the end of the exponential growth phase in several media investigated. The maximum of AI-2 activity was different in each Shewanella species, ranging from 4% to 46% of the positive control. CONCLUSION: The data are consistent with those of fully sequenced bacterial genomes and show that the potential for luxS related signalling is dependent on phylogenetic affiliation rather than ecological niche and is largest in certain groups of Gammaproteobacteria in the marine environment. This is the first report on AI-2 production in Shewanella species; its signalling role in these organisms remains to be elucidated.