The Bose–Hubbard model with squeezed dissipation

The stationary properties of the Bose–Hubbard model under squeezed dissipation are investigated. The dissipative model does not possess aU (1) symmetry but conserves parity. We find that 〈a j 〉 = 0 always holds, so no symmetry breaking occurs. Without the onsite repulsion, the linear case is known to be critical. At the critical point the system freezes to an EPR state with infinite two mode entanglement. We show here that the correlations are rapidly destroyed whenever the repulsion is switched on. As we increase the latter, the system approaches a thermal state with an effective temperature defined in terms of the squeezing parameter in the dissipators. We characterize this transition by means of a Gutzwiller ansatz and the Gaussian Hartree–Fock–Bogoliubov approximation

Ornithine Decarboxylase Levels in Patients with Normal Colonic Mucosa

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The Alkyl tert-Butyl Ether Intermediate 2-Hydroxyisobutyrate Is Degraded via a Novel Cobalamin-Dependent Mutase Pathway

Fuel oxygenates such as methyl and ethyl tert-butyl ether (MTBE and ETBE, respectively) are degraded only by a limited number of bacterial strains. The aerobic pathway is generally thought to run via tert-butyl alcohol (TBA) and 2-hydroxyisobutyrate (2-HIBA), whereas further steps are unclear. We have now demonstrated for the newly isolated β-proteobacterial strains L108 and L10, as well as for the closely related strain CIP I-2052, that 2-HIBA was degraded by a cobalamin-dependent enzymatic step. In these strains, growth on substrates containing the tert-butyl moiety, such as MTBE, TBA, and 2-HIBA, was strictly dependent on cobalt, which could be replaced by cobalamin. Tandem mass spectrometry identified a 2-HIBA-induced protein with high similarity to a peptide whose gene sequence was found in the finished genome of the MTBE-degrading strain Methylibium petroleiphilum PM1. Alignment analysis identified it as the small subunit of isobutyryl-coenzyme A (CoA) mutase (ICM; EC 5.4.99.13), which is a cobalamin-containing carbon skeleton-rearranging enzyme, originally described only in Streptomyces spp. Sequencing of the genes of both ICM subunits from strain L108 revealed nearly 100% identity with the corresponding peptide sequences from M. petroleiphilum PM1, suggesting a horizontal gene transfer event to have occurred between these strains. Enzyme activity was demonstrated in crude extracts of induced cells of strains L108 and L10, transforming 2-HIBA into 3-hydroxybutyrate in the presence of CoA and ATP. The physiological and evolutionary aspects of this novel pathway involved in MTBE and ETBE metabolism are discussed

Continuous Synthesis and Excretion of the Compatible Solute Ectoine by a Transgenic, Nonhalophilic Bacterium▿

The compatible solute 1,4,5,6-tetrahydro-2-methyl-4-pyrimidinecarboxylic acid (ectoine) acts in microorganisms as an osmotic counterweight against halostress and has attracted commercial attention as a protecting agent. Its production and application are restricted by the drawbacks of the discontinuous harvesting procedure involving salt shocks, which reduces volumetric yield, increases reactor corrosion, and complicates downstream processing. In order to synthesize ectoine continuously in less-aggressive media, we introduced the ectoine genes ectABC of the halophilic bacterium Chromohalobacter salexigens into an Escherichia coli strain using the expression vector pASK-IBA7. Under the control of a tet promoter, the transgenic E. coli synthesized 6 g liter−1 ectoine with a space-time yield of 40 mg liter−1 h−1, with the vast majority of the ectoine being excreted

Production of the Chiral Compound (R)-3-Hydroxybutyrate by a Genetically Engineered Methylotrophic Bacterium▿

In this study, a methylotrophic bacterium, Methylobacterium rhodesianum MB 126, was used for the production of the chiral compound (R)-3-hydroxybutyrate (R-3HB) from methanol. R-3HB is formed during intracellular degradation of the storage polymer (R)-3-polyhydroxybutyrate (PHB). Since the monomer R-3HB does not accumulate under natural conditions, M. rhodesianum was genetically modified. The gene (hbd) encoding the R-3HB-degrading enzyme, R-3HB dehydrogenase, was inactivated in M. rhodesianum. The resulting hbd mutant still exhibited low growth rates on R-3HB as the sole source of carbon and energy, indicating the presence of alternative pathways for R-3HB utilization. Therefore, transposon mutagenesis was carried out with the hbd mutant, and a double mutant unable to grow on R-3HB was obtained. This mutant was shown to be defective in lipoic acid synthase (LipA), resulting in an incomplete citric acid cycle. Using the hbd lipA mutant, we produced 3.2 to 3.5 mM R-3HB in batch and 27 mM (2,800 mg liter−1) in fed-batch cultures. This was achieved by sequences of cultivation conditions initially favoring growth, then PHB accumulation, and finally PHB degradation

Variations in 13C/12C and D/H enrichment factors of aerobic bacterial fuel oxygenate degradation

8 pages, 3 figures.-- PMID: 17410802 [PubMed].-- Printed version published on Mar 15, 2007.Supplementary information (Suppl. figure S1, 6 pages) available at: http://pubs.acs.org/doi/suppl/10.1021/es0616175/suppl_file/es0616175si20061213_010401.pdfReliable compound-specific isotope enrichment factors are needed for a quantitative assessment of in situ biodegradation in contaminated groundwater. To obtain information on the variability on carbon and hydrogen enrichment factors (εC, εH) the isotope fractionation of methyl tertiary (tert-) butyl ether (MTBE) and ethyl tert-butyl ether (ETBE) upon aerobic degradation was studied with different bacterial isolates. Methylibium sp. R8 showed a carbon and hydrogen isotope enrichment upon MTBE degradation of -2.4 ± 0.1 and -42 ± 4‰, respectively, which is in the range of previous studies with pure cultures (Methylibium petroleiphilum PM1) as well as mixed consortia. In contrast, εC of the β-proteobacterium L108 (-0.48 ± 0.05‰) and Rhodococcus ruber IFP 2001 (-0.28 ± 0.06‰) was much lower and hydrogen isotope fractionation was negligible (εH < -0.2‰). The varying isotope fractionation pattern indicates that MTBE is degraded by different mechanisms by the strains R8 and PM1 compared to L108 and IFP 2001. The carbon and hydrogen isotope fractionation of ETBE by L108 (εC = - 0.68 ± 0.06‰ and εH = -14 ± 2‰) and IFP 2001 εC = -0.8 ± 0.1‰ and εH = -11 ± 4‰) was very similar and seemed slightly higher than the fractionation observed upon MTBE degradation by the same strains. The low carbon and hydrogen enrichment factors observed during MTBE and ETBE degradation by L108 and IFP 2001 suggest a hydrolysis-like reaction type of the ether bond cleavage compared to oxidation of the alkyl group as suggested for the strains PM1 and R8. The variability of carbon and hydrogen enrichment factors should be taken into account when interpreting isotope pattern of fuel oxygenates with respect to biodegradation in contamination plumes.We thank Ursula Günther, Monika Neytschev, and Cornelia Schumann for technical support at the UFZ. We are also grateful to Erik Arvin (Technical University of Denmark, Lyngby, Denmark) and Françoise Fayolle-Guichard and Frédéric Monot (Institute Françoise du Petrole, Cedex, France) for providing an enrichment culture and strain IFP 2001, respectively. Part of the work was financed by the German Federal Ministry of Education and Research (02 WN 0348) within the METLEN project and by the UFZ (SAFIRA). The fellowship of Mònica Rosell was supported by AXIOM-Marie Curie Host Fellowships For Early Stage Training (EST) (contract MEST-CT-2004-8332) and Catalonian fellowship for research in an outsider country (2005 BE 00008) in the framework of AXIOM project "Assessment of in situ Transformation of Xenobiotic Organic Material". She also received a regular PhD grant from Department of Universities, Research and Information Society of Generalitat de Catalunya (expedient 2005FIR 00348).Peer reviewe

Mass Occurrence of Anatoxin-a- and Dihydroanatoxin-a-Producing Tychonema sp. in Mesotrophic Reservoir Mandichosee (River Lech, Germany) as a Cause of Neurotoxicosis in Dogs

In August 2019, three dogs died after bathing in or drinking from Mandichosee, a mesotrophic reservoir of the River Lech (Germany). The dogs showed symptoms of neurotoxic poisoning and intoxication with cyanotoxins was considered. Surface blooms were not visible at the time of the incidents. Benthic Tychonema sp., a potential anatoxin-a (ATX)-producing cyanobacterium, was detected in mats growing on the banks, as biofilm on macrophytes and later as aggregations floating on the lake surface. The dogs&rsquo; pathological examinations showed lung and liver lesions. ATX and dihydroanatoxin-a (dhATX) were detected by LC-MS/MS in the stomachs of two dogs and reached concentrations of 563 and 1207 &micro;g/L, respectively. Anatoxins (sum of ATX and dhATX, ATXs) concentrations in field samples from Mandichosee ranged from 0.1 &micro;g/L in the open water to 68,000 &micro;g/L in samples containing a large amount of mat material. Other (neuro)toxic substances were not found. A molecular approach was used to detect toxin genes by PCR and to reveal the cyanobacterial community composition by sequencing. Upstream of Mandichosee, random samples were taken from other Lech reservoirs, uncovering Tychonema and ATXs at several sampling sites. Similar recent findings emphasize the importance of focusing on the investigation of benthic toxic cyanobacteria and applying appropriate monitoring strategies in the future