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Archives of Microbiology (v.178, #1)
No Title by Jan Dijksterhuis; Kenneth G. van Driel; Mark G. Sanders; Douwe Molenaar; Jos A. Houbraken; Rob A. Samson; Edwin P. Kets (pp. 1-7).
Talaromyces macrosporus forms ascospores that survive pasteurization treatments. Ascospores were dense (1.3 g ml–1), relatively dry [0.6 g H2O (g dry weight)–1] and packed with trehalose (9–17% fresh weight). Trehalose was degraded to glucose monomers between 30 and 100 min after heat activation of the spores. The maximal activity of trehalase was calculated as 400–520 nmol glucose formed min–1 (mg protein)–1 as judged by measurements of the trehalose content of spores during germination. During early germination, glucose was released from the cell (10% of the cell weight or more). The intracellular concentration of glucose only peaked briefly. After 160–200 min, the protoplast encompassed by the inner cell wall was ejected through the outer cell wall in a very quick process. Subsequently, respiration of spores increased strongly. The data suggested that trehalose is primarily present for the protection of cell components as glucose is released from the cell. Then, an impenetrable outer cell wall is shed before metabolic activity increases.
Keywords: Talaromyces Ascospores Dormancy Germination Trehalose Trehalase Heat-resistant fungi
No Title by Hor-Gil Hur; Richard D. Beger; Thomas M. Heinze; Jackson O. Lay; James P. Freeman; Joel Dore; Fatemeh Rafii (pp. 8-12).
Colonic bacteria were screened for bacteria involved in the conversion of phytoestrogens. A gram-positive anaerobic bacterium, strain HGH 136, capable of conversion of the isoflavonoid daidzein, was isolated and identified as a Clostridium sp. The bacterium cleaved the C-ring of daidzein to produce O-demethylangolensin (O-Dma). This compound was identified by comparison of the HPLC retention time and UV spectrum of the metabolite with chemically synthesized O-Dma. The identity of the metabolite was confirmed by liquid chromatography-mass spectrometry and NMR using synthetic O-Dma as a standard. The bacterium incubated with synthetic dihydrodaidzein also produced O-Dma. After 3 days of incubation, 28% of added daidzein and 12% of added dihydrodaidzein were converted to O-Dma. This is the first study in which an anaerobic bacterium involved in the ring cleavage of daidzein to produce O-Dma has been identified.
Keywords: Isoflavonoids Phytoestrogens Daidzein Anaerobic bacteria C-ring fission
No Title by Caroline M. Laemmli; René Schönenberger; Marc Suter; Alexander J. Zehnder; Jan R. van der Meer (pp. 13-25).
Ralstonia eutropha JMP134 (pJP4) harbors two functional gene clusters for the degradation of chlorocatechols, i.e. tfdCDEF (in short: tfd I ) and tfdD II C II E II F II (in short: tfd II ), which are both present on the catabolic plasmid pJP4. In this study, we compared the function of both gene clusters for degradation of chlorocatechols by constructing isolated and hybrid tfd I -tfd II clusters on plasmids in R. eutropha, by activity assays of Tfd enzymes, and by HPLC/MS of individual enzymatic catalytic steps in chlorocatechol conversion. R. eutropha containing the tfd II cluster alone or hybrid tfd-clusters with tfdD II as sole gene for chloromuconate cycloisomerase were impaired in growth on 3-chlorobenzoate, in contrast to R. eutropha harboring the complete tfd I cluster. Enzyme activities for TfdDII and for TfdEII were very low in R. eutropha when induced with 3-chlorobenzoate. By contrast, a relatively high enzyme activity was found for TfdFII. Spectral conversion assays with extracts from R. eutropha strains expressing tfdD II all showed accumulation of a compound with a similar UV spectrum as 2-chloro-cis,cis-muconate from 3-chlorocatechol. HPLC analysis of in vitro assays in which each individual step in 3-chlorocatechol conversion was reproduced by sequentially adding cell extracts of an Escherichia coli expressing one Tfd enzyme only demonstrated that TfdDII was unable to cause conversion of 2-chloro-cis,cis-muconate. No accumulation of intermediates was observed with 4-chlorocatechol. From these results, we conclude that at least TfdDII is a bottleneck in conversion of 3-chlorocatechol and, therefore, in efficient metabolism of 3-chlorobenzoate. This study showed the subtle functional and expression differences between similar enzymes of the tfd-encoded pathway and demonstrated that extreme care has to be taken when inferring functionality from sequence data alone.
Keywords: Ralstonia eutropha JMP134 (pJP4) 2-Chloro-cis,cis-muconate Modified ortho cleavage pathway Catabolic pathway Chloromuconate cycloisomerase tfd genes
No Title by Tahar Mechichi; Erko Stackebrandt; Nasser Gad'on; Georg Fuchs (pp. 26-35).
Six strains of denitrifying bacteria isolated from various oxic and anoxic habitats on different monocyclic aromatic substrates were characterized by sequencing 16S rRNA genes, determining physiological and morphological traits, and DNA-DNA hybridization. According to these criteria, strains S100, SP and LG356 were identified as members of Thauera aromatica. Strains B5–1 and B5–2 were tentatively affiliated to the species Azoarcus tolulyticus. Strains B4P and S2 were only distantly related to each other and to other described Thauera species. These two strains are proposed as the type strains of two new species, Thauera phenylacetica sp. nov. and Thauera aminoaromatica sp. nov., respectively. By 16S rRNA gene analysis, strain U120 was highly related to the type strains of Azoarcus evansii and Azoarcus anaerobius, whereas corresponding DNA-DNA reassociation values indicated only a low degree of genomic relatedness. Based upon a low DNA similarity value and the presence of distinguishing physiological properties, strain U120 is proposed as the type strain of a new species, Azoarcus buckelii sp. nov. Almost all of the new isolates were obtained with different substrates. The highly varied substrate spectra of the isolates indicates that an even higher diversity of denitrifying bacteria degrading aromatic compounds would be discovered in the different habitats by using a larger spectrum of aromatic substrates for enrichment and isolation.
Keywords: Thauera Azoarcus Thauera phenylacetica sp. nov. Thauera aminoaromatica sp. nov. Azoarcus buckelii sp. nov. Nitrate reduction Aromatic compounds anaerobic degradation
No Title by Julio M. Sanjuán-Pinilla; Socorro Muñoz; Joaquina Nogales; José Olivares; Juan Sanjuán (pp. 36-44).
The role of leucine biosynthesis by Sinorhizobium meliloti in the establishment of nitrogen-fixing symbiosis with alfalfa (Medicago sativa) was investigated. The leuA gene from S. meliloti, encoding α-isopropylmalate synthase, which catalyses the first specific step in the leucine biosynthetic pathway, was characterized. S. meliloti LeuA– mutants were Leu auxotrophs and lacked α-isopropylmalate synthase activity. In addition, leuA auxotrophs were unable to nodulate alfalfa. Alfalfa roots did not seem to secrete enough leucine to support growth of leucine auxotrophs in the rhizosphere. Thus, this growth limitation probably imposes the inability to initiate symbiosis. However, in addition to the leucine auxotrophy, leuA strains were impaired in activation of nodulation genes by the transcriptional activator NodD1 in response to the plant flavone luteolin. By contrast, nod gene activation by NodD3, which does not involve plant-derived inducers, was unaffected. Our results suggest that a leucine-related metabolic intermediate may be involved in activation of nodulation genes by NodD1 and luteolin. This kind of control could be of relevance as a way to link bacterial physiological status to the response to plant signals and initiation of symbiosis.
Keywords: Leucine Symbiosis Rhizobia Legume Transcriptional activation
No Title by Akira Hiraishi; Yoshitomo Yonemitsu; Mayumi Matsushita; Yong Shin; Hiroshi Kuraishi; Kazuyoshi Kawahara (pp. 45-52).
Three strains of "Agrobacterium sanguineum", an aerobic marine bacterial species described previously, were re-characterized from phylogenetic and taxonomic viewpoints. 16S rDNA sequence comparisons showed that the "A. sanguineum" strains belong to the α–4 subgroup of α-Proteobacteria, with members of the genera Erythromicrobium and Porphyrobacter as their closest relatives. DNA-DNA hybridization studies indicated that the "A. sanguineum" strains were distinguishable from any previously known species of these genera. Bacteriochlorophyll a, monosaccharide-type glycosphingolipids, 2-OH fatty acids of C14:0, C15:0, C16:0, and C16:1, and ubiquinone-10 were detected in the "A. sanguineum" strains. The G+C of the DNA was 63.8–64.0 mol%. Two of the "A. sanguineum" strains, IAM 12620 (=ATCC 25659) and ATCC 25661, were able to grow with biphenyl and dibenzofuran as sole carbon source in the presence of 0.05% yeast extract. The medium in these cultures turned yellowish-orange at the exponential phase of growth due to the release of soluble chromogenic metabolites. The remaining "A. sanguineum" strain, ATCC 25660, and all test strains of Erythromicrobium and Porphyrobacter neither grew nor produced yellow-orange pigment with biphenyl or dibenzofuran. In PCR experiments, bphA1 gene, coding for the large subunit protein of biphenyl dioxygenase, was detected in "A. sanguineum" IAM 12620 and ATCC 25661. Based on these results, we propose classifying "A. sanguineum" IAM 12620 and ATCC 25661 as a new species of the genus Porphyrobacter with the name Porphyrobacter sanguineus sp. nov.
Keywords: "Agrobacterium sanguineum" Porphyrobacter sanguineus Aerobic bacteriochlorophyll-containing bacteria Biphenyl degradation Dibenzofuran degradation
No Title by Jan Kaden; Alexander S. Galushko; Bernhard Schink (pp. 53-58).
Syntrophic cocultures of Geobacter sulfurreducens and Wolinella succinogenes oxidize acetate with nitrate as terminal electron acceptor. It has been postulated earlier that electrons are transferred in these cocultures not via hydrogen, but via a different carrier, e.g., a small c-type cytochrome that is detected in the supernatant of growing cultures. In the present study, L -cysteine, which was provided as a reducing agent, was found to mediate the electron transfer between the two partners. Low concentrations of L -cysteine or L -cystine (10–100 µM) supported syntrophic growth, and no acetate oxidation was observed in the absence of cysteine or cystine. Cell suspensions of G. sulfurreducens or coculture cell suspensions reduced cystine to cysteine, and suspensions of W. succinogenes or coculture suspensions oxidized cysteine with nitrate, as measured by the formation or depletion of free thiol groups. Added cysteine was rapidly oxidized by the coculture during growth, but the formed cystine was not entirely rereduced even under acceptor-limited conditions. The redox potential prevailing in acetate-oxidizing cocultures was –160 to –230 mV. Sulfide at low concentrations supported syntrophic growth as well and could replace cysteine. Neither growth nor acetate degradation was found with D-cysteine, homocysteine, cysteamine, 3-mercaptopropionate, dithiothreithol, thioglycolate, glutathione, coenzyme M, dimethylsulfoxide, trimethylamine-N-oxide, anthraquinone-2,6-disulfonate, or ascorbate.
Keywords: Syntrophy Acetate oxidation Geobacter sulfurreducens Wolinella succinogenes Cysteine Interspecies electron transfer
No Title by Christine A. Brantner; Charles C. Remsen; Heather A. Owen; Lorie A. Buchholz; Mary Collins (pp. 59-64).
The methanotrophic bacterium Methylomicrobium album BG8 uses methane as a sole source of carbon and energy. This bacterium forms an extensive intracytoplasmic membrane. The first enzymes of the methane oxidation pathway are the membrane-bound particulate methane monooxygenase and the periplasmic methanol dehydrogenase. Immunoelectron microscopy with specific antibodies was used to localize these enzymes to the intracytoplasmic membrane.
Keywords: Methylomicrobium album BG8 Methane monooxygenase Methanol dehydrogenase MMO MDH Immunoelectron microscopy pMMO
No Title by Patrick Curtis; Cindy H. Nakatsu; Allan Konopka (pp. 65-70).
Acidic (pH 2.9) soil was used as an inoculum to culture heterotrophic bacteria at pH values of 3–4. Four isolates were obtained; on the basis of 16S rDNA sequence, they were shown to be members of the β- and γ-Proteobacteria. The three isolates that were most closely related to Burkholderia spp. had simple nutritional requirements and could grow in glucose-mineral salts media; two of these used a broad array of organic substrates. The 16S rDNA sequence of the fourth isolate was most similar (96%) to Frateuria aurantia. The isolates were aciduric rather than acidophilic; their pH ranges for growth were approximately 3.5–8. Unlike many bacteria whose acid tolerance represents the capacity to survive acid exposure, these microorganisms carried out exponential growth at pH<4 and their growth rates at pH 3.9 ranged from 60 to 98% of those found at pH 7. The cell yields on glucose of two strains were identical at pH 4 and pH 7. The acidic soils appeared to contain a very diverse bacterial community as assessed by denaturing gradient gel electrophoresis fingerprinting of PCR amplicons of a portion of the 16S rDNA gene. Electronic supplementary material to this paper can be obtained by using the Springer LINK server located at http://dx.doi.org/10.1007/s00203-002-0427-1.
Keywords: Acid soils Bacterial diversity Bacterial growth
No Title by Claudia Herles; Annett Braune; Michael Blaut (pp. 71-74).
An NADH oxidase from the strictly anaerobic Eubacterium ramulus was purified to homogeneity. The enzyme is composed of two types of subunits with molecular masses of 40 and 30 kDa. The molecular mass of the native enzyme is 450 kDa according to gel filtration and PAGE analysis. Six to eight mol of FAD were found per mol of native enzyme. The NADH-specific enzyme was inhibited by N-bromosuccinimide and sulfhydryl reagents such as N-ethylmaleimide, CuCl2 or ZnCl2. The physiological function of the purified enzyme is unclear, but the demonstration of NADH-dependent O2-consumption suggests that it plays a role in the scavenging of oxygen.
Keywords: NADH oxidase Eubacterium ramulus
No Title
by Hor-Gil Hur; Richard D. Beger; Thomas M. Heinze; Jackson O. Lay; James P. Freeman; Joel Dore; Fatemeh Rafii (pp. 75-75).