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Archives of Microbiology (v.179, #2)
Relevance of airborne fungi and their secondary metabolites for environmental, occupational and indoor hygiene by Guido Fischer; Wolfgang Dott (pp. 75-82).
Airborne fungal contaminants are increasingly gaining importance in view of health hazards caused by the spores themselves or by microbial metabolites. In addition to the risk for infection, the allergenic and toxigenic properties, as well as the inflammatory effects are discussed in this review as possible health impacts of bioaerosols. A major problem is the lack of threshold values for pathogenic and non-pathogenic fungi, both in the workplace and in outdoor air. While the relevance of mycotoxins has been intensely studied in connection with contamination of food and feed, the possible respiratory uptake of mycotoxins from the air has so far not been sufficiently taken into account. Toxic secondary metabolites are expected to be present in airborne spores, and may thus occur in airborne dust and bioaerosols. Potential health risks cannot be estimated reliably unless exposure to mycotoxins is determined qualitatively and quantitatively. Microbial volatile organic compounds (MVOC) have been suggested to affect human health, causing lethargy, headache, and irritation of the eyes and mucous membranes of the nose and throat. The production of MVOC by fungi has been discussed in connection with domestic indoor microbial pollution, but the relevance of fungal metabolites in working environments remains insufficiently studied.
Keywords: Airborne fungi Mycotoxins MVOC Volatile compounds Indoor air Compost Occupational hygiene
I do it my way: regulation of ammonium uptake and ammonium assimilation in Corynebacterium glutamicum by Andreas Burkovski (pp. 83-88).
In order to utilize different nitrogen sources and to survive situations of nitrogen limitation, microorganisms have developed several mechanisms to adapt their metabolism to changes in the nitrogen supply. In this communication, recent advances in our knowledge of ammonium uptake, its assimilation, and connected regulatory systems in Corynebacterium glutamicum are discussed with respect to the situation in the bacterial model organisms Escherichia coli and Bacillus subtilis. The regulatory network of nitrogen control in C. glutamicum differs substantially from that in these bacteria, for example, by the presence of AmtR, the unique "master regulator" of nitrogen control, the absence of a NtrB/NtrC two-component signal transduction system, and a different sensing mechanism in C. glutamicum.
Keywords: Ammonium Corynebacterium Mycobacterium Nitrogen control Nitrogen regulation
Development of a genetic system for Magnetospirillum gryphiswaldense by Daniel Schultheiss; Dirk Schüler (pp. 89-94).
Genetic analysis of bacterial magnetosome biomineralization has been hindered by the lack of an appropriate methodology for cultivation and genetic manipulation of most magnetotactic bacteria. In this report, a genetic system for Magnetospirillum gryphiswaldense is described. The system includes a plating technique that allows the screening of magnetic vs non-magnetic colonies, and a protocol for the transfer of foreign DNA by electroporation and high-frequency conjugation. Various broad-host-range vectors of the IncQ, IncP, and pBBR1 groups were found to be capable of replication in M. gryphiswaldense. Several antibiotic resistance markers that can be expressed in M. gryphiswaldense were identified. Tn5 transposons delivered on a suicide plasmid showed transpositional insertion into random chromosomal sites.
Keywords: Broad-host-range vectors Conjugation Electroporation Magnetospirillum gryphiswaldense Magnetotactic bacteria Magnetosome biomineralization Transposon mutagenesis
Novel carotenoid glucoside esters from alkaliphilic heliobacteria by Shinichi Takaichi; Hirozo Oh-oka; Takashi Maoka; Deborah O. Jung; Michael T. Madigan (pp. 95-100).
Pigments of three species of alkaliphilic heliobacteria of the genus Heliorestis, H. daurensis, H. baculata and an undescribed species Heliorestis strain HH, were identified using spectroscopic methods. In these species, bacteriochlorophyll g esterified with farnesol was present, as for other heliobacteria. The carotenoids consisted of 4,4′-diaponeurosporene, also found in other heliobacteria, plus the novel pigments OH-diaponeurosporene glucoside esters (C16:0 and C16:1). In addition, trace amounts of biosynthetic intermediates, OH-diaponeurosporene and OH-diaponeurosporene glucoside, were found. Trace amounts of a carotenoid with 20 carbon atoms, 8,8′-diapo-ζ-carotene, were also found in these species as well as in the non-alkaliphilic heliobacteria. The non-alkaliphilic species Heliophilum fasciatum also contained trace amounts of the two OH-diaponeurosporene glucoside esters. The results are used to predict the pathway of carotenoid biosynthesis in heliobacteria.
Keywords: Carotenoid Carotenoid glycoside esters Diapocarotene 4,4′-Diaponeurosporene Bacteriochlorophyll g Heliobacteria Heliophilum fasciatum Heliorestis daurensis Heliorestis baculata
A zinc-containing mannitol-2-dehydrogenase from Leuconostoc pseudomesenteroides ATCC 12291: purification of the enzyme and cloning of the gene by Gerald Hahn; Björn Kaup; Stephanie Bringer-Meyer; Hermann Sahm (pp. 101-107).
Mannitol-2-dehydrogenase (EC 1.1.1.67) of Leuconostoc pseudomesenteroides ATCC 12291 catalyzing the NADH-dependent reduction of d-fructose to d-mannitol was purified to homogeneity. Native mannitol-2-dehydrogenase has a molecular mass of 155 kDa as determined by gel filtration chromatography. In SDS–PAGE, a single band appeared corresponding to a molecular mass of 43 kDa which indicated that the enzyme was composed of four identical subunits. Enzyme activity was completely inhibited by EDTA and could be restored by zinc ions, but not by Mn2+ or Mg2+ which demonstrated that zinc is a cofactor. Purified mannitol-2-dehydrogenase exhibited a maximal specific activity of 400 μmol fructose reduced min−1(mg protein)−1, using NADH as electron donor. The enzyme showed a high substrate specificity for d-fructose and d-mannitol, however it accepted NADPH as a cofactor with 32% activity (V max) relative to NADPH (100%). The mdh gene, encoding mannitol-2-dehydrogenase, was identified by hybridization with a degenerate gene probe complementary to the nucleotide sequence encoding the first eight N-terminal amino acids of the enzyme. The mdh gene was cloned on a 4.2-kb DNA fragment, subcloned, and expressed in Escherichia coli. Sequencing of the gene revealed an open reading frame of 1,017 bp, encoding a protein of 338 amino acids with a predicted molecular mass of 36.0 kDa. Plasmid-encoded mdh was functionally expressed, with 70 U/mg of cell-free protein in E. coli. Multiple sequence alignments showed that mannitol-2-dehydrogenase was affiliated with members of the Zn2+-containing medium-chain alcohol/polyol dehydrogenase/reductase protein family (MDR).
Keywords: Mannitol-2-dehydrogenase Leuconostoc pseudomesenteroides NAD+-dependent dehydrogenase Zinc-containing Medium-chain alcohol/polyol dehydrogenase/reductase protein family MDR mdh gene
A comparative study of bchG from green photosynthetic bacteria by L. Jesús Garcia-Gil; Frederic B. Gich; Xavier Fuentes-Garcia (pp. 108-115).
The gene bchG, coding for bacteriochlorophyll a synthase from a variety of green sulfur bacteria and the filamentous anoxygenic phototrophic bacteria, Chloroflexus aurantiacus, Chloronema sp., and Roseiflexus castenholzii HL08, was partially sequenced and compared. The deduced amino acid consensus sequences for green sulfur bacteria and green filamentous anoxygenic phototrophic bacteria were found to belong to the UbiA enzyme family of polyprenyltransferases with the most similar sequences being those of photosynthetic organisms. All deduced amino acid sequences showed a highly conserved region, which includes the motif DRXXD, characteristic of polyprenyltransferases, which was extended to DREVDAINEP for green sulfur bacteria. Neighbor-joining analysis of a protein similitude matrix displayed a relatively high distance between green sulfur bacteria and the other groups. Sequences from green sulfur bacteria were more closely related to those of purple bacteria than to those of filamentous anoxygenic phototrophic bacteria. In addition, internal grouping within green sulfur bacteria was congruent regarding taxonomic features including cell shape, presence of gas vacuoles and NaCl requirement. In addition to bchlG, another gene encoding for a second chlorophyll synthetase, previously tentatively identified as chlG, was also found in Chlorobium tepidum, showing the highest similarities with polyprenyltransferases from chlorophyll-a-containing organisms.
Keywords: bchG, Bacteriochlorophyll a (Bacterio)chlorophyll synthase Green phototrophic bacteria Polyprenyltransferase
Molecular and biochemical characterization of two tungsten- and selenium-containing formate dehydrogenases from Eubacterium acidaminophilum that are associated with components of an iron-only hydrogenase by Andrea Graentzdoerffer; David Rauh; Andreas Pich; Jan R. Andreesen (pp. 116-130).
Two gene clusters encoding similar formate dehydrogenases (FDH) were identified in Eubacterium acidaminophilum. Each cluster is composed of one gene coding for a catalytic subunit (fdhA-I, fdhA-II) and one for an electron-transferring subunit (fdhB-I, fdhB-II). Both fdhA genes contain a TGA codon for selenocysteine incorporation and the encoded proteins harbor five putative iron–sulfur clusters in their N-terminal region. Both FdhB subunits resemble the N-terminal region of FdhA on the amino acid level and contain five putative iron–sulfur clusters. Four genes thought to encode the subunits of an iron-only hydrogenase are located upstream of the FDH gene cluster I. By sequence comparison, HymA and HymB are predicted to contain one and four iron–sulfur clusters, respectively, the latter protein also binding sites for FMN and NAD(P). Thus, HymA and HymB seem to represent electron-transferring subunits, and HymC the putative catalytic subunit containing motifs for four iron–sulfur clusters and one H-cluster specific for Fe-only hydrogenases. HymD has six predicted transmembrane helices and might be an integral membrane protein. Viologen-dependent FDH activity was purified from serine-grown cells of E. acidaminophilum and the purified protein complex contained four subunits, FdhA and FdhB, encoded by FDH gene cluster II, and HymA and HymB, identified after determination of their N-terminal sequences. Thus, this complex might represent the most simple type of a formate hydrogen lyase. The purified formate dehydrogenase fraction contained iron, tungsten, a pterin cofactor, and zinc, but no molybdenum. FDH-II had a two-fold higher K m for formate (0.37 mM) than FDH-I and also catalyzed CO2 reduction to formate. Reverse transcription (RT)-PCR pointed to increased expression of FDH-II in serine-grown cells, supporting the isolation of this FDH isoform. The fdhA-I gene was expressed as inactive protein in Escherichia coli. The in-frame UGA codon for selenocysteine incorporation was read in the heterologous system only as stop codon, although its potential SECIS element exhibited a quite high similarity to that of E. coli FDH.
Keywords: Eubacterium acidaminophilum Formate dehydrogenase isoenzymes Iron-only hydrogenase Formate hydrogen lyase Tungsten Selenocysteine
Expression of the iron-responsive irpA gene from the cyanobacterium Synechococcus sp. strain PCC 7942 by Kathryn A. Durham; David Porta; Michael R. McKay; George S. Bullerjahn (pp. 131-134).
Expression of the iron-stress-induced irpA gene of Synechococcus sp. strain PCC 7942 was investigated by constructing luminescent pirpA::luxAB promoter fusions. Growth of Fe-replete and Fe-limited cultures yielded high levels of luminescence only under conditions of iron deficiency. Promoter fusion deletions revealed that low Fe irpA transcription is dependent on a 25-nucleotide sequence that includes a region of dyad symmetry centered 19 nucleotides from the transcription start. Assaying luminescence at defined iron concentrations in trace-metal-buffered media showed that irpA transcription is activated at concentrations below 100 nm Fe. Overall, the expression pattern and promoter structure of irpA suggests a novel form of metal-dependent regulation in this species.
Keywords: Iron deficiency Cyanobacteria Promoter fusions Bioreporter Synechococcus
Growth of sulfate-reducing bacteria and methanogenic archaea with methylated sulfur compounds: a commentary on the thermodynamic aspects by Johannes C. M. Scholten; J. Colin Murrell; Donovan P. Kelly (pp. 135-144).
Methylated sulfur compounds such as dimethylsulfoniopropionate, dimethylsulfide, methanethiol, and other methylated sulfur compounds can act as sources of carbon and energy for the growth under anoxic conditions of a number of sulfate-reducing bacteria and methanogenic archaea. We summarise the range of degradative reactions that do or might occur in such organisms, and present thermodynamic data for these processes. These data enable estimates of the feasibility of the reactions as growth-supporting systems, and of the possible maximum growth yields of the bacteria and archaea catalysing them. We compare our new estimates with the few data that are currently available from the literature, and show that some published growth-yield assessments need reevaluation.
Keywords: Sulfate reduction Methanogens Methylated sulfur compounds Growth yields Free energy Thermodynamics