Check out our New Publishers' Select for Free Articles

Archives of Microbiology (v.192, #2)

How do bacteria sense and respond to low temperature? by S. Shivaji; Jogadhenu S. S. Prakash (pp. 85-95).

Rigidification of the membrane appears to be the primary signal perceived by a bacterium when exposed to low temperature. The perception and transduction of the signal then occurs through a two-component signal transduction pathway consisting of a membrane-associated sensor and a cytoplasmic response regulator and as a consequence a set of cold-regulated genes are activated. In addition, changes in DNA topology due to change in temperature may also trigger cold-responsive mechanisms. Inducible proteins thus accumulated repair the damage caused by cold stress. For example, the fluidity of the rigidified membrane is restored by altering the levels of saturated and unsaturated fatty acids, by altering the fatty acid chain length, by changing the proportion of cis to trans fatty acids and by changing the proportion of anteiso to iso fatty acids. Bacteria could also achieve membrane fluidity changes by altering the protein content of the membrane and by altering the levels of the type of carotenoids synthesized. Changes in RNA secondary structure, changes in translation and alteration in protein conformation could also act as temperature sensors. This review highlights the various strategies by which bacteria senses low temperature signal and as to how it responds to the change.

Keywords: Cold adaptation; Bacteria; Desaturases; Fatty acid synthesis; Two-component signal transduction pathway; DNA supercoiling

Spore-to-spore agar culture of the myxomycete Physarum globuliferum by Pu Liu; Qi Wang; Yu Li (pp. 97-101).

The ontogeny of the myxomycete Physarum globuliferum was observed on corn meal agar and hanging drop cultures without adding sterile oat flakes, bacteria or other microorganisms. Its complete life cycle including spore germination, myxamoebae, swarm cells, plasmodial development, and maturity of fructifications was demonstrated. Details of spore-to-spore development are described and illustrated.

Keywords: Agar culture; Hanging drop culture; Plasmodial slime molds

Functional characterization of GDP-mannose pyrophosphorylase from Leptospira interrogans serovar Copenhageni by Matías D. Asención Diez; Ana Demonte; Jorge Giacomelli; Sergio Garay; Daniel Rodrígues; Birgit Hofmann; Hans-Juerguen Hecht; Sergio A. Guerrero; Alberto A. Iglesias (pp. 103-114).

Leptospira interrogans synthesizes a range of mannose-containing glycoconjugates relevant for its virulence. A prerequisite in the synthesis is the availability of the GDP-mannose, produced from mannose-1-phosphate and GTP in a reaction catalyzed by GDP-mannose pyrophosphorylase. The gene coding for a putative enzyme in L. interrogans was expressed in Escherichia coli BL21(DE3). The identity of this enzyme was confirmed by electrospray-mass spectroscopy, Edman sequencing and immunological assays. Gel filtration chromatography showed that the dimeric form of the enzyme is catalytically active and stable. The recombinant protein was characterized as a mannose-1-phosphate guanylyltransferase. S _0.5 for the substrates were determined both in GDP-mannose pyrophosphorolysis: 0.20 mM (GDP-mannose), 0.089 mM (PPi), and 0.47 mM; and in GDP-mannose synthesis: 0.24 mM (GTP), 0.063 mM (mannose-1-phosphate), and 0.45 mM (Mg²⁺). The enzyme was able to produce GDP-mannose, IDP-mannose, UDP-mannose and ADP-glucose. We obtained a structural model of the enzyme using as a template the crystal structure of mannose-1-phosphate guanylyltransferase from Thermus thermophilus HB8. Binding of substrates and cofactor in the model agree with the pyrophosphorylases reaction mechanism. Our studies provide insights into the structure of a novel molecular target, which could be useful for detection of leptospirosis and for the development of anti-leptospiral drugs.

Keywords: Leptospira interrogans ; Mannose metabolism; Pyrophosphorylase

Genome organisation of the marine Roseobacter clade member Marinovum algicola by Silke Pradella; Orsola Päuker; Jörn Petersen (pp. 115-126).

The Roseobacter clade, belonging to the family Rhodobacteraceae of the class Alphaproteobacteria, is one of the major bacterial groups in marine environments. A remarkable wealth of diverse large plasmids has been detected in members of this lineage. Here, we analysed the genome structure and extrachromosomal DNA content of four strains of the roseobacter species Marinovum algicola by pulsed-field gel electrophoresis. They were originally isolated from toxic dinoflagellates and possess multireplicon genomes with sizes between 5.20 and 5.35 Mb. In addition to the single circular chromosomes (3.60–3.74 Mb), whose organisation seem to be conserved, 9 to 12 extrachromosomal replicons have been detected for each strain. This number is unprecedented for roseobacters and proposes a sophisticated regulation of replication and partitioning to ensure stable maintenance. The plasmid lengths range from 7 to 477 kb and our analyses document a circular conformation for all but one of them, which might represent a linear plasmid-like prophage. In striking contrast to other roseobacters, up to one-third of the genomic information (1.75 Mb) is plasmid borne in Marinovum algicola. The plasmid patterns of some strains are conspicuously different, indicating that recombination and conjugative gene transfer are dominant mechanisms for microevolution within the Roseobacter clade.

Keywords: Marinovum algicola ; Genome organisation; Extrachromosomal DNA; Roseobacter clade; Pulsed-field gel electrophoresis

Ergot alkaloid biosynthesis in Aspergillus fumigatus: conversion of chanoclavine-I to chanoclavine-I aldehyde catalyzed by a short-chain alcohol dehydrogenase FgaDH by Christiane Wallwey; Marco Matuschek; Shu-Ming Li (pp. 127-134).

Ergot alkaloids are toxins and important pharmaceuticals which are produced biotechnologically on an industrial scale. A putative gene fgaDH has been identified in the biosynthetic gene cluster of fumigaclavine C, an ergot alkaloid of the clavine-type. The deduced gene product FgaDH comprises 261 amino acids with a molecular mass of about 27.8 kDa and contains the conserved motifs of classical short-chain dehydrogenases/reductases (SDRs), but shares no worth mentioning sequence similarity with SDRs and other known proteins. The coding region of fgaDH consisting of two exons was amplified by PCR from a cDNA library of Aspergillus fumigatus, cloned into pQE60 and overexpressed in E. coli. The soluble tetrameric His₆-FgaDH was purified to apparent homogeneity and characterized biochemically. It has been shown that FgaDH catalyzes the oxidation of chanoclavine-I in the presence of NAD⁺ resulting in the formation of chanoclavine-I aldehyde, which was unequivocally identified by NMR and MS analyzes. Therefore, FgaDH functions as a chanoclavine-I dehydrogenase and represents a new group of short-chain dehydrogenases. K _M values for chanoclavine-I and NAD⁺ were determined at 0.27 and 1.1 mM, respectively. The turnover number was 0.38 s⁻¹.

Keywords: Aspergillus fumigatus ; Biochemical characterization; Chanoclavine-I aldehyde; Ergot alkaloid biosynthesis; Gene expression; Short-chain alcohol dehydrogenase; Chanoclavine-I oxidase

Lipid peroxidation in the fungus Curvularia lunata exposed to nickel by Katarzyna Paraszkiewicz; Przemysław Bernat; Marcin Naliwajski; Jerzy Długoński (pp. 135-141).

The effect of Ni²⁺ on fungal growth, cellular fatty acid profile and lipid peroxidation was studied (with an emphasis on the kinetics of these processes) in the strain of filamentous fungus Curvularia lunata. In the cultures supplemented with 0.2 and 0.6 mM Ni²⁺ the lag phase was extended and the specific growth rate decreased, however, the maximum yield of biomass at the stationary phase reached, respectively, 97 and 27% of the control. The treatment with Ni²⁺ changed the proportion of 18 C atom fatty acids, with the most significant decrease in the content of linoleic acid (18:2) followed by a rise in the degree of fatty acid saturation. In the mycelia exposed to Ni²⁺ the levels of TBARS (lipid peroxidation products) increased and ranged between 156 and 823% over the control. The presented data reveal that the oxidative stress resulting, among others, in membrane lipid peroxidation is involved in the mechanisms of the nickel toxicity towards C. lunata and suggest that this fungus exhibits an ability to cope, to some extent, with the increased level of lipid peroxides.

Keywords: Curvularia lunata ; Fatty acids; Filamentous fungi; Lipid peroxidation; Nickel

Interaction of transcription activator GvpE with TATA-box-binding proteins of Halobacterium salinarum by Katharina Teufel; Felicitas Pfeifer (pp. 143-149).

GvpE is the transcriptional activator of the gvp gene cluster involved in gas vesicle formation in Haloabacterium salinarum. A 20-nucleotide sequence is required for the GvpE-mediated activation of the two oppositely oriented gvp promoters, P A and P D. This sequence is located adjacent to the TATA-box and the transcription factor-B-binding site BRE, suggesting an interaction between GvpE and proteins of the transcription initiation apparatus. Here, we analysed the interaction of GvpE with the five different TATA-box-binding proteins, TBP, of Hbt. salinarum PHH1. The His-tagged TbpA through TbpE proteins were produced in Escherichia coli, bound to Ni–NTA matrices and tested for interaction with GvpE by protein–protein affinity chromatography. All Tbp_His proteins retained the two different GvpE proteins from lysates of Haloferax volcanii transformants expressing the respective gvpE reading frame in pJAS35. Also, both GvpE_His proteins bound to Ni–NTA matrices retained TbpB, whereas the 20-kDa soluble gas vesicle protein GvpH_His neither bound TbpB nor GvpE from the respective lysates of Hfx. volcanii. From these results, it appears that GvpE interacts with any TBP of Hbt. salinarum. This interaction might attract TBP and subsequently TFB and RNAP to the promoter and thus enhance transcription of the gvp gene cluster.

Keywords: Transcriptional activator; Gas vesicles; Archaeal transcription regulation; TBP

Sections

Personal tools

Archives of Microbiology (v.192, #2)

Sections

Personal tools

Local resources

Archives of Microbiology (v.192, #2)