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Archives of Microbiology (v.176, #6)
No Title by Angela Smirnova; Hongqiao Li; Helge Weingart; Stephan Aufhammer; Antje Burse; Katharina Finis; Alexander Schenk; Matthias S. Ullrich (pp. 393-399).
Pathogenic bacteria with habitats inside and outside a given host react to changes in environmental parameters by synthesizing gene products specifically needed during pathogenic or saprophytic growth. Temperature effects have been investigated in detail for pathogens of warm-blooded hosts, and major principles governing the temperature-sensing mechanism have been uncovered. Generally, transcription of virulence genes in these pathogens is induced at higher temperatures (37–41 °C), which are typical for body cavities and host tissues. However, effects of temperature on virulence determinants in plant pathogenic bacteria have not been focused on in detail. Interestingly, almost all virulence genes of plant pathogenic bacteria studied with respect to temperature exhibit increased transcription at temperatures well below the respective growth optima. This includes virulence determinants such as those directing bacteria-to-plant gene transfer, plant cell-wall-degrading enzymes, phytotoxins, ice nucleation activity, exopolysaccharide production, and the type III protein secretion machinery. Although many of the studied phytopathogens cause "cold-weather" diseases, the ecological rationale for this phenomenon remains to be studied in detail. This mini-review summarizes our current knowledge on thermoregulation of cellular processes taking place in bacterial phytopathogens in response to temperature changes. Since the temperature range of interest is different from that relevant to pathogens of mammals, one envisions novel principles of thermo-sensing in bacteria interacting with plants.
Keywords: Temperature Plant pathogens Virulence Temperature-sensing mechanism Environmental signals Phytotoxin Protein secretion Differential gene expression Two-component systems
No Title by William A. Samsonoff; Robert MacColl (pp. 400-405).
This review considers the properties of biliproteins from cyanobacteria and red algae that grow in extreme habitats. Three situations are presented: cyanobacteria that grow at high temperatures; a red alga that grows in acidic conditions at high temperature; and an Antarctic red alga that grows in the cold in dim light conditions. In particular, the properties of their biliproteins are compared to those from organisms from more usual environments. C-phycocyanins from two cyanobacteria able to grow at high temperatures are found to differ in their stabilities when compared to C-phycocyanin from mesophilic algae. They differ in opposite ways, however. One is more stable to dissociation than the mesophilic protein, and the other is more easily dissociated at low temperatures. The thermophilic proteins resist thermal denaturation much better than the mesophilic proteins. The most thermophilic cyanobacterium has a C-phycocyanin with a unique blue-shifted absorption maximum which does not appear to be part of the adaptation of the cyanobacterium to high temperature. The C-phycocyanin from the high-temperature red alga is able to resist dissociation better than mesophilic C-phycocyanins. Electron micrographs show the phycobilisomes of these algae. The Antarctic alga grows under ice at some distance down the water column. Its R-phycoerythrin has a novel absorption spectrum that gives the alga an improved ability to harvest blue light. This may enhance its survival in its light-deprived habitat.
Keywords: Phycobilisomes Biliproteins Extremophiles Antarctic algae Cyanophytes Red algae
No Title by Barbara N. Erdlenbruch; Donovan P. Kelly; Colin J. Murrell (pp. 406-414).
Novel isolates of Achromobacter xylosoxidans, Tsukamurella wratislaviensis and a Rhodococcus sp. are described. These grew with short-chain alkanesulfonates as their sole source of carbon and energy. T. wratislaviensis strain SB2 grew well with C3–C6 linear alkanesulfonates, isethionate and taurine, Rhodococcus sp. strain CB1 used C3–C10 linear alkanesulfonates, taurine and cysteate, but neither strain grew with ethanesulfonate. In contrast, A. xylosoxidans strain AE4 grew well with ethanesulfonate, making it the first bacterium to be described which can grow with this compound. It also grew with unsubstituted C3–C5 alkanesulfonates and isethionate. Hydrolysis was excluded as a mechanism for alkanesulfonate metabolism in these strains; and evidence is given for a diversity of uptake and desulfonatase systems. We provide evidence for an initial monooxygenase-dependent desulfonation in the metabolism of ethanesulfonate and propanesulfonate by A. xylosoxidans strain AE4.
Keywords: Achromobacter Tsukamurella Rhodococcus Ethanesulfonate Propanesulfonate Alkanesulfonate oxidation Monooxygenase Desulfonation
No Title by Adrian A. Vojnov; Holly Slater; Mari-Anne Newman; Michael J. Daniels; Maxwell J. Dow (pp. 415-420).
The rpf gene cluster of Xanthomonas campestris pv. campestris is involved in the co-ordinate positive regulation of the production of extracellular enzymes and the extracellular polysaccharide xanthan. Several of the rpf genes are involved in a regulatory system involving the small diffusible molecule DSF (for diffusible signal factor). Synthesis of DSF requires RpfF, and a two-component sensory transduction system involving RpfC has been implicated in the perception of the signal and signal transduction. Here we show that mutations in both rpfF and rpfC lead to reductions in the levels of cyclic glucan. The levels of cyclic glucan synthetase in membrane preparations from rpfF and rpfC mutants were, however, unaltered from the wild-type. Similar alterations in the level of cyclic glucan without changes in cyclic glucan synthetase activity were seen when wild-type bacteria were exposed to osmotic stress. These results extend the range of cellular functions subject to regulation by the rpf genes and DSF system.
Keywords: Xanthomonas campestris Cyclic glucan Diffusible signal molecule
No Title by Jens Frankowski; Matteo Lorito; Felice Scala; Roland Schmid; Gabriele Berg; Hubert Bahl (pp. 421-426).
The chitinolytic rhizobacterium Serratia plymuthica HRO-C48 was previously selected as a biocontrol agent of phytopathogenic fungi. One endochitinase (E.C. 3.2.1.14), CHIT60, and one N-acetyl-β-1,4-D-hexosaminidase (E.C. 3.2.1.52), CHIT100, were purified and characterized. The endochitinase CHIT60, with an apparent molecular mass of 60.5 kDa, had a N-terminal amino acid sequence highly similar to that of chitinases A from Serratia liquefaciens and Serratia marcescens. The enzyme activity had its peak at 55 °C and pH 5.4, and increased by more than 20% in the presence of 10 mM Ca2+, Co2+ or Mn2+. Activity was inhibited by 80% in the presence of 10 mM Cu2+. CHIT100 appeared to be a monomeric enzyme with a molecular mass of 95.6 kDa and a pI of 6.8. Optimal activity was obtained at 43 °C and pH 6.6, and decreased by more than 90 % in the presence of 10 mM Co2+ or Cu2+. CHIT100 (100 µg ml–1) inhibited spore germination and germ tube elongation of the phytopathogenic fungus Botrytis cinerea by 28 % and 31.6 %, respectively. With CHIT60 (100 µg ml–1), the effect was more pronounced: 78 % inhibition of of germination and 63.9 % inhibition of germ tube elongation.
Keywords: Serratia plymuthica Chitinase Biocontrol
No Title by Yuxian Xia; John M. Clarkson; Keith A. Charnley (pp. 427-434).
Three acid phosphatase (AcP) isozymes, pI 8.1, 8.0 and 7.8, were isolated, purified and partially characterised from optimised cultures of the entomopathogenic fungus Metarhizium anisopliae. The enzymes had similar molecular masses (approximately 44.0 kDa), and could degrade sugar phosphates found in the haemolymph of a host insect, the tobacco hornworm Manduca sexta. The AcP activity in haemolymph of mycosed insects increased significantly over controls, and some new isozymes were present. The infection-related isoforms were similar in molecular mass and pI to some of the in vitro AcP isozymes of M. anisopliae. Results of dot blot and Western blot analyses using anti-AcP antibodies suggested that at least one Metarhizium phosphatase isoform was present in haemolymph of infected caterpillars. Antibodies did not cross-react with immune (chemically stimulated) or non-immune haemolymph from Manduca sexta. Consistent with the appearance of highly active fungal phosphatase in caterpillar blood, free phosphate concentration increased dramatically during the late stages of infection to a level two to five times that of controls. Phosphate was limiting to growth of the fungus at the concentration found in control haemolymph and supplementation of phosphate significantly increased fungal growth in vitro in haemolymph. These results suggest that Metarhizium AcP may play a key role in providing phosphorus for fungal growth at the expense of the insect.
Keywords: Acid phosphatase Manduca sexta Metarhizium anisopliae Pathogenesis
No Title by Heike Rütters; Henrik Sass; Heribert Cypionka; Jürgen Rullkötter (pp. 435-442).
In this study, cellular lipid compositions of two mesophilic sulfate-reducing bacteria were analyzed by high performance liquid chromatography-mass spectrometry (HPLC-MS). In Desulfosarcina variabilis and Desulforhabdus amnigenus, alkylether-containing phospholipids were detected which had previously only been found in significant amounts in deeply branching hyperthermophilic bacteria and archaea. Combining information from HPLC-MS analysis and chemical degradation experiments, ether lipids were identified as 1-alkyl-2-acyl-phosphatidyl ethanolamines, glycerols and cholines. In Desulforhabdus amnigenus, n-penta-, n-hexa- and n-heptadecyl ethers were present (in order of decreasing abundance), whereas Desulfosarcina variabilis solely contained n-hexadecyl ether side chains.
Keywords: Ether lipids Sulfate-reducing bacteria Phospholipids HPLC-ESI-MS
No Title by Krishnan Chandra Raj; Lonnie O. Ingram; Julie A. Maupin-Furlow (pp. 443-451).
Acetobacter pasteurianus, an obligately oxidative bacterium, is the first organism shown to utilize pyruvate decarboxylase (PDC) as a central enzyme for oxidative metabolism. In plants, yeast, and other bacteria, PDC functions solely as part of the fermentative ethanol pathway. During the growth of A. pasteurianus on lactic acid, the central intermediate pyruvate is cleaved to acetaldehyde and CO2 by PDC. Acetaldehyde is subsequently oxidized to its final product, acetic acid. The presence of the PDC enzyme in A. pasteurianus was confirmed by zymograms stained for acetaldehyde production, enzyme assays using alcohol dehydrogenase as the coupling enzyme, and by cloning and characterization of the pdc operon. A. pasteurianus pdc was also expressed in recombinant Escherichia coli. The level of PDC activity was regulated in response to growth substrate, highest with lactic acid and absent with mannitol. The translated PDC sequence (548 amino acids) was most similar to that of Zymomonas mobilis, an obligately fermentative bacterium. A second operon (aldA) was also found which is transcribed divergently from pdc. This operon encodes a putative aldehyde dehydrogenase (ALD2; 357 amino acids) related to class III alcohol dehydrogenases and most similar to glutathione-dependent formaldehyde dehydrogenases from α-Proteobacteria and Anabeana azollae.
Keywords: Pyruvate decarboxylase Alcohol dehydrogenase Aldehyde dehydrogenase Acetic acid bacteria Lactate Metabolism Ethanol oxidation Ethanol fermentation
No Title by Guntram Christiansen; Elke Dittmann; Lorena Via Ordorika; Rosmarie Rippka; Michael Herdman; Thomas Börner (pp. 452-458).
Previous studies largely carried out with environmental samples or axenic and non-axenic cultures suggested that cyanobacteria may be a rich source of hitherto unexplored bioactive compounds. This has been confirmed in the present study by a screening of 146 axenic strains from the Pasteur Culture Collection (PCC) of cyanobacteria. Use of degenerate PCR primers, designed on the basis of conserved sequence motifs in the aminoacyl-adenylation domain of peptide synthetases, revealed the presence of the corresponding genes in the majority (75.3%) of the strains examined. Among unicellular cyanobacteria, only Chamaesiphon sp. strain PCC 6605, two strains of Gloeocapsa and most Microcystis isolates (22 out of 24) contained these genes; no amplicons were detected for any members of the genera Cyanothece, Gloeobacter and Gloeothece and the genetically diverse representatives of Synechococcus and Synechocystis. By contrast, eight out of ten pleurocapsalean members, 16 out of 25 oscillatorian strains, and all but two of the 63 filamentous heterocystous cyanobacteria tested gave positive amplification results. This information will be highly valuable for further exploring the corresponding cyanobacterial peptides and for elucidating the bioactivity of such non-ribosomally synthesized molecules.
Keywords: Non-ribosomal peptide synthetase (NRPS) genes Degenerate peptide synthetase PCR (PS-PCR) Aminoacyl-adenylation domain Secondary metabolites Bioactive compounds
No Title by Mattias C. Gustafsson; Colin N. Palmer; Roland C. Wolf; Claes von Wachenfeldt (pp. 459-464).
Bacillus subtilis strain 168 encodes two flavocytochromes P450, Cyp102A2 and Cyp102A3. The cyp102A3 gene is preceded by, and organized in an operon with, a gene for a transcriptional regulator, encoded by fatR. The paralogous gene, cyp102A2, is most likely transcribed as a mono-cistronic message. We show that fatR encodes a protein that binds to an operator sequence that is present upstream of its own reading frame, thereby repressing the expression of the fatR-cyp102A3 operon. Unsaturated fatty acids and phytanic acid have the capacity to interact with FatR and to abrogate its binding to the operator sequence.
Keywords: Bacillus subtilis, cytochrome P450, FatR, Cyp102A1, Cyp102A2, Cyp102A3, P450BM-3
No Title by Ulrike Gerischer; Nicholas L. Ornston (pp. 465-469).
The interdependence of genetic linkage in transformation and physical distance was studied in the bacterium Acinetobacter sp. strain ADP1. Transformation experiments were performed using 17 strains containing different mutations within the 21-kb pca-qui-pob gene cluster as recipients for the DNA of one of two strains carrying a mutation causing a temperature-sensitive phenotype. The different phenotypes of the transformants (temperature-sensitive or wild-type-like) were used to evaluate linkage. Combination of the recipient and donor strains resulted in physical distances ranging from 2 bp to 10,533 bp. A logarithmic relationship of decreasing linkage and increasing distance was observed, thus leading to calibration of a system for analysis of physical distance derived from linkage data. Limitations of this application are described here: Certain mutations (3 out of 17 mutations used in this study) are an exception to the observed relationship and result in much lower linkage than expected. Observed DNA sequence repetitions leading to DNA rearrangements may be the cause of this anomaly.
Keywords: Acinetobacter Transformation Linkage Protocatechuate 3,4-dioxygenase