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Archives of Microbiology (v.177, #3)

No Title by Jörg Overmann; Karin Schubert (pp. 201-208).

Most symbiotic prokaryotes known to date have been found in association with eukaryotes, whereas only few (3.5%) bacteria or archaea are known that have established interactions with other prokaryotes. As revealed by direct microscopic investigations, however, multiple morphotypes of highly structured associations of different prokaryotes exist in nature. These so-called consortia appear to represent the most developed type of bacterial interaction. Phototrophic consortia are associations of green sulfur bacteria that surround a central chemotrophic bacterium. In some natural environments, almost all cells of green sulfur bacteria occur in the associated state, i.e. as epibionts of phototrophic consortia. In contrast to earlier speculations, the central bacterium belongs to the β-Proteobacteria. Within the consortia, the green sulfur bacterial epibionts grow photolithoautotrophically, utilizing exogenous sulfide as photosynthetic electron donor. The entire consortium does not appear to be independent of organic carbon compounds, since it exhibits chemotaxis towards 2-oxoglutarate and, as demonstrated by microautoradiography, can also incorporate this compound. Intact consortia exhibit a scotophobic response in which the bacteriochlorophylls of the epibionts function as light sensors, whereas the chemotrophic central bacterium confers motility upon the association. Hence, a signal exchange must occur between the different bacteria. Based on their 16S rRNA gene sequences, the epibionts represent distinct phylotypes that are often only distantly related to known species of green sulfur bacteria. Since phototrophic consortia have recently become available in enrichment cultures, they can now serve as suitable model systems for the investigation of the molecular mechanisms of cell-cell recognition and signal exchange, and for studies of the coevolution of nonrelated prokaryotes.

Keywords: Phototrophic consortia "Chlorochromatium" "Pelochromatium" Green sulfur bacteria Symbiosis Cell-cell recognition Signal exchange

No Title by Sonja-Verena Albers; Arnold J. Driessen (pp. 209-216).

Analysis of the recently completed genome sequence of the thermoacidophilic archaeon Sulfolobus solfataricus reveals that about 4.2% of its proteome consists of putative secretory proteins with signal peptides. This includes members of the four major classes of signal peptides: secretory signal peptides, twin-arginine signal peptides, possible lipoprotein precursors, and type IV pilin signal peptides. The latter group is surprisingly large compared to the size of the groups in other organisms and seems to be used predominately for a subset of extracellular substrate-binding proteins.

Keywords: Sulfolobus solfataricus Archaea Signal peptide Secretion Type IV pilin signal peptide Sugar-binding protein

No Title by Scott L. Jones; Pascal Drouin; Brian J. Wilkinson; Philip D. Morse (pp. 217-222).

Listeria monocytogenes is a food-borne, pathogenic, psychrotolerant bacterium that grows at refrigeration temperatures. Long-range membrane order of the parent (10403S) and of a cold-sensitive mutant (cld-1) deficient in odd-numbered, branched-chain fatty acids was measured using the width of the central line of spectra of an electron paramagnetic resonance probe, 4,4-dimethyl-2-heptyl-2-hexyloxazolidine-N-oxyl (7N14), that locates deep in the hydrocarbon region of the membranes. The line width decreased from 0.9 to 0.5 milliTesla (mT) over the temperature range of 0–10 ° for strain 10403S and –5 to 32 °C for strain cld-1 independent of protein state (heat denatured or intact). This provided new evidence for phase transitions in the membranes. When strain cld-1 was grown in medium supplemented with 2-methylbutyric acid, which restores anteiso fatty acids and the ability to grow at low temperature, the change in central line width as a function of temperature resembled that of strain 10403S. The temperatures at which the central line width became 0.8 mT corresponded to those at which growth became very slow in both strains (3–5 °C for 10403S, 15 °C for cld-1) as determined by Arrhenius plots. These data underscore the critical role of odd-numbered anteiso fatty acids in influencing the lower temperature limits of growth through their effects on long-range membrane fluidity.

Keywords: EPR Line width Membrane fluidity Low-temperature growth Listeria monocytogenes Food safety

No Title by Kai Klopprogge; Roman Grabbe; Michael Hoppert; Ruth A. Schmitz (pp. 223-234).

In the diazotroph Klebsiella pneumoniae, NifL and NifA regulate transcription of the nitrogen fixation genes in response to molecular oxygen and combined nitrogen. We recently showed that Fnr is the primary oxygen sensor. Fnr transduces the oxygen signal towards the negative regulator NifL by activating genes whose products reduce the FAD moiety of NifL under anoxic conditions. These Fnr-dependent gene products could be membrane-bound components of the anaerobic electron transport chain. Consequently, in this study we examined the localization of NifL within the cell under various growth conditions. In K. pneumoniae grown under oxygen- and nitrogen-limited conditions, approximately 55% of the total NifL protein was found in the membrane fraction. However, when the cells were grown aerobically or shifted to nitrogen sufficiency, less than 10% of total NifL was membrane-associated. In contrast to NifL, NifA was located in the cytoplasm under all growth conditions tested. Further studies using K. pneumoniae mutant strains showed that, under derepressing conditions but in the absence of either the primary oxygen sensor Fnr or the primary nitrogen sensor GlnK and the ammonium transporter AmtB, NifL was located in the cytoplasm and inhibited NifA activity. These findings suggest that under nitrogen- and oxygen-limitation, a significantly higher membrane affinity of NifL might create a spatial gap between NifL and its cytoplasmic target protein NifA, thereby impairing inhibition of NifA by NifL. Localization of GlnK further showed that, under nitrogen-limited conditions but independent of the presence of oxygen, 15–20% of the total GlnK is membrane-associated.

Keywords: Klebsiella pneumoniae Nitrogen fixation NifL NifA GlnK FAD cofactor

No Title by Heinz Wilkes; Ralf Rabus; Thomas Fischer; Antje Armstroff; Astrid Behrends; Friedrich Widdel (pp. 235-243).

The anaerobic degradation pathway of the saturated hydrocarbon n-hexane in a denitrifying strain (HxN1) was examined by gas chromatography-mass spectrometry of derivatized extracts from cultures grown with unlabeled and deuterated substrate; several authentic standard compounds were included for comparison. The study was focused on possible reaction steps that follow the initial formation of (1-methylpentyl)succinate from n-hexane and fumarate. 4-Methyloctanoic, 4-methyloct-2-enoic, 2-methylhexanoic, 2-methylhex-2-enoic and 3-hydroxy-2-methylhexanoic acids (in addition to a few other methyl-branched acids) were detected in n-hexane-grown but not in n-hexanoate-grown cultures. Labeling indicated preservation of the original carbon chain of n-hexane in these acids. Tracing of the deuterium label of 3-d ₁-(1-methylpentyl)succinate in tentative subsequent products indicated a deuterium/carboxyl carbon exchange in the succinate moiety. This suggests that the metabolism of (1-methylpentyl)succinate employs reactions analogous to those in the established conversion of succinyl-CoA via methylmalonyl-CoA to propionyl-CoA. Accordingly, a pathway is proposed in which (1-methylpentyl)succinate is converted to the CoA-thioester, rearranged to (2-methylhexyl)malonyl-CoA and decarboxylated (perhaps by a transcarboxylase) to 4-methyloctanoyl-CoA. The other identified fatty acids match with a further degradation of 4-methyloctanoyl-CoA via rounds of conventional β-oxidation. Such a pathway would also allow regeneration of fumarate (for n-hexane activation) from propionyl-CoA formed as intermediate and hence present a cyclic process.

Keywords: (1-Methylpentyl)succinate n-Hexane Anaerobic oxidation Denitrification C-skeleton rearrangement Fatty acid oxidation Methyl-branched fatty acids

No Title by Ryohei Ueno; Naoto Urano; Motofumi Suzuki; Shigeru Kimura (pp. 244-250).

A novel thermotolerant strain of the achlorophyllous micro-alga Prototheca was isolated from a hot spring. The isolate was found to produce an appreciable amount of ethanol and CO₂ from glucose under anoxic conditions at both 25 and 40 °C; this type of alcohol fermentation has not yet been reported in the genus Prototheca. Moreover, it also evolved gas from sucrose after a time lag at 40 °C. Its taxonomic characteristics coincided with those of Prototheca zopfii var. hydrocarbonea, and phylogenetic analysis, based on a small-subunit (SSU) rDNA sequence, also revealed a close relationship between the two strains. D-lactic acid, ethanol, CO₂ and a trace of acetic acid were produced from glucose, but L-lactic acid, formic acid, and H₂ were not. At 25 °C, D-lactic acid and ethanol were produced in approximately equimolar amounts under N₂/H₂/CO₂, whereas ethanol production was predominant under N₂. More ethanol was produced at 40 °C than at 25 °C irrespective of the gas composition in the atmosphere. This is the first report on gas production from glucose and on the changes in the fermentative patterns as a function of temperature for the genus Prototheca.

Keywords: Prototheca zopfii Fermentation Anaerobic metabolism Thermotolerant Ethanol CO2 Chlorella SSU rDNA sequence

No Title by Pia-Manuela Voicu; Marius Poitelea; Martin Schweingruber; Mircea Rusu (pp. 251-258).

The fission yeast Schizosaccharomyces pombe is a natural auxotroph for inositol and fails to grow in the complete absence of it. It was previously reported that a small concentration of inositol in the culture medium supports vegetative growth, but not mating and sporulation, and a tenfold of that concentration also supports mating and sporulation. The purpose of the present work was to investigate whether a moderate inositol starvation specifically affected events of the sexual program of development. A homothallic culture grown to the stationary phase in medium with a small inositol concentration was sterile but cells in the stationary phase of growth synchronously entered and completed the sexual cycle when inositol was added, without need of previous cell divisions. This suggests the involvement of inositol in a mechanism (or mechanisms) of the sexual program. The events of the program that were affected by inositol starvation were investigated. Commitment to mating and production of pheromone M were shown not to be inositol-dependent. A diploid strain homozygous at the mating-type locus and carrying a pat1–114 temperature-sensitive mutation in homozygous configuration sporulated under inositol starvation at the restrictive temperature; therefore starvation did not directly affect meiosis or sporulation. In contrast, production of pheromone P and the response of cells to pheromones were found to be inositol-dependent. The possibility that inositol or one of its derivative compounds is involved in pheromone P secretion and in pheromone signal reception is discussed.

Keywords: Schizosaccharomyces pombe Inositol Mating Sporulation

No Title by Ramón I. Santamaría; Fernando Leal; Margarita Díaz; José M. Fernández-Abalos (pp. 259-266).

Streptomyces development is a complex process that eventually finishes with the formation of individual unigenomic spores from the aerial hyphae. Intraspecific and interspecific signals must play a key role in triggering or blocking this process. Here we show that interaction between two types of microorganisms, Streptomyces and yeasts, leads to alteration of the Streptomyces developmental program. This alteration is due to the action of invertase produced by the yeast on the sucrose present in the culture media, making glucose and fructose readily available for growth.

Keywords: Streptomyces Yeast Invertase Glucose Fructose Differentiation

No Title by Patrick C. Woo; Patricia K. Leung; Hoi-Wah Tsoi; Benedict Y. Chan; Tak-Lun Que; Kwok-Yung Yuen (pp. 267-273).

During screening for antigenic proteins in Burkholderia pseudomallei, a novel insertion sequence, ISBp1, was found by sequence similarity searches. ISBp1 contains two overlapping ORFs of 261 bp (orfA) and 852 bp (orfB), encoding 87 and 284 amino acid residues, respectively, and an imperfect inverted repeat. The putative protein encoded by orfA (OrfA) is similar to the OrfA in insertion sequences of the IS3 family in other bacteria, showing 49% and 76% amino acid identity and similarity, respectively, with the transposase encoded by ISD1 of Desulfovibrio vulgaris vulgaris. The putative protein encoded by orfB (OrfB) is similar to the OrfB in insertion sequences of the IS3 family in other bacteria, showing 43% and 62% amino acid identity and similarity, respectively, with the transposase encoded by IS1222 of Enterobacter agglomerans. Sequence analysis of OrfA showed the presence of an α-helix-turn-α-helix motif, as well as the putative leucine zipper at its 3′ end, for possible DNA binding to the terminal inverted repeats. Sequence analysis of OrfB showed the presence of a DDE motif of aspartic acid, aspartic acid, and glutamic acid, a highly conserved motif present in OrfB of other members of the IS3 family. Furthermore, several other conserved amino acid residues, including the arginine residue located seven amino acids downstream from the glutamic acid residue, were observed. PCR amplification of the ISBp1 gene showed a specific band in 65% of the 26 B. pseudomallei strains tested. Southern blot hybridization after XhoI or SacI digestion showed nine different patterns of hybridization. The number of copies of ISBp1 in those strains that possessed the insertion sequence ranged from three to 12. Using several insertion sequences and a combination of insertion-sequence-based and non-insertion-sequence-based methods such as ribotyping will probably increase the discriminatory power of molecular typing in B. pseudomallei.

Keywords: Burkholderia pseudomallei Insertion sequence ISBp1

No Title by Huarong Tan; Yuqing Tian; Haihua Yang; Gang Liu; Liping Nie (pp. 274-278).

A 1.4-kb DNA fragment from Streptomyces ansochromogenes accelerated mycelium formation of S. ansochromogenes when present on a multicopy plasmid. The DNA fragment contains one complete open reading frame, designated samR, encoding a protein with 213 amino acids that contains a likely DNA-binding helix-turn-helix motif close to its N-terminus. The deduced SamR protein resembles the product of the hppR gene, which is involved in the regulation of catabolism of 3-(3-hydroxyphenyl) propionate in Rhodococcus globerulus. A samR disruption mutant was constructed that presented a bald phenotype and failed to form aerial hyphae and spores. We suggest that samR plays an important role in the emergence of aerial hyphae from substrate mycelium. An almost identical gene of Streptomyces coelicolor was also subjected to gene disruption. Surprisingly, the mutant was able to develop an aerial mycelium, but it remained white and deficient in sporulation instead of forming gray spores.

Keywords: Streptomyces differentiation samR gene Gene disruption

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Archives of Microbiology (v.177, #3)

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Archives of Microbiology (v.177, #3)