|
|
|
|
|
|
Methylation-Independent Aerotaxis Mediated by the Escherichia coli Aer Protein. Sergei I. Bibikov, 2004.Aer is a membrane-associated protein that mediates aerotactic responses in Escherichia coli . Its C-terminal half closely resembles the signaling domains of methyl-accepting chemotaxis proteins (MCPs), which undergo reversible methylation at specific glutamic acid residues to adapt their signaling outputs to homogeneous chemical environments . MCP-mediated behaviors are dependent on two specific enzymes, CheR (methyltransferase) and CheB (methylesterase) . The Aer signaling domain contains unorthodox methylation sites that do not conform to the consensus motif for CheR or CheB substrates, suggesting that Aer, unlike conventional MCPs, might be a methylation-independent transducer . Several lines of evidence supported this possibility . (i) The Aer protein was not detectably modified by either CheR or CheB . (ii) Amino acid replacements at the putative Aer methylation sites generally had no deleterious effect on Aer function . (iii) Aer promoted aerotactic migrations on semisolid media in strains that lacked all four of the E . coli MCPs . CheR and CheB function had no influence on the rate of aerotactic movements in those strains . Thus, Aer senses and signals efficiently in the absence of deamidation or methylation, methylation changes, methylation enzymes, and methyl-accepting chemotaxis proteins . We also found that chimeric transducers containing the PAS-HAMP sensing domain of Aer joined to the signaling domain and methylation sites of Tar, an orthodox MCP, exhibited both methylation-dependent and methylation-independent aerotactic behavior . The hybrid Aear transducers demonstrate that methylation independence does not emanate from the Aer signaling domain but rather may be due to transience of the cellular redox changes that are thought to trigger Aer-mediated behavioral responses . Development and Application of a Selective PCR-Denaturing Gradient Gel Electrophoresis Approach To Detect a Recently Cultivated Bacillus Group Predominant in Soil. Vesela A. Tzeneva, 2004.The worldwide presence of a hitherto-nondescribed group of predominant soil microorganisms related to Bacillus benzoevorans was analyzed after development of two sets of selective primers targeting 16S rRNA genes in combination with denaturing gradient gel electrophoresis (DGGE) . The high abundance and cultivability of at least some of these microorganisms makes them an appropriate subject for studies on their biogeographical dissemination and diversity . Since cultivability can vary significantly with the physiological state and even between closely related strains, we developed a culture-independent 16S rRNA gene-targeted DGGE fingerprinting protocol for the detection of these bacteria from soil samples . The composition of the B . benzoevorans relatives in the soil samples from The Netherlands, Bulgaria, Russia, Pakistan, and Portugal showed remarkable differences between the different countries . Differences in the DGGE profiles of these communities in archived soil samples from the Dutch Wieringermeer polder were observed over time during which a shift from anaerobic to aerobic and from saline to freshwater conditions occurred . To complement the molecular methods, we additionally cultivated B . benzoevorans-related strains from all of the soil samples . The highest number of B . benzoevorans relatives was found in the soils from the northern part of The Netherlands . The present study contributes to our knowledge of the diversity and abundance of this interesting group of microbes in soils throughout the world . Analysis of the Interaction between the Transcription Factor  G and the Anti-Sigma Factor SpoIIAB of Bacillus subtilis.Louise Evans, 2003.The activation of G, a transcription factor, in Bacillus subtilis is coupled to the completion of engulfment during sporulation . SpoIIAB, an anti-sigma factor involved in regulation of
F, is also shown to form a complex with
G in vitro . SpoIIAA, the corresponding anti-anti-sigma factor, can disrupt the SpoIIAB:G complex, releasing free
G . The data suggest the existence of an as-yet-unknown mechanism to keep
G inactive prior to engulfment .
ß-Lactamase Genes of the Penicillin-Susceptible Bacillus anthracis Sterne Strain. Yahua Chen, 2003.Susceptibility to penicillin and other ß-lactam-containing compounds is a common trait of Bacillus anthracis . ß-lactam agents, particularly penicillin, have been used worldwide to treat anthrax in humans . Nonetheless, surveys of clinical and soil-derived strains reveal penicillin G resistance in 2 to 16% of isolates tested . Bacterial resistance to ß-lactam agents is often mediated by production of one or more types of ß-lactamases that hydrolyze the ß-lactam ring, inactivating the antimicrobial agent . Here, we report the presence of two ß-lactamase (bla) genes in the penicillin-susceptible Sterne strain of B . anthracis . We identified bla1 by functional cloning with Escherichia coli . bla1 is a 927-nucleotide (nt) gene predicted to encode a protein with 93.8% identity to the type I ß-lactamase gene of Bacillus cereus . A second gene, bla2, was identified by searching the unfinished B . anthracis chromosome sequence database of The Institute for Genome Research for open reading frames (ORFs) predicted to encode ß-lactamases . We found a partial ORF predicted to encode a protein with significant similarity to the carboxy-terminal end of the type II ß-lactamase of B . cereus . DNA adjacent to the 5' end of the partial ORF was cloned using inverse PCR . bla2 is a 768-nt gene predicted to encode a protein with 92% identity to the B . cereus type II enzyme . The bla1 and bla2 genes confer ampicillin resistance to E . coli and Bacillus subtilis when cloned individually in these species . The MICs of various antimicrobial agents for the E . coli clones indicate that the two ß-lactamase genes confer different susceptibility profiles to E . coli; bla1 is a penicillinase, while bla2 appears to be a cephalosporinase . The ß-galactosidase activities of B . cereus group species harboring bla promoter-lacZ transcriptional fusions indicate that bla1 is poorly transcribed in B . anthracis, B . cereus, and B . thuringiensis. The bla2 gene is strongly expressed in B . cereus and B . thuringiensis and weakly expressed in B . anthracis . Taken together, these data indicate that the bla1 and bla2 genes of the B . anthracis Sterne strain encode functional ß-lactamases of different types, but gene expression is usually not sufficient to confer resistance to ß-lactam agents . Bacterial Community Structure and Location in Stilton Cheese. Danilo Ercolini, 2003.The microbial diversity occurring in Stilton cheese was evaluated by 16S ribosomal DNA analysis with PCR-denaturing gradient gel electrophoresis . DNA templates for PCR experiments were directly extracted from the cheese as well as bulk cells harvested from a variety of viable-count media . The variable V3 and V4-V5 regions of the 16S genes were analyzed . Closest relatives of Lactococcus lactis, Enterococcus faecalis, Lactobacillus plantarum, Lactobacillus curvatus, Leuconostoc mesenteroides, Staphylococcus equorum, and Staphylococcus sp . were identified by sequencing of the DGGE fragments . Fluorescently labeled oligonucleotide probes were developed to detect Lactococcus lactis, Lactobacillus plantarum, and Leuconostoc mesenteroides in fluorescence in situ hybridization (FISH) experiments, and their specificity for the species occurring in the community of Stilton cheese was checked in FISH experiments carried out with reference cultures . The combined use of these probes and the bacterial probe Eub338 in FISH experiments on Stilton cheese sections allowed the assessment of the spatial distribution of the different microbial species in the dairy matrix . Microbial colonies of bacteria showed a differential location in the different parts of the cheese examined: the core, the veins, and the crust . Lactococci were found in the internal part of the veins as mixed colonies and as single colonies within the core . Lactobacillus plantarum was detected only underneath the surface, while Leuconostoc microcolonies were homogeneously distributed in all parts observed . The combined molecular approach is shown to be useful to simultaneously describe the structure and location of the bacterial flora in cheese . The differential distribution of species found suggests specific ecological reasons for the establishment of sites of actual microbial growth in the cheese, with implications of significance in understanding the ecology of food systems and with the aim of achieving optimization of the fermentation technologies as well as preservation of traditional products .
|
© 2005
Transgalactic Ltd (manufacturer of Bioscreen C software) |
Privacy Statement | P.O. Box
1393, 00101 Helsinki, Finland,
Last modified: May 25, 2005
| ||||||
