Biomedical subjects

Wiep Klaas Smits

Publications and source records attributed to Wiep Klaas Smits.

7 recordsLinked to original sources

PubMed2006

Phenotypic variation in bacteria: the role of feedback regulation.

To survive in rapidly changing environmental conditions, bacteria have evolved a diverse set of regulatory pathways that govern various adaptive responses. Recent research has reinforced the notion that bacteria use feedback-based circuitry to generate population heterogeneity in natural situations. Using artificial gene networks, it has been shown that a relatively simple 'wiring' of a bacterial genetic system can generate two or more stable subpopulations within an overall genetically homogeneous population. This review discusses the ubiquity of these processes throughout nature, as well as the presumed molecular mechanisms responsible for the heterogeneity observed in a selection of bacterial species.

Adaptation, Physiological↗

PubMed2005

Stripping Bacillus: ComK auto-stimulation is responsible for the bistable response in competence development.

In Bacillus subtilis competence for genetic transformation develops only in a subpopulation of cells in an isogenic culture. The molecular mechanisms underlying this phenotypic heterogeneity are unknown. In this study, we stepwise simplify the signal transduction cascade leading to competence, yielding a strain devoid of all regulatory inputs for this process that have been identified so far. We demonstrate that auto-stimulation of ComK, the master regulator for competence development, is essential and in itself can be sufficient to generate a bistable expression pattern. We argue that transcriptional regulation determines the threshold of ComK to initiate the auto-stimulatory response, and that the basal level of ComK (in a wild-type strain governed by MecA-mediated proteolytic control) determines the fraction of cells that reach this threshold, and thus develop competence.

Adaptation, Physiological↗

PubMed2005

Tricksy business: transcriptome analysis reveals the involvement of thioredoxin A in redox homeostasis, oxidative stress, sulfur metabolism, and cellular differentiation in Bacillus subtilis.

Thioredoxins are important thiol-reactive proteins. Most knowledge about this class of proteins is derived from proteome studies, and little is known about the global transcriptional response of cells to various thioredoxin levels. In Bacillus subtilis, thioredoxin A is encoded by trxA and is essential for viability. In this study, we report the effects of minimal induction of a strain carrying an IPTG (isopropyl-beta-D-thiogalactopyranoside)-inducible trxA gene (ItrxA) on transcription levels, as determined by DNA macroarrays. The effective depletion of thioredoxin A leads to the induction of genes involved in the oxidative stress response (but not those dependent on PerR), phage-related functions, and sulfur utilization. Also, several stationary-phase processes, such as sporulation and competence, are affected. The majority of these phenotypes are rescued by a higher induction level of ItrxA, leading to an approximately wild-type level of thioredoxin A protein. A comparison with other studies shows that the effects of thioredoxin depletion are distinct from, but show some similarity to, oxidative stress and disulfide stress. Some of the transcriptional effects may be linked to thioredoxin-interacting proteins. Finally, thioredoxin-linked processes appear to be conserved between prokaryotes and eukaryotes.

Bacillus subtilis↗

PubMed2005

The Rok protein of Bacillus subtilis represses genes for cell surface and extracellular functions.

Rok is a repressor of the transcriptional activator ComK and is therefore an important regulator of competence in Bacillus subtilis (T. T. Hoa, P. Tortosa, M. Albano, and D. Dubnau, Mol. Microbiol. 43:15-26, 2002). To address the wider role of Rok in the physiology of B. subtilis, we have used a combination of transcriptional profiling, gel shift experiments, and the analysis of lacZ fusions. We demonstrate that Rok is a repressor of a family of genes that specify membrane-localized and secreted proteins, including a number of genes that encode products with antibiotic activity. We present evidence for the recent introduction of rok into the B. subtilis-Bacillus licheniformis-Bacilllus amyloliquefaciens group by horizontal transmission.

Bacillus subtilis↗

PubMed2004

Genome2D: a visualization tool for the rapid analysis of bacterial transcriptome data.

Genome2D is a Windows-based software tool for visualization of bacterial transcriptome and customized datasets on linear chromosome maps constructed from annotated genome sequences. Genome2D facilitates the analysis of transcriptome data by using different color ranges to depict differences in gene-expression levels on a genome map. Such output format enables visual inspection of the transcriptome data, and will quickly reveal transcriptional units, without prior knowledge of expression level cutoff values. The compiled version of Genome2D is freely available for academic or non-profit use from http://molgen.biol.rug.nl/molgen/research/molgensoftware.php.

Bacterial Proteins↗

PubMed2004

Visualization of differential gene expression by improved cyan fluorescent protein and yellow fluorescent protein production in Bacillus subtilis.

The distinguishable cyan and yellow fluorescent proteins (CFP and YFP) enable the simultaneous in vivo visualization of different promoter activities. Here, we report new cloning vectors for the construction of cfp and yfp fusions in Bacillus subtilis. By extending the N-terminal portions of previously described CFP and YFP variants, 20- to 70-fold-improved fluorescent-protein production was achieved. Probably, the addition of sequences encoding the first eight amino acids of the N-terminal part of ComGA of B. subtilis overcomes the slow translation initiation that is provoked by the eukaryotic codon bias present in the original cfp and yfp genes. Using these new vectors, we demonstrate that, within an isogenic population of sporulating B. subtilis cells, expression of the abrB and spoIIA genes is distinct in individual cells.

Bacillus subtilis↗

PubMed2002

Improving the predictive value of the competence transcription factor (ComK) binding site in Bacillus subtilis using a genomic approach.

Generally, the presence of a consensus sequence in the promoter of a gene is taken as indication for regulation by the transcription factor that binds to this sequence. In light of the recent developments in genome research, we were interested to what extent this supposition is valid. We examined the relationship between the presence of a binding site for ComK, the competence transcription factor of Bacillus subtilis, and actual transcriptional activation by ComK. Bacillus subtilis contains 1062 putative ComK-binding sites (K-boxes) in its genome. We employed DNA macroarrays to identify ComK-activated genes, and found that the presence of a K-box is an unreliable predictor for regulation. Only approximately 8% of the genes containing a K-box in the putative promoter region are regulated by ComK. The predictive value of a K-box could be improved by taking into consideration the degree of deviation from the K-box consensus sequence, the presence of extra ComK-binding motifs and the positions of RNA polymerase-binding sites. Finally, many of the ComK-activated genes show no apparent function related to the competence process. Based on our findings, we propose that the ComK-dependent activation of several genes might serve no biological purpose and can be considered 'evolutionary noise'.

Bacillus subtilis↗