New approach for the detection of non-ribosomal peptide synthetase genes in Bacillus strains by polymerase chain reaction.

Bacillus strains produce non-ribosomal lipopeptides that can be grouped into three families: surfactins or lichenysins, iturins and fengycins or plispastatins. These biosurfactants show a broad spectrum of biological activities. To detect strains able to produce these lipopeptides, a new polymerase chain reaction screening approach was developed using degenerated primers based on the intraoperon alignment of adenylation and thiolation nucleic acid domains of all enzymes implicated in the biosynthesis of each lipopeptide family. The comparative bioinformatics analyses of each operon led to the design of four primer pairs for the three families taking into account the differences between open reading frames of each synthetase gene. Tested on different Bacillus sp. strains, this technique was used successfully to detect not only the expected genes in the lipopeptide producing strains but also the presence of a plispastatin gene in Bacillus subtilis ATCC 21332 and a gene showing a high similarity with the polyketide synthase type I gene in the B. subtilis ATCC 6633 genome. It also led to the discovery of the presence of non-ribosomal peptide synthetase genes in Bacillus thuringiensis serovar berliner 1915 and in Bacillus cereus LMG 2098. In addition, this work highlighted the differences between the fengycin and plipastatin operon at DNA level.

Identification of direct and indirect targets of the Gln3 and Gat1 activators by transcriptional profiling in response to nitrogen availability in the short and long term.

Nitrogen catabolite repression (NCR) consists in the specific inhibition of transcriptional activation of genes encoding the permeases and catabolic enzymes needed to degrade poor nitrogen sources. Under nitrogen limitation or rapamycin treatment, NCR genes are activated by Gln3 or Gat1, or by both factors. To compare the sets of genes responding to rapamycin or to nitrogen limitation, we used DNA microarrays to establishing the expression profiles of a wild type strain, and of a double gln3Delta-gat1Delta strain, grown on glutamine, after addition of rapamycin, on proline, or after a shift from glutamine to proline. Analysis of microarray data revealed 392 genes whose expression was dependent on the nitrogen source quality. 91 genes were activated in a GATA factor-dependent manner in all growth conditions, suggesting a direct role of Gln3 and Gat1 in their expression. Other genes were only transiently up-regulated (stress-responsive genes) or down-regulated (genes encoding ribosomal proteins and translational factors) upon nitrogen limitation, and this regulation was delayed in a gln3Delta-gat1Delta strain. Repression of amino acid and nucleotide biosynthetic genes after a nitrogen shift did not depend on Gcn4. Several transporter genes were repressed as a consequence of enhanced levels of NCR-responsive permeases present at the plasma membrane.

The uses of genome-wide yeast mutant collections.

We assess five years of usage of the major genome-wide collections of mutants from Saccharomyces cerevisiae: single deletion mutants, double mutants conferring 'synthetic' lethality and the 'TRIPLES' collection of mutants obtained by random transposon insertion. Over 100 experimental conditions have been tested and more than 5,000 novel phenotypic traits have been assigned to yeast genes using these collections.

Arg82p is a bifunctional protein whose inositol polyphosphate kinase activity is essential for nitrogen and PHO gene expression but not for Mcm1p chaperoning in yeast.

In Saccharomyces cerevisiae, the synthesis of inositol pyrophosphates is essential for vacuole biogenesis and the cell's response to certain environmental stresses. The kinase activity of Arg82p and Kcs1p is required for the production of soluble inositol phosphates. To define physiologically relevant targets of the catalytic products of Arg82p and Kcs1p, we used DNA microarray technology. In arg82delta or kcs1delta cells, we observed a derepressed expression of genes regulated by phosphate (PHO) on high phosphate medium and a strong decrease in the expression of genes regulated by the quality of nitrogen source (NCR). Arg82p and Kcs1p are required for activation of NCR-regulated genes in response to nitrogen availability, mainly through Nil1p, and for repression of PHO genes by phosphate. Only the catalytic activity of both kinases was required for PHO gene repression by phosphate and for NCR gene activation in response to nitrogen availability, indicating a role for inositol pyrophosphates in these controls. Arg82p also controls expression of arginine-responsive genes by interacting with Arg80p and Mcm1p, and expression of Mcm1-dependent genes by interacting with Mcm1p. We show here that Mcm1p and Arg80p chaperoning by Arg82p does not involve the inositol polyphosphate kinase activity of Arg82p, but requires its polyaspartate domain. Our results indicate that Arg82p is a bifunctional protein whose inositol kinase activity plays a role in multiple signalling cascades, and whose acidic domain protects two MADS-box proteins against degradation.

Functional profiling of the Saccharomyces cerevisiae genome.

Determining the effect of gene deletion is a fundamental approach to understanding gene function. Conventional genetic screens exhibit biases, and genes contributing to a phenotype are often missed. We systematically constructed a nearly complete collection of gene-deletion mutants (96% of annotated open reading frames, or ORFs) of the yeast Saccharomyces cerevisiae. DNA sequences dubbed 'molecular bar codes' uniquely identify each strain, enabling their growth to be analysed in parallel and the fitness contribution of each gene to be quantitatively assessed by hybridization to high-density oligonucleotide arrays. We show that previously known and new genes are necessary for optimal growth under six well-studied conditions: high salt, sorbitol, galactose, pH 8, minimal medium and nystatin treatment. Less than 7% of genes that exhibit a significant increase in messenger RNA expression are also required for optimal growth in four of the tested conditions. Our results validate the yeast gene-deletion collection as a valuable resource for functional genomics.

In Saccharomyces cerevisiae, the inositol polyphosphate kinase activity of Kcs1p is required for resistance to salt stress, cell wall integrity, and vacuolar morphogenesis.

A problem for inositol signaling is to understand the significance of the kinases that convert inositol hexakisphosphate to diphosphoinositol polyphosphates. This kinase activity is catalyzed by Kcs1p in the yeast Saccharomyces cerevisiae. A kcs1Delta yeast strain that was transformed with a specifically "kinase-dead" kcs1p mutant did not synthesize diphosphoinositol polyphosphates, and the cells contained a fragmented vacuolar compartment. Biogenesis of the yeast vacuole also required another functional domain in Kcs1p, which contains two leucine heptad repeats. The kinase activity of Kcs1p was also found to sustain cell growth and integrity of the cell wall and to promote adaptive responses to salt stress. Thus, the synthesis of diphosphoinositol polyphosphates has wide ranging physiological significance. Furthermore, we showed that these phenotypic responses to Kcs1p deletion also arise when synthesis of precursor material for the diphosphoinositol polyphosphates is blocked in arg82Delta cells. This metabolic block was partially bypassed, and the phenotype was partially rescued, when Kcs1p was overexpressed in the arg82Delta cells. This was due, in part, to the ability of Kcs1p to phosphorylate a wider range of substrates than previously appreciated. Our results show that diphosphoinositol polyphosphate synthase activity is essential for biogenesis of the yeast vacuole and the cell's responses to certain environmental stresses.