Diversity in (p)ppGpp metabolism and effectors.

Bacteria produce guanosine tetraphosphate and pentaphosphate, collectively named (p)ppGpp, in response to a variety of environmental stimuli. These two remarkable molecules regulate many cellular processes, including the central dogma processes and metabolism, to ensure survival and adaptation. Work in Escherichia coli laid the foundation for understanding the molecular details of (p)ppGpp and its cellular functions.

Lowering GTP level increases survival of amino acid starvation but slows growth rate for Bacillus subtilis cells lacking (p)ppGpp.

Bacterial cells sense external nutrient availability to regulate macromolecular synthesis and consequently their growth. In the Gram-positive bacterium Bacillus subtilis, the starvation-inducible nucleotide (p)ppGpp negatively regulates GTP levels, both to resist nutritional stress and to maintain GTP homeostasis during growth. Here, we quantitatively investigated the relationship between GTP level, survival of amino acid starvation, and growth rate when GTP synthesis is uncoupled from its major homeostatic regulator, (p)ppGpp.

GTP dysregulation in Bacillus subtilis cells lacking (p)ppGpp results in phenotypic amino acid auxotrophy and failure to adapt to nutrient downshift and regulate biosynthesis genes.

The nucleotide (p)ppGpp inhibits GTP biosynthesis in the Gram-positive bacterium Bacillus subtilis. Here we examined how this regulation allows cells to grow in the absence of amino acids. We showed that B.

Direct regulation of GTP homeostasis by (p)ppGpp: a critical component of viability and stress resistance.

Cells constantly adjust their metabolism in response to environmental conditions, yet major mechanisms underlying survival remain poorly understood. We discover a posttranscriptional mechanism that integrates starvation response with GTP homeostasis to allow survival, enacted by the nucleotide (p)ppGpp, a key player in bacterial stress response and persistence. We reveal that (p)ppGpp activates global metabolic changes upon starvation, allowing survival by regulating GTP.

Dual RpoH sigma factors and transcriptional plasticity in a symbiotic bacterium.

Sinorhizobium meliloti can live as a soil saprophyte and can engage in a nitrogen-fixing symbiosis with plant roots. To succeed in such diverse environments, the bacteria must continually adjust gene expression. Transcriptional plasticity in eubacteria is often mediated by alternative sigma (σ) factors interacting with core RNA polymerase.

Only one of five groEL genes is required for viability and successful symbiosis in Sinorhizobium meliloti.

Many bacterial species contain multiple copies of the genes that encode the chaperone GroEL and its cochaperone, GroES, including all of the fully sequenced root-nodulating bacteria that interact symbiotically with legumes to generate fixed nitrogen. In particular, in Sinorhizobium meliloti there are four groESL operons and one groEL gene. To uncover functional redundancies of these genes during growth and symbiosis, we attempted to construct strains containing all combinations of groEL mutations.

Multiple groESL operons are not key targets of RpoH1 and RpoH2 in Sinorhizobium meliloti.

Among the rhizobia that establish nitrogen-fixing nodules on the roots of host plants, many contain multiple copies of genes encoding the sigma factor RpoH and the chaperone GroEL/GroES. In Sinorhizobium meliloti there are two rpoH genes, four groESL operons, and one groEL gene. rpoH1 mutants are defective for growth at high temperature and form ineffective nodules, rpoH1 rpoH2 double mutants are unable to form nodules, and groESL1 mutants form ineffective nodules.