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The stringent response in Myxococcus xanthus is regulated by SocE and the CsgA C-signaling protein
1Department of Microbiology, University of Georgia, Athens Georgia 30602-2605 USA.
Abstract:
Myxococcus xanthus fruiting body development is induced by amino acid limitation. The decision to grow or develop is established by the RelA-dependent stringent response and A-signaling. We identified two new members of this regulatory hierarchy, socE and the C-signaling gene csgA. SocE depletion arrests growth and induces sporulation under conditions that normally favor growth as well as curtailing DNA and stable RNA synthesis, inhibiting cell elongation, and inducing accumulations of the stringent nucleotides ppGpp and pppGpp [(p)ppGpp]. This system separates C-signaling, which does not occur under these conditions, from CsgA enzyme activity. Amino acid substitutions in the CsgA coenzyme binding pocket or catalytic site eliminate growth arrest. relA mutation also eliminates growth arrest. Eleven pseudorevertants selected for growth following SocE depletion contained mutations in csgA or relA. These results suggest that CsgA induces the stringent response and while SocE inhibits it. Unlike the csgA mutant, wild-type and socE csgA cells maintained high levels of (p)ppGpp throughout development. We suggest that CsgA maintains growth arrest throughout development to divert carbon from A-signaling and other sources into developmental macromolecular synthesis.
Insights
Myxococcus xanthus development involves stringent response regulators. SocE inhibits this response, while CsgA induces it, controlling growth arrest and sporulation.
Area of Science:
- Microbial development
- Bacterial cell cycle regulation
- Molecular genetics
Background:
- Myxococcus xanthus fruiting body development is triggered by nutrient limitation, particularly amino acids.
- The stringent response (mediated by RelA) and A-signaling are key regulators of the grow-or-develop decision.
- Previous understanding identified RelA and A-signaling as central to this regulatory hierarchy.
Purpose of the Study:
- To identify novel components of the Myxococcus xanthus developmental regulatory network.
- To elucidate the roles of socE and csgA in coordinating growth and development.
- To understand the interplay between C-signaling, stringent response, and developmental pathways.
Main Methods:
- Genetic analysis involving gene depletion and mutation studies (socE, csgA, relA).
- Phenotypic characterization of mutant strains under various growth and starvation conditions.
- Measurement of stringent nucleotides (ppGpp and pppGpp) levels during development.
Main Results:
- SocE depletion mimics starvation, inducing sporulation and arresting growth by curtailing nucleic acid synthesis and cell elongation.
- SocE depletion leads to the accumulation of stringent nucleotides (p)ppGpp.
- Mutations in csgA or relA abolish the growth arrest phenotype induced by SocE depletion, with pseudorevertants showing mutations in these genes.
- CsgA appears to induce the stringent response, while SocE inhibits it.
- Wild-type and socE csgA cells maintain high (p)ppGpp levels during development, unlike csgA mutants.
Conclusions:
- CsgA is identified as a key inducer of the stringent response, essential for growth arrest during development.
- SocE acts as an inhibitor of the stringent response, suggesting a regulatory balance between SocE and CsgA.
- The stringent response, maintained by CsgA, is crucial for diverting cellular resources towards macromolecular synthesis required for development.