Reducing ppGpp Level Rescues an Extreme Growth Defect Caused by Mutant EF-Tu
2014 (English)In: PLoS ONE, ISSN 1932-6203, Vol. 9, no 2, e90486- p.Article in journal (Other academic) Published
Salmonella enterica grows extremely slowly when it depends on tufA499 (encoding the Gln125Arg mutant form of EF-Tu) to drive protein synthesis. We screened a plasmid library for multi-copy suppressors of the slow growth phenotype and identified spoT as a candidate. The spoT gene encodes a dual function enzyme with both ppGpp synthetase and hydrolase activities. When spoT was cloned behind an arabinose-inducible promoter the growth rate of the mutant strain increased in response to arabinose addition. We found that the slow-growing mutant strain had a relatively high basal level of ppGpp during exponential growth in rich medium. Overexpression of spoT significantly reduced this level of ppGpp suggesting that inappropriately high ppGpp levels might cause the slow growth rate associated with tufA499. We tested this hypothesis by inactivating relA (codes for RelA, a ribosome-associated ppGpp synthetase) in the mutant strain. This inactivation decreased the level of ppGpp in the mutant strain and increased its growth rate. Based on these data we propose that ribosomes depending on tufA499 for their supply of ternary complex (EF-Tu•GTP•aa-tRNA) experience amino acid starvation and that RelA on these starving ribosomes produces an excess of the alarmone ppGpp. This results in a suboptimal partitioning of transcription activity between genes important for fast growth in rich medium and genes important for growth in a poor medium. Accordingly, mutant bacteria growing in a rich medium act physiologically as though they were growing in a nutrient-poor environment. We propose that this generates a vicious circle and contributes to the extreme slow-growth phenotype associated with mutant EF-Tu. Reducing the level of ppGpp increases the growth rate of the mutant because it breaks this circle and reduces the wasteful misdirection of resources in the cell.
Place, publisher, year, edition, pages
2014. Vol. 9, no 2, e90486- p.
tufA; ppGpp; RelA; Salmonella enterica; growth regulation
Research subject Microbiology; Molecular Cellbiology
IdentifiersURN: urn:nbn:se:uu:diva-159663DOI: 10.1371/journal.pone.0090486ISI: 000332396200210OAI: oai:DiVA.org:uu-159663DiVA: diva2:446168
Jessica M. Bergman and Disa L. Hammarlöf contributed equally to this work.2011-10-062011-10-052015-02-03Bibliographically approved