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Keywords:

  • Stringent response;
  • rrn expression;
  • Corynebacterium

Abstract

The stringent response in Corynebacterium glutamicum was investigated. Sets of rrncat fusions were constructed in their native chromosomal position to examine the effects of amino acid starvation in a rel+ strain and a Δrel mutant defective in (p)ppGpp metabolism. The expression of the six rrn operons in the rel+ control was stringently regulated and reduced to 79% upon induction of amino acid starvation. The Δrel mutant displayed a relaxed regulation and was unable to reduce the rrn expression under amino acid depletion conditions. In addition, the Δrel mutant grew more slowly in minimal medium than a rel+ control. This growth effect was restored by a plasmid-encoded copy of rel or, alternatively, by supplementation of the minimal medium with the amino acid mixture casamino acids. In particular, the Δrel strain of C. glutamicum displayed a requirement for the amino acids histidine and serine.