Helicobacter pylori: a eubacterium lacking the stringent response

Abstract

Accumulation of 16S rRNA and production of guanosine polyphosphates (pppGpp and ppGpp) were studied during amino acid starvation in three wild-type strains of Helicobacter pylori. All strains exhibit a relaxed phenotype with respect to accumulation of 16S rRNA. This constitutes the first example of a wild-type eubacterium showing a relaxed phenotype. The guanosine polyphosphate levels do not rise as a result of amino acid starvation, as expected for relaxed organisms. However, in both growing and starved cells, basal levels of the two polyphosphates appeared to be present, demonstrating that the enzymatic machinery for guanosine polyphosphate production is present in this organism. These findings are discussed within the framework of the hypothesis that stringent control is a physiological control mechanism more important for the fitness of prokaryotes growing in the general environment than for those that inhabit protected niches.

FIG. 1

Protein synthesis and rRNA accumulation in H. pylori NCTC11637. Protein synthesis (panels a) was measured by the incorporation of ³H-labeled amino acids into acid-insoluble material; accumulation of 16S RNA (panels b) was measured by a specific oligonucleotide-rRNA hybridization technique, as described in Materials and Methods. (A) Experiments were performed during either exponential growth (solid circles) or starvation for isoleucine (open circles); PA was added at 5.5 h. (B) Same as for panel A, except that starvation was obtained by the addition of serine hydroxamate at 6.5 h. kcpm, 1,000 cpm.

FIG. 2

Guanosine polyphosphates in H. pylori NCTC11637. (A) (p)ppGpp in growing and amino acid-starved cells. Lane 1, control (S. typhimurium TA997), 10 min after addition of PA; lanes 2 to 5, H. pylori 0, 45 min, 6 h, and 16 h after addition of PA, respectively; lanes 6 and 7, H. pylori control samples 3.5 h and 16 h after time 0, Abbreviations: Or., origin; 5p, pppGpp; 4p, ppGpp. (B) Basic ppGpp levels in H. pylori NCTC11637. The spots corresponding to ppGpp on the polyethyleneimine-cellulose chromatograms from the experiment shown in panel A were counted with a PhosphorImager scan analysis apparatus. The counts were normalized to the corresponding optical densities at 600 nm (OD). Experiments were performed during either exponential growth (solid circles) or starvation for isoleucine (open circles). The computer-generated image shown in panel A was acquired with Adobe Photoshop 4.0 software on a Umax Astra 1200 scanner.