Lack of production of (p)ppGpp in Halobacterium volcanii under conditions that are effective in the eubacteria

Abstract

The stringent halobacterial strain Haloferax volcanii was subjected to a set of physiological conditions different from amino acid starvation that are known to cause production of guanosine polyphosphates [(p)pp Gpp] in eubacteria via the relA-independent (spoT) pathway. The conditions used were temperature upshift, treatment with cyanide, and total starvation. Under none of these conditions were detectable levels of (p)ppGpp observed. This result, in conjunction with our previous finding that (p)ppGpp synthesis does not occur under amino acid starvation, leads to the conclusion that in halobacteria both growth rate control and stringency are probably governed by mechanisms that operate in the absence of ppGpp. During exponential growth, a low level of phosphorylated compounds with electrophoretic mobilities similar, but not identical, to that of (p)ppGpp were observed. The intracellular concentration of these compounds increased considerably during the stationary phase of growth and with all of the treatments used. The compounds were identified as short-chain polyphosphates identical to those found under similar conditions in Saccharomyces cerevisiae.In 1969, Cashel and Gallant reported that wild-type Escherichia coli is capable of producing two unusual compounds originally named magic spots I and II and later identified as guanosine tetra-and pentaphosphates, respectively [collectively referred to as (p)ppGpp] (3). These guanosine nucleotides are generated in a relA-dependent manner by the relA gene product, (p)ppGpp synthetase I, and in a relA-independent manner by the spoT gene product, the SpoT enzyme, which is also implicated in (p)ppGpp degradation. Kinetic studies have shown that pppGpp is formed from GTP, that ppGpp is derived from pppGpp, and that pppGpp inhibits its own synthesis (12).In eubacteria, the rate of stable RNA synthesis at different growth rates is subject to a control mechanism that is distinct from that of other cellular molecules (growth rate control of RNA synthesis). An inverse correlation between the ppGpp concentration, produced in this case by the relA-independent pathway, and the rate of stable RNA synthesis was observed at a wide range of different growth rates (5), which suggested that ppGpp could act as an effector molecule negatively regulating stable RNA synthesis in growth rate control. The isolation by Xiao et al. (21) of relA spoT mutants unable to produce ppGpp permitted Gaal and Gourse (8) to show that ppGpp either is not the mediator or does not act alone, since growth rate control is normal in the double mutants. Hernandez and Bremer have recently shown that in wild-type E. coli, three factors increase with the growth rate: RNA polymerase concentration, RNA polymerase activity, and the distribution of active RNA polymerase between stable and mRNA genes. In an E. coli⌬relA⌬spoT mutant that does not produce ppGpp, RNA polymerase synthesis and activity increase with the growth rate but the distribution of active RNA polymerase between stable and mRNA genes does not. This...

Characterization of the stringent and relaxed responses of Streptococcus equisimilis

“…It remains uncertain whether the compound contains carbon atoms such as phosphorylated sugars. Instead, it could contain short-chain polyphosphates, which have been shown to accumulate in, for example, Halobacterium volcanii when entering the stationary phase (37). Similar phosphate compounds have been characterized in Saccharomyces cerevisiae (25,38) and are apparently ubiquitous in nature (23).…”

An HflX-Type GTPase from Sulfolobus solfataricus Binds to the 50S Ribosomal Subunit in All Nucleotide-Bound States

“…This coupling allows bacterial cells to quickly redirect the cellular metabolism during the stringent response. The stringent response in archaea apparently differs from that in bacteria, as in Sulfolobus it is not linked to decreasing GTP concentrations (7), and the bacterial alarmone ppGpp is probably generally absent in archaea (7,32). An important question is how archaea link ribosome biogenesis with the energy state of the cell.…”

Occurrence of the regulatory nucleotides ppGpp and pppGpp following induction of the stringent response in staphylococci

“…A stringent response mediated by (p)ppGpp has been detected in some gram-positive and gram-negative bacteria and higher organisms after amino acid starvation or induction by a variety of antibiotics (7,18,26). However, in halobacteria (25) and streptococci (21), stringency is not necessarily coupled with (p)ppGpp production. Thus, in Streptococcus pyogenes and Streptococcus rattus, chloramphenicol reverses the inhibition of RNA synthesis caused by mupirocin, but there is no generation of ppGpp in the presence of mupirocin alone.…”