The concentrations of stable RNA and ribosomes in Rickettsia prowazekii

Abstract

The obligate intracellular parasite, Rickettsia prowazekii, is a slow-growing bacterium with a doubling time of about 10 h. In the present study, DNA and RNA were obtained from the rickettsiae by two independent methods, i.e. simultaneous isolation of DNA and RNA from the same sample by phenol:chloroform extraction and CsCI gradient centrifugation. In addition, ribosomal RNA was obtained by sedimentation of partially purified ribosomes from the rickettsiae. The results demonstrated that, after correction for the cell volumes, the concentrations of stable RNA and ribosomes in R. prowazekii, a slow-growing organism, were about 62 fg micron-3 and 17,000 per micron3, respectively, which were very similar (66 fg micron-3 and 21,000 per micron3) to those in Escherichia coli with a generation time of 40 min. However, on a per cell basis, R. prowazekii had 5.6 fg of RNA and 1500 ribosomes per cell, which was only about 8% of the amount of both stable RNA (71.2 fg) and ribosomes (24,000) per cell as was found in E. coli. These results indicated that R. prowazekii possesses a ribosome concentration greater than might have been predicted from its slow growth rate. This high concentration of ribosomes could be due to a large population of nonfunctioning ribosomes, a low efficiency of amino acid production, or a high rate of protein turnover. However, this study also demonstrated that the rickettsiae have very limited protein turnover. Knowledge of the kinetics and control mechanisms for protein synthesis in R. prowazekii remains to be established to determine the logic of the extra rickettsial ribosomes.

Transcriptional analysis of the 16s rRNA gene in Rickettsia prowazekii

“…In E. coli, redundant rrn operons, two strong promoters per operon, and transcriptional regulatory sequences on each rrn are believed to ensure that the production of rRNA is adequate for the bacteria to adapt to rapid growth rates (9)(10)(11). We demonstrated previously that in the genome of R. prowazekii, a slowly growing intracellular organism, there is only one 16S rRNA gene (16); however, surprisingly, the concentration of rRNA is very similar to that in more rapidly growing E. coli cells (17). Within the region upstream of the rickettsial rrs, a promoter region responsible for the rrs expression was identified by RNase protection assays, in vitro transcription assays, and primer extension assays.…”

Physiological responses of Pseudomonas putida KT2442 to phosphate starvation

“…strain S14 ribosomes exist in large excess over the demand for protein synthesis during carbon starvation (Flardh e t al., 1992) and similar observations were reported for P. pzttida KT2442 (Givskov e t al., 1994a). The presence of excess ribosomes has also been reported for the obligate intracellular parasite Rickettsiaprowa&2i which grows with a generation time of about 10 h in the cytoplasm of eukaryotic host cells (Pang & Winkler, 1994).…”

Evaluating rRNA as an indicator of microbial activity in environmental communities: limitations and uses

“…rRNA concentration may correlate well with growth rate in some strains of bacteria, but correlations can differ significantly between strains (Wade and Robinson, 1965;Kemp et al, 1993;Pang and Winkler, 1994;Binnerup et al, 2001;Worden and Binder, 2003). Even at the 'species' level of bacteria, the relationship between rRNA and growth rate can differ significantly between subpopulations (Rosset et al, 1966;Licht et al, 1999).…”

“…2. The relationship between rRNA concentration and growth rate can differ significantly among taxa; therefore, relative rRNA abundance will likely not provide robust information regarding which taxa are relatively more active in a community (Mandelstam and Halvorson, 1960;Wade and Robinson, 1965;Rosset et al, 1966;Kemp et al, 1993;Pang and Winkler, 1994;Oda et al, 2000;Binnerup et al, 2001;Worden and Binder, 2003). 3.…”