Rickettsia prowazekii requires host cell serine and glycine for growth

Abstract

The growth requirement of Rickettsia prowazekii for the amino acids serine and glycine was assessed in both wild-type cell lines and a mutant cell line. X-irradiated L929 cells supported the growth of R. prowazekii when the cells were incubated in Eagle minimal essential medium supplemented with serum. In contrast, in this medium, X-irradiated Vero cells did not support the growth of rickettsiae unless cycloheximide, serine, or glycine was added. Other nonessential amino acids, additional glucose, and potential products of host cell metabolism of serine and glycine were nonstimulatory. The concentration of serine or glycine required to support rickettsial growth had no effect on the doubling time of uninfected, unirradiated Vero cells. A comparison of intracellular amino acid pools indicated that the serine and glycine concentrations in mock-infected Vero cells were approximately 31 and 14% of the respective concentrations in mock-infected L929 cells. The pools of both amino acids in Vero cells increased markedly upon treatment of the cells with cycloheximide. Interconversion of serine and glycine catalyzed by serine hydroxymethyltransferase was detected in cell-free extracts of purified rickettsiae. However, this enzymatic activity did not permit rickettsial growth in a glycine-requiring clone (772-56d) of the Chinese hamster ovary cell CHO-Kl in the absence of glycine supplementation. These data indicate that R. prowazekii depends on the host cell for serine or glycine.

Some lessons fromRickettsiagenomics

“…The homoserine dehydrogenase ( hom , thrA , EC 1.1.1.3), which catalyses l ‐homoserine synthesis and thus open the glycine, serine and threonine metabolism route is lacking (MAP00260). This corroborates experimental data showing that R. prowazekii growth depends on the host cell for serine or glycine [40]. In the same paper, the use of a host cell mutant provided in vivo evidence of a rickettsial enzymatic activity responsible for interconversion of both amino acids.…”

Identification of two previously unrecognized genes (guaA and argC) important for uropathogenesis

“…In fact, during the vital step of microbial proliferation in vivo, if certain nutrients are unavailable or withheld within the host, then the capacity of a pathogen to synthesize or acquire these nutrients becomes crucial. Although factors utilized to acquire iron are well accepted as being important for pathogenesis (Litwin and Calderwood, 1993), the importance of acquiring or synthesizing other nutritional factors is less appreciated but supported by a variety of both old (Bacon et al, 1950;Garber et al, 1952;Furness and Rowley, 1956;Levine and Maurer, 1958;Ivanovics et al, 1968;Hatch, 1975;Baselski et al, 1978) and more recent reports (Hosieth and Stocker, 1981;Straley and Harmon, 1984;Austin et al, 1987;Nnalue and Stocker, 1987;O'Callaghan et al, 1988;Bowe et al, 1989;Leung and Finlay, 1991;Mahan et al, 1993;Marquis et al, 1993;McAdam et al, 1995;Ullman and Carter, 1995). Furthermore, the frequent identification of biosynthetic genes as virulence traits in studies that have screened libraries of random gene fusions or randomly generated transposon mutants emphasizes the importance of metabolic genes in microbial pathogenesis (Fields et al, 1986;Leung and Finlay, 1991;Mahan et al, 1993).…”

“…Although nucleotide and amino acid auxotrophy has been shown to attenuate many pathogens, the majority of reports are on intracellular pathogens such as salmonella, listeria, mycobacteria, yersinia, chlamydia and rickettsia (Bacon et al, 1950;Furness and Rowley, 1956; # 1996 Blackwell Science Ltd, Molecular Microbiology, 22, 217-229 Hatch, 1975;Hosieth and Stocker, 1981;Straley and Harmon, 1984;Austin et al, 1987;Nnalue and Stocker, 1987;O'Callaghan et al, 1988;Bowe et al, 1989;Leung and Finlay, 1991;Mahan et al, 1993;Marquis et al, 1993;McAdam et al, 1995;Ullman and Carter, 1995). We are unaware of any such reports involving extraintestinal isolates of E. coli.…”

Intracytoplasmic growth and virulence of Listeria monocytogenes auxotrophic mutants

“…Availability of nutrients may not be the only factor regulating intracellular bacterial growth as the intracellular concentration of specific amino acids and the bacterial capacity to compete with host cells may be limiting factors. The growth of Rickettsia prowazekii depends on the intracellular concentration of serine, glycine, and proline, which varies among cell lines (2,3). A latent chlamydial infection becomes activated when host cell protein synthesis is inhibited, increasing the availability of amino acids arising from host protein turnover (12).…”