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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-K1 in the absence of glycine supplementation. These data indicate that R. prowazekii depends on the host cell for serine or glycine.
Insights
Rickettsia prowazekii requires serine and glycine for growth. These amino acids are supplied by host cells, as demonstrated by experiments with L929 and Vero cell lines, indicating a host-dependent nutritional requirement.
Area of Science:
- Microbiology
- Cell Biology
- Nutritional Biochemistry
Background:
- Rickettsia prowazekii is an obligate intracellular bacterium with complex growth requirements.
- Understanding the nutritional needs of R. prowazekii is crucial for developing effective treatments and control strategies.
- Previous studies have suggested potential amino acid dependencies, but specific requirements remain to be fully elucidated.
Purpose of the Study:
- To investigate the specific growth requirements of Rickettsia prowazekii for the amino acids serine and glycine.
- To compare the ability of different host cell lines (L929 and Vero) to support R. prowazekii growth in the presence or absence of supplemented amino acids.
- To determine if R. prowazekii possesses the enzymatic machinery to synthesize or interconvert serine and glycine.
Main Methods:
- Culturing R. prowazekii in X-irradiated L929 and Vero cells using Eagle minimal essential medium with serum.
- Supplementing the medium with cycloheximide, serine, glycine, other nonessential amino acids, or glucose to assess their impact on rickettsial growth.
- Measuring intracellular amino acid pools in mock-infected and treated host cells.
- Analyzing cell-free extracts of purified rickettsiae for serine hydroxymethyltransferase activity.
- Testing rickettsial growth in a glycine-requiring CHO-K1 cell clone.
Main Results:
- X-irradiated L929 cells supported R. prowazekii growth without supplementation.
- X-irradiated Vero cells required the addition of cycloheximide, serine, or glycine for rickettsial growth.
- Serine and glycine concentrations were significantly lower in Vero cells compared to L929 cells.
- Cycloheximide treatment increased serine and glycine pools in Vero cells.
- R. prowazekii extracts showed serine hydroxymethyltransferase activity, but this did not rescue growth in glycine-deficient CHO-K1 cells.
Conclusions:
- Rickettsia prowazekii exhibits a dependency on host cells for the supply of serine or glycine.
- Vero cells have lower endogenous levels of serine and glycine, making them less suitable for supporting R. prowazekii growth without supplementation.
- While R. prowazekii possesses some enzymatic capacity for amino acid interconversion, it cannot fulfill its serine/glycine requirements independently.
- These findings highlight the critical role of host cell metabolism in sustaining R. prowazekii infections.