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Sinorhizobium meliloti cells require biotin and either cobalt or methionine for growth
1Research Branch, Agriculture and Agri-Food Canada, Ottawa, Ontario K1A 0C6, Canada. watsonrj@em.agr.ca
Abstract:
Sinorhizobium meliloti is usually cultured in rich media containing yeast extract. It has been suggested that some components of yeast extract are also required for growth in minimal medium. We tested 27 strains of this bacterium and found that none were able to grow in minimal medium when methods to limit carryover of yeast extract were used during inoculation. By fractionation of yeast extract, two required growth factors were identified. Biotin was found to be absolutely required for growth, whereas previously the need for this vitamin was considered to be strain specific. All strains also required supplementation with cobalt or methionine, consistent with the requirement for a vitamin B(12)-dependent homocysteine methyltransferase for methionine biosynthesis.
Insights
Sinorhizobium meliloti requires biotin and either cobalt or methionine for growth in minimal media. These essential nutrients were identified by fractionating yeast extract, clarifying previous strain-specific observations.
Area of Science:
- Microbiology
- Bacterial Physiology
- Nutritional Requirements
Background:
- Sinorhizobium meliloti is typically grown in nutrient-rich media containing yeast extract.
- Previous studies suggested yeast extract components might be essential for growth in minimal media.
Purpose of the Study:
- To identify essential growth factors in yeast extract for Sinorhizobium meliloti.
- To clarify the nutritional requirements of Sinorhizobium meliloti in minimal media.
Main Methods:
- Testing 27 Sinorhizobium meliloti strains for growth in minimal media with controlled yeast extract carryover.
- Fractionation of yeast extract to isolate required growth factors.
- Supplementation experiments with identified factors and related metabolites.
Main Results:
- No tested Sinorhizobium meliloti strains grew in minimal media without specific yeast extract components.
- Biotin was identified as an absolutely essential growth factor for all strains.
- Cobalt or methionine supplementation was required, indicating a need for vitamin B12-dependent homocysteine methyltransferase.
Conclusions:
- Biotin is a universal requirement for Sinorhizobium meliloti growth, contrary to previous strain-specific findings.
- Methionine biosynthesis in Sinorhizobium meliloti relies on a vitamin B12-dependent pathway, necessitating cobalt or methionine supplementation.