Is the in Vitro Growth of Nitrosocaldus yellowstonensis a Thermophilic Archaeon Limited by the Availability of Sulfur in the Growth Medium?
By: Fernando Nungaray
Department: Biology
Faculty Advisor: Dr. José R. De La Torre
As one of the three fundamental groups of cellular life, archaea inhabit a wide range of mesophilic and thermophilic environments. Despite their abundance in various ecological niches, little is known regarding their biology; difficulties cultivating these organisms in a lab setting proves to be a hurdle researchers face. Our lab studies thermophilic ammonia-oxidizing archaea (ThAOA) that live in the sediments of hot springs and play a key role in the carbon and nitrogen cycle. Our model organism Nitrosocaldus yellowstonensis HL72 was cultivated by our laboratory from a hot spring in Yellowstone National Park. However, the growth of N. yellowstonensis in our laboratory cultures only reaches low cellular densities (~10^8 cells per mL). Like all living organisms, N. yellowstonensis requires sources of Carbon, Hydrogen, Oxygen, Nitrogen, Phosphorus, and Sulfur (CHONPS) to grow and build biomass. When we examined the formulation of the standard growth medium for N. yellowstonensis, known as SFCM, we found that sulfur was only present as sulfate at extremely low concentration (0.5 µM). This leads us to ask whether sulfur might be a limiting reagent for growth under these culture conditions. To address this question, we measure the specific growth rate and the total growth yield (in cells/mL) of N. yellowstonensis in regular SFCM and SFCM supplemented with sulfate (1 mM). Our initial results indicate that growth rates may be faster with the addition of extra sulfate: cultures inoculated in SFCM alone take ~2 weeks to reach saturation, whereas cultures with added sulfate reach saturation after 5-6 days. These results appear to indicate that sulfur is indeed a limiting factor for growth in our lab cultures and that our experiments may benefit from increasing the concentration in SFCM.