The Impact of Pyroglutamate:Sulfolobus acidocaldariusHas a Growth Advantage overSaccharolobus solfataricusin Glutamate-Containing Media

Abstract

Microorganisms are well adapted to their habitat but are partially sensitive to toxic metabolites or abiotic compounds secreted by other organisms or chemically formed under the respective environmental conditions. Thermoacidophiles are challenged by pyroglutamate, a lactam that is spontaneously formed by cyclization of glutamate under aerobic thermoacidophilic conditions. It is known that growth of the thermoacidophilic crenarchaeon Saccharolobus solfataricus (formerly Sulfolobus solfataricus) is completely inhibited by pyroglutamate. In the present study, we investigated the effect of pyroglutamate on the growth of S. solfataricus and the closely related crenarchaeon Sulfolobus acidocaldarius. In contrast to S. solfataricus, S. acidocaldarius was successfully cultivated with pyroglutamate as a sole carbon source. Bioinformatical analyses showed that both members of the Sulfolobaceae have at least one candidate for a 5-oxoprolinase, which catalyses the ATP-dependent conversion of pyroglutamate to glutamate. In S. solfataricus, we observed the intracellular accumulation of pyroglutamate and crude cell extract assays showed a less effective degradation of pyroglutamate. Apparently, S. acidocaldarius seems to be less versatile regarding carbohydrates and prefers peptidolytic growth compared to S. solfataricus. Concludingly, S. acidocaldarius exhibits a more efficient utilization of pyroglutamate and is not inhibited by this compound, making it a better candidate for applications with glutamate-containing media at high temperatures.

The biology of thermoacidophilic archaea from the order Sulfolobales

“…solfataricus pyroglutamate may form from glutamate at high temperature and low pH to inhibit growth of thermophilic archaea (Stark et al 2017). However, in S. acidocaldarius, pyroglutamate is not inhibitory and even serves as a carbon source, making S. acidocaldarius a better thermoacidophilic platform organism for applications with glutamate-containing media (Vetter et al 2019). Finally, it has not been determined whether the carboxylic acids formed during exponential growth can be re-used by Sulfolobus species, as it has been shown for other aerobic organisms.…”

Exposure to 1-Butanol Exemplifies the Response of the Thermoacidophilic Archaeon Sulfolobus acidocaldarius to Solvent Stress

“…Concerning central metabolism, the 5-oxoprolinase, involved in the degradation of pyroglutamate, was one of the most upregulated genes in response to 1-butanol exposure (Table S1) ( 47 ). In addition, the gene cluster including saci_2293 (2-keto-4-pentenoate hydratase/2-oxohepta-3-ene-1,7-dioic acid hydratase), saci_2294 (aromatic ring hydroxylase), and saci_2295 (catechol 2,3-dioxygenase or other lactoylglutathione lyase family enzyme) was also significantly upregulated in both lifestyles upon 1-butanol exposure.…”

“…Pyroglutamate is formed spontaneously under thermoacidophilic conditions by cyclization of glutamate. It can be used as the sole carbon source by S. acidocaldarius with 5-oxoprolinase as the key enzyme that catalyzes the ATP-dependent formation of glutamate ( 47 ). The upregulation of genes encoding proteins involved in the catechol pathway ( saci_2293 to saci_2295 ) indicates the degradation of aromatic amino acids ( 48 ).…”

Physiological Characterization of Sulfolobus acidocaldarius in a Controlled Bioreactor Environment

“…While there is broad consensus on the optimal growth temperature of S. acidocaldarius being at 75 °C [ 7 , 8 , 9 , 10 , 33 ] the described optimal cultivation pH still varies [ 5 , 6 , 7 , 8 , 9 , 10 ]. Our study determined a pH optimum of 3.0 in regards to the cell density during continuous cultivation ( Figure 2 ), contradicting the recent publication by Cobban et al [ 11 ], in which higher biomass yields were observed at pH 2.0 and 4.0 compared to pH 3.0.…”