Switching osmolyte strategies: response of Methanococcus thermolithotrophicus to changes in external NaCl

• Published in: Biochimica et biophysica acta Vol. 1524; no. 1; pp. 1 - 10
• Main Authors: Martin, Deana D, Ciulla, Rose A, Robinson, Patrice M, Roberts, Mary F
• Format: Journal Article
• Language: English
• Published: Netherlands Elsevier B.V 15.11.2001
• Subjects: Chromatography, High Pressure Liquid; Glutamates - metabolism; High-performance liquid chromatography; Intramolecular Transferases - metabolism; Lysine - analogs & derivatives; Lysine - metabolism; Magnetic Resonance Spectroscopy; Methanococcus - chemistry; Methanococcus - growth & development; Methanogen; Nuclear magnetic resonance spectroscopy; Osmolar Concentration; Osmolyte; Osmoregulation; Osmotic Pressure; Potassium - analysis; Potassium ion; Sodium Chloride - chemistry; Sodium Chloride - pharmacology; Time Factors; β-Amino acid; Methanogen; Potassium ion; Osmoregulation; Nuclear magnetic resonance spectroscopy; Osmolyte; High-performance liquid chromatography; β-Amino acid
• ISSN: 0304-4165; 0006-3002; 1872-8006
• DOI: 10.1016/S0304-4165(00)00131-8

Methanococcus thermolithotrophicus, a thermophilic methanogenic archaeon, produces and accumulates β-glutamate and l-α-glutamate as osmolytes when grown in media with <1 M NaCl. When the organism is adapted to grow in >1 M NaCl, a new zwitterionic solute, N ϵ-acetyl-β-lysine, is synthesized and becomes the dominant osmolyte. Several techniques, including in vivo and in vitro NMR spectroscopy, HPLC analyses of ethanol extracts, and potassium atomic absorption, have been used to monitor the immediate response of M. thermolithotrophicus to osmotic stress. There is a temporal hierarchy in the response of intracellular osmolytes. Changes in intracellular K + occur within the first few minutes of altering the external NaCl. Upon hypoosmotic shock, K + is released from the cell; relatively small changes occur in the organic osmolyte pool on a longer time scale. Upon hyperosmotic shock, M. thermolithotrophicus immediately internalizes K +, far more than would be needed stoichiometrically to balance the new salt concentration. This is followed by a decrease to a new K + concentration (over 10–15 min), at which point synthesis and accumulation of primarily l-α-glutamate occur. Once growth of the M. thermolithotrophicus culture begins, typically 30–100 min after the hyperosmotic shock, the intracellular levels of organic anions decrease and the zwitterion ( N ϵ-acetyl-β-lysine) begins to represent a larger fraction of the intracellular pool. The observation that N ϵ-acetyl-β-lysine accumulation occurs in osmoadapted cells but not immediately after osmotic shock is consistent with the hypothesis that lysine 2,3-aminomutase, an enzyme involved in N ϵ-acetyl-β-lysine synthesis, is either not present at high levels or has low activity in cells grown and adapted to lower NaCl. That lysine aminomutase specific activity is 8-fold lower in protein extracts from cells adapted to low NaCl compared to those adapted to 1.4 M NaCl supports this hypothesis.