N epsilon-acetyl-beta-lysine: an osmolyte synthesized by methanogenic archaebacteria.

Abstract

Methanosarcina thermophila, a nonmarine methanogenic archaebacterium, can grow in a range of saline concentrations. At less than 0.4 M NaCi, Ms. thermophila accumulated glutamate in response to increasing osmotic stress. At greater than 0.4 M NaCI, this organism synthesized a modified (3-amino acid that was identified as N6-acetyl-.8-lysine by NMR spectroscopy and ion-exchange HPLC.This (-amino acid derivative accumulated to high intracellular concentrations (up to 0.6 M) in Ms. thermophila and in another methanogen examined-Methanogenium cariaci, a marine species. The compound has features that are characteristic of a compatible solute: it is neutrally charged at physiological pH and it is highly soluble. When the cells were grown in the presence of exogenous glycine betaine, a physiological compatible solute, N6-acetyl--lysine synthesis was repressed and glycine betaine was accumulated. N8-Acetyl-(3-lysine was synthesized by species from three phylogenetic families when grown in high solute concentrations, suggesting that it may be ubiquitous among the methanogens. The ability to control the biosynthesis of N'-acetyl-(3-lysine in response to extracellular solute concentration indicates that the methanogenic archaebacteria have a unique (3amino acid biosynthetic pathway that is osmotically regulated.Microorganisms can proliferate in a diverse range of saline concentrations from low saline environments such as freshwater lakes to saturated brines found in solar salterns (1, 2). Cell size and the intracellular water activity must remain relatively constant to maintain physiological processes. Eukaryotic and eubacterial microorganisms have evolved mechanisms that enable them to minimize water loss when the extracellular solute concentration exceeds that of the cell cytoplasm (1-3). The mechanism of this adaptation involves the uptake or synthesis of low molecular weight organic compounds known as physiological compatible solutes (4, 5). These compounds reduce the osmotic potential between the extracellular milieu and the cytoplasm and protect enzymes from the low water activity that results from solute accumulation.Methanogenic archaebacteria have been isolated from environments with NaCl concentrations ranging from <0.05 M for many nonmarine species to >4 M for halophilic species (6). Individual species can also adapt to a range of saline concentrations. Methanosarcina thermophila, which was isolated from a thermophilic sludge digestor, grows in medium containing 0.05-1.2 M NaCl (7-9), and the marine species Methanogenium cariaci (10) grows in medium containing 0.17-1.4 M NaCl (D.N. and M.F.R., unpublished results). Compatible solutes have been detected in methanogenic bacteria (11-13). Several species of marine methanogens synthesize ,-glutamate in response to external NaCl (11, 13). Methanogens have also been reported to accumulate glycine betaine if it is provided in the medium (12). However, the mechanism for adaptation to high osmotic stress has not been investigated. Here we report the structure of ...

A prominent role for glucosylglycerol in the adaptation of Pseudomonas mendocina SKB70 to osmotic stress

“…Furthermore, glycine betaine suppressed the accumulation of all three endogenous osmolytes ( Table 2). This is a common phenomenon that has been observed in several other bacterial species on which betaine also confers enhanced osmotic tolerance (8,9,40,41,42). This ability to modulate the accumulation of endogenous osmolytes indicates a clear bacterial preference for glycine betaine which is highly compatible with metabolic functions at high cytoplasmic concentrations (8,11,35).…”

“…This ability to modulate the accumulation of endogenous osmolytes indicates a clear bacterial preference for glycine betaine which is highly compatible with metabolic functions at high cytoplasmic concentrations (8,11,35). It may also illustrate a preference for transport over de novo biosynthesis which is probably bioenergetically more costly and, thus, less conservative for survival under extreme conditions (42). Although glycine betaine is the preferred osmolyte in strain SKB70, it confers only a modest level of enhanced osmotic tolerance compared with other stressed bacterial species that preferentially accumulate betaine.…”

“…Potassium and glutamate are ubiquitous bacterial osmolytes which are usually accumulated together as mutual counterions. Most other osmolytes are low-molecular-weight organic compounds which share the following features: high solubility in water, a neutral net electric charge at a physiological pH, and a lack of toxicity toward enzymes when assayed in vitro at high but physiologically relevant concentrations (8,11,35,48).Although they are accumulated to significant levels, some osmolytes have escaped detection by usual chemical methods because they lacked a reactive group (39,42) or because of specific deficiencies of the analytical methods employed (37). Natural-abundance 13C nuclear magnetic resonance (NMR) spectroscopy is a nondestructive method enabling the detection of all organic compatible solutes that accumulate to significant levels in bacteria, in plants, or in animal tissues.…”

“…Although they are accumulated to significant levels, some osmolytes have escaped detection by usual chemical methods because they lacked a reactive group (39,42) or because of specific deficiencies of the analytical methods employed (37). Natural-abundance 13C nuclear magnetic resonance (NMR) spectroscopy is a nondestructive method enabling the detection of all organic compatible solutes that accumulate to significant levels in bacteria, in plants, or in animal tissues.…”

Effect of Temperature on Stability and Activity of Elongation Factor 2 Proteins from Antarctic and Thermophilic Methanogens

“…This may indicate that the in vitro assay conditions do not reflect physiological conditions in vivo and that intracellular factors may be important for stabilizing the protein. M. thermophila is known to produce and accumulate small, highly water-soluble molecules called compatible solutes in response to hyperosmotic conditions (29). Compatible solutes have been shown to stabilize proteins against heat stress (14,16,28) and may therefore play a role in thermal stabilization of the M. thermophila EF-2 protein in vivo.…”