NMR studies of osmoregulation in methanogenic archaebacteria. [NMR (nuclear magnetic resonance)]

Miscellaneous · Tue Jan 01 00:00:00 EST 1991

OSTI ID:7112895

Robertson, D E

Methanogens are strict anaerobic archaebacteria whose metabolism centers around the reduction of CO[sub 2] to CH[sub 4]. Their environments are often extreme (high temperatures, high salt, few nutrients, etc.) and they may have evolved unique ways to handle these stresses. It is proposed that methanogenic archaebacteria respond to osmotic stress by accumulating a series of organic solutes. In two strains of marine methanogens, Methanogenium cariaci and Methanococcus thermolithotrophicus, four key organic solutes are observed: L-[alpha]-glutamate, [beta]-glutamate, N[sup e]-acetyl-[beta]-lysine, and glycine betaine. The first three of these are synthesized de novo; glycine betaine is transported into the Mg. cariaci cells from the medium. In the absence of betaine, Mg. cariaci synthesizes N[sup e]-acetyl-[beta]-lysine as the dominant osmolyte. Mc. thermolithotrophicus also synthesizes N[sup e]-acetyl-[beta]-lysine but only at salt concentrations greater than 1 M. In Mc. thermolithotrophicus intracellular potassium ion concentrations, determined by [sup 39]K NMR spectroscopy, are balanced by the total concentration of anionic amino acid species, [alpha]-glutamate and [beta]-glutamate. Turnover of the organic solutes has been monitored using [sup 13]C-pulse/[sup 12]C-chase, and [sup 15]N-pulse/[sup 14]N-chase experiments. The [beta]-amino acids exhibit slower turnover rates compared to L-[alpha]-glutamate or aspartate, consistent with their role as compatible solutes. Biosynthetic information for the [beta]-amino acids was provided by [sup 13]C-label incorporation and steady state labeling experiments. [beta]-glutamate shows a lag in [sup 13]C uptake from [sup 13]CO[sub 2], indicative of its biosynthesis from a precursor not in equilibrium with the soluble L-[alpha]-glutamate pool, probably a macromolecule. A novel biosynthetic pathway is proposed for N[sup e]-acetyl-[beta]-lysine from the diaminopimelate pathway.

• Research Organization: Boston Coll., Chestnut Hill, MA (United States)
• OSTI ID: 7112895
• Resource Relation: Other Information: Thesis (Ph.D.)
• Country of Publication: United States
• Language: English

Related Subjects

59 BASIC BIOLOGICAL SCIENCES
BETAINE
OSMOSIS
GLUTAMIC ACID
LYSINE
METHANOGENIC BACTERIA
NUCLEAR MAGNETIC RESONANCE
BIOCHEMISTRY
GLYCINE
MEMBRANE TRANSPORT
AMINES
AMINO ACIDS
AMMONIUM COMPOUNDS
BACTERIA
CARBOXYLIC ACIDS
CHEMISTRY
DIFFUSION
DRUGS
LIPOTROPIC FACTORS
MAGNETIC RESONANCE
MICROORGANISMS
ORGANIC ACIDS
ORGANIC COMPOUNDS
QUATERNARY COMPOUNDS
RESONANCE
550700* - Microbiology
550500 - Metabolism