Identification of a Salt-Induced Primary Transporter for Glycine Betaine in the Methanogen Methanosarcina mazei Gö1

Abstract

The salt adaptation of the methanogenic archaeon Methanosarcina mazei Gö1 was studied at the physiological and molecular levels. The freshwater organism M. mazei Gö1 was able to adapt to salt concentrations up to 1 M, and the addition of the compatible solute glycine betaine to the growth medium facilitated adaptation to higher salt concentrations. Transport studies with cell suspensions revealed a salt-induced glycine betaine uptake activity in M. mazei Gö1, and inhibitor studies argue for a primary transport device. Analysis of the genome of M. mazei Gö1 identified a homolog of known primary glycine betaine transporters. This gene cluster was designated Ota (osmoprotectant transporter A). Its sequence and gene organization are very similar to those of the glycine betaine transporter OpuA of Bacillus subtilis. Northern blot analysis of otaC revealed a salt-dependent transcription of this gene. Ota is the first identified salt-induced transporter for compatible solutes in Archaea.

Insights into ABC Transport in Archaea

“…These highaffinity transport systems for glycine betaine are activated upon osmotic upshock (Lai et al, 2000;Proctor et al, 1997;Roessler et al, 2002). In Methanosarcina mazei Goe1 it was shown that the expression of the otaA/B/C gene cluster, which encodes a putative ABC transporter, was highly induced upon growth in medium containing high salt concentrations (Roessler et al, 2002).…”

Lysine-2,3-Aminomutase and β-Lysine Acetyltransferase Genes of Methanogenic Archaea Are Salt Induced and Are Essential for the Biosynthesis of N ε -Acetyl-β-Lysine and Growth at High Salinity

“…The blots were hybridized against the ablA or ablB probes or against a probe derived from the coenzyme M reductase gene (mcr). The product of mcr is involved in methanogenesis, and as its expression was shown to be only little affected by the salt concentration (36), it was used as an internal control.…”

“…A prerequisite for molecular studies is the identification of genes involved in the accumulation of compatible solutes. However, this is lagging behind, and the first gene cluster, encoding a primary ABC-type transporter for the compatible solute glycine betaine in methanogens, was described only very recently (36). Methanosarcina species were shown before to accumulate the unique compatible solute N ε -acetyl-␤-lysine at high salinities.…”

Differential Regulation of Ota and Otb, Two Primary Glycine Betaine Transporters in the Methanogenic Archaeon <i>Methanosarcina mazei</i> Gö1

“…Ota was shown biochemically to indeed catalyze glycine betaine transport [Schmidt, Spanheimer, Müller, unpubl.]. Northern blot analysis demonstrated that cellular mRNA levels of OtaC, encoding the binding protein of the ABC-transporter, were increased at 400 m M NaCl in steady state of growth [Roessler et al, 2002]. However, a quantitative and more defined analysis was not performed.…”

“…Only halophilic methanogens such as Methanohalophilus species can synthesize glycine betaine de novo, all others will take it up from the environment Roberts et al, 1992;Robertson et al, 1990]. Transport and inhibitor studies using whole cells suggested the presence of secondary ion-coupled glycine betaine transporters in Methanosarcina thermophila and Methanohalophilus portucalensis [Lai et al, 2000;Proctor et al, 1997] and a primary, ATP-driven transporter in Methanosarcina mazei Gö1 [Roessler et al, 2002]. Despite their importance for osmoprotection, regulation of solute transporter in archaea is only poorly understood.…”