Amino acid biosynthesis and sodium‐dependent transport in Methanococcus voltae, as revealed by ¹³C NMR

Abstract

Of several methanogenic bacteria examined only Methanococcus voltae readily incorporated exogenous amino acids into cell protein. This was easily shown, since growth in the presence of exogenous amino acids resulted in a loss of signal intensities from those carbon atoms normally labelled by [13C]acetate during biosynthesis. From 80% to 95% of the Ser, Lys, Pro or Val incorporated into protein could be supplied directly from the growth medium. In contrast, Asp and Glu, if supplied to the medium, accounted for only a small percentage of the total acidic amino acid used in protein synthesis. Constitutive transport systems took up a wide range of amino acids at rates of 0.1–4.1 nmol min−1 mg−1. The transport systems required Na+, with the possible exception of the basic amino acid lysine, and were inhibited by N‐ethylmaleimide or 3,3′,4′,5‐tetrachlorosalicylanilide. No interconversion of Ile to other amino acids was detected when cells were given [13C]Ile during growth, whereas the expected labelling of the Asp and Glu families of amino acids resulted when [13C]Asp was provided to the culture. Mc. voltae synthesized its amino acids from acetate via routes fully consistent with those found in Methanospirillum hungatei [Ekiel, I., Smith, I. C. P. & Sprott, G. D. (1983) J. Bacteriol. 156, 316–326]. Propionate could substitute for an auxotrophic requirement for Ile, resulting in the synthesis of Ile with the β‐carbon originating from the carboxyl of acetate and the α‐carbon from the carboxyl of propionate. No labelling of Ile from [13C]acetate could occur without the fatty acid. These results provide strong evidence for the carboxylation of propionate to form 2‐oxobutyrate as intermediate in Ile biosynthesis, and show that the metabolic defect in Ile biosynthesis occurs prior to 2‐oxobutyrate synthesis. The presence of constitutive amino acid transport systems and multiple routes for ile biosynthesis make Methanococcus voltae an attractive methanogen for genetic studies.

Mevalonic acid is partially synthesized from amino acids in Halobacterium cutirubrum: a 13C nuclear magnetic resonance study

“…As seen in Fig. 4 ence of large quantities of glutamic acid in the growth medium, which is similar to results observed in another archaebacterium, Methanococcus voltae (6). Threonine can also be labeled if it is omitted from the growth medium.…”

Characterization of Methanobacterium thermoautotrophicum Marburg mutants defective in regulation of L-tryptophan biosynthesis

“…We have not investigated whether or not the tryptophan transport system is sodium dependent. However, its energy requirement as well as its high K m are consistent with characteristics of secondary tryptophan transport systems described for the Archaea Halobacterium halobium (24) and Halobacterium salinarium (23) and of other archaeal secondary amino acid transport systems which have been shown to depend on sodium as a coupling ion (8,17,32). Transport was specific for the L form of tryptophan, and only L-tyrosine and L-arginine weakly competed with L-tryptophan for uptake.…”

Biosynthesis of Phosphoserine in the Methanococcales

“…Isotopic labeling studies using nuclear magnetic resonance showed that serine is produced from pyruvate in the methanogens Methanococcus voltae (8), Methanospirillum hungatei (9), and Methanosphaera stadtmanae (28). These results demonstrated that serine hydroxymethyltransferase is not a significant source of serine for these methanogens, but these experiments could not distinguish between the phosphorylated and nonphosphorylated serine biosynthetic pathways.…”