Glycine betaine as a direct substrate for methanogens (Methanococcoides spp.)

Abstract

Nine marine methanogenic Methanococcoides strains, including the type strains of Methanococcoides methylutens, M. burtonii, and M. alaskense, were tested for the utilization of N-methylated glycines. Three strains (NM1, PM2, and MKM1) used glycine betaine (N,N,N-trimethylglycine) as a substrate for methanogenesis, partially demethylating it to N,N-dimethylglycine, whereas none of the strains used N,N-dimethylglycine or sarcosine (N-methylglycine). Growth rates and growth yields per mole of substrate with glycine betaine (3.96 g [dry weight] per mol) were similar to those with trimethylamine (4.11 g [dry weight] per mol). However, as glycine betaine is only partially demethylated, the yield per methyl group was significantly higher than with trimethylamine. If glycine betaine and trimethylamine are provided together, trimethylamine is demethylated to dimethyl- and methylamine with limited glycine betaine utilization. After trimethylamine is depleted, dimethylamine and glycine betaine are consumed rapidly, before methylamine. Glycine betaine extends the range of substrates that can be directly utilized by some methanogens, allowing them to gain energy from the substrate without the need for syntrophic partners.

FIG 1

Metabolism of glycine betaine by Methanococcoides sp. NM1. All values are the averages of three replicates, with the error bars indicating 1 standard deviation. □, methane; ●, glycine betaine; ○, N,N-dimethylglycine; d, days.

FIG 2

Successive metabolism of trimethylamine, its intermediates, and glycine betaine by Methanococcoides sp. NM1. Both substrates were present in the medium from day 0. Note the different scale in the bottom graph showing the concentrations of intermediates of trimethylamine consumption. Only the first 10 days of the experiment are shown. The cultures were monitored for another 3 weeks but did not show any significant concentration changes. All values are the averages of three replicates, with the error bars indicating 1 standard deviation. □, methane; ●, glycine betaine; ○, N,N-dimethylglycine; , trimethylamine; ▼, ammonium; ◆ dimethylamine; ◊, methylamine.