Methanothermobacter thermautotrophicus modulates its membrane lipids in response to hydrogen and nutrient availability

Abstract

Methanothermobacter thermautotrophicus strain ΔH is a model hydrogenotrophic methanogen, for which extensive biochemical information, including the complete genome sequence, is available. Nevertheless, at the cell membrane lipid level, little is known about the responses of this archaeon to environmental stimuli. In this study, the lipid composition of M. thermautotrophicus was characterized to verify how this archaeon modulates its cell membrane components during growth phases and in response to hydrogen depletion and nutrient limitation (potassium and phosphate). As opposed to the higher abundance of phospholipids in the stationary phase of control experiments, cell membranes under nutrient, and energy stress were dominated by glycolipids that likely provided a more effective barrier against ion leakage. We also identified particular lipid regulatory mechanisms in M. thermautotrophicus, which included the accumulation of polyprenols under hydrogen-limited conditions and an increased content of sodiated adducts of lipids in nutrient-limited cells. These findings suggest that M. thermautotrophicus intensely modulates its cell membrane lipid composition to cope with energy and nutrient availability in dynamic environments.

Keywords: archaea; diether; polar lipids; stress response; tetraether.

FIGURE 1

Abundance of IPL relative to total lipids (including both core and IPL) during growth of Methanothermobacter thermautotrophicus under control (A), hydrogen limiting (B), and nutrient limiting (C) conditions at: late exponential phase (L-Exp), early, mid and late stationary phases (E-, M-, and L-Stat). The dashed line in (B) denotes the change in headspace from 80:20 H₂:CO₂ to N₂:CO₂ (vol:vol) 3 h before sampling E-Stat in hydrogen-limited experiments. Star symbol (*) in (C) represents no data. The experiments were conducted in triplicate and error bars represent standard error of the mean. G, glycosidic; Phos, phosphatidic; AR, archaeols/diethers; GDGT, tetraethers.

FIGURE 2

Abundance of major individual AR and GDGT lipids relative to total diethers or tetraethers, respectively, from cells of M. thermautotrophicus growing under control (A), hydrogen limiting (B), and nutrient limiting (C) conditions. For abbreviations see Supplementary Table S1.

FIGURE 3

Principal component analysis (PCA) of M. thermautotrophicus growing under control, hydrogen-limited and nutrient-limited conditions. Bi-plots of two main principal components, PC1 and PC2, displayed as (A) samples from distinct treatments and (B) lipid distribution. The arrow in (A) illustrates control samples transitioning from late exponential growth to stationary phase. [Na⁺] indicates IPL bound to sodium and masses m/z 722 and 792 represent the most abundant unmodified polyprenols (B), respectively, containing 10 and 11 isoprene units (see Supplementary Figure S4). For compounds abbreviations and detailed information on the PCA analysis please refer to Supplementary Table S1 and Section “Materials and Methods,” respectively.