The energetics of anabolism in natural settings

Abstract

The environmental conditions that describe an ecosystem define the amount of energy available to the resident organisms and the amount of energy required to build biomass. Here, we quantify the amount of energy required to make biomass as a function of temperature, pressure, redox state, the sources of C, N and S, cell mass and the time that an organism requires to double or replace its biomass. Specifically, these energetics are calculated from 0 to 125°C, 0.1 to 500 MPa and − 0.38 to +0.86 V using CO 2 , acetate or CH 4 for C, NO 3 À or NH 4 þ for N and SO 4 2À or HS − for S. The amounts of energy associated with synthesizing the biomolecules that make up a cell, which varies over 39 kJ (g cell), are then used to compute energy-based yield coefficients for a vast range of environmental conditions. Taken together, environmental variables and the range of cell sizes leads to a~4 orders of magnitude difference between the number of microbial cells that can be made from a Joule of Gibbs energy under the most (5.06 × 10 11 cells J − 1) and least (5.21 × 10 7 cells J − 1 ) ideal conditions. When doubling/replacement time is taken into account, the range of anabolism energies can expand even further.

Necromass as a Limited Source of Energy for Microorganisms in Marine Sediments

“…For SPG and the global study, we explore a range of cell masses ( C small = 5 fg C cell −1 , C medium = 14 fg C cell −1 , C large = 75 fg C cell −1 ) that is consistent with estimates for marine sediments globally (Braun et al, ; Kallmeyer et al, ). We assume the cell stoichiometry (C 166 H 314 N 43 O 89 P 3 S 1 ) and concentrations of biomolecules in a cell (Table S2) used by LaRowe and Amend () in a previous assessment of biomolecule anabolism.…”

“…where Δ G r 0 and Q r refer to the standard molal Gibbs energy and the reaction quotient of the indicated reaction, respectively, R represents the gas constant, and T denotes temperature in kelvin. Values of Δ G r 0 are calculated for every reaction at every depth using the revised‐HKF equations of state (Helgeson et al, ; Shock et al, ; Tanger & Helgeson, ), the SUPCRT software package (Johnson et al, ), and thermodynamic data taken from Amend and Helgeson (), Amend and Plyasunov (), Dick et al (), Helgeson et al (), LaRowe and Dick (), LaRowe and Amend (), Richard (), Richard and Helgeson (), Schulte et al (), Shock et al (), Shock and Helgeson (, ), and Sverjensky et al (). For SPG, we use a temperature of 5.0°C (D'Hondt et al, ) and a representative pressure of 513.6 bar.…”

“…For marine sediments globally, we explore a range of temperatures representing typical values (5–40°C) (LaRowe et al, ) and a nominal value for pressure (100 bar). Pressure changes resulting from different sediment depths have a negligible effect on the thermodynamic properties of anabolism and catabolism (LaRowe & Amend, ). Individual values of Q r are calculated for each biomolecule reaction at every age using …”

Microbial Controls on the Biogeochemical Dynamics in the Subsurface

“…The results by LaRowe and Amend (2016) clearly demonstrate that values of ΔG syn depend strongly on the combination of the redox state of the precursor compounds and that of the environment, with values varying by up to about 40 kJ (g cell) −1 depending on the different combinations. LaRowe and Amend also show that the contribution of ΔG poly to ΔG syn is significant when biomass synthesis occurs in the most conducive environmental conditions.…”

“…A more complex approach consists in explicitly accounting for the variety of molecules making up the cell, that is, individual amino acids, nucleotides, lipids, saccharides, amines and other compounds (McCollom and Amend 2005) and subsequently calculate the energetics associated to each of these biomolecules. The polymerization of these various compounds in their respective biomacromolecules can also be accounted for in the energetics of anabolism, as performed in, e.g., Amend et al (2013) and LaRowe and Amend (2016). To our knowledge, such approach as not yet been applied in a reactive-transport framework, despite being in principle compatible with RTM simulations.…”