Microbial material cycling, energetic constraints and ecosystem expansion in subsurface ecosystems.

Mayumi Seto,Yoh Iwasa

doi:10.1098/rspb.2020.0610

Abstract

To harvest energy from chemical reactions, microbes engage in diverse catabolic interactions that drive material cycles in the environment. Here, we consider a simple mathematical model for cycling reactions between alternative forms of an element (A and Ae), where reaction 1 converts A to Ae and reaction 2 converts Ae to A. There are two types of microbes: type 1 microbes harness reaction 1, and type 2 microbes harness reaction 2. Each type receives its own catabolic resources from the other type and provides the other type with the by-products as the catabolic resources. Analyses of the model show that each type increases its steady-state abundance in the presence of the other type. The flux of material flow becomes faster in the presence of microbes. By coupling two catabolic reactions, types 1 and 2 can also expand their realized niches through the abundant resource premium, the effect of relative quantities of products and reactants on the available chemical energy, which is especially important for microbes under strong energetic limitations. The plausibility of mutually beneficial interactions is controlled by the available chemical energy (Gibbs energy) of the system. We conclude that mutualistic catabolic interactions can be an important factor that enables microbes in subsurface ecosystems to increase ecosystem productivity and expand the ecosystem.

Highlights

Biogeochemical cycles are networks of chemical reactions or physical processes that are driven by organisms
The carbon cycle between carbon dioxide and organic matter under aerobic conditions is predominantly accomplished by plants and decomposers by coupling the catabolic pathways to synthesize ATP and anabolic pathways to build biomass by consuming ATP
Aerobic respiration is one of the catabolic reactions, that is, the chemical reactions functioning as energy sources to synthesize ATP

Summary

Introduction

Biogeochemical cycles are networks of chemical reactions or physical processes that are driven by organisms. Methane-consuming microbes obtain energy by transferring electrons from methane to oxygen gas, sulfate, nitrate, iron and manganese oxides, which eventually produce carbon dioxide (or hydrogen carbonate) as a by-product [12,13,14,15]. The association of these two microbes may cycle methane within the seafloor zones [16]. Two distinct catabolic types in a microbial consortium (assemblage) involved in a microscale cycle should be mutualistic because they feed each other with a compound that is a by-product for one but a catabolic resource for the other These two types are beneficial to each other in terms of the amount of energy that they can generate from catabolic reactions. The dynamics of x1, x2 and A are given as follows: dA dt

C K2C þ x2

Results

Discussion

14. Raghoebarsing AA et al 2006 A microbial