Atoms of multistationarity in chemical reaction networks

TL;DR

This paper introduces the concept of 'atoms of multistationarity' in chemical reaction networks, proving their foundational role in characterizing multistationarity in fully open CFSTRs and classifying minimal multistationary subnetworks.

Contribution

It establishes that atoms of multistationarity fully characterize multistationary networks in CFSTRs and provides a classification of all minimal multistationary subnetworks for certain small networks.

Findings

All 386 bimolecular, reversible two-reaction networks were classified.

Exactly 35 of these networks admit multiple positive steady states.

The minimal multistationary subnetworks form a poset with 11 atoms.

Abstract

Chemical reaction systems are dynamical systems that arise in chemical engineering and systems biology. In this work, we consider the question of whether the minimal (in a precise sense) multistationary chemical reaction networks, which we propose to call `atoms of multistationarity,' characterize the entire set of multistationary networks. Our main result states that the answer to this question is `yes' in the context of fully open continuous-flow stirred-tank reactors (CFSTRs), which are networks in which all chemical species take part in the inflow and outflow. In order to prove this result, we show that if a subnetwork admits multiple steady states, then these steady states can be lifted to a larger network, provided that the two networks share the same stoichiometric subspace. We also prove an analogous result when a smaller network is obtained from a larger network by `removing species.' Our results provide the mathematical foundation for a technique used by Siegal-Gaskins et al. of establishing bistability by way of `network ancestry.' Additionally, our work provides sufficient conditions for establishing multistationarity by way of atoms and moreover reduces the problem of classifying multistationary CFSTRs to that of cataloging atoms of multistationarity. As an application, we enumerate and classify all 386 bimolecular and reversible two-reaction networks. Of these, exactly 35 admit multiple positive steady states. Moreover, each admits a unique minimal multistationary subnetwork, and these subnetworks form a poset (with respect to the relation of `removing species') which has 11 minimal elements (the atoms of multistationarity).