89–98 — METABOLIC DEPENDENCY ARCHITECTURE
The Metabolic Dependency Architecture layer identifies how the components of a complete energetic or biosynthetic system are distributed among one organism, multiple organisms, host and symbiont, colony members, or an interacting consortium.
Operational definition
Layer type: Multi-organism organization layer Governs: Items 89–98
Governing question
Can the focal system complete the required metabolism by itself under the stated conditions, or is the pathway distributed across biological partners?
Included architectures
- conditional metabolic self-sufficiency;
- facultative cross-feeding;
- obligate cross-feeding;
- syntrophy;
- mutualistic symbiosis;
- host-subsidized commensalism;
- parasitism;
- acquired phototrophy;
- colonial or superorganismal division of labor;
- consortium-level metabolism.
Inclusion rule
An interaction belongs here when the presence, metabolism, or specialized activity of another biological unit materially changes the focal system’s ability to:
- acquire energy;
- acquire nutrients;
- dispose of electrons;
- maintain favorable thermodynamics;
- synthesize essential compounds;
- grow;
- survive;
- reproduce.
Dependency-versus-benefit distinction
Dependency architecture is not identical to ecological benefit.
Two organisms may exchange metabolites while:
- both benefit;
- only one benefits;
- one is harmed;
- the interaction changes with environmental conditions.
The architecture describes what is metabolically distributed. Mutualism, commensalism, and parasitism describe net biological consequences.
Syntrophy rule
Syntrophy is the strongest energetic form of distributed metabolism in this framework. One partner’s reaction becomes viable because another partner removes a product or supplies a coupled process that changes the thermodynamic conditions.
Original research and metabolic modeling show that metabolite exchange can create recurrent metabolic dependencies and that syntrophic organization can permit community-level survival where isolated components cannot sustain the same metabolism. (PubMed Central (PMC))
Appropriate unit rule
When the full pathway exists only through interorganismal exchange, the consortium—not the isolated species—is the correct unit for the complete energetic classification.
89. Metabolically self-sufficient under defined conditions
The system can complete its growth metabolism using environmental substrates without direct metabolite supply from another organism.
90. Facultative cross-feeding
Partner metabolites improve performance but are not always essential.
91. Obligate cross-feeding
One organism lacks a required product supplied by another.
92. Syntrophy
Partners jointly carry out a metabolism that is energetically or chemically unavailable to either partner alone under the same conditions.
93. Mutualistic symbiosis
Both partners receive a net energetic or material benefit.
94. Host-subsidized commensalism
One partner obtains resources while imposing little measurable energetic effect on the other.
95. Parasitism
The parasite diverts host-acquired matter and free energy toward its own maintenance and reproduction.
96. Acquired phototrophy
- permanent photosynthetic endosymbiont
- facultative photosymbiont
- kleptoplasty
- temporary retention of prey chloroplasts
97. Colonial or superorganismal division of labor
Different members specialize in:
- acquisition
- digestion
- defense
- reproduction
- transport
- temperature control
- storage
98. Consortium-level metabolism
The full energy pathway is distributed across multiple organisms.
Cross-feeding and syntrophy make it necessary to classify some energetic systems at the consortium level rather than attributing the whole process to one species. (PubMed Central (PMC))