11–14 — PRIMARY NUTRITIONAL IDENTITY
This is the established combinatorial core.
Operational definition
Layer type: Composite trophic-identity layer Governs: Items 11–14
Formal definition
The Primary Nutritional Identity classifies a living system through three independent source dimensions:
- the source of energetic drive;
- the source of electrons or reducing equivalents;
- the source of biomass carbon.
Governing question
From what does this organism obtain energy, electrons, and carbon under the stated conditions?
Three governing axes
Energy-source axis
photo- or chemo-
Electron-source axis
litho- or organo-
Carbon-source axis
auto- or hetero-
These axes combine into descriptors such as:
photolithoautotroph
photoorganoheterotroph
chemolithoautotroph
chemoorganoheterotroph
Inclusion rule
A classification belongs here when it identifies the principal source contribution under defined growth conditions.
A valid entry should specify whether the mode is:
- obligate;
- facultative;
- dominant;
- supplementary;
- mixed;
- stage-dependent;
- environmentally induced.
Critical distinctions
This layer prevents several common category errors:
- phototroph does not necessarily mean autotroph;
- heterotroph does not necessarily mean animal;
- lithotroph does not identify the terminal electron acceptor;
- autotrophy does not identify whether energy comes from light or chemistry;
- mixotrophy can involve multiple different combinations.
Exclusion rule
This layer does not classify:
- oxygen versus nitrate respiration;
- fermentation;
- acquisition by ingestion versus absorption;
- ecological roles such as producer or decomposer;
- ATP-production mechanism.
It is an identity profile, not a complete metabolic description.
11. Energy-source axis
11.1 Phototroph
Light supplies the primary energetic drive.
11.2 Chemotroph
Chemical transformations supply the primary energetic drive.
11.3 Photo-chemo flexible
The organism can change the relative contribution of phototrophy and chemotrophy.
12. Electron-source axis
12.1 Lithotroph
Electrons or reducing equivalents originate principally from inorganic donors.
Examples:
- H₂O
- H₂
- H₂S
- NH₃
- NO₂⁻
- Fe²⁺
12.2 Organotroph
Electrons originate principally from organic compounds.
12.3 Mixed litho-organotroph
Both inorganic and organic electron donors are used.
12.4 Electrotrophic modifier
Electrons are acquired directly or indirectly from extracellular conductive sources.
“Electrotroph” should be recorded as an acquisition modifier in addition to, rather than as a replacement for, the chemical identity of the electron source.
13. Carbon-source axis
13.1 Autotroph
Biomass carbon comes principally from inorganic carbon:
- CO₂
- bicarbonate
- related dissolved inorganic carbon
13.2 Heterotroph
Biomass carbon comes principally from preexisting organic compounds.
13.3 Mixotroph
Both autotrophic and heterotrophic carbon acquisition contribute materially.
Mixotrophy can include photosynthesis plus prey ingestion, dissolved-organic-carbon uptake, parasitism, or acquired photosynthetic capacity. It is widespread among aquatic protists and also occurs in bacteria. (PubMed Central (PMC))
14. Standard composite energetic identities
| Composite class | Energy | Electron source | Carbon source |
|---|---|---|---|
| Photolithoautotroph | light | inorganic | inorganic carbon |
| Photoorganoheterotroph | light | organic | organic carbon |
| Chemolithoautotroph | chemical | inorganic | inorganic carbon |
| Chemolithoheterotroph | chemical | inorganic | organic carbon |
| Chemoorganoheterotroph | chemical | organic | organic carbon |
| Mixed or facultative forms | variable | variable | variable |
Representative classifications:
- green plants: predominantly photolithoautotrophic
- cyanobacteria: predominantly photolithoautotrophic
- animals: chemoorganoheterotrophic
- fungi: chemoorganoheterotrophic
- nitrifying microbes: commonly chemolithoautotrophic
- purple nonsulfur bacteria: frequently photoorganoheterotrophic, with substantial metabolic flexibility
The three axes must remain independent: light use does not prove autotrophy, organic-carbon use does not identify the electron acceptor, and inorganic-electron use does not prove carbon fixation. (PubMed Central (PMC))