Carbon source in metabolism: Which organisms typically obtain their carbon for biosynthesis from organic compounds (i.e., are chemoorganotrophs/heterotrophs)?

Introduction / Context:
Microbes are classified by both energy source (light vs chemical) and carbon source (CO2 vs organic carbon). Chemoorganotrophs (heterotrophs) use organic compounds as both energy and carbon sources, while autotrophs fix CO2.

Given Data / Assumptions:

• We compare three archetypes: aerobic glucose respirers, chemolithoautotrophs, and photoautotrophs.
• Identify which typically build biomass from organic carbon.

Concept / Approach:
Aerobic, glucose-respiring bacteria oxidize organic substrates for energy and derive carbon skeletons from the same organics, thus they are chemoorganotrophic heterotrophs. Ammonia oxidizers derive energy from NH3 but usually fix CO2 (autotrophy). Cyanobacteria use light for energy and fix CO2 (photoautotrophy). Methanogens use CO2 as an electron acceptor/substrate in methanogenesis, not as an organic carbon source.

Step-by-Step Solution:
Identify carbon source for each group. Chemoorganotrophs use organic carbon → matches aerobic glucose respirers. Rule out chemolithoautotrophs and photoautotrophs (CO2 fixation). Select the heterotrophic option.

Verification / Alternative check:
Textbook metabolic classifications place most pathogens and many environmental heterotrophs (e.g., Pseudomonas, E. coli) in the chemoorganotroph category.

Why Other Options Are Wrong:

• Ammonia oxidizers / Cyanobacteria / Methanogens: Rely on CO2 as the primary carbon source; they are not typical organic-carbon heterotrophs.
• None of the above: Incorrect because aerobic glucose respirers are classic heterotrophs.

Common Pitfalls:
Equating “uses glucose for energy” with “autotrophy”; autotrophy refers to carbon source (CO2), not energy source.

Final Answer:
Aerobic, glucose-respiring bacteria obtain carbon from organic compounds.