In the context of nutritional factors of microbial growth, how do heterotrophic bacteria primarily obtain energy?

• A. By fixing $C_{O}2$ as the primary carbon and energy source (autotrophy)
• B. By using light as the primary energy source (phototrophy)
• C. By oxidizing organic compounds (chemical energy from preformed carbon-containing molecules)
• D. By oxidizing inorganic chemicals such as $H_{2}S$ or $F^e<2+>$ (chemolithotrophy)

Answer: (C)

Verified step by step guidance

1. Understand the definition of heterotrophic bacteria: these bacteria obtain their carbon and energy from organic compounds rather than fixing carbon dioxide (CO\_2) themselves.
2. Recognize that autotrophy involves fixing CO\_2 as the primary carbon and energy source, which is characteristic of autotrophic organisms, not heterotrophs.
3. Recall that phototrophy refers to organisms that use light as their primary energy source, which is typical of photosynthetic bacteria, not heterotrophic bacteria.
4. Identify chemolithotrophy as the process where bacteria oxidize inorganic chemicals such as H\_2S or Fe\^{2+} to obtain energy, which is distinct from heterotrophic metabolism.
5. Conclude that heterotrophic bacteria primarily obtain energy by oxidizing organic compounds, meaning they use chemical energy from preformed carbon-containing molecules, which aligns with their nutritional requirements.