Here's why:

* Heterotrophic means they obtain their energy and carbon from organic sources, such as sugars, proteins, and fats. These are produced by other living things.

* Autotrophic bacteria, on the other hand, can create their own food using inorganic sources (like carbon dioxide, sunlight, and water). This is the opposite of heterotrophic bacteria.

Therefore, heterotrophic bacteria are dependent on other organisms for their food source. They cannot survive without organic compounds.