Organisms capable of using CO2 as principal carbon source are called :

Autotrophs (from the Greek words autos meaning "self" and trophe meaning "nourishing") are organisms that can produce their own food using inorganic substances. They use Carbon Dioxide (CO2) as their primary or principal carbon source to synthesize complex organic compounds like carbohydrates, fats, and proteins.

• Photoautotrophs: Use sunlight as energy (e.g., green plants, algae) to convert CO2 and water into glucose via photosynthesis.
• Chemoautotrophs: Use energy from chemical reactions (e.g., certain bacteria) to fix carbon.

In contrast, Heterotrophs (including parasites and decomposers) cannot fix carbon from CO2 and must rely on organic carbon produced by other organisms for their nutritional requirements. Therefore, organisms that utilize CO2 as their main carbon source are strictly classified as autotrophs.