Bacteria whose carbon needs for growth and reproduction are fulfilled by carbon dioxide. Autotrophy refers to the carbon source, not the energy source for growth. Autotrophic bacteria are in contrast to heterotrophic bacteria. The nitrifying bacteria, Nitrosomonas and Nitrobacter are autotrophic bacteria. They obtain energy by oxidizing inorganic compounds, ammonia or nitrite, respectively (see lithotrophic), while reducing carbon dioxide.