What is the chemoautotrophic mode of nutrition?

In bacteria, there is mainly two modes of nutrition:

1. Autotrophic

2. Heterotrophic

The autotrophs are further divided into two types on the basis of their ability: 

1. Photoautotrophs

2. Chemoautotrophs 

Chemoautotrophs are those bacteria that obtain energy by the oxidation of electron donors in their environments. These molecules can be organic (chemoorganotrophs) compounds from carbon dioxide, or inorganics (chemolithotrophs), such as hydrogen sulfide, elemental sulfur, ferrous iron, molecular hydrogen, and ammonia. 

Chemotrophs can be either autotrophic or heterotrophic. They are found on ocean floors where sunlight cannot reach them because of the great depth. They evolved to not depend on solar energy. And, as a substitute for sunlight warmth, ocean floor often contains volcanoes that provide heat. 

This type of nutrition in bacteria is known as Chemoautotrophic mode of nutrition.