Bacteria obtain energy by breaking down complex organic and inorganic compounds or by fixing carbon dioxide using the energy from the sun. Bacteria are categorized into phototrophs, lithotrophs or organotrophs depending upon their energy source.
Bacteria lack a nucleus and cell organelles. They are classified by scientists as prokaryotic cells. Plant and animal cells contain a nucleus and are eukaryotic. There are many types of bacteria that have been identified. Phototrophs obtain energy from sunlight. They contain a substance called bacteriochlorophyll that absorbs different wavelengths of light than plants. Cyanobacteria, purple bacteria and green sulfur bacteria are examples of phototrophs.
The word lithotroph means rock eater. Lithotrophs break down chemicals that are poison to other life forms. Many live in deep sea vents and synthesize energy from the chemicals rising from the sea floor. Tube worms are examples of lithotrophic bacteria that live in or around these vents. Other lithotrophs have been discovered inside active volcanoes and sulfurous volcanic pools and geysers.
Organotrophs obtain energy by breaking down organic matter. Organotrophs permeate all living matter including humans and other mammals. Many organotrophs have beneficial uses. When organotrophs decompose organic matter, they leave behind the rich decomposed waste to fertilize the soil.