Heterotrophic bacteria are microorganisms which survive by deriving their energy using organic matter from other sources rather synthesizing their own organic matter. The Heterotrophic bacteria have several economic applications; Lactobacillus and Streptococcus are widely used for the production of milk products like curd and cheese. Streptomyces is a genus of Gram-positive bacteria with the ability to produce bioactive secondary metabolites such as antifungals, antivirals, antitumoral, anti-hypertensives, and mainly antibiotics and immunosuppressives. Many different kinds of heterotrophic bacteria are used for sewage treatment. Some heterotrophic bacteria like Alcanivorax or Methylocella Silvestris have an important applications in bio-remediation (cleaning the oil spills). Archaebacteria are a group of prokaryotes which live under very harsh and hostile conditions. Since the enzymes from these organisms can survive harsh conditions they have many industrial applications in biotechnology; Many of the thermostable enzymes used in the manipulation of DNA are derived from Archaebacteria, Methanogens of the Archaebacteria are mainly involved in the biogas production.