Advanced processes for nitrogen removal are intimately related to the microbial community metabolisms that take part in the transformations. For the design, optimization or improvement of domestic waste water treatment systems, engineers and microbiologists working together, have managed to implemented suitable tertiary reactors for the development of these communities, improving the efficiency of nutrient removal. This article presents a revision of the bacterial activity and its application in treatment systems. The article begins by giving an explanation about the influence of microorganism and human activity on the global nitrogen cycle. Then, it analyzes the particular processes in which the microorga1 Magister en ciencias, ingeniero civil, profesor asistente, Universidad de los Andes, Merida, Venezuela. sjaime@ula.ve. 2 Ph. D. Microbiologia, profesora asociada, Universidad del Valle, Santiago de Cali, Colombia. sanabria@univalle.edu.co ARTICULO CORTO