This book study the interaction between bacteria and phage in a gradostat environment. The gradostat is needed in order to investigate the influence of nutrient gradient on the phenomenon. Methods will include finding system bifurcations, fixed points and their stability and system dynamics. Possible applications of the subject are for the recently fashionable phage therapy. A chemostat (from Chemical environment is static) is a bioreactor to which fresh medium is continuously added, while culture liquid is continuously removed to keep the culture volume constant. By changing the rate with which medium is added to the bioreactor the growth rate of the microorganisms can be easily controlled. One of the most important features of chemostats is that micro-organisms can be grown in a physiological steady state. In steady state, all culture parameters remain constant (culture volume, dissolved oxygen concentration, nutrient and product concentrations, pH, cell density, etc.). Micro-organisms grown in chemostats naturally strive to steady state: if a low amount of cells are present in the bioreactor, the cells can grow at growth rates higher than the dilution rate.