Protecting external surfaces of the steel pipes, by application of the coating or cathodic protection do not eliminate the problem of corrosion which is induced by microorganisms on the inside of pipelines. Further understanding of this unfavourable and dangerous phenomenon caused by microorganisms has become a motivation to undertake this research project. Authors aim on determining if cathodic protection applied to the external surfaces of the pipelines have influence on the adhesion of the microorganisms on the inside surfaces. In the case that the standard parameters would be proved as are ineffective, then it would be investigated if adaptation of current parameters can change it. Therefore we decided to determine of the biodiversity of the microorganisms inhabiting gas line system, determine of the microorganisms velocity in dependence on the material of the gas line, and determine of the influence of the changing parameters of the current applied for cathodic protection on the adhesion and development of the identified bacteria on the steel surfaces.