 The fungal genus "Aspergillus" is capable of living under considerable environmental stress, and thus is capable of colonising the upper gastrointestinal tract where relatively few examples of the body's gut flora can survive due to highly acidic or alkaline conditions produced by gastric acid and digestive juices.While "Aspergillus" normally produces no symptoms, in individuals who are immunocompromised or suffering from existing conditions such as tuberculosis, a condition called aspergillosis can occur, in which populations of "Aspergillus" grow out of control.