microbial phenotype microaerophile http://purl.obolibrary.org/obo/omp.owl An oxygen growth range phenotype where growth and reproduction requires oxygen but at levels below that found in air (approx. 21%). A microbial phenotype that describes a microorganism that requires O2 for growth, but doesn't grow in the presence of atmospheric levels of O2. Optimal growth of a microaerophile occurs in environments with xx% - xx% O2. Optimal oxygen levels for growth of typical microaerophilic bacteria is 2 to 10% O2, and growth is impaired by atmospheric oxygen levels (approx. 21%).