Are Members of the Fungal Genus Pneumocystis (a) Commensals; (b) Opportunists; (c) Pathogens; or (d) All of the Above?

The author has declared that no competing interests exist. The author's research on Pneumocystis is funded by the United States National Institutes of Health Grant R01 AI076104 and the Medical Research Service, Department of Veterans Affairs. The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.