ABSTRACT
It is now clear that many different species make up the genus Pneumocystis. To begin discussion of the genome of ‘‘Pneumocystis,’’ it is necessary to define the genome being described and to understand the similarities and differences among the members of this genus. It appears that almost every mammalian species harbors at least one species of Pneumocystis, which can thrive only in its specific mammalian host. These organisms are as genetically distinct from one another as other bona fide fungal species are from each other [1,2]. A more complete discussion of nomenclature and genetic diversity of Pneumocystis is presented in Chap. 2.
