Similarly, the total number of species of fungi is thought to be very high although estimates vary widely from 250,000 to over 5 million. Only a few thousands of these have been thoroughly investigated. There are often different strains of the same species, morphologically similar but with potentially quite diverse metabolites. Different secondary metabolites can be generated by altering the growing conditions of fungi and many new and diverse chemical structures remain to be discovered. Penicillin with its beta lactam ring was derived from the fungus Penicillium chrysogenum
and the Cephalosporins, also containing the beta lactam ring, were originally derived from the fungus Cephalosporium.
Thus fungi are already established as a major source for many of the world's current antibacterial substances. However, much more remains to be unlocked by intelligent screening.