An evaluation of carbon and nitrogen assimilatory patterns for taxonomic differentiation of Penicillium species

A series of standardized medium formulations differing in carbon and nitrog en sources was evaluated for use in taxonomic differentiation of Penicilliu m species. Two media containing glucose as the carbon source and either nit rate or ammonium as the nitrogen source yielded optimal growth for most Pen icillium species, and were, therefore, selected as reference media for eval uating growth parameters on other medium formulations. The nitrogen status of the medium was altered either by the addition of phosphinothricin, a pot ent inhibitor of ammonium assimilation via the glutamine synthetase pathway , or by using urea, phenylalanine, proline, creatine, glycinebetaine, choli ne, or bovine serum albumin as a substituted nitrogen source. Sucrose, sorb itol, mannitol, cellobiose, cellulose, palmitic acid, and para hydroxybenzo ate were used as substitutes for glucose. The examination of colony area, h yphal density and changes in the color of pH indicators on day 7 yielded a set of 64 characters with a high degree of variation among Penicillium stra ins. The ability to assimilate various carbon and nitrogen sources appears to follow taxonomic lines in Penicillium. Furthermore, the acidification of the growth medium on a given nutrient source is a strong taxonomic trait i n Penicillium. A sorting protocol has been developed to allow a broadly bas ed discontinuous separation of taxa by segregating growth and acidification ratings into four broad categories, assigning an alphabetical coding to ea ch category and a staggered grouping of categories into two group with inte rmediate ratings included in both. The resolution power of the sorting sche me is demonstrated by the separation of 222 strains belonging to six test s pecies P. atramentosum, P. citreonigrum, P. commune P. corylophilum, P. oxa licum, and P. spinulosum from a dataset of 1860 Penicillium strains, includ ing 1472 isolates from house dust samples, 199 isolates isolates from outdo or habitats, 121 ex-type strains and 68 named strains from various culture collections. For each species, only a fraction of character groups included in the sorting protocol was required for separating matching isolates. In addition a total of 180 strains were found to match one of the six test spe cies except for a single character difference. These results support the us e of physiological media both for species and for infraspecific differentia tion of Penicillium taxa. The biochemical basis of species differentiation on the given physiological media is discussed.