Secondary metabolites characteristic of Penicillium citrinum, Penicillium steckii and related species

Abstract

Two new carboxylic acids, tanzawaic acid E (1) and F (2) in addition to the unknown benzopyran 3,7-dimethyl-1,8-dihydroxy-6-methoxy-isochroman (3), and the known mycotoxin 3,7-dimethyl-8-hydroxy-6-methoxyisochroman (4) were produced by a marine-derived strain of Penicillium steckii isolated from an unidentified tunicate. The carboxylic acids and the benzopyran were identified on the basis of mass spectrometry, and one and two dimensional NMR spectroscopic techniques. The structures 1 and 2 resemble tanzawaic acid A–D, previously isolated from Penicillium citrinum. Screening of isolates of species related to P. citrinum and P. steckii showed that P. citrinum (25 isolates) consistently produced citrinin and tanzawaic acid A, P. steckii (18 isolates) produced isochroman toxins (except 2) and tanzawaic acid E, P. sizovae consistently produced tanzawaic acid A, P. corylophilum (10 isolates) produced citreoisocoumarinol and P. sumatrense (15 isolates) always produced curvularin.

Introduction

Penicillium citrinum and other species in the former P. citrinum series of Raper and Thom (1949) are probably the most common of all eucaryotic microorganisms (Pitt, 1979). Raper and Thom (1949) emphasized that P. citrinum was the sole producer of the nephrotoxic mycotoxin citrinin in that series, but described many variants of P. citrinum in their monographs. Later studies report, however, that P. steckii (Jabbar and Rahim, 1962) and P.corylophilum (El-Kady et al., 1994) also produce citrinin, and furthermore, (Pitt, 1979) synonymized P. steckii with P. citrinum. Several other secondary metabolites have been described from these species, including isochroman toxin from P. steckii (Cox et al., 1979), tanzawaic acids from P. citrinum (Kuramoto et al., 1997) and compactins from the same species (Endo et al., 1976, Turner, 1971, Turner and Aldridge, 1983). Isolates of these species frequently occur in screening of soil-borne penicillia for bioactive compounds. It is desirable to firmly identify their taxonomic positions as they may produce mycotoxins in foods and feeds, but also in order to be able to exclude these ubiquitous filamentous fungi in large scale screening for new compounds. We have examined a large number of isolates of these species and identified the major compounds.