Fusarium acuminatum NRRL 6227 produces an antifungal metabolite that causes incubating conidia of several Penicillium species to swell 5-10 diameters while inhibiting germination. The swollen conidia are spherical, translucent, nonviable and easily shattered with a slight physical pressure; however, they remain resistant to osmotic shock. This antibiotic has been identified as a cyclic peptide composed of alanine, glutamic acid, leucine, threonine and tyrosine.