Citrinin—a Fungistatic Antibiotic and Narrowing Factor

Abstract

DURING growth, fungi produce substances which have morphogenetic effects when applied to apices of actively growing hyphae. Factors which induce vacuolation, branching and other effects have been described¹. The application of drops of culture nitrates to the margins of fungal colonies growing on agar is a suitable method for the demonstration of these morphogenetic factors, owing to the fact that developmental and ageing effects are most readily detected in this juvenile region. During a survey of culture filtrates from a large number of fungi which were being tested in this manner, one of the culture filtrates produced in the tips of the test fungus an abrupt and immediate change such that the subsequent growth of the axis was of considerably smaller diameter. The effect persisted after the treatment for more than 1 h and was followed by a gradual recovery until after 1.5–2 h the apex was again producing a hyphal tube of about the original diameter. No cytoplasmic change was evident in the treated tips. Branching was occasionally induced near the point of abrupt narrowing but was not invariably associated with the effect. The phenomenon of narrowing is of particular interest in relation to morphogenesis of the fungal colony as characteristically those hyphae produced behind the margin in the still developing but older regions of the colony are narrower than those at the extending margins. An understanding of the mechanism of hyphal narrowing could enlarge our knowledge of the process of ageing in fungi, and could also provide information helpful in elucidating the normal processes of hyphal extension growth.