Absorption of Hymexazol by Sensitive and Insensitive Microorganisms

Abstract

Selective absorption of hymexazol (3-hydroxy-5-methylisoxazole, Tachigaren^(R)) by organisms having a different sensitivity to the toxicant was investigated. Absorption of (3)-¹⁴C-labeled hymexazol by intact fungal cells revealed both active and passive absorption. Hymexazol was removed rapidly from aqueous solution by sensitive fungi, such as Pellicularia sasakii, Rhizoctonia solani (culture type 2, 1A and 1B), Fusarium roseum and F. oxysporm f. cucumerinum, whose growth was inhibited by the toxicant in vitro and in vivo. A group of insensitive organisms, such as Saccharomyces cerevisiae and Pseudomonus cruciviae absorbed less hymexazol. F. moniliforme and R. solani (culture type 3A and 3B), which have comparatively low sensitivities to hymexazol in vivo, absorbed less amount of the toxicant than the sensitive fungi. Washing the cells with buffer solution removed more hymexazol from insensitive fungi than sensitive fungi. The results suggested that absorption of hymexazol by fungal cells is an essential for its antimicrobial activity. The subsequent binding of hymexazol to the TCA and methanol insoluble fraction in cell constituents may be indicative of its site of action.