Chloromethane, a Novel Methyl Donor for Biosynthesis of Esters and Anisoles in Phellinus pomaceus

Abstract

Chloromethane (CH 3 Cl), a gaseous natural product released as a secondary metabolite by many woodrotting fungi of the family Hymenochaetaceae , has been shown to act as a methyl donor for biosynthesis of methyl esters of benzoic and furoic acid in the primary metabolism of Phellinus pomaceus. The broad-specificity methylating system could esterify a wide range of aromatic and aliphatic acids. In addition to CH 3 Cl, both bromo- and iodomethanes acted as methyl donors. Methylation did not appear to proceed via methanol or a coenzyme A intermediate. The initial growth-related accumulation of methyl benzoate during culture of P. pomaceus was paralleled by an increase in activity of the methylating system in the mycelium. Changes in percent incorporation of C 2 H 3 from exogenous C 2 H 3 Cl during growth indicated that although utilization of CH 3 Cl was initially closely coupled to biosynthesis of the compound, the system became less tightly channeled later in growth. This phase coincided with release of gaseous CH 3 Cl by the fungus. A biochemically distinct CH 3 Cl-utilizing system capable of methylating phenols and thiophenol was also identified in the fungus, but in contrast with the carboxylic acid-methylating system, it attained maximum activity in the idiophase. Preliminary investigations of a non-CH 3 Cl-releasing fungus, Fomitopsis pinicola , have shown the presence of a CH 3 Cl-utilizing system capable of methylating benzoic acid, suggesting that CH 3 Cl biosynthesis may occur in non-hymenochaetaceous fungi. Halogenated compounds hitherto found in nature are mainly stable end products of metabolism. The participation of CH 3 Cl in primary fungal metabolism demonstrates that some halometabolites may have a previously unrecognized role as intermediates in the biosynthesis of nonhalogenated natural products.