Degradation of the polyamine alkaloid aphelandrine by endophytic fungi isolated from Aphelandra tetragona.

Members of the genus Aphelandra (Acanthaceae) produce rare macrocyclic polyamine alkaloids which consist of spermine acylated with two units of 3-(4-hydroxyphenyl)prop-2-enoic acid. Endophytic fungi were isolated from roots and shoots of Aphelandra tetragona and tested for their ability to metabolize the main alkaloid aphelandrine, which accumulates exclusively in the roots of the plants. Several endophytes were able to metabolize aphelandrine but only root endophytes belonging to the Nectriaceae were good metabolizers. In addition, the endophytes were grown on an agar medium containing putrescine, spermidine, or spermine as the sole nitrogen source. All fungi were able to grow on putrescine, but only the good aphelandrine metabolizers grew well on spermidine or spermine. Acremonium sp. 15, one of the most active metabolizers, grew also on a medium containing aphelandrine as sole nitrogen source. A number of strains thought to be conspecific with Acremonium sp. 15 were also tested for their ability to metabolize aphelandrine. The ability of the endophytes to metabolize aphelandrine suggests an ecological adaptation of the symbionts to their host. The possibility of using the aphelandrine metabolism as a taxonomic character is briefly discussed.