The occurrence of the toxins, streptol, kirkamide and pavettamine in the gousiekte-causing Rubiaceae species

Abstract

Gousiekte (quick disease) is a cardiotoxicoses commonly found in ruminants and is caused by at least six species of the Rubiaceae family namely, Fadogia homblei, Pavetta harborii, Pav. schumanniana, Vangueria latifolium, V. pygmaea and V. thamnus. Bacterial endophytes are present in all plants that cause gousiekte and it might be possible that the bacterial species play a role in the production of the toxin. As a result of varying toxicity of plants that cause gousiekte, the parameters of the disease have not been confidently established. Pavettamine was previously identified as the gousiekte-causing toxin and shown to be present in all these species, however, the results obtained from experiments regarding pavettamine, have been very inconsistent. The toxins, kirkamide, streptol and streptol glucoside were previously found in Psychotria kirkii (Rubiaceae) and reported for their toxicity, the endophyte genome contains the genes responsible for encoding these toxins. The main aim of this study was to determine if kirkamide, streptol and its glucoside occur in some of the gousiekte-causing species and to investigate the role of the endophytes in the production of the toxin. Nine non-toxic species of the Rubiaceae family were analysed together with three gousiekte-causing species (F. homblei, V. pygmaea and V. thamnus) by means of 1H-NMR, GC-MS, UPLC-QToF and LC-MS analyses. The chemical analysis results were compared with genetic studies done by collaborators who determined if the bacterial endophyte genomes contain the genes for the biosynthesis of these toxins. None of the species carried the kirkamide gene, it was also not detected in the extracts during chemical analyses. The gene encoding streptol was identified in a few species namely, V. infausta, V. madagascariensis, V. pygmaea and V. randii. Streptol was detected in two positive controls namely V. pygmaea and V. infausta however in very low intensities although as expected not in the negative control F. homblei. Based on the results, it cannot be confidently said that either kirkamide or streptol plays a role in causing gousiekte. However, the results provide compelling evidence that the endophyte contributes to the production of the toxin streptol, as the toxin was only found in the species containing the endophyte gene for streptol.