Abstract
BackgroundSouth African plant species of the genera Fadogia, Pavetta and Vangueria (all belonging to Rubiaceae) are known to cause gousiekte (literally ‘quick disease’), a fatal cardiotoxicosis of ruminants characterised by acute heart failure four to eight weeks after ingestion. Noteworthy is that all these plants harbour endophytes in their leaves: nodulating bacteria in specialized nodules in Pavetta and non-nodulating bacteria in the intercellular spaces between mesophyll cells in Fadogia and Vangueria.Principal FindingsIsolation and analyses of these endophytes reveal the presence of Burkholderia bacteria in all the plant species implicated in gousiekte. Although the nodulating and non-nodulating bacteria belong to the same genus, they are phylogenetically not closely related and even fall in different bacterial clades. Pavetta harborii and Pavetta schumanniana have their own specific endophyte – Candidatus Burkholderia harborii and Candidatus Burkholderia schumanniana – while the non-nodulating bacteria found in the other gousiekte-inducing plants show high similarity to Burkholderia caledonica. In this group, the bacteria are host specific at population level. Investigation of gousiekte-inducing plants from other African countries resulted in the discovery of the same endophytes. Several other plants of the genera Afrocanthium, Canthium, Keetia, Psydrax, Pygmaeothamnus and Pyrostria were tested and were found to lack bacterial endophytes.ConclusionsThe discovery and identification of Burkholderia bacteria in gousiekte-inducing plants open new perspectives and opportunities for research not only into the cause of this economically important disease, but also into the evolution and functional significance of bacterial endosymbiosis in Rubiaceae. Other South African Rubiaceae that grow in the same area as the gousiekte-inducing plants were found to lack bacterial endophytes which suggests a link between bacteria and gousiekte. The same bacteria are consistently found in gousiekte-inducing plants from different regions indicating that these plants will also be toxic to ruminants in other African countries.
Highlights
Some species of Rubiaceae from South Africa are known to cause a disease of domestic ruminants called gousiekte, an Afrikaans name literally translated as ‘quick disease’
Other South African Rubiaceae that grow in the same area as the gousiekte-inducing plants were found to lack bacterial endophytes which suggests a link between bacteria and gousiekte
Several clones were obtained for the 16S rDNA region of P. harborii and only one unique sequence emerged, which indicates the presence of only one bacterium species
Summary
Some species of Rubiaceae from South Africa are known to cause a disease of domestic ruminants called gousiekte, an Afrikaans name literally translated as ‘quick disease’. Gousiekte is a disease of ruminants characterized by acute heart failure without early warning signs 4–8 weeks after the initial ingestion of certain bacteriophilous Rubiaceae. Pachystigma pygmaeum) is the most important of these plants, followed in descending order of importance by Fadogia homblei, Pavetta harborii, Vangueria thamnus Pachystigma thamnus), Pavetta schumanniana and Vangueria latifolia South African plant species of the genera Fadogia, Pavetta and Vangueria (all belonging to Rubiaceae) are known to cause gousiekte (literally ‘quick disease’), a fatal cardiotoxicosis of ruminants characterised by acute heart failure four to eight weeks after ingestion. Noteworthy is that all these plants harbour endophytes in their leaves: nodulating bacteria in specialized nodules in Pavetta and non-nodulating bacteria in the intercellular spaces between mesophyll cells in Fadogia and Vangueria
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