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Occurrence of tannin-protein complex degrading Streptococcus sp. in faeces of various animals

Osawa, R & Sly, LI 1992, Systematic and Applied Microbiology, vol. 15, no. 1, pp. 144-147.

Strains of the tannin-protein complex (T-PC) degrading Streptococcus bovis bacterium occur more commonly in browsing and omnivorous animals than in grazing and carnivorous animals. S. bovis bacteria dominates the streptococcal flora in the faeces of koalas (59.9% of streptococcal flora) and ringtail possums (59.1% of streptococcal flora), which are both animals with diets consisting primarily of tannin-rich eucalypt leaves.

  Tannins are biomolecules that bind to proteins to form chemical complexes that are highly resistant to degradation by digestive enzymes in the mammalian gut. They occur in various plants including eucalypts in high concentrations. In koalas, the bacterium S. bovis is known to play an important role in degrading T-PCs in the alimentary tract to facilitate digestion of dietary proteins. In this study, faecal samples of 14 mammal species were examined for the occurrence and quantity of T-PC degrading strains of S. bovis. The results were analysed in the context of each animal’s diet. Browsing animals such as koalas, ringtail possums and deer as well as omnivorous animals such as guinea pigs, pigs and brushtail possums commonly exhibited strains of T-PC degrading S. bovis in their faeces. In contrast, grazing herbivores such as cattle, sheep and horses and carnivores such as cats and dogs were less likely to contain T-PC degrading S. bovis in their faeces.

  Previous studies of animal digestion have suggested that browsing animals require some physiological defence against tannins due to their high consumption of tannin-rich plant matter, whereas grazing animals that feed predominantly on grass would not require such a defence. Despite some exceptions, this association was observed in the findings of this study which confirmed that browsing and omnivorous animals do require a defensive mechanism against tannins which grazing and carnivorous animals do not. The very high proportion of T-PC degrading S. bovis in the streptococcal flora in the faeces of koalas and ringtail possums indicates a more highly specialised adaptive strategy possessed by these species which consume high amounts of dietary tannins in their eucalypt-based diets.

  These findings contribute to our understanding of the dietary mechanisms and, more broadly, adaptations that allow the koala to sustain its high-tannin diet.


Summarised by Joanna Horsfall


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