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Digestion, nutrition & metabolism

Formation of a clear zone on tannin-treated brain heart infusion agar by a Streptococcus sp. isolated from faeces of koalas

Osawa, RO 1990, Applied and Environmental Microbiology, vol. 56, no. 3, pp. 829-831.

A strain of tannin-protein complex degrading bacterium was identified in the faeces of koalas. Colonies of the isolate formed a clear zone on a tannin-treated brain heart infusion agar and were characterised as Streptococcus bovis biotype I.

  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. Koalas, therefore, require a mechanism to ‘degrade’ these complexes to extract the protein for metabolism. In this study, fresh faecal samples were collected from twelve captive adult koalas at Lone Pine Koala Sanctuary, Brisbane. From these, faecal suspension samples were spread onto tannin-treated brain heart infusion agar media and incubated anaerobically for 72 hours at 37OC. For samples from eight out of the twelve koalas, smooth-surfaced white colonies of 2 – 3mm diameter grew on the agar plates. The colonies had defined clear zones around their edges. Analysis of the purified isolates revealed that these were gram-positive cocci of the species S. bovis biotype I. The formation of clear zones on the tannin-treated agar indicates that S. bovis biotype I is able to degrade the tannin-protein complex and may, therefore, play an important role in digestion in the koala.

  The detection of S. bovis biotype I in koala faeces indicates a potentially significant role for this bacterium in the digestion of Eucalyptus leaves. To confirm this suggestion, further research will be required to describe the pathway for tannin-protein complex degradation by S. bovis biotype I in the koala’s alimentary tract.


Summarised by Joanna Horsfall


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