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Phenotypic characterisation of CO2-requiring strains of Streptococcus bovis from koalas

Osawa, R & Sly, LI 1991, Applied and Environmental Microbiology, vol. 57, no. 10, pp. 3037-3039.

Of six strains of the bacterium Streptococcus bovis sampled from koala faeces, two strains that were previously reported as anaerobic were found to be able to grow in oxygen-reduced air that was supplemented with carbon dioxide. The unique characteristic in these aerobic strains was likely the presence of the enzyme β-N-acetylglucosaminidase.

  S. bovis is a bacterium that plays an important role in degrading the tannin-protein complexes, that occur in high concentrations in eucalypts, in the koala’s alimentary tract. The finding that two S. bovis strains were able to grow under reduced oxygen conditions, such as in a candle jar, initially suggested that these strains are ‘aerotolerant’; however, it was subsequently discovered that the strains required the presence of carbon dioxide in order to grow. Although most strains of S. bovis are reported to grow aerobically, in this study, none of the koala strains could grow in untreated air. Analysis of the six strains revealed that the aerobic strains and the CO2-requiring strains were biochemically identical except for the absence of the enzyme β-N-acetylglucosaminidase in the latter category, which might play a role in the degradation of ingested streptococcal bacteria.

  Following the evidence presented in this study, further research will be required to investigate whether the absence of β-N-acetylglucosaminidase is a feature that is common to all CO2-requiring strains or whether this feature varies within the species S. bovis. The findings reported here contribute to our growing understanding of the unique digestive mechanisms of the koala that sustain its highly specialised diet.

 

Summarised by Joanna Horsfall

 

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