Enteric bacteria contribute to nitrogen balance in diverse vertebrates because they produce urease, the enzyme needed to liberate nitrogen from urea. Although this system of urea-nitrogen recycling is as yet unknown in Amphibia, a recent study by researchers from Miami University of the wood frog (Rana sylvatica), a terrestrial hibernator that is strongly hyperuremic during winter, documented robust urease activity in bacteria inhabiting the hindgut. Despite a ~33% reduction in the number of bacteria, ureolytic capacity in hibernating winter frogs was superior to that of active summer frogs, and was further enhanced by experimentally augmenting urea within the host.

Bacterial inventories constructed using 16S rRNA sequencing revealed that the assemblages hosted by hibernating and active frogs were equally diverse but markedly differed in community membership and structure. Approximately 38% of the 96 observed bacterial genera were exclusive to one or the other group. Although ~60% of these genera possess urease-encoding genes and/or have member taxa that reportedly hydrolyze urea, hibernating frogs hosted a greater relative abundance and richer diversity of ureolytic organisms, including, notably, species of Pseudomonas and Arthrobacter. Amphibians, in whom urea accrual has a major osmoregulatory function, likely profit substantially by repurposing the nitrogen liberated from the bacterial hydrolysis of urea.

Thermal sensitivity of urease activity in a lysate prepared from bacteria collected from  frog hindgut or mouse caecum. Mean ± SEM;  N =3 samples (each a composite of three  individuals; see text for deta ils) were tested at each temperature. Means identified by dissimilar  letters were distinguishable (repeated – measures ANOVA;  P <0.05).

 

Reference
J. Wiebler (2018) Urea Hydrolysis by Gut Bacteria: First Evidence for Urea-Nitrogen Recycling in Amphibia Thesis ePub ahead of print [article]

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