Abstract
The gastrointestinal tract of animals is adapted to their primary source of food to optimize resource use and energy intake. Temperate bat species mainly feed on arthropods. These contain the energy-rich carbohydrate chitin, which is indigestible for the endogenous enzymes of a typical mammalian gastrointestinal tract. However, the gastrointestinal tract of bat species should be adapted to their diet and be able to digest chitin. We hypothesized that (i) European vespertilionid bat species have the digestive enzyme chitinase and that (ii) the chitinolytic activity is located in the intestine, as has been found for North American bat species. The gastrointestinal tracts of seven bat species (Pipistrellus pipistrellus, Plecotus auritus, Myotis bechsteinii, Myotis nattereri, Myotis daubentonii, Myotis myotis, and Nyctalus leisleri) were tested for chitinolytic activity by diffusion assay. Gastrointestinal tracts of P. pipistrellus, P. auritus, M. nattereri, M. myotis, and N. leisleri were examined for acidic mammalian chitinase by western blot analysis. Tissue sections of the gastrointestinal tract of P. pipistrellus were immunohistochemically analyzed to locate the acidic mammalian chitinase. Chitinolytic activity was detected in the stomachs of all bat species. Western blot analysis confirmed the acidic mammalian chitinase in stomach samples. Immunohistochemistry of the P. pipistrellus gastrointestinal tract indicated that acidic mammalian chitinase is located in the stomach chief cells at the base of the gastric glands. In conclusion, European vespertilionid bat species have acidic mammalian chitinase that is produced in the gastric glands of the stomach. Therefore, the gastrointestinal tracts of insectivorous bat species evolved an enzymatic adaptation to their diet.
Highlights
Animals have to ingest and digest food to ensure the continuous functioning of their internal metabolism by covering, for example, their energy, protein and vitamin requirements [1]
The chitinolytic activity in the stomach samples was highest between pH 5.0 and pH 6.0 (Fig. 2)
Expression of chitinase in the GI tract Western blot analysis of the M. musculus stomach showed a characteristic band at a relative molecular weight of 46 k, indicating the presence of acidic mammalian chitinase (AMCase)
Summary
Animals have to ingest and digest food to ensure the continuous functioning of their internal metabolism by covering, for example, their energy, protein and vitamin requirements [1]. Food needs to be processed quickly to reduce the energy demand caused by increased flight mass [2]. European bat species have a diet consisting predominantly of arthropods [5] They have short retention times [6] but a high digestive efficiency [7]. This suggests that their gastrointestinal (GI) tract is highly adapted to their diet since it digests arthropods quickly and thoroughly. Since arthropods consist of up to 75% chitin (energy content 21.2 kJ/g, [8]), it is highly plausible that bat species are able to digest chitinous material, as has been demonstrated in other vertebrates such as the European green lizard (Lacerta viridis), the common blackbird (Turdus merula) and the red fox (Vulpes vulpes) [9,10]
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