Bacterial Community of the Digestive Tract of the European Medicinal Leech (Hirudo verbana) from the Danube River.

The digestive tract of medicinal leeches from commercial suppliers has been investigated previously and comprises of a relatively simple bacterial community. However, the microbiome of medicinal leeches collected directly from the natural habitat has not been examined. In this study, we characterized the bacterial community in the digestive tract (anterior crop, posterior crop, and intestine) of the European medicinal leech, Hirudo verbana, collected from the Danube river using culture-independent and culture-dependent approaches. Culture-independent approach confirmed that the digestive tract of H. verbana carries a relatively simple bacterial community with species richness in the individual samples ranging from 43 to164. The dominant bacterial taxon was Mucinivorans sp. (49.7% of total reads), followed by Aeromonas sp. (18.7% of total reads). Several low abundance taxa, new for H. verbana, such as Phreatobacter, Taibaiella, Fluviicola, Aquabacterium, Burkholderia, Hydrogenophaga, Wolinella, and unidentified Chitinophagia, were also detected. The aerobic culturing approach showed Aeromonas veronii (Proteobacteria), the known leech symbiont, as the most dominant taxon followed by several Pseudomonas and Acidovorax spp. No significant differences in the bacterial community composition were detected among different parts of the digestive tract of individual leeches. However, the overall composition of the bacterial community among individual specimen varied significantly and this is possibly due to differences in leech age, feeding status, and blood source. Our results showed that the core bacterial community of H. verbana collected from the natural habitat is similar to that reported from the digestive tract of commercially supplied leeches maintained in the laboratory.