How do pyridine alkaloid secondary metabolites affect the gut microbiome of sunbirds?

Sunbirds (Cinnyris osea) feed on tobacco tree (Nicotiana glauca) nectar that contains the pyridine alkaloid toxic compounds nicotine and anabasine. Our aim was to understand the effect of the secondary metabolites nicotine and anabasine on the taxonomy of nectarivore`s gut microbiome. Using an experimental approach, sunbirds that were kept in captivity were divided into two groups. One group was fed with artificial nectar and an addition of nicotine and anabasine and the second group was fed only with artificial nectar. Excreta were collected in four-time intervals of 0, 2, 4 and 7 weeks and their microbiota were analysed using culturable and culture independent approaches. Non-metric Multidimensional scaling analysis (nMDS) results demonstrated that the secondary metabolites had significantly changed the gut microbiota of the sunbirds that were fed with the addition of pyridine alkaloids. Lactococus, Enterobacteriaceae_unclassified, Rothia, Leuconostoc, Klebsiella, Salmonella, Exiguabaterium and Aeromonas were found to contribute to these differences between the control and the treated birds. Moreover, four weeks after starting to feed the birds with the addition of nicotine and anabasine, genera with the ability to degrade these compounds proliferated from a total relative abundance of only 0.3% to 52.7% of the microbiota community. Nectar has a very poor protein content. Nicotine and anabasine contain nitrogen, thus, the significant change in the microbiota of the sunbirds’ gut with respect to the addition of these secondary metabolites has a role not only in the detoxification of the pyridine alkaloids but also in providing nitrogen supply to the host.