Molecular Networking combined with culture media variation reveal the metabolic potential of Pantoea eucrina isolated from a sponge living in a volcanic vents system

Ischia is an island located in the gulf of Naples (South Italy), and its environment represents a singular marine habitat because of the volcanic origin of the island. Here, the presence of underwater CO2 emissions, caused by the effect of secondary volcanism, creates a unique area of naturally lowered pH. Different sponges were collected in this acidified area and subjected to microbial isolation. Among the isolates, the Gram-negative strain Pantoea eucrina, isolated from the sponge Chondrosia reniformis, was selected for further studies. Its metabolome was explored by a combined approach involving culture media variation and Molecular Networking. This approach yielded a very complex molecular network, allowing the annotation of several metabolites, among them two biosurfactants clusters: lipoamino acids and surfactins. Noteworthy is the production of unusual new surfactin derivatives, which is reported here for the first time from Pantoea genus. Their production was only triggered by using inorganic nitrogen as sole nitrogen source, while it was totally abolished in the other conditions. Major metabolites belonging to N-lipoamino acids were characterized through HRMS/MS, 1D and 2D NMR spectroscopy, some of them were identified for the first time as natural products. Antimicrobial activity assessment of pure metabolites towards a panel of human pathogens indicated a relevant activity; in particular, the leucine containing N-lipoamino acids revealed to be very effective towards Staphylococcus aureus, Staphylococcus epidermidis and a clinical isolate of the emerging food pathogen Listeria monocytogenes.