Bacterial communities on Fucus sp. harvested in tidal zones with or without exposure to human sewage in Greenland

Seaweed from Greenland has potential as a food source. However, human sewage is discharged directly to the sea in the vicinity of the communities, a practice which could lead to the seaweed becoming contaminated by human pathogens. The objective of this study was to investigate the effect of wastewater discharge on the bacterial communities of wild populations of Fucus sp. sampled in the tidal zones in the vicinity of Sarfannguit, a smaller settlement (∼110 inhabitants) with limited discharge, and Sisimiut, Greenland's second biggest town (∼5500 inhabitants). Fecal indicator bacteria (coliforms, Escherichia coli and the human fecal molecular marker HF183 [Fucus sp. only]) were consistently detected on Fucus sp. and in seawater from Sisimiut. In contrast, coliforms and E. coli were only detected once in samples collected close to the waste dump site in Sarfannguit. Presence of fecal indicator bacteria in seawater and on Fucus sp. coincided, indicating the utility of surveying seawater. MALDI-TOF mass spectrometry analysis of bacterial isolates identified fish and human pathogens on seaweed from Sisimiut while >80% of isolates from Sarfannguit could not be identified using existing data bases. Amplicon sequence variants belonging to Rhodobacteraceae and Flavobacteriaceae were dominant families in all Fucus sp. samples. However, wastewater discharge effected major changes in the overall composition of the seaweed microbiota as evidenced by analysis of the beta diversity. In conclusion, the microbiota on Fucus sp. harvested in the intertidal zones in a small, relatively unimpacted community, and close to the wastewater discharge of a larger community showed marked differences and the presence of human pathogens on sewage impacted Fucus sp. from the large community. It is recommended that microbiological criteria and guidelines regarding suitable seaweed harvest and cultivation sites be established, especially considering potential sources of anthropogenic impact on the local marine environment.