Molecular detection of potentially harmful bacteria discharged into the Duluth-Superior Harbor in the ballast water of commercial ships

Background/Question/Methods Samples of untreated ballast water from 24 large commercial ships deballasting in the Duluth-Superior Harbor (DSH) were collected between 2010 and 2012. The 16S rDNA was sequenced using next-generation Illumina sequencing to identify bacteria resident in ballast water samples. Sequences were cross referenced to a database of bacteria that are potentially harmful to humans, fish, or wildlife or are environmentally disruptive. 

Results/Conclusions Sequences from relatively few traditional indicator bacterial genera (Vibrio, Escherichia, Enterococcus, etc.) were detected but sequences from other often overlooked and potentially harmful bacteria were found, including: Acinetobacter, Clostridium, Aeromonas, Piscirickettsia and Tenacibaculum. Tenacibaculum is a genus containing numerous marine fish pathogens and constituted 1.2% (2083 sequence copies) of the ballast water sequences obtained from a seagoing ship in the DSH. Next-generation Illumina sequencing can relatively quickly detect rare sequences of interest that may well be missed by other detection methods. Identifying bacteria from genera containing harmful strains in ship ballast water after a mid-ocean ballast water exchange indicates that potentially harmful bacteria may be transported, discharged, and go undetected under current ballast water management practices.