Bacterial communities in ballast tanks of cargo vessels-Shaped by salinity, treatment and the point of origin of the water but ?hatch? its typical microbiome

Ballast water is a main vector of introduction of potentially harmful or pathogenic aquatic organisms. The development of genetic tools for ballast water monitoring has been underway and highlighted as a source for accurate and reliable data for decision making. We used 16S rRNA gene amplicon sequencing to analyze the microbial communities found in the ballast water of fifteen commercial ships routed through two Estonian ports. In parallel, samples from the port area were collected at the same time each ship visited. Fluorescence micro-scopy was utilized to assess the effectiveness of the treatment applied to ballast water. In addition, supplemental samples were collected from Hamburg Port (Germany) and a ballast tank decontamination system used at this port. The composition and diversity of bacterial communities varied greatly between obtained samples. The application of UV treatment did not demonstrate significant reduction in species richness estimates. The composition of microbial communities was significantly influenced by salinity, treatment (mainly untreated or UV treated) and the point of origin of the ballast water. Over a hundred potentially pathogenic bacterial taxa were found in relatively high abundance, including in ballast water that had received UV treatment. These shortcomings of stand-alone UV treatment of ballast water, especially when weak treatment is applied insuffi-ciently, highlight the danger of possible harmful effects arising over time and the need for genetic tools for ballast water monitoring and management.

Automated summary

Ballast water is a major pathway for the introduction of potentially harmful or pathogenic aquatic organisms. Genetic tools can provide accurate and reliable data for monitoring and managing ballast water. Analysis of bacterial communities in ballast water using 16S rRNA gene amplicon sequencing revealed the presence of numerous potentially pathogenic bacterial taxa. UV treatment did not significantly reduce species richness estimates, emphasizing the risk of harmful effects when relying solely on UV treatment for ballast water disinfection.