Molecular Methods Reveal Responses of Bacterial Communities, Including Indicator Species, to Ballast Water Management

Ballast water (BW) is an important vector for the global transport of bacterial taxa, including pathogens. The application of molecular tools for evaluating and monitoring BW management practices could improve the accuracy and sensitivity of bacterial detections. However, few studies have examined treatment-associated changes in bacterial communities during shipboard operations using molecular methods, limiting both understanding of the efficacy of management practices and the ability to validate molecular tools for BW monitoring. Here, we evaluate changes in bacterial communities during two experimental voyages using BW treatment (BWT) and a combined management approach of BWT plus BW exchange (BWT+E). The bacterial indicator taxa E. coli and enterococci were analyzed using targeted qPCR and compared to the standard most probable number (MPN) culture-based approach, while changes in microbial community composition were monitored with 16S rRNA gene sequencing. While indicator organisms were below D-2 regulations after both BWT and BWT+E, 16S rRNA sequencing revealed changes in bacterial community composition and molecular markers of bacteria related to potential pathogens. qPCR estimates of indicator taxa were consistent with those obtained through standard culture methods but may offer increased sensitivity for detecting changes associated with management. Our results support the use of molecular approaches for assessing BWT efficacy and, pending further validation, compliance monitoring.