From Shipping to Swimming: Bacterial Monitoring and Diversity in Ballast Treatment Systems and Recreational Waters

Abstract

The use of indicator organisms as a proxy for pathogenic bacteria significantly reduces the cost and complexity of monitoring aquatic systems. Fecal indicator bacteria, such as Escherichia coli and Enterococcus spp., are commonly used by governmental agencies in recreational beach monitoring, wastewater treatment, and more recently as a tool in ballast water management. This research utilized culture-based and molecular techniques (qPCR and DNA sequencing) to explore two different applications of indicator bacteria: (1) a bench-scale experiment to explore the effectiveness of ballast water treatment techniques in freshwater and (2) an investigation of the sources of fecal contamination in a small Lake Superior tributary and surrounding recreational beaches. The ballast experiment addressed whether indicator bacteria are truly representative of other potentially harmful microbes after treatment (UV light and chlorination), as well as the scale of post-treatment bacterial regrowth. Both treatment techniques resulted in 99% reductions in culturable indicator and heterotrophic bacteria immediately following treatment (68-99% reductions when measured by qPCR). After 5 days, however, both lab and field incubations showed considerable regrowth of total bacteria (not reflected in indicators) and a distinct shift in bacterial community composition, including the regrowth of multiple pathogen containing genera (particularly Acinetobacter, Flavobacterium, Pseudomonas). The microbial source tracking project used library-independent and library-dependent methods to identify the sources of elevated E. coli in the recreational waters of Two Harbors, MN. Culturable E. coli abundance was correlated with turbidity and storm events, while human fecal sources appeared to be site-specific and independent from weather conditions. Both projects highlight the benefits and limitations of indicator bacteria in water quality monitoring and reinforce the importance of layering multiple analysis techniques to provide a more comprehensive understanding of microbial communities in ballast treatment systems and recreational waterways.