Diversity of Free-Living Amoebae in New Zealand Groundwater and Their Ability to Feed on Legionella pneumophila

Free-living amoebae (FLA) are common in both natural and engineered freshwater ecosystems. They play important roles in biofilm control and contaminant removal through the predation of bacteria and other taxa. Bacterial predation by FLA is also thought to contribute to pathogen dispersal and infectious disease transmission in freshwater environments via the egestion of viable bacteria. Despite their importance in shaping freshwater microbial communities, the diversity and function of FLA in many freshwater ecosystems are poorly understood. In this study, we isolated and characterized FLA from two groundwater sites in Canterbury, New Zealand using microbiological, microscopic, and molecular techniques. Different methods for groundwater FLA isolation and enrichment were trialed and optimized. The ability of these isolated FLA to predate on human pathogen Legionella pneumophila was assessed. FLA were identified by 18S metagenomic amplicon sequencing. Our study showed that Acanthamoeba spp. (including A. polyphaga) and Vermamoeba veriformis were the main FLA species present in both groundwater sites examined. While most of the isolated FLA co-existed with L. pneumophila, the FLA populations in the L. pneumophila co-culture experiments predominantly consisted of A. polyphaga, Acanthamoeba spp., Naegleria spp., V. vermiformis, Paravahlkampfia spp., and Echinamoeba spp. These observations suggest that FLA may have the potential to act as reservoirs for L. pneumophila in Canterbury, New Zealand groundwater systems and could be introduced into the local drinking water infrastructure, where they may promote the survival, multiplication, and dissemination of Legionella. This research addresses an important gap in our understanding of FLA-mediated pathogen dispersal in freshwater ecosystems.