Legionella and Legionella-hosts from natural saline spring-clusters. Spring-clusters study

Legionella are parasites of freshwater protozoa responsible for Legionellosis. High-sodium concentrations inhibit growth and virulence-characteristics of laboratory strains, particularly in elevated temperatures. In this work we examine how opposing selection pressures, sodium and grazing, help shape Legionella ecology within natural environments. Utilizing Legionella-specific primers, we examined abundance, diversity, and community-composition, in natural spring-clusters of varying sodium concentrations. High abundances with low diversity were noted in sodium-rich spring-clusters including those exhibiting combined high temperatures. Community-composition was characterized by few-dominant-unique Legionella ASVs, not related to previously described species. Protozoan microbial community-structure and composition patterns resembled those of Legionella, suggesting exposure to similar selection pressures. We examined Legionella cooccurrence with potential protozoan-hosts and found associations with Ciliophora and Amoebozoa representatives. These results indicate selection forces in saline environments favor a relatively small but abundant group of Legionella species, that may have evolved mechanisms to cope with both high-sodium and grazing pressures.