Diverse Legionella‐Like Bacteria Associated with Testate Amoebae of the Genus Arcella (Arcellinida: Amoebozoa)

Abstract

Diverse species of Legionella and Legionella-like amoebal pathogens (LLAPs) have been identified as intracellular bacteria in many amoeboid protists. There are, however, other amoeboid groups such as testate amoeba for which we know little about their potential to host such bacteria. In this study, we assessed the occurrence and diversity of Legionella spp. in cultures and environmental isolates of freshwater arcellinid testate amoebae species, Arcella hemispherica, Arcella intermedia, and Arcella vulgaris, via 16S rRNA gene sequence analyses and fluorescent in situ hybridization (FISH). Analysis of the 16S rRNA gene sequences indicated that A. hemispherica, A. intermedia, and A. vulgaris host Legionella-like bacteria with 94-98% identity to other Legionella spp. based on NCBI BLAST search. Phylogenetic analysis placed Legionella-like Arcella-associated bacteria (LLAB) in three different clusters within a tree containing all other members of Legionella and LLAPs. The intracellular localization of the Legionella within Arcella hosts was confirmed using FISH with a Legionella-specific probe. This study demonstrates that the host range of Legionella and Legionella-like bacteria in the Amoebozoa extends beyond members of "naked" amoebae species, with members of the testate amoebae potentially serving an ecological role in the dispersal, protection, and replication of Legionella spp. in natural environments.

Novel Endosymbionts in Rhizarian Amoebae Imply Universal Infection of Unrelated Free-Living Amoebae by Legionellales

“…It was proposed that, even if such conditions are met environmentally, other bacteria would quickly outcompete potentially freely replicating Legionellales (Fields et al, 2002). Although some amoebal hosts are lysed by their endosymbionts (La Scola et al, 2004) our and other studies did not find any evidence for lysis of the host cell after replication of the Legionellales indicating that Legionellales may form stable and long term symbiosis with their host (Gomaa et al, 2018). Subsequently, this means that not necessarily the biofilms, but the amoebae within, form a reservoir for Legionellales.…”

“…It is now widely accepted that the term 'amoebae' describes an assemblage of morphologically similar, but only very distantly related microeukaryotes (Adl et al, 2019;Burki et al, 2019). By far most recognized hosts of Legionellales are amoebae in the higher-order Amorphea, including host genera like Acanthamoeba, Vermamoeba (former Hartmannella vermiformis), Arcella, Vannella, Cochliopodium, and Nuclearia (Santos et al, 2003;Dirren and Posch, 2016;Mehari et al, 2016;Tsao et al, 2017;Gomaa et al, 2018;Galindo et al, 2019). Nonamorphean amoeba hosts seem rare, although Legionellales were also detected in the distantly related amoeba genus Naegleria (Excavata; (Delafont et al, 2013)).…”