Legionella pneumophila CRISPR-Cas suggests recurrent encounters with Gokushovirinae

Abstract

Legionella pneumophila is a ubiquitous freshwater pathogen and the causative agent of Legionnaires’ disease. This pathogen and its ability to cause disease is closely tied to its environmental encounters. From phagocytic protists, L. pneumophila has 'learned' how to avoid predation and exploit conserved eukaryotic processes to establish an intracellular replicative niche. Legionnaires' disease is a product of these evolutionary pressures as L. pneumophila uses the same molecular mechanisms to replicate in grazing protists and in macrophages of the human lung. L. pneumophila growth within protists also provides a refuge from desiccation, disinfection, and other remediation strategies. One outstanding question has been whether this protection extends to phages. L. pneumophila isolates are remarkably devoid of prophages and to date no Legionella phages have been identified. Nevertheless, many L. pneumophila isolates maintain active CRISPR-Cas defenses. So far, the only known target of these systems has been an episomal element that we previously named Legionella Mobile Element-1 (LME-1). In this study, we have identified over 150 CRISPR-Cas systems across 600 isolates, to establish the clearest picture yet of L. pneumophila’s adaptive defenses. By leveraging the sequence of 1,500 unique spacers, we can make two main conclusions: current data argue against CRISPR-Cas targeted integrative elements beyond LME-1 and the heretofore 'missing' L. pneumophila phages are most likely lytic gokushoviruses.

Benefits and Challenges of Applying Bacteriophage Biocontrol in the Consumer Water Cycle

“…However, Lammertyn et al [ 46 ] were the first to report on the isolation and preliminary characterisation of bacteriophages active against L. pneumophila , subsequently highlighting the potential of bacteriophage biocontrol of this environmental pathogen. While no additional studies have reported on the isolation of L. pneumophila bacteriophages, using genomic analyses of 600 L. pneumophila isolates, Deecker et al [ 47 ] recently reported that the L. pneumophila isolates analysed in their study were devoid of prophages, and that bacteriophages targeting L. pneumophila are most likely lytic gokushoviruses ( Microviridae family), which are found in various aquatic environments.…”