Genomic divergence and phenotypic heterogeneity of Legionella longbeachae reveal a putative novel proinflammatory serogroup with genome reduction and mobilome expansion.

A novel Legionella longbeachae serogroup (sg3) exhibits genome reduction to 4.01 Mb yet induces heightened inflammatory responses in human cells.

• Why it matters: Understanding the diversity and pathogenic mechanisms of L. longbeachae is crucial as it is an emerging respiratory pathogen with undercharacterized genomic features, impacting diagnosis and surveillance.
• What they did: Analyzing 242 isolates through pan-genomics and functional infection models, researchers identified a distinct lineage with genome reduction, loss of plasmids, and increased proinflammatory activity linked to mobilome expansion.
• The result: The findings reveal that genome reduction does not diminish pathogenicity; instead, mobilome expansion correlates with increased inflammation, suggesting the need for revised diagnostics and ongoing surveillance of this potentially more virulent lineage.