A novel variant of the

Area of Science:

• Microbiology
• Bacterial Pathogenesis
• Genomics

Background:

• The type VIIb protein secretion system (T7SSb) is crucial for interbacterial competition in Bacillota bacteria.
• EssC, a key ATPase component of T7SSb, influences substrate recognition and exhibits sequence variation.
• Previous studies identified seven EssC variants in Listeria monocytogenes, linked to specific secreted substrates.

Purpose of the Study:

• To investigate the diversity of the T7SSb, specifically EssC variants and associated proteins, within a large collection of Listeria monocytogenes genomes.
• To identify novel components and genomic locations of T7SSb-related proteins, including LXG-domain proteins.
• To explore the prevalence and diversity of EssC types across the Listeria genus.

Main Methods:

• Bioinformatic analysis of 37,930 Listeria monocytogenes genomes.
• Identification and characterization of EssC sequence variants and adjacent genes.
• Comparative genomics across different Listeria species.

Main Results:

• Discovery of a rare eighth EssC variant (EssC8) in Listeria monocytogenes lineage III, associated with a rearrangement hotspot (Rhs) repeat toxin and accessory proteins.
• Identification of nine novel LXG-domain proteins and four new chromosomal hotspots for LXG protein encoding.
• Confirmation that all eight Listeria monocytogenes EssC variants are present in other Listeria species, with additional novel EssC types discovered.
• Observation that Listeria species frequently encode multiple EssC types, highlighting T7SSb diversity within the genus.

Conclusions:

• Listeria monocytogenes possesses a highly diverse T7SSb, with significant variation in its EssC component and associated effector proteins.
• The identified novel proteins and genomic locations expand our understanding of T7SSb functionality and evolution.
• T7SSb diversity is a defining characteristic of the Listeria genus, likely playing a significant role in their ecological interactions and pathogenicity.