Genome-Wide In Silico Analysis of the Type VI Secretion System (T6SS) Within the Morganella Genus

Area of Science:

• Microbiology
• Genomics
• Bacterial Pathogenesis

Background:

• Morganella spp. are opportunistic pathogens in the human gut microbiota, known for adaptability and difficult-to-treat infections.
• Morganella spp. are listed on the WHO Bacterial Pathogen Priority List (BPPL) due to their clinical significance.
• Recent genomic studies highlight species-specific differences, particularly the presence of a unique type VI secretion system (T6SS) operon in M. sibonii.

Purpose of the Study:

• To investigate the distribution and diversity of type VI secretion systems (T6SS) across different Morganella species.
• To compare T6SS content, including effectors and immunity proteins, between clinically relevant species like M. sibonii and M. morganii.
• To explore the potential role of T6SS in bacterial competition and host-pathogen interactions within the Morganella genus.

Main Methods:

• Retrospective analysis of 293 Morganella genomes collected between 1966 and 2023.
• Annotation of T6SS clusters and subtypes using SecReT6 and RAST platforms.
• Phylogenetic analysis of tssB genes and in silico identification of putative effectors and immunity proteins using BlastP and Alphafold.

Main Results:

• M. sibonii isolates were found to possess four distinct T6SS clusters (subtypes i1, i3 v.1, i3 v.2, and i5).
• In contrast, the majority of M. morganii isolates lacked T6SS, with only one-third harboring a subtype i1 T6SS.
• M. morganii frequently carried a T6SS-predicted TseV effector (95%), while M. sibonii displayed a broader range of effectors.

Conclusions:

• Significant species-specific patterns in T6SS distribution exist within the Morganella genus.
• The presence and diversity of T6SS, particularly in M. sibonii, may contribute to their pathogenicity and ecological niche.
• T6SS likely plays a role in bacterial lifestyle competition and host-pathogen interactions, warranting further investigation into Morganella pathogenicity.