Aggregatibacteraphrophilus T6SS Effectors in Host-Bacterial Interactions

Area of Science:

• Microbiology
• Oral Biology
• Bacterial Pathogenesis

Background:

• Aggregatibacter aphrophilus possesses a unique type VI secretion system (T6SS) for interbacterial interactions.
• The T6SS in A. aphrophilus has not been previously linked to anti-eukaryotic activity or its specific effectors identified.
• Understanding T6SS function is crucial for deciphering bacterial competition and host colonization in the oral microbiome.

Purpose of the Study:

• Identify and characterize T6SS effectors in A. aphrophilus.
• Investigate the role of these T6SS effectors in interbacterial competition against A. actinomycetemcomitans.
• Determine the contribution of A. aphrophilus TSS effectors to host cell interactions and inflammatory responses.

Main Methods:

• Genetic inactivation of putative T6SS effector genes (glycosyl hydrolase and phospholipase D) in A. aphrophilus.
• Co-culture experiments with A. aphrophilus and A. actinomycetemcomitans in multispecies biofilms.
• Co-culture experiments with A. aphrophilus (wild-type and mutants) and human gingival keratinocytes to assess inflammatory responses.

Main Results:

• Inactivation of both identified T6SS effectors abolished interbacterial activity against A. actinomycetemcomitans.
• Neither effector directly modulated the acute inflammatory response in gingival keratinocytes.
• TSS-dependent elimination of A. actinomycetemcomitans by A. aphrophilus reduced overall inflammation, an effect dependent on the identified effectors.

Conclusions:

• A. aphrophilus T6SS effectors exhibit distinct functions in bacterial versus eukaryotic cell interactions.
• These T6SS effectors contribute to modulating host inflammatory responses indirectly by controlling bacterial load.
• The identified T6SS effectors represent novel targets for managing periodontal pathogens and their interactions with the oral-mucosal barrier.