Msh Pilus Mutations Increase the Ability of a Free-Living Bacterium to Colonize a Piscine Host

Area of Science:

• Microbiology
• Evolutionary Biology
• Animal-Bacterial Symbiosis

Background:

• Animal-bacterial symbioses are widespread and crucial for understanding host colonization.
• Investigating bacterial evolution during host association provides insights into symbiosis initiation.

Purpose of the Study:

• To elucidate the role of a specific mutation (mshL) in bacterial adaptation to a vertebrate host.
• To determine how bacterial behaviors outside the host influence the early stages of symbiosis.

Main Methods:

• Serial passage of Shewanella oneidensis through germ-free zebrafish digestive tracts.
• Genetic analysis to identify adaptive mutations and assess their functional impact (loss-of-function).
• Quantification of bacterial colonization, motility, surface adhesion, and immigration rates.

Main Results:

• A loss-of-function mutation in mshL enhanced zebrafish colonization by increasing bacterial presence in the water column.
• The mshL mutation facilitated higher per capita immigration rates into host digestive tracts.
• No competitive advantage was observed for mutant strains once established within the host.

Conclusions:

• Bacterial behaviors outside the host, such as altered surface association and motility, are critical for initiating novel host associations.
• The mshL gene mutation plays a significant role in the early colonization dynamics of Shewanella oneidensis in zebrafish.
• Understanding extrach host bacterial adaptations is key to deciphering the evolution of animal-microbe symbiosis.