Fermentation Practices Select for Thermostable Endolysins in Phages

Area of Science:

• Microbiology
• Enzymology
• Evolutionary Biology

Background:

• Bacteriophage endolysins are crucial for bacterial cell wall lysis and phage release.
• Endolysins display diverse modular structures, but evolutionary drivers remain unclear.
• Streptococcus thermophilus, a dairy fermenter, offers a focused ecological niche to study endolysin evolution.

Purpose of the Study:

• Investigate the diversity and evolution of endolysins from phages infecting Streptococcus thermophilus.
• Identify structural features of S. thermophilus endolysins and their functional significance.
• Determine if endolysin evolution is influenced by the specific environmental conditions of dairy fermentation.

Main Methods:

• Bioinformatic analysis of endolysins from S. thermophilus phages.
• Structural and functional characterization of identified endolysins.
• Enzyme activity assays at varying temperatures and calcium concentrations.
• Analysis of positive selection pressures on endolysin motifs.

Main Results:

• Observed limited endolysin diversity in S. thermophilus phages, with a dominant structural type.
• Discovered a novel, conserved calcium-binding motif within the prevalent endolysin structure.
• This motif significantly enhanced enzyme stability and activity at elevated temperatures.
• Demonstrated positive selection for this motif under conditions mimicking dairy fermentation.

Conclusions:

• Endolysin evolution in S. thermophilus is constrained, favoring a specific structural type adapted to dairy environments.
• The identified calcium-binding motif is a key adaptation for endolysin function in high-temperature fermentation.
• This finding highlights the role of ecological niche and environmental factors in shaping phage-encoded enzyme evolution.