The entry mechanism of membrane-containing phage Bam35 infecting Bacillus thuringiensis

Area of Science:

• Microbiology
• Virology
• Structural Biology

Background:

• The temperate double-stranded DNA bacteriophage Bam35 infects gram-positive Bacillus thuringiensis.
• Bam35 possesses an icosahedral protein coat, a viral membrane, and a linear 15-kbp DNA genome.
• Its protein coat assembly shares principles with bacteriophage PRD1, which infects gram-negative hosts.

Purpose of the Study:

• To dissect the infection process of bacteriophage Bam35 into distinct steps.
• To investigate the mechanisms of receptor binding, peptidoglycan penetration, and plasma membrane interaction.
• To identify factors influencing Bam35 entry into Bacillus thuringiensis cells.

Main Methods:

• Cell surface adsorption assays to study binding kinetics.
• Zymogram analysis to detect enzymatic activity associated with the virion.
• Biochemical assays to determine the role of divalent cations in viral entry.

Main Results:

• Bam35 rapidly adsorbs to the Bacillus thuringiensis cell surface.
• N-acetyl-muramic acid was identified as essential for Bam35 binding.
• Pptidoglycan-hydrolyzing activity was detected in association with the Bam35 virion.
• Bam35 penetration through the plasma membrane is dependent on divalent cations, unlike adsorption and peptidoglycan digestion.

Conclusions:

• Bacteriophage Bam35 employs a multi-step entry mechanism involving specific receptor recognition and enzymatic degradation of the host cell wall.
• Divalent cations play a critical role in facilitating the passage of Bam35 across the plasma membrane.
• Understanding these mechanisms provides insights into phage-host interactions in gram-positive bacteria.