Outer membrane proteins and cell surface structure of Selenomonas ruminantium

Area of Science:

• Microbiology
• Bacterial Cell Wall Structure
• Protein Biochemistry

Background:

• Selenomonas ruminantium is a Gram-negative bacterium.
• The outer membrane and peptidoglycan layer are crucial components of bacterial cell envelopes.
• Understanding these structures is key to bacterial physiology and pathogenesis.

Purpose of the Study:

• To determine the protein composition of Selenomonas ruminantium outer membranes.
• To investigate the association of outer membrane proteins with peptidoglycan.
• To confirm the absence of Braun lipoprotein and compare S. ruminantium to Escherichia coli mutants.

Main Methods:

• Sodium dodecyl sulfate polyacrylamide gel electrophoresis (SDS-PAGE).
• Two-dimensional gel electrophoresis (isoelectric focusing followed by SDS-PAGE).
• Electron microscopy of cell surface morphology.
• Lysozyme susceptibility assays.

Main Results:

• Two major outer membrane proteins (42,000 and 40,000 Da) were identified as peptidoglycan-associated.
• These proteins dissociated at 85°C.
• The absence of Braun lipoprotein was confirmed.
• Electron microscopy revealed a wrinkled outer membrane with blebs and vesicles.
• Cells underwent rapid lysis upon lysozyme addition.

Conclusions:

• Selenomonas ruminantium's outer membrane protein composition and cell surface characteristics are distinct.
• The strain lacks Braun lipoprotein, similar to certain Escherichia coli mutants.
• Its physiological and morphological properties align with "deep rough" and mlp/lpo mutants of E. coli K-12.