Three-dimensional reconstruction of bacteria with a complex endomembrane system.

Area of Science:

• Cell Biology
• Microbiology
• Bacterial Ultrastructure

Background:

• Cellular compartmentalization is a key evolutionary development.
• The Planctomycetes, Verrucomicrobiae, and Chlamydiae (PVC) superphylum was thought to exhibit internal membrane-bound compartments.
• The internal organization of these bacteria remains incompletely understood.

Purpose of the Study:

• To investigate the three-dimensional organization of the endomembrane system in Gemmata obscuriglobus.
• To determine if G. obscuriglobus cells are truly compartmentalized or nucleated.
• To clarify the relationship between PVC bacterial membrane systems and classical Gram-negative bacteria.

Main Methods:

• Three-dimensional imaging techniques were employed to visualize the endomembrane system.
• Analysis of membrane invaginations and their connectivity within G. obscuriglobus cells.
• Comparative analysis with known bacterial membrane systems.

Main Results:

• Gemmata obscuriglobus cells are not compartmentalized; all internal membrane-defined spaces are interconnected.
• No closed compartments or a distinct nucleus-like structure were identified.
• The membrane organization represents an extension of the typical Gram-negative bacterial membrane system.

Conclusions:

• The findings challenge the notion of compartmentalization in G. obscuriglobus and likely other PVC bacteria.
• Bacterial cell organization definitions may need revision.
• This study provides insights into the evolution of complex cellular structures and the eukaryotic endomembrane system.