Methods for imaging Shewanella oneidensis MR-1 nanofilaments

Area of Science:

• Microbiology
• Microbial Physiology
• Electron Microscopy

Background:

• Shewanella oneidensis MR-1 is known for producing extracellular appendages.
• Understanding the production and imaging of these structures is crucial for microbial research.

Purpose of the Study:

• To evaluate nanofilament production by Shewanella oneidensis MR-1.
• To investigate the influence of lifestyle (planktonic vs. sessile) and environmental conditions (aerobic vs. anaerobic) on nanofilament imaging.
• To determine the necessity of specific sample preparation techniques for visualizing these structures.

Main Methods:

• Scanning electron microscopy (SEM) was employed to image Shewanella oneidensis MR-1.
• Cells were cultured under both aerobic and anaerobic conditions in planktonic and sessile (biofilm) states.
• Sample preparation involved fixation, critical point drying, and conductive metal coating.

Main Results:

• Nanofilaments were successfully imaged on MR-1 cells across all tested conditions (planktonic/sessile, aerobic/anaerobic).
• Critical point drying was a mandatory step for imaging nanofilaments on planktonic cells.
• Critical point drying was not required for imaging nanofilaments on cells within biofilms.
• The described methods cannot distinguish between nanofilaments, nanowires, pili, or flagella.

Conclusions:

• The lifestyle of Shewanella oneidensis MR-1 significantly impacts the sample preparation requirements for imaging its nanofilaments.
• Specific preparation techniques, like critical point drying, are vital for visualizing extracellular structures in planktonic bacteria.
• Further methodological development is needed to differentiate various extracellular appendages produced by Shewanella oneidensis MR-1.