Visualisation of microalgal lipid bodies through electron microscopy

Area of Science:

• Microalgal biotechnology
• Cellular imaging techniques
• Lipid body analysis

Background:

• Lipid bodies are vital energy reserves in microalgae, crucial for biofuel production and other applications.
• Accurate visualization of lipid bodies is essential for understanding microalgal physiology and optimizing cultivation.
• Transmission electron microscopy (TEM) and cryo-scanning electron microscopy (cryo-SEM) are potential methods for microalgal lipid body detection.

Purpose of the Study:

• To compare the efficacy of TEM and cryo-SEM in detecting lipid bodies in microalgae.
• To evaluate different cryo-SEM preparation techniques (cryo-planing and freeze-fracturing).
• To determine the optimal microscopy method for visualizing microalgal lipid bodies.

Main Methods:

• Cells of Phaeodactylum tricornutum and Nannochloropsis oculata were harvested during mid-exponential and early stationary growth phases.
• Cryo-immobilisation followed by TEM was employed for high-resolution imaging.
• Cryo-SEM, utilizing both cryo-planing and freeze-fracturing, was used to assess lipid body visibility.

Main Results:

• TEM, after cryo-immobilisation, provided clear detection of lipid bodies, proving superior to cryo-SEM.
• Lipid bodies were rarely observed with cryo-SEM, except when internal crystalline structures (likely sterol esters or triacylglycerols) were exposed via freeze-fracturing.
• Cryo-planing with cryo-SEM failed to detect lipid bodies and was generally less effective for visualizing other organelles compared to TEM.

Conclusions:

• TEM is the preferred method for clear and reliable detection of lipid bodies in microalgae.
• Cryo-SEM techniques, including freeze-fracturing and cryo-planing, are less suitable for comprehensive lipid body visualization.
• While TEM excels at lipid body detection, cryo-SEM can reveal other organelles like chloroplasts.