28233 - Cell disruption

Extracellular Production:
- Involves secretion machinery within the cell.
- Risks include potential damage from proteases and external factors like pH.
- Refolding may be necessary to restore biological activity.
Intracellular Production:
- Requires cell disruption to isolate from cell debris, adding complexity to process.
- Typically limited to concentrations of ~20% of cell protein (approx. 10% of dry mass).
- Some polymers can accumulate to over 70% of dry cell mass.

It is generally preferred to have bio-products secreted (exocytosis) since this reduces downstream processing steps and overall costs.
However, certain organisms lack a secretion machinery, necessitating additional processes like cell disruption and flocculation for effective extraction and purification.

Design Considerations:
- Understand nature of products: high priced vs low priced, low molecular weight (MW) vs high MW.
- Processing steps differ for extracellular vs intracellular products.

Extracellular: Cell separation and isolation.
Intracellular: Recovery, disruption, isolation, purification, and polishing.

Cell disruption is a crucial operation in bioprocesses when intracellular proteins must be released.
Methods can be mechanical or enzymatic/chemical.
At large scales, mechanical disruption using high-pressure homogenizers is standard.

Cell Wall Structure: Resistance to disruption varies significantly, particularly in bacterial cells due to peptidoglycan layers.
Product Characteristics: Physical and chemical properties of the target product.
Contaminants: Consider how cell disruption may impact subsequent recovery steps.

Gram-positive Bacteria:
- Susceptible to lysozyme; consist mainly of peptidoglycan (15-50 nm thick).
- Simpler structure compared to Gram-negative bacteria.
Gram-negative Bacteria:
- Characterized by an outer membrane that excludes certain compounds (e.g., penicillin).
- Composed of lipopolysaccharides and have a thinner peptidoglycan layer.

Inclusion bodies are aggregates of insoluble proteins in bacteria that need to be recovered during downstream processing.

Eukaryotic cells are more complex than bacterial cells, making them generally easier to disrupt (e.g., mammalian cells) than plant cells which have strong cell walls.

Various cell types rated on ease of mechanical disruption:
- Mammalian cells: 7 (easily disrupted)
- Yeast: 3
- Gram-positive and Gram-negative bacteria: 2-5 (increasing difficulty)

Drastic reductions in extracellular solute concentrations can burst cells, especially those without walls or those weakened by antibiotics.

Lysozyme effectively digests Gram-positive bacteria. For Gram-negative bacteria, outer membrane defenses require chelating agents for effective processing.

Detergents like Triton-X and Tween can lyse plasma membranes of mammalian cells; less damaging than ionic detergents.

A continuous process that can reach pressures of 1500 bar (21750 psi), leading to efficient product release.
Multiple passes can enhance product recovery.

Uses sound waves to disrupt cells but generates heat, necessitating careful monitoring and cooling during the process.

Methods include direct counting (microscopy), laser particle sizing, and indirect measurements (protein concentration).

Cell disruption is essential for extracting intracellular compounds. Multiple methods exist depending on the product, its stability, and shear sensitivity. Success can be evaluated through a variety of analytical methods.