Why are filamentous fungal cells generally more sensitive to hydrodynamic shear than bacterial cells in bioreactors?

Introduction:
Bioprocess design for filamentous fungi (for example, Aspergillus or Penicillium) must account for the organism's morphology and mechanics. Compared with unicellular bacteria, filamentous systems form hyphae and pellets whose size, rigidity, and branching influence how they interact with turbulent eddies and impeller-induced shear. Understanding these differences helps prevent loss of productivity due to excessive fragmentation or lysis.

Given Data / Assumptions:

• Filamentous fungi produce hyphal networks and pellets.
• Cell wall composition includes chitin and glucans.
• Typical stirred tanks exhibit a range of eddy sizes and shear rates.

Concept / Approach:
Larger biological structures experience higher velocity gradients across their dimensions. Chitin-rich walls provide rigidity that can localize stress at branching points, while long hyphae couple more strongly to turbulent eddies. As a result, fungal aggregates are prone to shear-induced breakage, altering pellet size distribution, oxygen transfer, and metabolite profiles.

Step-by-Step Solution:

Verification / Alternative check:
Microscopic observations show hyphal fragmentation near impellers and in high-shear zones. Oxygen uptake and viscosity profiles shift as pellet sizes change with agitation, evidencing shear sensitivity when conditions are intensified.

Why Other Options Are Wrong:

• Each individual statement (a), (b), and (c) is valid but incomplete; together they explain the observed sensitivity.

Common Pitfalls:
Over-agitation to reduce viscosity can harm morphology and productivity. Balancing oxygen transfer with gentle hydrodynamics, or using airlift reactors, can protect filamentous cultures.

Final Answer:
all of the above