Broth rheology and morphology: Assuming no extracellular gum secretion, which culture type typically gives the highest broth viscosity during fermentation?

Introduction:
Microbial morphology directly impacts broth rheology. Understanding which morphologies create viscous, non-Newtonian behavior is crucial for choosing aeration and agitation strategies and for predicting mass-transfer limitations.

Given Data / Assumptions:

• No secretion of exopolysaccharide gums (so viscosity arises from cells themselves).
• Comparing unicellular forms (bacteria, yeast) to filamentous forms.
• Considering pelletized versus dispersed mycelial growth.

Concept / Approach:
Dispersed filamentous mycelia form long, flexible networks that entangle and dramatically increase apparent viscosity and elasticity (pseudoplastic, thixotropic behaviors). Pelletized fungi present lower surface area for entanglement and can yield lower bulk viscosity. Unicellular bacteria and yeasts, being small and non-filamentous, typically lead to near-Newtonian or mildly shear-thinning broths of much lower viscosity.

Step-by-Step Solution:
Identify morphology: long, poorly branched hyphae create fiber networks.Relate structure to rheology: networks entangle, increasing resistance to flow.Contrast with pellets: compact aggregates reduce network formation in the bulk.Conclude: dispersed mycelia produce the highest viscosities among the listed options.

Verification / Alternative check:
Power-law indices (n) < 1 and high consistency coefficients (K) are frequently observed for mycelial broths, along with pronounced thixotropic loops, confirming strong viscosity elevation relative to unicellular cultures.

Why Other Options Are Wrong:
Bacteria and yeast: small, spherical/rod cells with limited entanglement; viscosities close to water at modest cell densities.

Pelletized fungi: lower bulk entanglement; may increase apparent yield stress but generally less viscous than dispersed mycelia.

Common Pitfalls:

• Assuming all filamentous growth increases viscosity equally; morphology (pellet vs. dispersed) matters greatly.
• Overlooking agitation effects that can shift morphology between pellets and mycelia.

Final Answer:
Filamentous fungi growing as long, poorly branched chains (dispersed mycelia)