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Role of water mobility on mold spore germination
X Pham1, E Vittadini, R E Levin
1Department of Food Science, University of Massachusetts, Amherst, Massachusetts 01003, USA.
Abstract:
A sugar transport defected strain of Aspergillus nidulans (biA-1 sorA-2) was tested for spore germination in nutrient media containing various water activity (a(w)) values and varying amounts of non-nutritive, nontoxic carbohydrates (L-sorbose and cellulose). Freeze-dried media [containing the same nutrient level but different in sorbose/cellulose (s:c) ratio] were adjusted to 0.75-0.97a(w) at 25 degrees C before inoculation. Minimum a(w) for germination varied with s:c ratio. Because both sorbose and cellulose were not metabolizable and unable to be transported into the cells, the results reflected the molecular mobility of water. (2)H NMR T(2) relaxation time correlated well with spore germination time, and it distinguished the difference between water sorbed to cellulose and water in a solution associated with dissolved sorbose. On the other hand, mold germination time correlated poorly with a(w). It was highly dependent on the s:c ratio. Water mobility was found to correlate better with biological activity than a(w) because it differentiated the availability between water in dissolved sorbose and adsorbed water in cellulose.
Insights
This study shows that water mobility, not just water activity, is crucial for mold spore germination. Different carbohydrate ratios affect water availability, impacting germination success in Aspergillus nidulans.
Area of Science:
- Microbiology
- Biophysics
Background:
- Spore germination is influenced by water availability.
- Understanding water's role in microbial growth is essential for various applications.
Purpose of the Study:
- To investigate the relationship between water activity, water mobility, and spore germination in Aspergillus nidulans.
- To determine if water mobility is a better predictor of germination than water activity.
Main Methods:
- Tested a sugar transport-defective Aspergillus nidulans strain (biA-1 sorA-2) for spore germination.
- Used nutrient media with varying water activity (a(w)) and sorbose/cellulose ratios.
- Measured water mobility using (2)H NMR T(2) relaxation times.
Main Results:
- Minimum water activity for germination varied with the sorbose/cellulose ratio.
- Water mobility, measured by NMR, correlated well with spore germination time.
- Mold germination time was highly dependent on the sorbose/cellulose ratio, not just water activity.
Conclusions:
- Water mobility, reflecting molecular mobility of water, better predicts spore germination than water activity alone.
- The availability of water, influenced by its interaction with non-metabolizable carbohydrates, is key for germination.
- This highlights the importance of considering water's physical state in microbial ecology and biotechnology.