Abstract
NaCl, KCl, or PEG (polyethylene glycol)-amended potato dextrose broth (PDB), and potato dextrose agar (PDA) are essential for pure culture studies of water stress on fungi. Direct information on the actual water potential (WP) of this salt-amended PDB and PDA is lacking. Much fungal research in the past calculated WP of these salt-amended growth media by adding the WP of their constituents taken from individual salt dilution studies. But the WP of any complex solution will be modified by the level of synergism between its solutes. This study presents evidence of change in NaCl concentration due to synergism for attaining the same level of WP in NaCl solution, and NaCl amended PDB and PDA. The relation between WP and temperature and WP and salt concentration is also modified depending on the number of solutes in a growth medium. The WP of PEG-amended PDB increases with rising temperature, while that of NaCl/KCl amended PDB and PDA decreases with the increase of temperature. These results can be useful for doing pure culture studies on the biology and modeling the growth of air, water, and soil-borne fungi important in the food and agriculture industry and in terrestrial and aquatic ecosystems.
Highlights
Temperature and moisture are the major physical factors determining the biology of any microorganism in its environment
The quantity of salt (NaCl/KCl/polyethylene glycol (PEG)) weight given in Tables 1–4 were used to amend potato dextrose broth (PDB) and potato dextrose agar (PDA) to standardize a water potential (WP) range of 0 to −9 MPa with an interval of −1 MPa at 20◦C
This study has demonstrated that with PDB and agar, the final WP of a solution is not an additive function of the WP of its individual components
Summary
Temperature and moisture are the major physical factors determining the biology of any microorganism in its environment. Due to the ease of working with airborne microorganisms directly on their food substrate (host), and availability of more sensitive instrumentation for measuring environmental parameters influencing their biology, the advances in understanding the biology, and epidemiology of airborne microorganisms is much more advanced than for fungi residing in soils. The difficulty of measuring water potential (WP) in a heterogeneity of microenvironments in the soil makes it imperative to conduct pure culture studies of soilborne microorganisms under controlled conditions for understanding their activity and how it is influenced by the environment. Pure culture studies need a growth medium which supports the growth of a microorganism. Potato dextrose broth (PDB), and potato dextrose agar (PDA) are the most commonly used liquid and solid growth media to study colony morphology, biomass production, reproduction, survival and production of chemicals such as antibiotics.
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