Effects of Amino Acids on Ammonia Secretion and Extracellular Protease Activity by Three Oomycetes in Synthetic Medium With or Without Glucose

Author: mycolabadmin
2005-03-31
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Summary

This research investigated how different amino acids affect the growth and biochemical activities of three types of water molds that can cause diseases in fish. The study helps us understand how these fungi process nutrients and potentially cause infections. Impact on everyday life: • Better understanding of fish diseases that affect aquaculture and fish farming • Improved knowledge for developing treatments for fungal infections in fish • Enhanced understanding of how fungi break down proteins, which is relevant for both disease control and industrial applications • Potential applications in developing new antifungal treatments • Insights that could help protect fish populations in both wild and farmed conditions

Background

Zoosporic fungi are known to cause serious diseases in fish and shellfish by penetrating their bodies. These fungi can also infect protein-rich bodies like mosquitoes, mushroom grubs, and nematodes. Proteolytic enzymes are essential for insect pathogenic fungi to degrade host cuticle. While amino acids have been reported as suitable carbon sources for some Oomycetes, particularly Saprolegniales, some studies found inhibitory effects due to ammonia accumulation and pH rise in the medium.

Objective

To study the effects of three amino acids (isoleucine, aspartic acid, and phenylalanine) on biomass mycelial dry weights, pH values changes, ammonia secretions, and protease activity of three zoosporic fungi (Achlya proliferoides, A. racemosa and Saprolegnia furcata) common in the River Nile system and known as fish pathogens.

Results

Isoleucine and aspartic acid generally stimulated mycelial dry weight production when used as nitrogen sources, while phenylalanine was inhibitory. When amino acids served as both carbon and nitrogen sources, mycelial dry weights increased relative to controls but decreased at higher concentrations. Amino acids significantly increased pH values and ammonia secretion, particularly when glucose was absent. Extracellular protease activity varied depending on the fungal species, amino acid type, and concentration used.

Conclusion

The effects of amino acids on zoosporic fungi varied based on whether glucose was present in the medium. Amino acids generally increased mycelial growth, pH values, and ammonia secretion, with effects approximately doubled in glucose-free conditions. Protease activity responses varied by species and conditions, showing complex interactions between amino acids and fungal metabolism.

Published in:Mycobiology,
Study Type:Laboratory Research,
Source: 10.4489/MYCO.2005.33.1.023