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Screening and characterization of koji molds producing saline-tolerant protease
1Graduate Institute of Agricultural Chemistry, National Taiwan University, Taipei 10617, Taiwan.
Abstract:
Three mold strains isolated from soil in the Taipei area of Taiwan were compared with a commercial strain of Aspergillus oryzae for their proteolytic activities in an 18% NaCl aqueous solution system. Among these strains, the one subsequently identified and designated as Aspergillus sp. FC-10 produced protease with superior saline tolerance. In aflatoxin tests, this strain did not generate detectable aflatoxin after growing on steamed grain polished rice substrate for 24 days. Two types of extracellular proteases were preliminary fractionated by column chromatography on DEAE Sepharose CL-6B. Proteolytic activity of the nonadsorbed protease (P-I) was reduced to 9.4% in the 18% NaCl solution compared to its original activity determined in the buffer solution. However, the adsorbed protease (P-II) was particularly salt tolerant and stable, with 50% proteolytic activity retained throughout the 6-h stability test in 18% NaCl solution.
Insights
Researchers identified Aspergillus sp. FC-10 from Taiwan soil, which produces salt-tolerant protease. This mold strain shows no aflatoxin production, making it a promising candidate for industrial applications requiring high salt conditions.
Area of Science:
- Microbiology
- Enzymology
- Biotechnology
Background:
- Proteases are crucial enzymes with diverse industrial applications.
- Many industrial processes require enzymes that can function under extreme conditions, such as high salinity.
- Exploring novel microbial sources for robust enzymes is essential for biotechnological advancements.
Purpose of the Study:
- To isolate and characterize mold strains with high proteolytic activity in saline environments.
- To evaluate the salt tolerance and aflatoxin production of selected Aspergillus strains.
- To fractionate and analyze extracellular proteases from a promising salt-tolerant strain.
Main Methods:
- Isolation of mold strains from soil samples in Taipei, Taiwan.
- Comparison of proteolytic activity in an 18% NaCl solution with a commercial Aspergillus oryzae strain.
- Aflatoxin detection assays on a steamed grain polished rice substrate.
- Preliminary fractionation of extracellular proteases using DEAE Sepharose CL-6B column chromatography.
- Enzyme activity assays and stability tests in 18% NaCl solution.
Main Results:
- Aspergillus sp. FC-10 exhibited superior proteolytic activity in 18% NaCl compared to other isolated strains and commercial Aspergillus oryzae.
- Aspergillus sp. FC-10 did not produce detectable aflatoxins after 24 days of cultivation.
- Two extracellular proteases (P-I and P-II) were fractionated.
- Protease P-I showed significantly reduced activity (9.4%) in 18% NaCl.
- Protease P-II demonstrated remarkable salt tolerance, retaining 50% activity after 6 hours in 18% NaCl.
Conclusions:
- Aspergillus sp. FC-10 is a promising source of salt-tolerant protease with potential for industrial applications in high-salinity environments.
- The salt-tolerant protease P-II from Aspergillus sp. FC-10 is particularly suitable for use in conditions with high salt concentrations.
- The absence of aflatoxin production in Aspergillus sp. FC-10 enhances its safety profile for biotechnological use.