Abstract
Aspergillus aculeatus ZC-1005 (ZC-1005 was used as the abbreviation of this strain) is a hemicellulase-producing strain isolated from rotten citrus rind buried in the soil. Our previous study has shown its biochemical properties including high xylanase activity, mannanase activity, and degradation reaction with citrus mesocarp. In this study, we focused more on the enzyme safety evaluation and the genome sequencing via PacBio and Illumina platforms. High biological safety of the crude enzymes of ZC-1005 has been proven by the acute oral toxicity test, sub-chronic toxicity test, micronucleus test, and sperm malformation test. The genome of ZC-1005 had a GC content of 52.53%, with a size of 35,458,484 bp, and encoded 10,147 genes. Strain ZC-1005 harbored 269 glycosyl hydrolase (GH) genes of 64 families. The fungus produces cellulose-acting (GH3, GH5, GH12, and GH1) and hemicellulose-acting enzymes (GH16, GH31, GH2, and GH92). In genome annotation, we paid more attention to the genes encoding xylanase, such as gene 01512, gene 05833, gene 05469, gene 07781, gene 08432, gene 09042, gene 08008, and gene 09694. The collaboration between complete genome information and the degradation test confirmed that ZC-1005 could degrade cellulose and xylan. Our results showed that the citrus enzymatic decapsulation technology was efficacious and safe for canned citrus product processing, which may also solve the industrial waste problem. Therefore, ZC-1005 and the crude enzyme secreted from the strain were very promising to be used in the citrus processing industry.
Highlights
China is a major producer of citrus canned products (Miao et al, 2013; Shan, 2013)
The spores of ZC-1005 were washed with 0.9% NaCl to make a spore suspension (1 × 106/ml) and 1 ml of the suspension was transferred into an Erlenmeyer flask with 75 ml of fresh medium and incubated aerobically at 35◦C with shaking at 170 r/min for 60 h; after incubation, the fungal suspension was filtered with gauze and the filtrates were centrifuged (8,000 g, 4◦C, 10 min) to separate the supernatant; the supernatant was filtered through a 0.22-μm filter membrane (Millipore, United States) and the filtrates were collected as the crude enzymes used in this study
The citrus mesocarp was composed of 10–20 layers of parenchyma cells; the inner layer was composed of large cells with an irregular arrangement, while the surface cells were small, arranged orderly and tightly, and there were cellulose and pectin adhesion between the cells
Summary
Decapsulation technologies determine the quality of citrus products, which are crucial for the whole production process (Shan et al, 2009). The cutting-edge enzymatic stripping technology has significantly improved the quality of the citrus canned products, causing less environmental pollution (Zhang et al, 2008). The main methods used to degrade mesocarp are the classical acid–base two-step method, phosphate one-alkali method, EDTA-assisted low alkali method, and enzymatic decapsulation technology (Li et al, 2013). Enzymatic decapsulation technology has become a hot spot because it is a type of biological method This method decomposes pectin, cellulose, and hemicellulose in the citrus capsule by enzyme but not destroying the pulp (Shan et al, 2009). The technology solved the industrial waste problem and improved the product quality and safety (Wang and Jiang, 2011)
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