Aspergillus flavus is the most widely known species of the genus Aspergillus which is known as a species in 1809 and first reported as a plant pathogen in 1920. Many fungi produce mycotoxin, a toxic secondary metabolite. Most A. flavus produces aflatoxin, a type of mycotoxin that is harmful for human, animal, and plant health. Characterization study of this saprophyte is important for the management of various human, animal, and plant diseases as well for surveillance, and other epidemiological study.
The study focused on 3 subjects, morphological and physiological study, enzyme activity, and aflatoxin production from ground nut seeds collected from all over India. The growth of this fungus was compared in 4 different media for morphological study and in 4 different temperature on PDA media for physiological study. For enzyme activity, amylolytic, proteolytic, lipolytic, cellulolytic, pectinolytic and catalytic activity were determined. The presence of aflatoxin was performed using thin layer chromatography method.
Among 12 isolates, amylase activity was shown by only 12 isolates and there is no clear zone in the remaining 8 isolates. Five isolates did not produce any protease among the 20 tested. Where as 18 isolates were positive for pectin methyl production. In case of lipase, 3 isolates did not show any white precipitation and all other isolates showed white precipitate due to the activity of lipase. Cellulose activity was very low in all the tested isolates and only 2 (AF7 and AF14) isolates exhibited the activity of cellulose in culture plates. Specific activity of catalase was calculated for all the isolates and all the isolates showed varied level of activity. The highest activity (210 mg/ml) was recorded by AF3 isolate and the least activity (1.58 mg/ml) in AF12. Among the 20 of isolates tested, 12 isolates of Aspergillus flavus were toxigenic by fluorescing blue spots for the presence of AFB1/AFB2 or both and 8 isolates.
In summary, morphological, physiological, and biochemical studies are important to identify plant pathogenic fungus such Aspergillus flavus. Aflatoxin, being the widely produced mycotoxin of A. flavus is easily contaminates food and soil, thus its detection is required. Furthermore, by screening the extracellular enzymes activity, one can understand the ability of
particular fungus to produce certain enzymes that have major contribution in biotechnology.
Table of Contents
1. INTRODUCTION
2. MATERIALS AND METHODS
2.1 Aspergillus flavus isolates
2.2 Differentiation of the isolates (aflatoxin study)
2.3 Morphological characterization of A. flavus isolates
2.4 Physiological characterization of A. flavus isolates
2.5 Biochemical characterization of A. flavus isolates
3. RESULTS
4. DISCUSSIONS
5. REFERENCE
Objectives and Research Themes
This project aims to perform a detailed biochemical, morphological, and physiological characterization of 20 Aspergillus flavus isolates collected from groundnut seeds across India to evaluate their toxic nature and enzymatic potential.
- Detection and differentiation of toxigenic and non-toxigenic Aspergillus flavus strains.
- Evaluation of morphological variations across different culture media (PDA, CZ, YESA, AFPA).
- Determination of optimal physiological growth conditions regarding temperature.
- Screening for extracellular enzyme production, including amylase, protease, lipase, pectinase, and cellulase.
- Analysis of catalase activity and isoform profiles using HPTLC and NATIVE-PAGE.
Excerpt from the Book
INTRODUCTION
Aspergillus flavus is the most widely known species of the genus Aspergillus which is known as a species in 1809 and first reported as a plant pathogen in 1920 (Leslie, 2008). Like other Aspergillus species, this fungus has a worldwide distribution due to its numerous conidia production, which easily disperses by air movements and possibly by insects. Aspergillus flavus is mainly a saprophyte in the soil, where it plays a major role as a nutrient recycler, supported by plant and animal debris and contaminates a wide variety of agricultural products in the field, storage areas, processing plants, and during distribution. The ability of A. flavus to survive in unfavorable conditions allows it to easily out-compete other organisms for substrates in the soil or plant. It grows better with water activity (aw) ranges from 0.86 – 0.96 with an optimum temperature of 37 °C, but able to grow in the range of 12 – 48 °C. This optimum temperature contributes its pathogenicity in human being. (Hedayati et al., 2007; Ruiqian et al., 2004)
Aspergillus flavus belongs to Subgenus Circumdati sections Flavi and the taxonomy of this species is as follows: Domain: Eukaryote, Kingdom: Fungi, Phylum: Ascomycota, Class: Eurotiomycetes, Order: Eurotiales, Family: Trichocomaceaae, Genus: Aspergillus, Species: Aspergillus flavus Link.
Summary of Chapters
INTRODUCTION: Provides an overview of the taxonomy, ecological distribution, and pathogenicity of Aspergillus flavus, highlighting its role as a significant plant pathogen and mycotoxin producer.
MATERIALS AND METHODS: Describes the isolation of 20 A. flavus strains, the HPTLC methodology for aflatoxin detection, and the specific culture media and biochemical assays used for characterization.
RESULTS: Presents the experimental findings regarding the toxigenic status of the isolates, their growth characteristics on various media, and their enzymatic activity profiles.
DISCUSSIONS: Interprets the findings by correlating the morphological observations and enzymatic profiles with the toxigenic potential of the different A. flavus isolates.
Keywords
Aspergillus flavus, Aflatoxin, HPTLC, Morphological characterization, Physiological characterization, Biochemical characterization, Extracellular enzymes, Amylase, Protease, Lipase, Pectinase, Cellulase, Catalase, NATIVE-PAGE, Groundnut seeds.
Frequently Asked Questions
What is the fundamental focus of this study?
The study focuses on the biochemical, morphological, and physiological characterization of twenty Aspergillus flavus isolates to identify variations among toxigenic and non-toxigenic strains.
What are the central thematic areas?
The research covers fungal taxonomy, aflatoxin detection via HPTLC, metabolic enzyme profiling, and the impact of different culture media on fungal growth.
What is the primary goal of the research?
The goal is to understand the variation among toxic and nontoxic isolates regarding their morphological and biochemical parameters for better disease management and industrial application.
Which scientific methods were employed?
The study utilized HPTLC for aflatoxin analysis, spectrophotometry for enzyme assays, and NATIVE-PAGE electrophoresis for analyzing catalase isoform profiles.
What is addressed in the main body of the work?
The work details the systematic screening of extracellular enzymes and the comparative growth performance of A. flavus across various controlled environmental conditions and media types.
Which keywords characterize this report?
Key terms include Aspergillus flavus, Aflatoxin, extracellular enzymes, HPTLC, and NATIVE-PAGE.
How were toxigenic strains identified?
Toxigenic strains were identified by their ability to produce blue fluorescent spots on HPTLC plates, indicating the presence of aflatoxin B1 and B2.
What was the observation regarding catalase activity?
Catalase activity varied significantly among isolates, with the highest activity recorded in isolate AF3 and the lowest in AF12.
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- Lisa Nathalie (Autor), 2011, A study on Aspergillus flavus, Múnich, GRIN Verlag, https://www.grin.com/document/177288
