Aspergillus sp.

Genus/species: Aspergillus sp.

Classification: Ascomycete

Morphology:

  • Cell: hyphae are septate and hyaline
  • Colony: consists of mats of hyphae that make up a mycelium
  • Malt agar: Grows well on malt agar. Aspergillus is a problem in grain production
  • WL (Wallerstein Laboratory Nutrient Agar): Slow growing on the media designed for yeast, but will grow eventually
  • Spore: Ascospores are the sexual reproductive cells that are produced in the clestothesia
  • Zygote: Conidia are the asexual reproductive cells that are produced in specialized hyphae called condiaphores
  • Ascus: Clestothesia
  • Liquid Growth:Forms a loosely interwoven mat, confluent at later times that is floating freely just below the surface of the medium. Aerial hyphae protruded towards the surface and conidiophores of normal morphology were produced. By the time condition was fully developed, the mat of mycelium entirely filled the liquid layer and its hydrophobic upper layer was exposed to the air. On suitable media conidial maturation proceeded normally.

Physiological Traits:

Commonly, fungi grow on carbon-rich substrates such as monosaccharides (such as glucose) and polysaccharides (such as amylose). Aspergillus species are common contaminants of starchy foods (such as bread and potatoes), and grow in or on many plants and trees. Typical microorganisms used to make alcohol, such as yeasts of the genus Saccharomyces, cannot ferment these starches, and so koji mold such as Aspergillus oryzae is used to break down the starches into simpler sugars.

Ecological Traits:

Aspergillus is commonly isolated from soil, plant debris, and indoor air environment.  Aspergillus rot is widespread on substrates containing a disposable source for carbohydrates such as mono- and polysaccharides. Rot is common in crops and fruits and contaminate also sugary and starchy foods.

Distinguishing Features:

Hyphae are septate and hyaline. The conidiophores originate from the basal foot cell located on the supporting hyphae and terminate in a vesicle at the apex. Vesicle is the typical formation for the genus Aspergillus. The morphology and color of the conidiophore vary from one species to another. Covering the surface of the vesicle entirely or partially on the upper surface are the flask-shaped phialides.  The phialides are either uniseriate, attaching to the vesicle directly or are biseriate,  attaching to the vesicle via a supporting cell called a metula. Over the phialides are the round conidia forming radial chains.

Role in wine:

Aspergillus rot is caused by different members of the genus Aspergillus which are widely distributed worldwide. On grapes particularly A. alliaceus, A. carbonarius, A. niger, and A. ochraceus occur. In total, the genus Aspergillus comprises more than 200 taxa including species with numerous sub-species.  Some of these subspecies produce mycotoxins that are carcinogenic and make the fungi important to exclude from wine production. Some alcoholic beverages, such as Japanese sake, are often made from rice or other starchy ingredients that must first be broken into simpler sugars as in malting barley.

Aspergillus is usually a large portion of what is referred to as mildew or mold.  Mildew is a primary focus in cleaning and can act as a substrate for a more undesirable organism that can tolerate the toxins produced by the fungi.  Some people have developed severe allergies to Aspergillus, so it is important to try to remove any visible colonies and inhibit the resurgence of the mold to protect workers and consumers at a winery.

Aspergillus using the actual must/grape for a substrate must be dealt with because the final wine can be significantly altered by the metabolism of sugar from the nascent wine.  Gluconic acid is known to be formed from glucose by the action of an enzyme, glucose oxidase, and common to such molds as Aspergillus (McCloskey, 1974).  This oxidation of glucose can have a profound sensory effect as well as lower the alcohol content of the finished wine by binding up the substrate that Saccharomyces needs to produce alcohol.

The mold can affect the wine in the vineyard or in the winery.  In the vineyard, if appropriate measures are taken the proliferation of the organisms can be reduced.  Simple measures such as opening the canopy by removing unnecessary leaves and reducing crop number so that clusters are not in close contact will allow for improved air flow reducing moisture content.  Pulling leaves will also allow sunlight to reach the berries and improve spray penetration.  The winery can also be a source of mold.  Winery equipment should not have porous surfaces.  Everything should be cleaned often with substances known to be safe for the wine and the consumer, but still take advantage of a sensitivity of the mold to inhibit the growth of the mold.

Sensitivities:

  • SO2: The growth of Aspergillus species (A. flavus, A. ochraceus, Aspergillus terreus) was inhibited by 50 mg L− 1 dissolved SO2 on a malt extract-based medium at 0.995 and 0.95 aw. Some Penicillium species and Aspergillus niger were tolerant of up to 250 mg L− 1(Magen et al., 2007)
  • Sorbate: Potassium sorbate was found to completely inhibit fungal growth at 0.134%, two-thirds of the normal use level, when the pH of the broth was 5.5.
  • DMDC: Inhibits growth but its effects degrade after 24 hours
  • pH: adherence of A. fumigatus conidia is significantly inhibited at acidic pH (less than 4.6)
  • Acids: Fatty acids (lauric, myristic, and palmitic acids) and their monoglycerides (monolaurin, monomyristic acid, and palmitin, respectively) inhibited mold growth in a study by Altieri et al., 2007
  • Ethanol: Ethanol can be utilized by A. nidulans as a sole carbon source, through the action of two enzymes: alcohol dehydrogenase I (ADHI) and aldehyde dehydrogenase (AldDH)
  • Anaerobiosis: Studies with P. verrucosum and A. ochraceus with up to 50% CO2 suggest that spore germination is not markedly affected, although germ tube extension and hence colonisation is significantly inhibited by 50–75% CO2, especially at 0.90–0.995 aw for both P. verrucosum and A. ochraceus (Cairns-Fuller, 2004) and (Cairns-Fuller et al., 2005)
  • Temperature: The optimum temperature range for development of Aspergillus is 17–42°, minimum temperature for growth is 11–13°C.

References:

  • Cairns-Fuller, V., 2004. Dynamics and control of ochratoxigenic strains of Penicillium verrucosum and Aspergillus ochraceus in the stored grain ecosystem. PhD Thesis, Cranfield University, Silsoe, U.K.
  • Cairns-Fuller V., D. Aldred and N. Magan, Water, temperature and gas composition interactions affect growth and ochratoxin A production by isolates of Penicillium verrucosum on wheat grain, Journal of Applied Microbiology 99 (2005), pp. 1215–1221
  • Magan N, D Aldred. Int J Food Microbiol. Post-harvest control strategies: minimizing mycotoxins in the food chain. 2007 Oct 20;119(1-2):131-9. Epub 2007 Jul 31.
  • Felenbok, B. Gene Expression in Filamentous Fungi. Journal of Biotechnology Volume 17, Issue 1, January 1991, Pages 11-17
  • Tiralongo, J., T. Wohlschlager, E. Tiralongo, M. Kiefel, Inhibition of Aspergillus fumigatus conidia binding to extracellular matrix proteins by sialic acids: a pH effect? Microbiology 2009 155: 3100-3109
  • Altieri C, D. Cardillo, A. Bevilacqua, M.J. Sinigaglia. Inhibition of Aspergillus spp. and Penicillium spp. by fatty acids and their monoglycerides. Food Prot. 2007 May;70(5):1206-12.
  • http://www.nature.com/nprot/journal/v2/n4/images/nprot.2007.113-F1.jpg

Tags

Yeast & Mold