Part 1 of 3

When I began studying indoor air quality, I noticed that fungi were often generically classified into broad categories. This was especially true when looking at the results from a direct microscopic exam. I began to ask myself “what are these classifications?” In researching this subject, I have learned that by understanding and utilizing the answer to that question can be very helpful when interpreting results from direct examinations. So, what exactly are Ascomycetes, Basidiomycetes, and Zygomycetes?

Starting with the April newsletter, we will begin to take a look into the Kingdom of the Fungi. This kingdom is broken into 5 phyla; three of which are significant in the studies of indoor air quality. Those are: Ascomycota , Basidiomycotoa, and Zygmycota . We will begin our tour with the phylum of Ascomycota more commonly known as Ascomycetes.

The Ascomycetes include many common fungi that have proven to be problematic indoors. Members of this classification include: Saccharomyces sp., Aspergillus sp., Candida sp., Neurospora sp., Penicillium sp., Stachybotrys sp., Chaetomium sp., Fusarium sp., Pleospora sp., and Xylaria sp.. Interestingly, this classification also includes many other common types of fungi such as: morels, truffles, brewer’s yeast and baker’s yeast, Dead Man’s Fingers, cup fungi, and the majority of lichens. Ascomycetes like to thrive on dead biomass meaning that they will eat almost anything organic. Inside the home that may consist of wood products, drywall, carpet, particle board, sugars, starches, and anything containing glue. As long the temperature and humidity stay ideal, these fungi will literally eat you out of house and home.

Ascomycetes are unique. They may undergo sexual and asexual reproduction. During the sexual state, Ascomycetes produce their ascopores in a sac like structure which gives many the ability to shoot their spores straight up into the atmosphere. The majority of Ascomycetes asexually reproduce and are often referred to as mitospores. This is because they use mitosis as their reproductive pathway. New spores are produced at the ends of specialized hyphae called conidiophores and then break off into the atmosphere. These types of Ascomycetes are commonly known as the molds.

Spores from Ascomycetes can be dispersed through several different mechanisms: they can be picked up and moved by the wind through air currents, they can be transported on the fur of animals, they may become airborne by the force of a water droplet, carried around on the soles of our shoes, or shot from their reproductive sac like a gun. Regardless of their mechanism, Ascomycete spores find a way to be around us all of the time.

When analysts perform direct examinations, spores are identified by characteristics which allow them to be assigned to a class. It is the responsibility of laboratory analysts to assign the most specific classification possible when identifying a fungal spore. Molds that are frequently associated with indoor air quality may be easily identified to a genus due to their unique appearance, while others may be painted into a broader classification such as Penicillium/Aspergillus or Acremonium-like. Molds that are not commonly found in indoor air may be assigned to a more general classification such as that of an Ascomycete or a Hyphomycete. Nonetheless, always be mindful when looking at the concentration of the identified molds on your lab report. All have the ability to be problematic indoors under their optimal conditions.