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Leather camera case left in the basement over the summer months in Guelph, Ontario, Canada.

  The greenish/yellowish/brownish powdery stuff over the surface is mould (Eurotium and its Aspergillus state)!

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Left: yellow cleistothecia of Eurotium       Right: Micrograph shows squash of cleistothecium with uyoung asci and ascospores

Basements in Canada take the place of the attics found in much of the rest of the  world.  Great places to store all kinds of junk such as cases, boxes, clothes, books, and  the like.  They can also be 'finished' to make some extra rooms for office, bedroom, workroom, playroom or whatever.  The flaw is that basements below ground stay cool in summer months and  the humidity in summer rises to very high levels.  

There is a group of fungi called xerophytes (they use the same word for cacti that can survive for long periods with limited available water).   The xerophytic fungi, however, have a very good trick.   While most fungi require free  water (i.e. liquid water) for growth,  the xerophytic fungi can use water vapour (i.e. gaseous water).  These fungi, therefore, can GROW in basements in summer by plucking the water molecules right out of the air as they pass by. GOOD TRICK!  The xerophytic fungi grow ABOVE 60% Relative Humidity and the higher the RH, the faster the fungi grow. 

Fungi of course need organic 'food' as well.  But all that stuff in the basement such as cardboard boxes, paper, old shoes, clothes on hangers, cases etc. is a delight for our fungus friends.    So it is not too long before fungus colonies grow on anything organic in the basement (they are particularly fond of cellulose but keratin (hair, feathers, leather) is OK too!) and when you go down the basement you will often notice a distinctive  'musty' odour.    The xerophytic fungi belong to the genera Aspergillus and Penicillium and their relatives.    The fungus on the camera case proved to be a Eurotium (Ascomycota) with an Aspergillus (Deuteromycota) conidial state.   In the fall, when the hot air furnace kicks in, it will blow the Aspergillus spores all over the house.  Aspergillus is one of the major causes of mould allergies in humans, horses, poultry etc. 

What to do about xerophytes?  In my Special of the Month for April 01,   I write the following:

If someone in your home has mould allergies, it is important to start off right away with a dehumidifier in the basement.   If you can keep the relative humidity in the basement below 60% (dehumidifier in the summer) NO XEROPHILIC MOULDS WILL GROW IN YOUR BASEMENT IN THE SUMMER.  

Students:   

1.   I don't worry about the winter - why?

2.  Suppose the camera case had been made of plastic or synthetic fibres?

3.  Clean the case.  How?