Aspergillus niger question

Karen Snetselaar karen at athena.cs.uga.edu
Thu Nov 12 18:58:41 EST 1992


In article <1992Nov12.101737.459 at ncsu.edu> samodena at csemail.cropsci.ncsu.edu (S. A. Modena) writes:
>In article <1992Nov11.172607.11998 at mail.cornell.edu> Kathie Hodge <kh11 at cornell.edu> writes:
>
>.....[ deleted an interesting bit on Aspergillus niger ssp. ].....
>>.............................................  They
>>haven't been known as significant agents of human disease, but they are
>>certainly facultative pathogens,  A. niger can cause a nasty infection of
>>the outer ear.
>>
>>Kathie Hodge
>>kh11 at cornell.edu
>
>When I see descriptions like this, I ask: is it known whether these
>fungi contain viruses or plasmids that confer these variable/facultative
>abilities?
>
>Steve
>---

(A. niger can also cause respiratory problems, like other members of
the genus).  Human pathogenic fungi usually cause serious problems only
with immunocompromised or otherwise weakened patients.  So in this
instance, host factors may be more important than fungal variation in
explaining the "facultative" nature of the infections.

There are some instances where extranuclear elements are responsible
for fungal variation.  In _Cryphonectria parasitica_, which causes
chestnut blight, a double-stranded RNA element confers hypovirulence
(loss of infection capability) on strains that have it.  And, in
_Ustilago maydis_, a plasmid-like element carried by some strains
kills other strains.  The "Killer" strains carry a nuclear gene that
confers resistance.  I can't think of other examples, anybody else?
What role does the 2 micron plasmid found in yeast cells have in
"natural" systems?
I think there might be other reasons for apparent fungal variation too.
One might simply be our inability to distinguish among these organisms that
have few morphological characters, so they seem to us to be variable.
Also many filamentous fungi have this distressing habit of hyphal fusion
between compatible strains, and subsequent nuclear migration, so a spore or
a mycelium might contain several or many different nuclear genomes.

Karen



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