Excluding bacteria 2

D.H David.Hagerberg at mbioekol.lu.se
Tue Oct 20 04:02:28 EST 1998


Thank you all for the interesting suggestions of how to keep a
soil-samples from fieldstudies free of fungi and bacteria respectively.
This is necessary for me in my investigations of the effects of
weathering of soils by bacteria and fungi respectively and in
cooperation.

I was given some extra arguments for not using antibiotics besides those
I already had. So what to use instead? There was mainly four
suggestions:

1. Do not do field-studies, do greenhouse-studies! Unfortenately it is
requested that my studies apply to 60-year-old pine stands. I have seen
large pots, but no one I ever seen has been large enough for a
60-year-old pine. Besides I can see some slight problems in getting the
pine from the forest and into the greenhouse and I have not enough time
to bring up a 60-year-old from seeds. Had it not been for those
problems, I would have been in the greenhouse right now!

2. Measure bacterial/fungal activity and correlate with effect! Activity
based on respiration has been suggested, which do well for both bacteria
and fungi. However I think the thymidine/leucin-incorporation-technique
is easier, but then I do not get the fungi. This is a good suggestion,
but there ought to be some cooperative effects, which I want to know,
but I cannot figure out how I could get them if I am not able to
investigate the effects of fungi and bacteria respectively.

3. Investigate the effects of sterilizing agents/methods on longevity of
sterilization of a soil-sample reintroduced to unsterile soil! This is
also an interesting suggestion, but then we are back to antibiotics,
microwaves and autoclaving, or are there other methods that would do
better? The samples should stay sterile in respect to fungi/bacteria for
at least one year.

4. Select some organisms and study just them! That is one of my goals,
but these organisms has to be found and I think I have to investigate
the community before I select the key species.

Right now we are using mesh-bags of sterile sand, which we are
introducing into the forest soil. The mesh bag keeps the roots out or
ought to do that, but the least crack and a fine root finds it and get
in. Our idea is to use mesh bag of finer grade, which will keep the
fungal hyphae and spores out. But the problem keeping bacteria out is 
hard to solve. Perhaps it is impossible - yet.

Sincerely

David Hagerberg
Lund University



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