Determination of methanogen/acetogen conc's

[Andreas Brune]

In article <Cvq3yM.72I at serval.net.wsu.edu>, jpeterse at che.wsu.edu (James N. Petersen) says:
>
>We are interesting in being able to accurately determine the
>number of acetogens and methanogens in a given sample which
>has been grown under methanogenic conditions.  Is anyone aware of
>any protocols for accomplishing this?  If so, could you give
>me references to the same?  We need to perform several samples 
>on a daily basis.
>
You didn't say whether you are dealing with defined cocultures or a wild 
mixture of bacteria. I assume the latter is the case. But what do you
mean by 'accurate'? 

I don't have a reference to solve this problem, but a few thoughts:
You could count the methanogens (MG) by their F420 
fluorescence using a epifluorescence microscope. 

It's more difficult with the homoacetogens (HA) (if there are 
other bacteria present, too).
You may have to do serial dilutions in Balch tubes, using a H2/CO2 
atmosphere and test for acetate formation. Testing for CH4 formation 
would give you the number of MGs. If you do at least 3 parallels 
you get a good idea of the 'most probable number' (there are tables to 
avoid dealing with the statistics...).

This will only work though for the bug which outnumbers the other 
one, since they both use the same substrate to form their 
characteristic products. If the MG outnumbers the HA, you could count the
HA using a different substrate, e.g. trimethoxybenzoate, which MGs 
don't use. If it's the other way round this may still work (if you're lucky)
since usually MGs outcompete the HAs for hydrogen.

If this is of any help contact me for more info. (Unfortunately, 
I'll be out of town for a week...)

Andreas