Sulfate reduction in bowel-chemostat

R carman rjcarman at bev.net
Tue Jun 18 04:58:06 EST 1996

We are using chemostats to model the human large bowel ecosystem.  The 
amout of inorganic sulfate entering the chemostat vessel (2 umol/d) is 
about the low end of the normal range entering the human colon from 
the ileum (1 to 10 mmol/d). About 7 to 10 d after inoculating the 
chemostat with feces, a black precipitate settles out and coats the 
wall of the chemosat vessel. Up to this point, we can monitor sulfate 
reduction by assaying the amount of sulfide in the chemostat effluent.  
After this time the sulfide levels exceed the theoretical maximum 
possible, though it is true that we do not take into account any 
organic sulfate present in medium components. It looks like sulfide is 
forming aggregates and coming out of suspension, hence the black 
precipitate.  In addition, the sulfide traps we use to reduce the 
smell of gas exiting the chemostat follow the same pattern.  They 
start colorless but eventually become black.  As we would like to run 
the chemostat for up to 30 days and during that time monitor sulfate 
reduction, we have a problem!

Do any of you see the same thing?  Does anybody have any advice that 
may help us work out the problem?

Bob Carman
Phone 1 800 TECHLAB
E mail: rjcarman at vt.edu

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