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
