I noticed that after an initial reduction of almost 50-70%, then subsequently the concentration kept on increasing from the initial reduced value, but still the values were less than the initial concentration of the sulfide and at the same time growth measured by optical density consistently increasing. I used different bacterial isolates P. putida and as well B. cereus. To enhance their bioactivity, the synthetic wastewater contained sucrose as source of carbon, sodium sulfide as electron donor ans source of sulfide, KH2PO4 as source of potassium and phosphate (nutirent), sodium bicarbonate as source of inorganic carbon, sodium nitrate as electron acceptor. In addition to trace elements. Yet I noticed this abnormal fluctuating reduction, instead of reduction consistently. Please advise me on what to do?
Based on the somewhat limited info on your experimental design, here a few hypotheses:
1) How do you measure sulfide? Would your essay pick up -SH groups of proteins?
2) the sulfide might precipitate with some of your trace elements and could maybe be released when the microbes use the trace elements
3) maybe sulfide is released from protein degradation after some time?
4) Unlikely, but possible: Contamination with a sulfate reducer?
Sulfide measurement is sensitive to many factors including binding, precipitation, and pH fluctuation. Growth of the bacteria will affect the concentration as well.
Still, check if hydrogen sulfide is evaporating from your solution.
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