ASGSB 1998 Annual Meeting Abstracts

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EFFECT OF pH ON IGEPON®SOAP DEGRADATION UNDER DENITRIFYING CONDITIONS.  V. Hsu¹, M. Alazraki², and R.F. Strayer². ¹Department of Biology, Washington University, ²Dynamac Corporation, Kennedy Space Center.

The effect of pH on Igepon® soap degrading/denitrifying bacteria was examined using anaerobic shake flask cultures. Igepon® soap was selected for use on International Space Station. Because of the sensitivity of bacteria to extremes of pH and the expected pH increase during denitrification, pH was expected to be a significant environmental factor. The high pH levels that can accompany denitrification were predicted to inhibit bacterial growth. In addition, inoculum sources for denitrifying soap degraders were examined. Enrichment cultures were inoculated with either bacteria from hydroponically-grown wheat roots or the liquid medium of an Intermediate Scale Aerobic Bioreactor (ISAB). Both cultures were subjected to anaerobic conditions in a soap and nitrate medium and were able to degrade soap using denitrification. The enrichment cultures were used to inoculate anaerobic shake flasks buffered at pH 7.2 or 9.0. Half the flask medium was replaced daily for a retention rate of two days exposing bacteria to a maximum soap concentration of 1000ppm each day. Soap degradation, turbidity (bacterial growth), and pH were assayed regularly for each flask. Cultures grew most rapidly and degraded soap more readily in pH 7.2. The root cultures at pH 7.2 achieved a steady state of soap degradation that removed all but trace amounts of soap within six days of culture initiation. ISAB cultures at pH 7.2 required 10 days to reach a steady state of degradation. The root and ISAB cultures at pH 9.0 had limited growth and minimal soap degrading activity. These results indicated that denitrifying bacteria grown at high pH have significantly reduced soap degrading ability. Either inoculum could be used for a microgravity anaerobic bioreactor to process Igepon®-containing gray water. Both would require pH control to maximize the effectiveness of gray water processing. (Supported by the NASA Space Life Sciences Training Program)

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