The feasibility of inducing a resting stage in cultures of Clostridium ljungdahlii and Clostridium autoethanogenum was evaluated. Additionally, the effects of medium pH and benzyl viologen, a electron mediator, were tested separately for resting C. ljungdahlii cultures. Cells were grown on nitrogen-rich basal media, a modified Reinforced Clostridial Media and DSMZ 640 for C. ljungdahlii and C. autoethanogenum respectively, and then transferred to nitrogen-limited media to induce the resting stage. The performance of the resting cultures was evaluated by product formation (ethanol and acetate), culture stability, and cell viability. It was found that C. ljungdahlii was able to be induced into a stable non-growing stage with basal medium supplemented with vitamins and trace elements and devoid of the major nitrogen sources: yeast extract, beef extract, and proteose peptone, RCM.NA.SVE. However, there was no significant product formation in the resting cultures of C. ljungdahlii. Three pH levels, 6.8 (the control), 5.5, and 4.5, were tested for affects on C. ljungdahlii resting cell performance. The medium pH of resting cultures in NG.RCM.NA.SVE did not improve product formation of non-growing C. ljungdahlii cultures. The more acidic pH of the non-growing media reduced the culture viability from 100 % at pH 6.8 to 44.4 and 11.1 % at pH 5.5 and 4.5 respectively. Three levels of benzyl viologen concentration were tested for affects on C. ljungdahlii resting cell performance: 0, 50, and 100 part per million. The addition of benzyl viologen did not enhance the cultures? product formation capabilities. The benzyl viologen in the resting cell media also negatively affected the culture viability leaving only 33.3 and 55.5 % of the cultures viable with 100 and 50 ppm benzyl viologen respectively. C. autoethanogenum cultures were not able to be induced into stable non-growing cultures. With various nitrogen-source limitations from the basal medium cultures experienced either significant increases or decreases in culture density over time. The ethanol product selectivity in both non-growing and growing cultures of C. autoethanogenum in nitrogen-limited media was improved from the growing C. autoethanogenum in the basal medium. The ethanol to acetate production ratio was improved to 1:4.5 in two different nitrogen-limited media (one without yeast extract or trypticase peptone in which the culture density decreased, and only devoid of yeast extract in which the culture grew) from 1:7 in the basal growth medium. All cultures of C. autoethanogenum remained viable after transfer from the growth media to the non-growth media. From these studies it appears that ethanol is a primary metabolite for both C. ljungdahlii and C. autoethanogenum on sugar substrates.
| Identifer | oai:union.ndltd.org:NCSU/oai:NCSU:etd-08142006-111149 |
| Date | 08 December 2006 |
| Creators | Cotter, Jacqueline Louise |
| Contributors | Mari Chinn |
| Publisher | NCSU |
| Source Sets | North Carolina State University |
| Language | English |
| Detected Language | English |
| Type | text |
| Format | application/pdf |
| Source | http://www.lib.ncsu.edu/theses/available/etd-08142006-111149/ |
| Rights | unrestricted, I hereby certify that, if appropriate, I have obtained and attached hereto a written permission statement from the owner(s) of each third party copyrighted matter to be included in my thesis, dissertation, or project report, allowing distribution as specified below. I certify that the version I submitted is the same as that approved by my advisory committee. I hereby grant to NC State University or its agents the non-exclusive license to archive and make accessible, under the conditions specified below, my thesis, dissertation, or project report in whole or in part in all forms of media, now or hereafter known. I retain all other ownership rights to the copyright of the thesis, dissertation or project report. I also retain the right to use in future works (such as articles or books) all or part of this thesis, dissertation, or project report. |
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