Date of Award

Spring 3-1-2013

Degree Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

Biology

First Advisor

Dr. George E. Pierce

Second Advisor

Dr. Sidney A. Crow, Jr

Third Advisor

Dr. Eric S. Gilbert

Abstract

Rhodococcus is a soil microbe known for its metabolic versatility. Cyanide is one of many compounds that Rhodococcus can detoxify. This work identified several inducers which affect the activity of two cyanide-metabolizing enzymes produced by R. rhodochrous DAP 96253, cyanidase and β-cyanoalanine synthase-like enzyme. Chemical inducers were added to growth media and cells were tested for the ability to transform cyanide to ammonia or hydrogen sulfide as a quantifiable measure of cyanidase or β-cyanoalanine synthase-like activity, respectively. Urea-supplemented YEMEA-grown R. rhodochrous DAP 96253 has been shown to inhibit germination of selected fungal spores. By varying supplements in growth media, several new compounds were identified which also enable Rhodococcus to inhibit germination. This inhibition is achieved through non-contact co-culture between organisms. Properties of anti-fungal activity were studied for each supplement. It was shown that supplemented R. rhodochrous DAP 96253 is able to inhibit germination of single or mixed cultures the selected fungi, Aspergillus niger, Aspergillus fumigatus, and Penicillium sp. Depending on the supplemental compound added to growth media, spores were unable to recover after a maximum 48 hour exposure to R. rhodochrous DAP 96253. Rhodococcus effectively inhibits germination of spores when actively growing on agar or when removed from the plate. Lastly, the effects of co-culturing three strains of YEMEA-grown Rhodococcus sp. with supplemented, YEMEA-grown R. rhodochrous DAP 96253 were examined to determine if supplemented R. rhodochrous DAP 96253 affected unsupplemented Rhodococcus sp. When co-cultured with cobalt- and urea-supplemented or just urea-supplemented YEMEA-grown R. rhodochrous DAP 96253, the three strains tested, R. rhodochrous DAP 96253, R. rhodochrous 96622, and R. erythropolis 47072 exhibited cyanidase enzyme levels comparable to those seen in directly induced cells. Additionally, after co-culture with urea-supplemented YEMEA-grown R. rhodochrous DAP 96253, YEMEA-grown cultures became inhibitory to germination of spores of A. niger. Overall, these findings showed that, with proper supplementation, R. rhodochrous DAP 96253 can be inhibitory to selected fungal species and is simultaneously able to stimulate antifungal activity in other, unsupplemented Rhodococcus sp.

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