BIODEGRADATION OF HEXAHYDRO-1,3,5-TRINITRO-1,3,5-TRIAZINE (RDX) USING PHOTOSYNTHETIC BACTERIA

Hexahydro-1,3,5-trinitro-1,3,5-triazine (RDX) is an emerging contaminant according to the Environmental Protection Agency (EPA). RDX was introduced as a secondary explosive during World War II. It is still used in many explosive such as hand grenades. RDX enters the environment mostly through the manufacturing process or from the use of explosives. RDX is a suspected carcinogen and can also affect the nervous system of humans. Therefore, RDX has become a chemical of concern across many United States military bases and open and closed manufacturing plants. The goal of this research was to evaluate the biodegradation of RDX via two phototrophic bacteria: Rhodobacter sphaeroides ATCC® 17023™ and Synechocystis sp. PCC 6803. The ability to degrade RDX via a phototrophic bacteria could make remediation more passive. A passive remediation option could be an easier and more cost effective way to remediate RDX. Biodegradation of RDX has been successful with other bacteria, but Synechocystis sp. PCC 6803 was studied because it is robust and grows well in aerobic environments. The specific objectives for this research were to: 1. Determine if electron acceptors nitrate (1 mM), sulfate (10 mM), and perchlorate (1 mM) influence R. sphaeroides’ ability to degrade RDX under ideal conditions (growth conditions with succinate as electron donor). 2. Determine if R. sphaeroides can degrade RDX with oxygen present. The work conducted showed that: 1. Adding electron acceptors to incubations with R. sphaeroides, electron donor, and RDX while in the presence of light did not significantly change the time required to degrade RDX. After 49 hours RDX was degraded 100% in samples with no electron acceptor and with perchlorate, 99% in samples with sulfate, and 94% in samples with nitrate. 2. Exposing R. sphaeroides to air drastically inhibited the degradation of RDX. After 19 days, 40% of RDX still remained in the samples. The same samples in anaerobic conditions degraded RDX in only 49 hours. 3. BG-11 media degraded RDX significantly under a cool-white fluorescent light. 4. Synechocystis’s growth was affected when BG-11 nutrient stock concentration was degraded. 5. Synechocystis completely degraded RDX with and without an electron shuttle and in anaerobic environments and in the presence of air. 6. Synechocystis reduced RDX more efficiently when placed in incubations with growth media as opposed to being placed in incubations with HEPES buffer. RDX degradation via a bacteria, Synechocystis, in aerobic conditions has not been published. The work conducted showed that RDX can be degraded by Synechocystis and R. sphaeroides (in the presence of air and electron acceptors). However, more research needs to be conducted. Reduction of RDX by R. sphaeroides in field conditions needs to be examined. Also, the mechanisms of Synechocystis that degrade RDX need to be furthered studied. 3. Determine if Synechocystis can degrade RDX and if so, under what conditions