RESPONSE OF MAMMOTH CAVE CYANOBACTERIA TO ULTRAVIOLET LIGHT

Cyanobacteria are prokaryotes with photosynthetic capabilities commonly found in marine and freshwater environments. Fossil evidence indicates they were prolific in the Precambrian oceans 3.5 billion years ago and helped to give rise to the oxygen-rich atmosphere. Microcystis, Oscillitoria, Leptolyngbya, Planktothrix, Nostoc, Dolichospermum and Hapalosiphon are types of cyanobacteria that have continued to thrive and have adapted to grow near lights used for tours in the cave passages at Mammoth Cave National Park. During preliminary cyanotoxin testing, 10 out of 11 cave sites with visible algal growth tested positive for microcystin (total concentration range was below detection to 3.67 μg/L analyzed using Enzyme Linked Immuno-Sorbent Assays). No microcystins were detected at control sites in Mammoth Cave where algae were not visible. The algae inhabiting the cave are considered a nuisance, detracting from the natural cave ecosystem. Therefore, tests were done using ultraviolet (UV) light exposure to control the growth of the algae without using strong chemicals. The exposure lengths included 0, 0.5, 2 and 5 minutes. The treatments were monitored at 1 day, 1, 2 and 4 weeks for changes in cyanobacteria metabolism. The 2 and 5 minute UV treatment caused a 6-13% reduction in the maximum quantity yield of photosystem II, an indicator of photosynthesis efficiency, implying that the light-collecting photosystem was damaged by the UV light. Concurrently, there was a 10-40% increase in peroxidase activity in algae exposed to UV light. Peroxidase activity is often indicative of oxidative stress. Long term growth tests are currently being conducted to determine if the UV exposure successfully shut down algae reproduction.