Hydrilla verticillata is an aquatic submerged weed which propagates and forms  dense  mats on  the surface of the water. It was introduced to Wakulla Springs, Fl , the largest freshwater spring in the world in 1997. Hydrilla is an  invasive plant causing serious economic impacts in infested waters, however, little is known about the  microorganisms associated with hydrilla and their role in the  hydrilla bloom. In this study  phylogenetic and functional diversity of the  bacterial community during hydrilla bloom and its elimination following herbicide treatment was evaluated using BIOLOG and PCR-denaturing gradient gel electrophoresis (PCR-DGGE).  Approximately 1 liter of water samples were collected during and after the hydrilla bloom  from four different sites in Wakulla Springs and filtered through 0.2µm filters.  Prior to filtration, 150 µl of each sample was inoculated  into each well of a 96- well BIOLOG EcoPlate with 31 different carbon sources in triplicates . DNA was extracted from the filters followed by PCR amplification utilizing universal 16S rRNA gene primers .The amplified products were separated by DGGE. The prominent bands were excised from the gel, reamplified and sequenced

Results/Conclusions  

The DGGE profiles during and after the hydrilla bloom were different for all the samples, however,  little spatial variability during and after the bloom was detected in the DGGE fingerprints . The microbial communities analyzed from samples after the bloom  indicated the abundance of sequence types representating Betaproteobacteria eg. Gallionella sp. and  Nitrosomonas sp. whereas Alphaproteobacteria (primarily the family Rhodobacteriaceae) and uncultured bacteria were the most dominant types observed during the bloom suggesting a change in bacterial community. Our results indicate that the microbial population changes before and after the bloom which also  corresponds to the different carbohydrate utilization patterns in BIOLOG. The molecular based approach for microbial identification provided useful data to evaluate the role and response of microbes to  hydrilla bloom. The results indicate that hydrilla can have an impact on biotic environments. Further studies are needed to determine if the observed changes in the bacterial communities are detrimental to the balance in the ecosystem.  Improved understanding of the relationship between microbial assemblages and the hydrilla bloom  may expand our knowledge on the causes of hydrilla bloom dynamics and hydrilla management  in aquatic systems.