PARENT SESSION
Poster Session 3: Aquatic Ecology
Monday, August 8, 5:00 PM - 6:30 PM, Exhibit Hall 210 D, Level 2, Palais des congrès de Montréal

Bacterial Succession on Acer saccharinum Leaves in the Illinois River Floodplain.

Kellerhals, Doyn^*,1, Lemke, Michael¹, ¹ University of Illinois at Springfield, Springfield, IL, USA

ABSTRACT- Ecological succession of species is a well-established concept for macrobiota. The objective of this study was to monitor changes of species in the Domain Bacteria on and in maple leaves beginning with the microbial community colonizing leaf buds and following changes through decomposition on the flood plain of the Illinois River. In addition to tracking changes through this temporal variable, a spatial comparison was made among leaves falling on the floodplain, those wetted by flood waters, leaves in a drier, upland habitat, and those permanently soaked in river water. It was expected that bacterial diversity would increase as leaves mature and that a replacement community would emerge when the leaf drops to the river floodplain. Leaves were sampled over a 21-month period and change in organic mass was determined (AFDM). The microbial assemblage was monitored through 16S rDNA extraction followed by community fingerprinting on DGGE. Relative band location and intensity were evaluated using graphical peak intensity measurements. Domain Bacteria DNA was examined at the bud stage, at the mature leaf stage, and on samples collected at 6 to 10 week intervals after leaf fall. For the last category, 8.0g of maple leaves were placed in fiberglass mesh leaf bags (n=3) and placed in three locations: floodplain ground, river, and upland, non-flooding sites. DNA extracts, purified using Sephadex G-200 columns and amplified by PCR with 338F - GC clamp and 518R primers were run on DGGE (8% acrylamide, 30-70% denaturing gradient). Results initially show nearly twice as much decomposition in leaves exposed to flood water (70.1%) than for those not wetted by flood waters (36.0%) with more similar decomposition values as leaf mass is reduced to most recalcitrant elements. Molecular results showed limited diversity before leaf fall. More bands were found after leaf fall and on leaves exposed to flood water, some unique bands not found on unexposed leaves were present. Preliminary sequence analysis of bands produced sequences similar to those found for uncultured organisms in environmental samples from lakes, freshwater and soils. As expected, diversity in bacterial communities increases initially after leaf fall, decreases as leaves become more decomposed and introduction of new communities occurs after leaf fall and flooding.

Key words: Succession, Bacterial Communities, Floodwater Inoculation, DGGE