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Composition and variability of the wetwood bacterial community occurring in native California cottonwoods.
Hofstra, Thomas*,1, Altermann, Susanne1, Goff, Lynda1, Langenehim, Jean1, 1 Ecology and Evolutionary Biology, Santa Cruz, CA
ABSTRACT- Trees with the economically important disease wetwood are hosts to an anaerobic community of bacteria. In this three level ecosystem, the Eukaryotic host is fermented by Eubacteria, whose products are utilized in methanogenisis by Archaea. A forest of wetwood-affected trees is analogous to many anaerobic habitat islands. Wetwood conditions vary within trees, and with tree size, age, location and species. The wetwood community is limited to bacteria that are competitive under wetwood conditions and bacterial community composition should reflect variation in these conditions. These characteristics suit this system to a study of the relationship between habitat patch quality and community composition in fragmented ecosystems. Because of the difficulty in identifying wetwood bacteria in situ, this study is only possible since the development of culture-independent molecular techniques. Using 16S rDNA to systematically identify wetwood bacteria relative to cultured species, I describe the wetwood bacterial community in Populus balsamifera ssp. trichocarpa and P. fremontii from several sites. Based on this, fluorescent in situ hybridization and denaturing gradient gel electrophoresis coupled with primary components analysis are used to describe wetwood community variability within and between hosts, sites and host species. Most Eubacterial sequences from P. balsamifera wetwood group with Bacteroides and Clostridium, which have been isolated from wetwood by other researchers. Bacteroides is ubiquitous in wetwood. Others group with Sporomusa, Termitobacter, Actinobacteria, Heliobacterium, Desulfosporosinus, Desulfotomaculum, and Sinorhizobium, which have not been previously reported in wetwood. The only Archaeal sequence found groups with Methanobacterium and is more common in larger trees. Preliminary results suggest a similar community in P. fremontii wetwood. The wetwood community does not vary in the same tree at the same height, but varies with height, distance from cambium, and from tree to tree. It appears that wetwood habitat quality relates to bacterial community composition in the wetwood of native California Populus spp.
KEY WORDS: wetwood, Populus, bacteria, 16S