Oregon Health & Science University
Marine bivalves of the family Teredinidae (commonly known as shipworms),burrow in wood for shelter and ingest the excavated wood particles as they burrow. The gills of shipworms harbor a dense community of at least four closely related gamma proteobacterial endosymbiont types (Luyten et al. 2006, Distel et al. 2002a) and one of these, Teredinibacter turnerae, has been cultivated and studied extensively. T. turnerae has the demonstrated capacity to fix N[subscript 2] and produce cellulases when grown in culture (Distel et al. 2002b, Waterbury et al. 1983) and a significant proportion of the genome of T. turnerae T7901 is dedicated to production of bioactive metabolites (Yang et al. 2009). The majority of cellulose consuming organisms contain cellulolytic microbes in their digestive tracts, yet the cellulase producing endosymbionts of Lyrodus pedicellatus are localized to bacteriocytes within the gills (Distel et al. 1991, Distel et al. 2002a). The gill endosymbiotic community has been studied extensively, but the digestive tissues have not been thoroughly investigated. In this study cultivation and characterization of additional shipworm gill endosymbiont strains was undertaken and resulted in isolated strains covering five different clades of shipworm symbiont types from numerous host species including Philippine shipworm species and the Pacific Northwestern Bankia setacea. Metabolic analyses showed that some of these symbionts lack the ability to fix N[subscript 2] and the aptitude for degradation of crystalline cellulose varies across strains. Teredinibacter turnerae strains have demonstrated the ability to inhibit growth of other symbiont types in culture. Fluorescence in situ hybridizations (FISH) combined with laser scanning confocal microscopy (LSCM) with colony reared Lyrodus pedicellatus (Distel et al. 2002a) revealed a pattern of spatial segregation of symbionts within gill bacteriocytes (host cells inhabited by bacteria) according to symbiont phylogeny. In the study presented here FISH with LSCM and general bacterial and symbiont specific 16S rRNA oligonucleotide probes has demonstrated symbiont segregation in the gills of five additional shipworm species. Novel strains predicted to be symbionts based on 16S rRNA gene sequence analysis, were confirmed as residents of shipworm gill tissue through FISH. Strains lacking the ability to fix atmospheric N[subscript 2] were not detected in bacteriocytes together with N[subscript 2] fixing symbionts based on dual probe FISH and LSCM with oligonucleotide probes specific to cultivated strains lacking the ability to fix N[subscript 2] and T. turnerae. Strains inhibited by T. turnerae strains were not detected in bacteriocytes with T. turnerae. While the shipworm gill microbial community had been characterized previously, a micrographic examination of shipworm digestive tissues was lacking. FISH of caecum and intestinal tissues detected very few microbes in the caecum and a rich community of bacteria in the intestines. The shipworm microbial community is highly specialized for degradation of lignocellulosic substrate and shows high potential for production of bioactive compounds. This unique combination of traits makes the consortium of shipworm symbionts a rich source for discovery of compounds applicable in both medical and cellulosic biofuels technologies.
Institute of Environmental Health
School of Medicine
Betcher, Meghan Anne, "Insights into the shipworm (bivalvia: Teredinidae)-bacterial symbiosis : novel isolates and micrographic localization studies" (2011). Scholar Archive. 775.