Characterization of the physicochemical microhabitat and epibiotic bacterial community associated with Alvinella pompejana, a hydrothermal vent annelid.

摘要

Alvinella pompejana, a polychaetous annelid inhabiting narrow tubes along the surfaces of high temperature hydrothermal vent chimneys, hosts a rich community of episymbiotic bacteria along its dorsal surface. The goal of this dissertation was to study the influence of the tube environment on the epibiont community structure using a multidisciplinary approach. The physicochemical habitat inside A. pompejana tubes was described using a small-volume water sampler, in situ thereto-chemical sensor, and wet chemical analysis. Temperatures inside hot tubes ranged from 42.2°C to 84.0°C, while cool tubes ranged from 15.0°C to 40.0°C. Dye trace experiments demonstrated vigorous outward flow from the tubes. Tube fluids were anoxic and contained low levels of free H₂S in situ (0.2 μM), with most of the sulfide existing as aqueous FeS molecular clusters. Fluids contained 22.50 mM to 27.50 μM sulfate, 13.96 to 20.00 μM nitrate, and 2.50 to 9.73 μM ammonium, with pH ranging from 5.33 to 6.40. Trace metals were present in micro- to nanomolar amounts. Mg was 72 to 91% of deep seawater values. Many fluid components were geochemically altered from theoretical mixing values.; Genetic fingerprint analysis (PCR-DGGE) was used to evaluate epibiont community structure at different spatial scales. Microheterogeneity along individual worms suggested that thermochemical gradients inside the tube influence epibiont community structure. DNA fingerprinting showed a latitudinal gradient in the major community members from 13°N to 32°S. Sequencing of DNA bands from the DGGE profiles revealed that all A. pompejana epibionts were epsilon Proteobacteria. Interestingly, one epibiont was common to A. pompejana, A. caudata (a congener), and H. bergii (a cohabitant). These results suggest the A. pompejana epibionts are acquired from the environment. A complementary study of internal transcribed spacer (ITS) sequences and genome-level fingerprint patterns (rep-PCR) of vestimentiferan endosymbionts showed strain-level variation was influenced by a variety of factors.; Carbon source utilization of heterotrophic A. pompejana epibionts was assessed using Biolog EcoPlates. Fingerprint analysis (PCR-DGGE) was used in conjunction with metabolic profiling to monitor temporal changes in community structures sampled at different time points during the experiment. A total of 21 different carbon sources were utilized, some of which are readily available in the tube environment. DGGE band sequences revealed that the original inocula were dominated by epsilon Proteobacteria, but gamma Proteobacteria were enriched within four hours of incubation at 37°C. This dissertation has provided new insights into the ecology of the A. pompejana epibiont assemblage and provides a comprehensive evaluation of several popular methods for microbial community structure analysis.