Epsilon-Proteobacterial Dominance in Microbial Mats Located at the Champagne Hydrothermal Vent Site on NW Eifuku Volcano, Mariana Arc

By far the most extensive hydrothermal vent related microbial mats discovered during the 2004 Ring of Fire cruise were those found at NW Eifuku Volcano located along the Mariana Island Arc. The Champagne Hydrothermal Vent Site located near the summit of NW Eifuku Volcano (1,650 meters below sea level) consists of multiple white smoker chimneys venting highly gaseous fluids (Max temp ∼103° C). Large amounts of liquid carbon dioxide bubbles and clathrates were observed exuding from the seafloor contributing to an extremely low Eh (i.e., highly reducing conditions) and giving the location its name. Luxuriant white flocculent mats were discovered and collected in and around the Champagne Vent Site in April, 2004. Molecular analyses of small subunit ribosomal DNA (SSU rDNA) from these mats using both T-RFLP community fingerprinting and PCR-generated clone library analyses showed that the bacterial community is dominated by ɛ -Proteobacteria represented by the thiovulum-group along with lesser levels of Thermotogales represented by the thermotoga-group (as determined using the Ribosomal Database Project). Initial estimates of the relative abundance of phylotypes place the thiovulum-group at 50% and 67%, and the thermotoga-group at 18% and 9%, for T-RFLP and clone library methods, respectively. Phylogenetic analysis of SSU rDNA sequence data also suggests that these most dominant phylotypes are most likely chemoautotrophic and involved in sulfur-cycling. Due to the extreme nature of their habitat, many of these bacteria often grow where no macrofauna are present. However, on the edges of these areas, once sufficient mixing has taken place, abundant macrofauna can be seen vigorously feeding upon these microbial mats. This further demonstrates the transfer of chemosynthetically-derived energy up the food chain supporting large communities of macrofauna. Similar types of microbial mats have been observed at Axial Volcano on the Juan de Fuca Ridge, where they were dominated by a diverse community of ɛ -Proteobacteria known to both oxidize and reduce multiple sulfur compounds.