Spatial and Temporal Variability in Microbial Communities from Pre- and Post-Eruption Microbial Mats Collected from Loihi Seamount, Hawaii

Loihi Seamount is an active submarine volcano that marks the southernmost extent of the Hawaiian hotspot. Loihi rises over 3000 meters from the seafloor and summits nearly 1000 meters below sea level. Hydrothermal activity was discovered at Loihi in 1987, yielding diffuse vent effluent (Tmax 37°C) with associated high CO2 and Fe(II) concentrations and luxuriant microbial mats near the summit of the volcano. The Seamount erupted in 1996 forming a new 300 meter deep caldera (Pele's Pit) with hydrothermal venting up to 200°C. Pele's Pit now contains multiple hydrothermal vents with hydrothermal fluids ranging from 8-65°C with concentrations of Fe(II) between 50 and 750 μM. Community fingerprints from over 50 microbial mat samples collected from Loihi Seamount from 1993 to 2004, with temperatures ranging from ambient (4°C) up to ~200°C, were analyzed using cluster analysis of terminal restriction fragment length polymorphisms (T-RFLP) coupled with traditional clone library and sequence analysis. These mat samples form two distinct community clusters (Loihi Cluster I and Loihi Cluster II) representing a combined 82% of all samples collected. Loihi Cluster I is the largest group and contains the most mat samples collected over time. Loihi Cluster I is dominated by phylotypes related to the obligate lithotrophic Fe-oxidizing isolate `` Mariprofundus ferroxydans'' and contains lesser amounts of α-Proteobacteria, δ-Proteobacteria and Flavobacteria. Loihi Cluster II is comprised of only post-eruption communities that generally contain more diversity (in terms of richness) than Loihi Cluster I commuities. Loihi Cluster II communities are dominated by a unique clade of phylotypes belonging to the Nitrospira division and by ɛ-Proteobacteria. Loihi Cluster II also contains phylotypes associated with Thiomicrospira spp. and from within the `` M. ferroxydans'' clade. The presence of ɛ-Proteobacteria and Thiomicrospira spp. in this group suggest these microbial mats are potentially more involved with sulfur-cycling than Loihi Cluster I, which are dominated exclusively by putative iron-cycling bacteria and do not contain any known sulfur-oxidizing bacteria.