Microbial biomass in the hydrothermal plumes associated with the 1998 axial volcano eruption

The Axial Response Team (ART-1) documented greatly intensified chronic-style hydrothermal plumes at Axial Volcano following a 1998 eruptive event. Significantly higher numbers of bacteria were found in the plume versus background stations and depths, due largely to 5 samples with high numbers (to 1.8 x 10(5) /ml) in far field stations. Highest ratios (0.20) of metal depositing capsuled bacteria to total bacteria were found in the near-field (over caldera) plume. An unusual capsule form (FeCap), that dominated the near field plume capsule populations, was present in all plume samples, but were absent in background samples. Multi-cell filaments, metal-encrusted sheathed clusters and matrix-enmeshed colonies, all uncommon in the water column, were also present in plume samples.