Geomicrobiology of Basalts from an Age Transect at East Pacific Rise 950'N

Seafloor exposed basalts at mid-ocean ridges, hotspots and rocky outcrops represent a ubiquitous microbial habitat. The microbial abundance and diversity at this site have been characterized, but functional potential and microbial activity are still poorly understood. We collected seafloor basalt samples during R/V Atlantis cruise AT42-21 in December 2019 at East Pacific Rise (EPR) 9° 50'N to gain insight into microbial community function and activity. Eight basalt samples were retrieved using Human Occupied Vehicle (HOV) Alvin during Dive 5049 with the primary objective of traversing several lava flows east of the EPR axial trough and collecting lava samples of differing ages. The selected terrain was documented to be older than the 2005-2006 eruption at EPR according to the bathymetry and historical data from the 1991-1992 and 2005-2006 eruptions. Four different potential ages were selected along a planned transect of eight samples from off-axis to the axial summit trough. Our goal was to characterize the microbiology (abundance, diversity, and metabolic activity) of these seafloor basalt samples. All samples were subsampled and processed for metagenomic and transcriptomic analysis, and cell counts. Preliminary results for microbial abundance ranged between 102-104 cells cm-3 for basalt samples. Results of the metagenomic analysis are presented here as well. Exoenzyme assays were also conducted for six of the basalt samples using substrates targeting lipase, leucine-aminopeptidase, glycine-aminopeptidase and alkaline phosphatase. Activities for these targeted exoenzymes were detectable for all six basalt samples and rates for the killed controls and blank controls were significantly lower than the measured rates for the samples. The results from this study provide insight regarding changes in the microbial community and activity as the samples range from older samples that are further from the axis, to the younger samples that are closer to the axis.