When interrogating the pressurized habitats of pelagic and subsurface regions questions remain concerning the extent of in situ pressure adaptation present in, and the effects of decompression impacts on, the microbes present.   In this presentation results from the application of pressure-retaining seawater (PRS) samplers on microbial cell numbers, activity, and community composition will be described for bathyal, abyssal and hadal water column samples collected in the San Clemente Basin, the Atacama Trench and the Puerto Rico Trench (PRT).  In addition, the effect of pressure on the activity and community structure of deep subsurface samples in the PRT will be described.  Compared with traditional seawater sampling PRS sampling resulted in increased microbial cell numbers, greater bi-orthogonal non-canonical amino acid tagging (BONCAT) protein synthesis anabolic activity, and enhanced relative abundances of select taxa including TACK-group/Thaumarchaeota/Nitrososphaerota.  PRT deep subsurface sampling was accomplished using multi-coring, gravity coring, and piston-coring.  Trench axis sediments were characterized by increased cell numbers and total organic carbon, and decreased oxygen penetration.  Cells from anaerobic surficial trench sediment incubations exhibited greatest BONCAT activity at atmospheric pressure.  However, BONCAT FACS sorting and DNA sequencing of active cells at 84 megapascals pressure resulted in high fractions of Omnitrophota in surficial sediments and Atribacteriota JS1 in 4 and 8 m depth sediments.  These results are in contrast to the BONCAT FACS sorting of the same samples incubated at atmospheric pressure which yielded Pseudomonadota genera.   Taken together these results argue for 1) the adoption of less disruptive (e.g., PRS) sampling approaches in deep-sea investigations, and 2) provide evidence of extremely high-pressure adapted taxa in a deep-sea, deep-subsurface environment. 

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