The High Pressure Temperature Gradient Block – A Novel Tool for Rapid Exploration of Pressure and Temperature Responses in Geomicrobiological Samples

Abstract:

Our newly constructed High Pressure Temperature Gradient Block (HPTGB) offers the possibility to simultaneously incubate multiple samples under 15 different temperatures and three different pressures. The HPTGB consists of a 1.5 m long, thermally insulated aluminum block with three lines of 15 sample slots each. Each slot holds a high-pressure cylinder with a maximum pressure rating of 60 MPa that can accommodate up to three incubation vials of 10 ml each or one vial with an attached syringe for incubations with elevated gas concentrations. Each line has an individual pressure system, consisting of a modified HPLC pump and a back-pressure regulator. There are individual shut-off valves for each high-pressure cylinder, allowing the termination of incubation for single cylinders without interruption of the entire pressure line. A linear temperature gradient with a maximum range of -20 to +150°C can be established. Heating and cooling is achieved by recirculating liquid thermostats.

This system provides the opportunity for incubation experiments in a variety of temperature and pressure conditions. It allows for rapid screening of preferential P/T conditions by simultaneously incubating a large number of samples over a wide P/T range.

Initially, the HPTGB will be used to explore the upper temperature limit of life on samples from IODP Exp. 370 (Temperature Limit of the Deep Biosphere off Muroto) by conducting ³⁵S-radiotracer measurements and quantifying bacterial sulfate reduction rates (SRR) under high pressure, temperature and gas concentrations. Not only high temperature but also high pressure is necessary to cultivate microorganisms from the biotic fringe. The HPTGB will be a crucial tool to develop a better understanding of microbial activity at the upper temperature limit of life.