Combined technologies for high-pressure sampling, transfer, enrichment, and filtration from deep-sea hydrothermal vents

Abstract:

A majority of the prokaryotes on Earth inhabit the deep biosphere where high-pressure conditions can impact microbial diversity and activity, but can also pose technological challenges to exploration. Sampling within these ecosystems inevitably must consider the effects of elevated in situ pressures on enrichment experiments and diversity measurements, as well as the potential effects of sample decompression on such studies. Recent work in the bathypelagic and hadal regions has shown that maintaining in situ pressures during sample retrieval, storage, and processing can effect both diversity and metabolic activity measurements [2-5]. While several high-pressure samplers have been developed in the last several decades [e.g. 1,2,6], maintaining high-pressure conditions throughout sample processing is less common [2,3]. In a recent expedition to the Mid Cayman Rise, we combined several technologies to maintain in situ pressures (up to ~500 bar) in hydrothermal fluids throughout sample retrieval, transfer, enrichment, and filtration. Variable-volume, floating-piston samplers with high-pressure gas compensators [3,6] were used for sample retrieval; transfer to similar, smaller-volume, storage and enrichment devices [2] was conducted shipboard immediately following sampler retrieval. Subsequent enrichment experiments were carried out by inoculating pre-heated and pre-pressurized enrichment media with pressurized hydrothermal fluid. Further, fluid was filtered at in situ pressures using a high-pressure filter holder, and immediately fixed for subsequent -omics analyses. Comparison to decompressed samples will allow us to evaluate the effects of decompression on enrichment and diversity measurements from the deepest known hydrothermal system and provide insights for future life detection missions to Ocean Worlds.

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