Characterizing the Piezosphere: The Effects of Decompression on Microbial Growth Dynamics

Abstract

The extent to which the full diversity of the subsurface microbiome can be captured via cultivation is likely hindered by the inevitable loss of cellular viability from decompression during sampling, enrichment, and isolation. Furthermore, the pressure tolerance of previously isolated strains that span surface and subsurface ecosystems can shed light into microbial activity and pressure adaptation in these transition zones. However, assessments of the effects of elevated pressure on the physiology of piezotolerant and piezosensitive species may be biased by high-pressure enrichment techniques. Here, we compared two high-pressure cultivation techniques—one that requires decompression of the whole cultures during sampling and one that employs the previously described isobaric PUSH devices—to explore the effects of repeated decompression during incubations performed to characterize isolates from deep environments. Two model sulfate-reducing prokaryotes were used to test the effects of decompression/repressurization cycles on growth rates, cell yields, and pressure tolerance. The mesophilic bacterium Desulfovibrio salexigens was cultivated from 0.1 to 50 MPa, and the hyperthermophilic archaeon Archaeoglobus fulgidus was tested from 0.1 to 98 MPa. For both cultivation methods, D. salexigens showed exponential growth up to 20 MPa, but faster growth rates were observed for isobaric cultivation. Furthermore, at 30 MPa minor growth was observed in D. salexigens cultures only for isobaric conditions. Isobaric conditions also extended exponential growth of A. fulgidus to 60 MPa, compared to 50 MPa when cultures were decompressed during subsampling. For both strains, growth rates and cell yields decreased with increasing pressures, and the most pronounced effects of decompression were observed at the higher end of the pressure ranges. These results highlight that repeated decompression can have a significant negative impact on cell viability, suggesting that decompression tolerance may depend on habitat depth. Furthermore, sampling, enrichment, and cultivation in isobaric devices is critical not only to explore the portion of the deep biosphere that is sensitive to decompression, but also to better characterize the pressure limits and growth characteristics of piezotolerant and piezosensitive species that span surface and subsurface ecosystems.

Cultivation of Piezotolerant and Piezophilic Hyperthermophiles with a Newly Developed Constant High Pressure and Temperature Culturing and Monitoring System

“…Another critical issue associated with HT-HHP cultivation is the effects of depressurization on the physiology of pressure- incubated microbial cells. Previous studies reported that although depressurization did not kill piezophiles, repeated pressurization and depressurization cycles negatively impacted the growth rate and cell yield of these cells ( Cario et al , 2022 ). This finding highlights the importance of maintaining isobaric conditions throughout the incubation period.…”

“…Even when a culture strain is isolated from the deep sea, it is typically cultured and stored at ambient pressure, except for obligate piezophiles. Although previous studies reported the negative effects of depressurization during the HHP cultivation of piezophilic cells ( Cario et al , 2022 ), the effects of an initial change in pressure from the ambient pressure-inoculum to the HHP culture, particularly on the early stages of the growth of piezophiles, remain unclear because of the limited availability of cultivation systems allowing isobaric inoculation. To adapt to the significant increase in pressure, it may be necessary for inoculated piezophiles to undergo physiological changes during the early stages of growth.…”

Biological functions at high pressure: transcriptome response of Shewanella oneidensis MR-1 to hydrostatic pressure relevant to Titan and other icy ocean worlds

“…This means that, with current systems, a microbial culture must undergo decompression before sampling, which potentially influences the subsequent analyses and results. In addition, faster rates of decompression increase cell damage (Park and Clark, 2002 ; Cario et al, 2022 ).…”

Microbial membrane lipid adaptations to high hydrostatic pressure in the marine environment

“…In this regard, previous studies have adjusted microscope setups to be able to perform high-resolution quantitative imaging of live cells under HHP (Bourges et al, 2020). In addition, the development of microfluidic chip now allows to observe phenotype change of microbes under HHP in real-time, without depressurization (Cario et al, 2022b). Another way to determine potential changes in the membrane lipids upon HHP, might be to determine the microbial genomic potential to synthesize unsaturated and branched-chain fatty acids, which have been seen to increase as a response to HHP.…”