Assessing microbial processes in deep-sea hydrothermal systems by incubation at in situ temperature and pressure

McNichol, Jesse; Sylva, Sean P.; Thomas, François; Taylor, Craig D.; Sievert, Stefan M.; Seewald, Jeffrey S.

doi:10.1016/j.dsr.2016.06.011

Cited by 46 publications

(98 citation statements)

References 52 publications

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“…However, our rates are similar to Mandernack and Tebo (1999) who cite short incubation times (≤ to our study) as an explanation for higher rates. Therefore, the short timescale of incubations and maintenace of deep-sea pressure and temperature (McNichol et al, 2016) probably explains why carbon fixation rates reported here are consistently higher than most other studies.…”

Section: 4contrasting

confidence: 53%

“…In this study, we addressed these limitations by incubating subseafloor microbial communities with nitrate, oxygen, and hydrogen amendments (which are depleted by microbial activity upon sampling (McNichol et al, 2016)) as well as a 13 CO 2 label (to track carbon fixation). Microbes were maintained at in situ pressure and temperature for ≈ 24 h using isobaric gas-tight samplers (25MPa; McNichol et al, 2016;Seewald et al, 2002).…”

Section: 2mentioning

confidence: 99%

“…were used to determine the fingerprint of microbial activity in the natural environment (McNichol et al, 2016). Then, given the range of values for CGE, we estimated how much carbon could be fixed by microbes that had consumed these substrates during active growth.…”

Section: Extrapolations To Natural Environmentmentioning

confidence: 99%

“…The consumption of nitrate and oxygen were also measured -likely the only electron acceptors of importance during incubations. The means by which electron equivalents used to reduce these substrates was calculated has been previously described (McNichol et al, 2016). Total electrons oxidized from sulfide and hydrogen were not directly measurable due to incomplete oxidation of sulfide (McNichol et al, 2016), so this value was inferred by taking the sum of electron equivalents to carbon fixation and electron equivalents to electron acceptors.…”

Section: Chemosynthetic Growth Efficiency (Cge) Determinationsmentioning

confidence: 99%

“…Microbes were maintained at in situ pressure and temperature for ≈ 24 h using isobaric gas-tight samplers (25MPa; McNichol et al, 2016;Seewald et al, 2002). Most experiments were carried out at in situ vent fluid temperature (24 ∘ C), while an additional two were incubated at higher temperature (50 ∘ C) that likely characterizes deeper subseafloor environments.…”

Section: 2mentioning

confidence: 99%

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Productivity, metabolism and physiology of free-living chemoautotrophic Epsilonproteobacteria

McNichol¹

2016

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Chemoautotrophic ecosystems at deep-sea hydrothermal vents were discovered in 1977, but not until 1995 were free-living autotrophic Epsilonproteobacteria identified as important microbial community members. Because the deep-sea is food-starved, the autotrophic metabolism of hydrothermal vent Epsilonproteobacteria may be very important for deep-sea consumers. However, quantifying their metabolic activities in situ has remained difficult, and biochemical mechanisms underlying their autotrophic physiology are poorly described. To gain insight into environmental processes, an approach was developed for incubations of microbes at in situ pressure and temperature (25 MPa, 24 o C) with various combinations of electron donors/acceptors (H 2 , O 2 and NO 3 -and 13 HCO 3 -) as a tracer to track carbon fixation. During short (18-24 h) incubations of low-temperature vent fluids from Crab Spa (9 o N East Pacific Rise), the concentration of electron donors/acceptors and cell numbers were monitored to quantify microbial processes. Measured rates were generally higher than previous studies, and the stoichiometry of microbially-catalyzed redox reactions revealed new insights into sulfur and nitrogen cycling. Single-cell, taxonomically-resolved tracer incorporation showed Epsilonproteobacteria dominated carbon fixation, and their growth efficiency was calculated based on electron acceptor consumption. Using these data, in situ primary productivity, microbial standing stock, and average biomass residence time of the deep-sea vent subseafloor biosphere were estimated. Finally, the population structures of the most abundant genera Sulfurimonas and Thioreductor were shown to be strongly influenced by pO 2 and temperature respectively, providing a mechanism for niche differentiation in situ. To gain insights into the core biochemical reactions underlying autotrophy in Epsilonprotebacteria, a theoretical metabolic model of Sulfurimonas denitrificans was developed. Validated iteratively by comparing in silico yields with data from chemostat experiments, the model generated hypotheses explaining critical, yet so far unresolved reactions supporting chemoautotrophy in Epsilonproteobacteria. For example, it provides insight into how energy is conserved during sulfur oxidation coupled to denitrification, how reverse electron transport produces ferredoxin for carbon fixation, and why aerobic growth yields are only slightly higher compared to denitrification. As a whole, this thesis provides important contributions towards understanding core mechanisms of chemoautrophy, as well as the in situ productivity, physiology and ecology of autotrophic Epsilonproteobacteria.

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Section: 4contrasting

confidence: 53%