Aerobic microbial life in oxic sediment of South Pacific Gyre persists up to 101.5 million years

Abstract:

During the Integrated Ocean Drilling Program (IODP) Expedition 329, we observed the presence of aerobic microbial communities and dissolved oxygen throughout the sedimentary sequence from the seafloor to the sediment-basement interface at all sites we explored in the South Pacific Gyre (SPG) [1]. This finding indicated that the sedimentary biosphere in the oligotrophic ocean region has no depth limit and continues down to the basement. However, the physiology of these aerobic microbial communities, including substrate metabolism remain poorly constrained. Here we show that diverse aerobic members of communities in SPG sediments (4.3‒101.5 Ma) are capable of readily incorporating carbon and nitrogen substrates and dividing. Most of the 6986 individual cells analyzed with nanometer-scale secondary ion mass spectrometry (NanoSIMS) actively incorporated isotope-labeled substrates. Many cells responded rapidly to incubation conditions, increasing total numbers by 4 orders of magnitude and taking up labeled carbon and nitrogen within 68 days after incubation. The response was generally faster (on average, 3.09 times) for nitrogen incorporation than for carbon incorporation. In contrast, anaerobic microbes were only minimally revived from this oxic sediment. Our results suggest that microbial communities widely distributed in organic-poor abyssal sediment consist mainly of aerobes that retain their metabolic potential under extremely low-energy conditions for up to 101.5 Ma..

[1] D'Hondt, S. et al., Nature Geoscience, 8(4), 299-304, 2015.