The emplacement of subaqueous gravity-driven sediment flows imposes a significant physical and geochemical impact on underlying sediment and microbial communities. Although previous studies have established lasting mineralogical and biological signatures of turbidite deposition, the response of bacteria and archaea within and beneath debris flows remains poorly constrained. Both bacterial cells associated with the underlying sediment and those attached to allochthonous material must respond to substantially altered environmental conditions and selective pressures. As a consequence, turbidites and underlying sediments provide an exceptional opportunity to examine (i) the microbial community response to rapid sedimentation and (ii) the preservation and identification of displaced micro-organisms. We collected Illumina MiSeq sequence libraries across turbidite boundaries at ~26 cm sediment depth in La Jolla Canyon off the coast of California, and at ~50 cm depth in meromictic Twin Lake, Hennepin County, MN. 16S rRNA gene signatures of relict and active bacterial populations exhibit persistent differences attributable to turbidite deposition. In particular, both the marine and lacustrine turbidite boundaries are sharply demarcated by the abundance and diversity of Chloroflexi, suggesting a characteristic sensitivity to sediment disturbance history or to differences in organic substrates across turbidite profiles. Variations in the abundance of putative dissimilatory sulfate-reducing Deltaproteobacteria across the buried La Jolla Canyon sediment–water interface reflect turbidite-induced changes to the geochemical environment. Species-level distinctions within the Deltaproteobacteria clearly conform to the sedimentological boundary, suggesting a continuing impact of genetic inheritance distinguishable from broader trends attributable to selective pressure. Abrupt, <1-cm scale changes in bacterial diversity across the Twin Lake turbidite contact are consistent with previous studies showing that relict DNA signatures attributable to sediment transport may be more easily preserved in low-energy, anoxic environments. This work raises the possibility that deep subsurface microbial communities may inherit variations in microbial diversity from sediment flow and deformation events.
Bibliographical noteFunding Information:
This research was supported by funding from The National Science Foundation through The National Center for Earth-Surface Dynamics (to BEF) and The McKnight Foundation (to JVB). Coring was undertaken with resources and assistance of LacCore, UMN (NSF-IF-0949962). Additional research support and postdoctoral funding (to BKH) were provided through the Center for Dark Energy Biosphere Investigations (C-DEBI). This is C-DEBI contribution 408. We are grateful to M. Gilbertson, K. Wenner, and C. Crosby for assistance with freeze core sampling, and to C. Crosby, P. Fliss, K. Wenner, and E. Stevens for support in core collection. M. Gilbertson and E. Ricci provided assistance with DNA extraction and amplification. Sequencing was performed by the University of Minnesota Genomics Center (UMGC). We thank D. Jones for assistance with sequence processing. We thank L. Lemke and three anonymous reviewers for valuable editorial comments on assembly of this manuscript.
The National Science Foundation through The National Center for Earth-Surface Dynamics, The McKnight Foundation; The National Science Foundation through The Center for Dark Energy Biosphere Investigations
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