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Harvard Forest Symposium Abstract 2018

  • Title: Illuminating Microbial Dark Matter in Soil: A Cell-Sorted Metagenomics Approach
  • Primary Author: Lauren Alteio (University of Massachusetts - Amherst )
  • Additional Authors: Jeffrey Blanchard (University of Massachusetts - Amherst )
  • Abstract:

    Atmospheric carbon dioxide is a potent greenhouse gas, and in 2016 levels of CO2 surpassed 400 parts per million (ppm) at a rate that is expected to increase.. This symbolic turning-point in global change further reinforces scientific motivation to understand patterns and drivers of climatic shift. Soils are a critically important component in atmospheric gas exchange, as they contain approximately two-thirds of global carbon stores which have the potential for release to the atmosphere via respiratory activity of soil organisms. The Harvard Forest Long-Term Ecological Research (LTER) site in Petersham, MA is home to experimental soil warming sites heated continuously to 5°C above ambient since 1991 and 2001, providing ample time for natural selection of genotypes better adapted to the altered environment. The net short-term effect of warming on forest soil communities is increased microbial activity, resulting in elevated CO2 flux to the atmosphere and lower soil organic carbon levels. Several challenges remain to directly link soil communities to changes in soil CO2 efflux. Consequently, it is essential that we develop more targeted methods for analyzing community composition and function of active community members in situ. We stained viable cells using SYBR green followed by Fluorescence Activated Cell Sorting (FACS) and sequencing of 90 subpools of 100 cells from warmed and control samples from both organic and mineral soil horizons. This approach, termed mini-metagenomics, resulted in >2,000 distinct genome bins. Phylogenomic analysis revealed a surprising diversity of unknown or uncultured bacteria and viruses. The mini-metagenome results were used to map traditional metagenomic and metatranscriptomic data from the warming sites. These data are used to determine whether long-term warming has changed community structure of active microorganisms and detect evidence of selection in response to warming. We are able to link heterogeneity in genome composition to soil chemistry transformations resulting from warming through identification of the soil chemical fingerprint using FT-ICR mass spectrometry. The results suggest ongoing changes in community structure and ecosystem function.

  • Research Category: Biodiversity Studies