Oral Presentation Australian Society for Microbiology Annual Scientific Meeting 2019

Ecological and genomic attributes of novel bacterial taxa that thrive in subsurface soil horizons (#188)

Noah Fierer 1
  1. University of Colorado, Boulder, CO, United States

While most bacterial and archaeal taxa living in surface soil horizons remain undescribed, this problem is exacerbated in deeper soils owing to the highly oligotrophic conditions found in the subsurface. Additionally, previous studies of soil microbiomes have focused almost exclusively on surface soils, even though the microbes living in deeper soils also play critical roles in a wide range of biogeochemical processes. We examined soils collected from 20 distinct profiles across the U.S. to characterize the bacterial and archaeal communities that live in subsurface soils and to determine whether there are consistent changes in soil microbial communities with depth across a wide range of soil and environmental conditions. We found that, irrespective of location, bacterial and archaeal diversity decreased with depth, as did similarity of microbial communities to those found in surface horizons. We observed five phyla that consistently increased in relative abundance with depth across our soil profiles: Chloroflexi, Nitrospirae, Euryarchaeota, and candidate phyla GAL15 and Dormibacteraeota. Leveraging the unusually high abundance of Dormibacteraeota at depth, we assembled genomes representative of this candidate phylum and identified traits that are likely to be beneficial in low nutrient environments, including the synthesis and storage of carbohydrates, the potential to use carbon monoxide (CO) as a supplemental energy source, and the ability to form spores. Together these attributes likely allow members of the candidate phylum to flourish in deeper soils and provide insight into the survival and growth strategies employed by the microbial taxa that thrive in oligotrophic soils. I will finish by highlighting microbial adaptations to oligotrophy more generally and the strategies that can be used to study those microbes with long generation times and low rates of activity that are typically difficult to study using more traditional cultivation-based approaches.