Wanted Dead or Alive: On the Hunt for Microbes below the Ocean Floor

Brandi Reese, Texas A&M University, Corpus Christi

The ocean covers over 70% of the Earth and the sediment and rocks beneath the seafloor is home to one of the larger and most diverse biomes on the planet. We still know very little about the microbes – bacteria, archaea, fungi, and viruses – that make their home in this environment. The marine subsurface biome has only recently been appreciated as a metabolically active ecosystem, profoundly affecting global elemental cycles. However, they may not all be alive and we need to sort out the living microorganisms from the dead and the ones that are dormant. Due to extreme difficulty in sampling this environment, relatively few locations have been studied in depth and over time. Therefore, the diversity, abundance, energy metabolisms, and active fraction of subsurface organisms have traditionally been poorly constrained. My research uses sequencing to comprehensively survey microbial communities in deeply buried marine environments. Unlike other environments, the deep subsurface provides a unique opportunity to study biogeography across four dimensions. These samples are not only isolated by linear space on a global scale, but they are also temporally isolated by, in some cases, tens of millions of years.