What's Up Down There? Microbial Diversity in Caves

In studying metabolic versatility, microbial ecologists often focus on those microbes that grow in extremes of temperature, osmolarity, pressure, and pH; however, these physical settings often contain microbes within high-energy systems such as sulfidic hot springs or photosynthetically driven biofilm communities. The vast majority of microbial species are not situated within such energetically favorable settings. Rather, they eke out existences under extremes of near-starvation or oligotrophy, defined as having less than 2 mg of total organic carbon (TOC) per liter. With diverse oligotrophic communities found in oceans, sediments, and within the subsurface, researchers are attempting to understand how various microbial species manage to live under such nutrient-poor conditions. Amid this heightened interest, access to such oligotrophic environments remains challenging, and doing research at such sites often requires very costly equipment, including oceangoing vessels or subsurface drilling equipment.