Re-evaluating the abundance of microorganisms

There are significantly fewer microorganisms on Earth than previously thought, according to a recent study. A report in 1998 had estimated that there are 35.5 × 10²⁹ bacteria and archaea in sub-sea floor sediments. However, this study focused on coastal regions, and other studies measuring the abundance of microorganisms in more nutrient-deprived areas, such as open-ocean gyres, had reported much lower numbers. To address this discrepancy, Kallmeyer et al. compiled data from both nutrient-rich coastal regions and nutrient-deprived areas, and estimated that there are 2.9 × 10²⁹ cells in the sub-sea floor sediment; this is similar to the estimated number of microorganisms in sea water (1.2 × 10²⁹) and soil (2.6 × 10²⁹). Together, these measurements suggest that, although the number is still vast, there are 50–78% fewer bacteria and archaea on Earth than previously thought.