10^11 - 10^12 species
||Locey KJ, Lennon JT. Scaling laws predict global microbial diversity. Proc Natl Acad Sci U S A. 2016 May 24 113(21):5970-5. doi: 10.1073/pnas.1521291113 Abstract, p.5971 right column top paragraph & p.5973 right column 2nd paragraphPubMed ID27140646
||Abstract: "[Investigators] document a universal dominance scaling law that holds across 30 orders of magnitude, an unprecedented expanse that predicts the abundance of dominant ocean bacteria. In combining this scaling law with the lognormal model of biodiversity, [they] predict that Earth is home to upward of 1 trillion (10^12) microbial species. Microbial biodiversity seems greater than ever anticipated yet predictable from the smallest to the largest microbiome."
||P.5971 left column bottom paragraph: "When extended to global scales, this dominance scaling law closely predicts the abundance of dominant ocean bacteria. Using the lognormal model of biodiversity, published estimates of global microbial N [number of individuals in an assemblage], and published and predicted values of Nmax, [investigators] predict that Earth is occupied by 10^11–10^12 microbial species. This estimate is also supported by the scaling of S [species richness] with N." P.5973 right column 2nd paragraph: "[Investigators] estimate that Earth is inhabited by 10^11–10^12
microbial species. This prediction is based on ecological theory reformulated for large-scale predictions, an expansive dominance scaling law, a richness scaling relationship with empirical and theoretical support, and the largest molecular surveys compiled to date."