Bacterial use of siderophores increases olivine dissolution rates by nearly an order of magnitude

Abstract

Mafic minerals, such as olivine, are an important source of metals and alkalinity to Earth's surface, impacting the planet's long term carbon cycle and climate. Yet, environmental controls on their dissolution rates remain poorly understood. Recent studies show that exogenous siderophores can enhance olivine dissolution abiotically, but it remains unclear how important siderophores are in microbially enhanced dissolution. Here, we isolated the effect of microbial siderophores on olivine dissolution using the bacteria Shewanella oneidensis, including both wild type and a mutant strain incapable of siderophore production. We show that S. oneidensis required siderophores to access mineral bound Fe, without which dissolution was not enhanced above background abiotic rates. Furthermore, dissolution rates with the bacteria were eight fold higher than those in abiotic solutions with the same concentrations of exogenous siderophores, implying a synergy between siderophores and other biotic mechanisms. After reaching stationary phase, dissolution in the S. oneidensis wild type treatment slowed, whereas that in the mutant + siderophore treatments continued at high rates. These results suggest that while siderophores are critical for biotically enhanced olivine dissolution, other microbe-related mechanisms magnify their effect.