The Environmental Bioinorganic Chemistry of Aquatic Microbial Organisms describes the interactions between metals and aquatic prokaryotic and eukaryotic microorganisms in their environment. Metals influence microbial growth in the aquatic environment as they can be either toxic to aquatic microbes, if present at too high concentrations in the environment, or limiting, if bio-essential and present at very low concentrations. In turn, microorganisms influence the biogeochemical cycling of metals as they affect trace metal concentrations, distributions between particulate and dissolved phase, and chemical speciation. At the sub cellular level, metalloproteins are the catalysts driving many steps in the biogeochemical cycles of major elements such as carbon, nitrogen and sulfur. Metals thus provide a link between the abundance and activity of enzymes, the growth of microorganisms, and the biogeochemical cycles of major climate influencing elements. Furthermore, the evolution of the chemistry of aquatic environments and atmosphere has left its mark on the microbial proteome as a direct result of changes in the solubility of metals. The aquatic microbial metallome thus has the potential to reveal information about key biogeochemical processes, their spatial and seasonal occurrence, and also to reveal how the geochemical environment is shaping the microbial population itself. The aim of this Research Topic is to highlight recent advances in our understanding of how metals influence the activity of aquatic microbes, and how microbes influence the biogeochemical cycling of metals. Applications of techniques in proteomics, spectroscopy, mass spectrometry and genomics are all leading to a greater understanding of the interactions between the microbial metallome and the “aquatic metallome” and thus the influence of metals on the biogeochemical cycles of climatically important elements such as carbon, nitrogen and sulfur. Both reviews and original research on the occurrence and abundance of microbial metal proteins and peptides, the utilisation of metals by aquatic microbes, the influence of microbially produced exudates on metal speciation and the biogeochemical cycling, and the toxicity of metals to microbial organisms are welcome.