In most environments, iron is ...
Published by Lynn Egan, Lachat Instruments- A Hach Company Brand - Chemist III/Product Applications manager
In most environments, iron is a limiting nutrient. Microbes produce a molecule called a siderophore in order to recover iron from their environment. I would guess that some are more efficient at this than others, and also that a google or google scholar search will turn up some candidate microbes. (https://www.google.com/?gws_rd=ssl#q=microbes+efficient+at+iron+uptake )