Iron-oxidizing bacteria are associated with ferric hydroxide precipitates (Fe-plaque) on the roots of wetland plants

The presence of Fe-oxidizing bacteria in the rhizosphere of four different species of wetland plants was investigated in a diverse wetland environment that had Fe(II) concentrations ranging from tens to hundreds of micromoles per liter and a pH range of 3.5 to 6.8. Enrichments for neutrophilic, puta tively lithotrophic Fe-oxidizing bacteria were successful on roots from all four species; acidophilic Fe-oxidizing bacteria were enriched only on root s from plants whose root systems were exposed to soil solutions with a pH o f <4. In Sagittaria australis there was a positive correlation (P < 0.01) b etween cell numbers and the total amount of Fe present; the same correlatio n was not found for Leersia oryzoides. These results present the first evid ence for culturable Fe-oxidizing bacteria associated with Fe-plaque in the rhizosphere.