Biodegradation of Organic Pollution Involving Soil Iron(III) Solubilized by Bacterial Siderophores as an Electron Acceptor

Summary

Microbial degradation of organic matter, like any oxidation process, requires an oxidizing agent. The role of the latter may be played by oxygen (the most common electron acceptor). However, under microaerobic conditions (ground water, subsurface soil) the supply of oxygen is limited, which, in its turn, may limit the biodegradation rate. An alternative possibility is the use of other electron acceptors, among which iron(III) is generally abundant in soil, yet being poorly soluble at physiological pH values. In this case its bioavailability can be essentially increased, e.g. by adding a chelating agent: NTA, EDTA, etc.

It should be noted that such an externally introduced chelator would increase also the bioavailability of a number of heavy metals which might then be easily accumulated in plants or otherwise affect the biota, including possible suppression of biodegrading microorganisms. This drawback can be avoided by using bacterial siderophores which selectively solubilize iron(III) and can be used by dissimilatory iron(III)-reducing bacteria that couple iron(III) reduction to oxidative degradation of organics. In this chapter, the possibilities are discussed for applying bacterial siderophores, as well as iron(III)-solubilizing bacterial cultures both “compatible” with the bacteria-biodegraders in sharing the resulting iron(III) chelate and viable in the presence of the organic matter to be degraded, as well as other possible contaminants. Plant-associated bacteria of the genus Azospirillum seem to be beneficial for the above applications as co-inoculants in concert with bacteriabiodegraders.