Factors influencing the fate of chromium in soils : microbial ecology, physiology and metal transformation studies

Abstract

Chromium is a common contaminant in soil environments, especially at Department of Energy sites. The fate of chromium in the environment is influenced by a number of factors including the microbial processes and the interactions with soil constituents such as carbon sources, iron minerals and electron shuttling compounds. The overall goals of these studies were to isolate and characterize microorganisms that may play a role in the fate of chromium in soil systems, identify the microbial community associated with a simulated low-level waste site and determine the role carbon source, iron minerals and electron shuttles play on Cr(VI) toxicity and reduction by Arthrobacter spp. and Cellulomonas sp. strain ES6. Three strategies for isolating potential cellulose-degrading isolates (direct isolation on agar plates, liquid enrichments and soil laden continuous flow columns) were implemented through which thirteen isolates were obtained. Clone library, PhyloChip and quantitative PCR analyses of the bacterial community within a simulated low-level waste site at the Idaho National Laboratory suggested that the presence of cellulosic waste influenced the bacterial community structure with soil depth at the site. The influence of potential cellulose degradation products as carbon sources on Cr(VI) toxicity and reduction by Arthrobacter sp. isolate EF01 and A. aurescens TC1 was assessed through bench-scale studies. Results indicated that Cr(VI) toxicity to both Arthrobacter spp. was tied to carbon metabolism. Additional studies with Cellulomonas sp. strain ES6 demonstrated that Cr(VI) reduction by this organism was also influenced by carbon source as well as by the addition of electron shuttles and iron minerals. Overall, the results of this dissertation provide insight into the potential interactions between microorganisms, soil constituents and chromium in situ.