Submitted to: Applied and Environmental Microbiology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 10/21/2001
Publication Date: 10/22/2001
Interpretive Summary: The movement of contaminants of petroleum products and toxic metal contaminants in ground water (aquifers) can be enhanced if the contaminants can attach to large molecules that move more readily than they. Such an enhancement of movement is called facilitated transport. A large molecule that is produced and released into the environment by a soil bacterium had been identified as such a molecule. It increased the movement of both a hydrocarbon contaminant and toxic metals in an aquifer sand. Using chemical and genetic methods we identified the bacterium producing the large molecule as a member of a group of bacteria that are associated with leguminous plants. Chemical analysis of the molecule revealed that it was composed of several sugars, mainly glucose, that were attached to one another in long and branched chains, and attached to the sugars were fatty compounds. The sugars carried a negative electric charge, and the fatty compounds by nature are not soluble in water. The negative electric charge associated with the sugars accounted for the molecule's ability to attract, bind and transport positively charged toxic metals, and the fatty components of the molecule accounted for its ability to attract, bind, and transport non-water soluble petroleum contaminants. The identification of the bacterium that produces the molecule implies that the bacterium has potential to produce large quantities of the molecule that can be used in engineered methods designed to clean up contaminated soil and aquifers.
Technical Abstract: The soil bacterium 9702-M4 synthesizes an exopolymer that facilitates the transport of hydrophobic pollutants such as polyaromatic hydrocarbons, and heavy toxic metals such as lead and cadmium in soil and aquifer environments. Using various analytic methods we have shown that the exopolymer of 9702-M4 is composed of both an extacellular polysaccharide (EPS), and a rough lipopolysaccharide (RLPS). The EPS component is composed mainly of 4-glucose linkages with monomers of galactose, mannose, glucuronic acid, and pyruval and acetyl substituents. Biolog analysis, growth rate determinations, and %G+C content identified 9702-M4 as a strain of Sinorhizobium meliloti. Sequence analysis of a 16S rDNA fragment gave 9702-M4 a phylogenetic designation most closely related S. fredii. The RLPS and lack of smooth LPS further supported the phylogenic designation of Sinorhizobium. The lipid fraction and the negative charge associated with carbonyl groups of the exopolymer appear to account separately for its adsorption of both polyaromatic hydrocarbons and cationic toxic metals.