Biodegradation of Toxic Chemicals

1. Carbon flow from toxic chemicals to membrane biomass

In collaboration with Dr. Alvarez at University of Iowa, I am conducting degradation experiment on the five pseudomonas species that can degrade toluene (Fig. 1). Our approach is to utilize 13C-labeled toluene to determine the carbon flow from toluene to membrane fatty acids and phospholipids, thereby we can develop indicators for effective biodegradation and therefore bioremediation.
Figure 1

http://www.ge-at.iastate.edu/people/faculty/fang/Biodeg1.gif

2. Microbial response to toxic chemicals

We grew five reference pseudomonad strains that express different toluene degradation pathways: Pseudomonas putida mt-2, Pseudomonas putida F1, Burkholderia cepacia G4, Burkholderia pickettii PKO1, and Pseudomonas mendocina KR1 in media with and without toluene (Fang et al., 2000). All strains showed significant changes in phospholipid content and composition as an adaptive response to toluene exposure, as well as considerable diversity in response mechanisms. For example, the phospholipid content of toluene-grown PKO1, F1, and KR1 was 10.9% to 34.7 % of that found in succinate-grown strains, while the phospholipid content of mt-2 and G4 increased by 56% and 94%, respectively, when grown on toluene. In addition, PKO1, F1, and mt-2 responded to the presence of toluene by synthesizing more phosphatidylglycerol, whereas G4 and KR1 synthesized phospholipids with polyunsaturated fatty acids (C18:2) on one or both of the sn-2 positions. These changes in phospholipid composition and concentration probably reflect the sensitivity and degree of tolerance of these strains to toluene, and suggest that different mechanisms are utilized by dissimilar bacteria to maintain optimal lipid ordering in the presence of such environmental pollutants.