Physiological role of isocitrate lyase in dibenzo-p-dioxin and dibenzofuran metabolism by Sphingomonas wittichii RW1

BACKGROUND: Sphingomonas wittichii RW1 is one out of three strains capable of metabolizing dioxin as a sole source for carbon and energy. Under laboratory conditions the degradation rates for these aromatics are relatively high (5 and 8 h for dibenzofuran (DBF) and dibenzo-p-dioxin (DD), respectively). However, their degradation rates are much lower in the environment due to several factors. One of these factors is the availability of other carbon sources. Acetate is a metabolized carbon source by S. wittichii RW1 and its presence in the environment would have a negative impact on DBF and DD degradation. In addition, expression of most of the genes for DBF and DD degradation were downregulated when grown on acetate compared to their growth on DBF and DD. We hypothesized that blocking the acetate utilization pathway in S. wittichii RW1 would prevent it from using acetate when present along with DD and DBF in contaminated sites. RESULTS: Blocking the glyoxylate shunt by deleting isocitrate lyase gene (icl) prevented the mutant strain (RW1Δicl) from using acetate as a sole carbon source thus depending on available DBF and DD in polluted sites. Our results showed that deletion of icl did not affect growth of S. wittichii RW1 on DBF and DD but blocked it from growing on acetate. CONCLUSION: Our results introduces an engineered strain that can be used as a new candidate to clean dioxin-contaminated sites which are rich with acetate.