Center for Microbial Ecology, Michigan State University, East Lansing, MI, USA.
Plant, Soil and Microbial Sciences, Michigan State University, East Lansing, MI, USA.
Sci Total Environ. 2020 Apr 10;712:135525. doi: 10.1016/j.scitotenv.2019.135525. Epub 2019 Nov 21.
Polychlorinated dibenzo-p-dioxins and dibenzofurans are a group of chemically-related pollutants categorically known as dioxins. Some of their chlorinated congeners are among the most hazardous pollutants that persist in the environment. This persistence is due in part to the limited number of bacteria capable of metabolizing these compounds, but also to their limited bioavailability in soil. We used Sphingomonas wittichii strain RW1 (RW1), one of the few strains able to grow on dioxin, to characterize its ability to respond to and degrade clay-bound dioxin. We found that RW1 grew on and completely degraded dibenzo-p-dioxin (DD) intercalated into the smectite clay saponite (SAP). To characterize the effects of DD sorption on RW1 gene expression, we compared transcriptomes of RW1 grown with either free crystalline DD or DD intercalated clay, i.e. sandwiched between the clay interlayers (DDSAP). Free crystalline DD appeared to cause greater expression of toxicity and stress related functions. Genes coding for heat shock proteins, chaperones, as well as genes involved in DNA repair, and efflux were up-regulated during growth on crystalline dioxin compared to growth on intercalated dioxin. In contrast, growth on intercalated dioxin up-regulated genes that might be important in recognition and uptake mechanisms, as well as surface interaction/attachment/biofilm formation such as extracellular solute-binding protein and LuxR. These differences in gene expression may reflect the underlying adaptive mechanisms by which RW1 cells sense and deploy pathways to access dioxin intercalated into clay. These data show that intercalated DD remains bioavailable to the degrading bacterium with implications for bioremediation alternatives.
多氯二苯并对二恶英和多氯二苯并呋喃是一组化学相关的污染物，被明确归类为二恶英。它们的一些氯化同系物是在环境中持续存在的最危险的污染物之一。这种持久性部分是由于能够代谢这些化合物的细菌数量有限，但也由于它们在土壤中的生物利用度有限。我们使用能够在二恶英上生长的少数菌株之一斯氏假单胞菌 RW1（RW1）来表征其对粘土结合二恶英的响应和降解能力。我们发现 RW1 在蒙脱石皂石（SAP）中生长并完全降解了嵌入的二苯并对二恶英（DD）。为了表征 DD 吸附对 RW1 基因表达的影响，我们比较了在自由结晶 DD 或嵌入粘土（DDSAP）中生长的 RW1 的转录组。自由结晶 DD 似乎导致了更多的与毒性和应激相关的功能的表达。与在嵌入的二恶英上生长相比，编码热休克蛋白、伴侣以及参与 DNA 修复和外排的基因在生长在结晶二恶英上时被上调。相比之下，在嵌入的二恶英上生长上调了可能在识别和摄取机制以及表面相互作用/附着/生物膜形成中起重要作用的基因，例如细胞外溶质结合蛋白和 LuxR。这些基因表达的差异可能反映了 RW1 细胞感知和利用途径来获取嵌入粘土中的二恶英的潜在适应机制。这些数据表明，嵌入的 DD 仍然对降解细菌具有生物可利用性，这对生物修复替代方案具有影响。
