Biodegradation of p-xylene—a comparison of three psychrophilic Pseudomonas strains through the lens of gene expression

Abstract

p-Xylene is considered a recalcitrant compound despite showing a similar aromatic structure to other BTEXs (benzene, toluene, ethylbenzene, xylene isomers). This study evaluated the p-xylene biodegradation potential of three psychrophilic Pseudomonas strains (Pseudomonas putida S2TR-01, Pseudomonas synxantha S2TR-20, and Pseudomonas azotoformans S2TR-09). The p-xylene metabolism-related catabolic genes (xylM, xylA, and xylE) and the corresponding regulatory genes (xylR and xylS) of the selected strains were investigated. The biodegradation results showed that the P. azotoformans S2TR-09 strain was the only strain that was able to degrade 200 mg/L p-xylene after 60 h at 15 °C. The gene expression study indicated that the xylE (encoding catechol 2,3-dioxygenase) gene represents the bottleneck in p-xylene biodegradation. A lack of xylE expression leads to the accumulation of intermediates and the inhibition of biomass production and complete carbon recovery. The activity of xylene monooxygenase and catechol 2,3-dioxygenase was significantly increased in P. azotoformans S2TR-09 (0.5 and 0.08 U/mg, respectively) in the presence of p-xylene. The expression of the ring cleavage enzyme and its encoding gene (xylE) and activator (xylS) explained the differences in the p-xylene metabolism of the isolated bacteria and can be used as a novel biomarker of efficient p-xylene biodegradation at contaminated sites.

Immobilized cold-active enzymes onto magnetic chitosan microparticles as a highly stable and reusable carrier for p-xylene biodegradation

“…Our previous study showed that cold-active XMO and C1,2D complete dearomatization of p-xylene and no intermediate was detected in soil and groundwater samples. The mixture of theses enzymes is suitable for conditions that rapid remediation is needed (such as cold sites) and also stimulate the degradation processes in the contaminated site (Miri et al, 2022b). In this study, free and immobilized enzymes (XMO and C1,2D) were used for p-xylene biodegradation (Figure 5).…”

“…Cold-active enzymes have the potential to provide greater value in terms of sustainable immobilization and production and may be preferred due to their higher catalytic activity compared to their mesophilic counterparts for the biodegradation of contaminants in cold environments. Our previous finding also showed that the inherent instability of these enzymes is one of the important challenges in the industrial and commercial application of these enzymes (Miri et al, 2021a;Miri et al, 2022b). However, the reusability of immobilized enzymes on solid carriers for soil matrices such as biochar was not feasible (Miri et al, 2022a).…”

Current Trends and Future Perspectives in the Remediation of Polluted Water, Soil and Air—A Review

“…For example, Ding et al [102] achieved 97.1% bioremediation efficiency of naproxen-contaminated water using Cymbella sp. In addition, studies have shown the possibility of microbiological activity for the degradation of organic compounds such as naphthalene [103], xylene [104] and PAHs [105]. Research by Jiang et al [106] found that bacteria exposed to Cr 6+ experience oxidative stress, thereby reducing their bioremediation efficiency.…”