Abstract
Extractive biodegradation of phenanthrene by Sphingomonas polyaromaticivorans was previously carried out in cloud point system (CPS). In this study, we explored the possibility of further increasing the efficiency of the culture by repeatedly reusing cells and the system for biodegradation. Three different recycling strategies were adopted. In reuse of cells plus CPS, cells were reused for 3 times while maintaining high degradation rates (> 90%). Thereafter, the accumulation of metabolites in the dilute phase resulted in a decrease in cell viability. This inhibition was avoided in recycling the cells plus coacervate phase by replacing the dilute phase with fresh Medium. However, due to the slow adaptation of the cells to the new degradation environment and the reduction in the volume of the coacervate phase, the cells were only reused twice and their activity decreased. However, the same long degradation cycle (5 days) as the reuse of cells plus coacervate phase reduced the overall degradation efficiency of phenanthrene. Finally, a combined strategy of 3 times of cells plus CPS reuse and individual cells reuse once was employed and run for two cycles. 3 rounds of reuse of cells plus CPS improved cells utilization and phenanthrene degradation efficiency. Then, the subsequent round of reuse of cells alone relieved the effect of increasing metabolites on cell viability. This study provides a potential application for reusing cells to continuously degrade phenanthrene in soil and water in CPS.
Highlights
Polycyclic aromatic hydrocarbons (PAHs) are the most important class of pollutants in the environment (Trellu et al 2016)
Microorganism The strain used in the experiment was S. polyaromaticivorans, deposited in China Center of Industrial Culture Collection (CICC), with an Accession Number of Analysis methods The metabolites of phenanthrene was a carotenoid pigment was produced during the biodegradation by S. polyaromaticivorans
In the cloud point system (CPS), the pigment in the cells was extracted into the coacervate phase, which resulted in a lighter color of cells and colorless dilute phase (Fig. 1b)
Summary
Polycyclic aromatic hydrocarbons (PAHs) are the most important class of pollutants in the environment (Trellu et al 2016). They are extremely harmful due to the high bioaccumulation toxicity (Alharbi et al 2018). The addition of a surfactant to form a solubilizing system is a commonly used bioavailability strengthening method (Miller 1995). This has been used to promote microbial degradation of PAHs and has been reported many times (Lamichhane et al 2017). Xiao et al found that rhamnolipid slightly higher than CMC concentration (0.02–0.5 g/L) can promote the degradation of dichlorodiphenyltrichloroethane by white rot fungus Phlebia lindtneri GB1027, but excessive concentration (> 1.0 g/L) will produce toxic
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