Bo Ruan,Pingxiao Wu,Meiqing Chen,Xiaolin Lai,Liya Chen,Langfeng Yu,Beini Gong,Chunxi Kang,Zhi Dang,Zhenqing Shi,Zehua Liu
In this study, batch experiments were carried out to evaluate the biodegradation of phenol by Sphingomonas sp. GY2B, which were immobilized in polyvinyl alcohol (PVA) – sodium alginate – kaolin beads under different conditions. The optimal degradation performance was achieved by GY2B immobilized in beads containing 1.0% (w/v) of kaolin, 10% (w/v) of PVA, 0.3% (w/v) of sodium alginate, 10% (v/v) of biomass dosage, and exposed to an initial phenol concentration of 100 mg/L. The experimental results indicated that PVA-sodium alginate-kaolin beads can accelerate the degradation rate of phenol by reducing the degradation time and also improve degradation rate. The biodegradation rate of phenol by immobilized cells (16.79 ± 0.81 mg/(L·h)) was significantly higher than that of free cells (11.49 ± 1.29 mg/(L·h)) under the above optimal conditions. GY2B immobilized on beads was more competent than free GY2B in degradation under conditions with high phenol concentrations (up to 300 mg/L) and in strong acidic (pH = 1) and alkaline (pH = 12) environments. Higher phenol concentrations inhibit the biomass and reduce the biodegradation rate, while the lower biodegradation rate at low initial phenol concentrations is attributed to mass transfer limitations. The Haldane inhibitory model was in agreement with the experimental data well, revealing that phenol showed a considerable inhibitory effect on the biodegradation by Sphingomonas sp. GY2B, especially at concentrations higher than 90 mg/L. Intra-particle diffusion model analysis suggests that adsorption of phenol by immobilized beads was controlled by both rapid surface adsorption as well as pore diffusion mechanism. It's worth noting that the presence of 1 mg/L Cr(VI) enhanced the biodegradation of phenol by free cells, while Cr(VI) showed no obvious impact on the removal of phenol by immobilized cells. In addition, immobilized cells were reused 16 times and removed 99.5% phenol, and when stored at 4 °C for 90 days, more than 99% phenol was removed. These results showed that immobilized cells can significantly improve the microbial degradation performance, and protect microorganisms against unfavorable environment. It is implied that PVA -sodium alginate-kaolin beads have great potential to be applied in a practical and economical phenolic wastewater treatment system.
Yujia Zhou,Zhiming Li,Xinghui Xie,Xingtao Zhou,Jielun Hu,Shaoping Nie
Gellan is a microbial polysaccharide synthesized by Sphingomonas paucimobilis , and is widely utilized in the food and pharmaceutical industries, as well as in other fields. However, much remains unknown about the key genes involved in the gellan synthesis pathway. In this study, ultraviolet (UV) and atmospheric room temperature plasma (ARTP) were employed to induce mutations in S . paucimobilis ATCC31461 (Sp31461 NC), and ultimately resulting a high-yield mutant strain (Sp31461 UA) with a yield increase of 120 % from 3.6 g/L to 8.3 g/L. The growth curve, monosaccharide composition and molecular weight indicated that mutagenesis accelerated the growth of the strain, but did not affect gellan's basic physicochemical property. A combined analysis of transcriptomic and metabolomic demonstrated that the differentially expressed genes and metabolites resulting from mutations were primarily enriched in pathways related to energy metabolism, among which potential key genes such as pgi , clpB , ycaJ associated with gellan yield, were further verified by quantitative reverse transcription polymerase chain reaction (qRT-PCR) and gene overexpression. Notably, the strain overexpression the pgi gene resulted in a 20 % increase in gellan yield compared to the Sp31461 UA strain, reaching 10.0 g/L. In summary, the energy metabolism pathway in S . paucimobilis is closely linked to gellan biosynthesis, and high-yield strains of gellan can be developed through mutagenesis breeding and the overexpression of key genes identified by transcriptomics and metabolomics. This research offers valuable scientific insights for the industrial production and application of gellan.
Dichloromethane (DCM) is a recalcitrant volatile organic compound that exhibits biological toxicity and bioaccumulation. In this study, gaseous DCM was removed using an electroactive bacterial biofilter (EBB) with graphite rod as the anode and carbon felt as the cathode. The highest removal efficiency (97.09%) was achieved at a cathodic potential of −600 mV (vs. Ag/AgCl). The EBB had a maximum elimination capacity of 79.29 g m −3 h −1 when the inlet load was 96.48 g m −3 h −1 . There was no substrate inhibition phenomenon observed in the EBB, and the Michaelis–Menten model was used to describe the kinetics of the EBB. High-throughput sequencing indicated that electroactive genera such as Rhodanobacter sp., Sphingomonas sp., Pseudomonas sp., Chryseobacterium sp . , Pseudochrobactrum sp., and Mycobacterium sp. dominated the EBB. The microbial communities were stable and were slightly affected by the DCM inlet concentration. The results can be applied for the effective treatment of recalcitrant volatile organic compounds (VOCs).
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