Characteristics And Pathway Of Triphenyltin Degradation By Bacillus Thuringiensis

Organotin compounds (OTC), which have endocrine disrupting properties, are highly toxicto the ecological environment and human. The main way to remove OTC is microbialdegradation. To accelerate the application of bioderadation in the ecological restoration, thecharacteristics and pathway of triphenyltin (TPhT) degradation was investigated in the currentstudy.The TPhT degrading bacterium, selected from the TPhT polluted environment by researchgroup previously, was identified as Bacillus thuringiensis through physiological and biochemicalexperiments and16S rDNA sequencing. TPhT biodegradation by B. thuringiensis, includingoptimizing degradation conditions, differences in cell morphology before and after degradation,changes of cell activity and ion metabolism, biodegradation metabolite analysis and mechnisam,was conducted.The optimum cell age for TPhT degradation was12h. The optimal concentration ofinorganic salt medium was as follows: Na2HPO4·12H2O150mg·L-1, KH2PO450mg·L-1, NH4Cl30mg·L-1and MgSO45mg·L-1. Biodegradation of1mg L-1TPhT enhanced by suitableconcentration of sucrose fatty acid ester, tea saponin and Tween80were22.0%,8.6%and14.3%, respectively.After degradation, the cell surface changed from smooth and plump to wrinkle with viscousmaterials production, whereas the shape of cell was still intact. TPhT could stimulate cell growthand promoted carbon source assimilation. During the biodegradation process, cells in theinorganic salt medium released a certain amount of Na+, NH4+, K+, Mg2+, PO43-and Cl-. Tween80increased extracellular Cl-, PO43-and K+utilization, and reduced intracellular Na+, NH4+andMg2+release.Phenyltin biodegradation initially proceeded by cleaving the aromatic ring, not by splittingthe covalent bonds between the benzene rings and tin atom. Ring-cleavage reactions in thebenzenes of TPhT occurred individually and synchronously, producing diphenyltin (DPhT),monophenyltin (MPhT) and tin accordingly. DPhT and MPhT were also degraded by B.thuringiensis. The degradation efficiency of three kinds OTCs treated by B. thuringiensis were inthe following order: MPhT＞DPhT＞TPhT.