Isolation And The Growth Characterization Of Tea Saponin-Grown Bacteria And Their Induced Degradation On Pcbs With Tea Saponin

Poly chlorinated biphenyls (PCBs) is a class of typical persistent organic compounds with widespread distribution, low content and slow degradation in the environment. Many scholars consider it may be an effective way to remediate the PCBs contaminated environment with addition of biodegradation inducer. In this paper, PCB77, PCB118and PCB138were selected as the typical representative pollutants of PCBs, and tea saponins (TS), a pentacyclic triterpenoid compound, was used as biodegradation inducer, indigenous bacteria strains from the soil with TS were tested and the growth conditions were investigated, and the biodegradation of PCBs induced by TS in water solution or soil was caried out. The main conclusions are as follows:(1) Two TS-biodegrading bacteria named as YTS and WTS were separated from the soil with TS concentration of20%and30%respectively. According to the16S rDNA sequences and the phylogenetic trees of the YTS and WTS strains, both of the two bacteria belonged to Cellulomonas. (2) WTS and YTS exhibited to be effective in enhancing degradation of TS. Compared to the treatment without microbes, the TS removals were increased by82.84%and86.98%with addition of YTS and WTS respectively after15days. The TS removal followed a first order degradation model. The TS degradation rate constants were increased by134.37%and142.71%, respectively, by WTS and YTS compared to the control.(3) TS minimal inhibitory concentration (MIC) against WTS and YTS was tested by two fold dilution method. By observing the growth of WTS and YTS on the plate medium, the MIC of WTS was300mg/mL, and MIC of YTS was200mg/mL.(4) Factors on the growth of YTS and WTS such as the initial TS concentration, temperature, and pH were discussed. The results showed that YTS grew better when pH was8, and YTS grew well under the condition of25-37℃and5-20mg/mL of TS, and WTS grew well under the condition of pH5-8,25-32℃and5-20mg/mL of TS.(5) The effects of heavy metal Pb2+and Cd2+stress on the growth of YTS and WTS were studied. As a result, the sensitivity of the two bacteria to the heavy metals was different. When the concentration of Pb2+was less than or equal to50mg/L, there were no inhibition to YTS and WTS. When the concentration of Cd2+was less than or equal to30mg/L, the growth of YTS was completely inhibited, so YTS was more sensitive to Cd2+than WTS. Even though WTS had considerable ability to tolerate Cd2+, there was a significant negative correlation between the growth curve of WTS and Cd2+.(6) TS had significant promotion effect on the biodegradation of PCBs by YTS and WTS in water solution. After12days, more than90%of PCBs were degraded in the WTS+TS and YTS+TS treatments, the degradation rates were from50%to75%in the WTS and YTS treatments, but they were less than35%in the control. The degradation of PCBs followed a first order model. In the presence of TS, the degradation rate constants of PCB77, PCB118and PCB138were increased by4.3times,4.8times and2.8times, respectively, by WTS, and7.1times,9.1times and8.9times, respectively, by YTS compared to those treatments with bacteria strains but no TS.(7) In the study of PCBs induced degradation with TS by WTS and YTS in soil, the regularity of degradation of PCB77, PCB118and PCB138was not obvious.The results of significant analysis showed that, there were no significant differences between the degradation of PCBs of the four treatments, including WTS treatment, YTS treatment, YTS+TS treatment and WTS+TS treatment. This indicated that TS exhibited to be no effective significant in inducing degradation of PCBs in the soil.The biodegradation of PCBs in water solution were affected significant in the presence of TS, but the induced degradation of PCBs could be inhibited in the soil. This provides the basic theory for the further research of the practical application of TS in the remediation of PCBs contamination.