Construction of a Tetracycline Degrading Bacterial Consortium and Its Application Evaluation in Laboratory-Scale Soil Remediation

• Main Authors: Xueling Wu, Yichao Gu, Xiaoyan Wu, Xiangyu Zhou, Han Zhou, Charles Amanze, Li Shen, Weimin Zeng
• Format: Article
• Language: English
• Published: MDPI AG 2020-02-01
• Series: Microorganisms
• Subjects: biodegradation of tetracycline; construction of bacterial consortium; lab-scale soil remediation; high-throughput sequencing; tetracycline resistance genes; mobile gene elements
• Online Access: https://www.mdpi.com/2076-2607/8/2/292

As an environmental pollutant, tetracycline (TC) can persist in the soil for years and damage the ecosystem. So far, many methods have been developed to handle the TC contamination. Microbial remediation, which involves the use of microbes to biodegrade the pollutant, is considered cost-efficient and more suitable for practical application in soil. This study isolated several strains from TC-contaminated soil and constructed a TC-degrading bacterial consortium containing <i>Raoultella</i> sp. XY-1 and <i>Pandoraea</i> sp. XY-2, which exhibited better growth and improved TC degradation efficiency compared with single strain (81.72% TC was biodegraded within 12 days in Lysogeny broth (LB) medium). Subsequently, lab-scale soil remediation was conducted to evaluate its effectiveness in different soils and the environmental effects it brought. Results indicated that the most efficient TC degradation was recorded at 30 &#176;C and in soil sample Y which had relatively low initial TC concentration (around 35 mg/kg): TC concentration decreased by 43.72% within 65 days. Soil properties were affected, for instance, at 30 &#176;C, the pH value of soil sample Y increased to near neutral, and soil moisture content (SMC) of both soils declined. Analysis of bacterial communities at the phylum level showed that <i>Proteobacteria</i>, <i>Bacteroidetes</i>, <i>Acidobacteria</i>, and <i>Chloroflexi</i> were the four dominant phyla, and the relative abundance of <i>Proteobacteria</i> significantly increased in both soils after bioremediation. Further analysis of bacterial communities at the genus level revealed that <i>Raoultella</i> sp. XY-1 successfully proliferated in soil, while <i>Pandoraea</i> sp. XY-2 was undetectable. Moreover, bacteria associated with nitrogen cycling, biodegradation of organic pollutants, soil biochemical reactions, and plant growth were affected, causing the decline in soil bacterial diversity. Variations in the relative abundance of tetracycline resistance genes (TRGs) and mobile gene elements (MGEs) were investigated, the results obtained indicated that <i>tetD</i>, <i>tetG</i>, <i>tetX,</i> <i>intI1</i>, <i>tnpA-04</i>, and <i>tnpA-05</i> had higher relative abundance in original soils, and the relative abundance of most TRGs and MGEs declined after the microbial remediation. Network analysis indicated that <i>tnpA</i> may dominate the transfer of TRGs, and <i>Massilia</i>, <i>Alkanibacter</i>, <i>Rhizomicrobium</i>, <i>Xanthomonadales</i>, <i>Acidobacteriaceae</i>, and <i>Xanthomonadaceae</i> were possible hosts of TRGs or MGEs. This study comprehensively evaluated the effectiveness and the ecological effects of the TC-degrading bacterial consortium in soil environment.