Antibiotic-induced role interchange between rare and predominant bacteria retained the function of a bacterial community for denitrifying quinoline degradation.

AIM Quinoline is a recalcitrant pollutant in coking wastewater which has been broadly investigated with many isolates possessing aerobic quinoline degrading ability. However, studies on anaerobic degradation and the corresponding bacteria are very scarce. This study attempted to investigate the role of diverse functional members and the redundancy of quinoline degradation in a lab-scale quinoline denitrifying bioreactor. METHODS AND RESULTS Antibiotics were added to the batch culture under denitrifying conditions to disturb the microbial community of the quinoline-degrading bioreactor. According to the results, the nitrate removal rate remained stable, and the quinoline removal rate increased by 9.7% after treatment with streptomycin. However, PCoA analysis of 16S rRNA gene sequencing data of these samples indicated a significant shift in microbial community structures. Specifically, twelve operational taxonomic units (OTUs), including OTU1 (Pseudomonas) and OTU2 (Achromobacter), were significantly enriched. OTU1 replaced OTU8 (Thauera) as the most predominant denitrifying quinoline degrading member. However, OTU8 and other predominant OTUs (Comamonas and Pseudoxanthomonas), which were hypothesized to contribute essentially to quinoline degradation in the origin bioreactor, became almost undetectable. CONCLUSION Functional redundancy due to high biological diversity allowed the role reversal of predominant quinoline-degrading bacteria and other rare bacteria when disturbed by antibiotic stress. Although the abundance of OTU1 was much lower initially, it replaced the essential role of the predominant member OTU8 in the bioreactor community for quinoline degradation once the environmental condition changed. SIGNIFICANCE AND IMPACT OF THE STUDY This study indicated that the high biological diversity in a wastewater treatment bacterial community is crucial for maintaining the degrading function of organic pollutants, especially in a changing environment due to external disturbance or stress.