Genetic Bioaugmentation of Activated Sludge with Dioxin-Catabolic Plasmids Harbored by Rhodococcus sp. Strain p52

Abstract

Horizontal transfer of catabolic plasmids is used in genetic bioaugmentation for environmental pollutant remediation. In this study, we examined the effectiveness of genetic bioaugmentation with dioxin-catabolic plasmids harbored by Rhodococcus sp. strain p52 in laboratory-scale sequencing batch reactors (SBRs). During 100 days of operation, bioaugmentation decreased the dibenzofuran content (120 mg L) in the synthetic wastewater by 32.6%-100% of that in the nonbioaugmented SBR. Additionally, dibenzofuran was removed to undetectable levels in the bioaugmented SBR, in contrast, 46.8 ± 4.1% of that in the influent remained in the nonbioaugmented SBR after 96 days. Moreover, transconjugants harboring pDF01 and pDF02 were isolated from the bioaugmented SBR after 2 days, and their abilities to degrade dibenzofuran were confirmed. After 80 days, the copy numbers of strain p52 decreased by 3 orders of magnitude and accounted for 0.05 ± 0.01% of the total bacteria, while transconjugants were present at around 10 copies mL sludge and accounted for 8.2 ± 0.3% of the total bacteria. Evaluation of the bacterial community profile of sludge by high-throughput 16S rRNA gene sequencing revealed that genetic bioaugmentation led to a bacterial community with an even distribution of genera in the SBR. This study demonstrates the promise of genetic bioaugmentation with catabolic plasmids for dioxins remediation.

Digital PCR as an Emerging Tool for Monitoring of Microbial Biodegradation

“…Horizontal gene transfer always occurs when microbes harboring conjugative or mobilizable plasmids containing genes coding catalytic enzymes are introduced into donor bacteria without contaminants degrading capacity [91]. It was proven that horizontal gene transfer assessment is effective during biostimulation [92] and bioaugmentation [93] monitoring. Through biostimulation, diversity of pollutant-degrading bacteria and the effective transfer of petroleum hydrocarbon degrading genes (i.e., alkB and phnAc) among resident microorganisms was enhanced for petroleum hydrocarbons degradation [92].…”

“…For bioaugmentation, augmented Rhodococcus sp. strain p52 harboring catalyzing dioxin degradation genes (i.e., dbfA and dfdA) located in broad-host conjugative plasmids would transfer the catalytic capacity to other bacteria without degradation ability to enhance biodegradation, while the strain itself would disappear for its unfitness for the environment [93].…”

“…However, we have not found any research that utilized the dPCR technique to monitor horizontal gene transfer during contaminants' degradation. Typically, the ratio of functional gene and target gene (i.e., specific gene sequence for microbial enumeration [93]) abundance is a constant. We usually detect the horizontal gene transfer through measuring the change of this ratio.…”

The role of mobile genetic elements in organic micropollutant degradation during biological wastewater treatment

“…(2011) Dibenzofuran (120 mg/L) Rhodococcus sp. strain p52 (Donor cells decreased 3 orders of magnitude after 80 days) pDF01 and pDF02 (dioxin catabolic plasmids) Yes Yes Laboratory-scale sequencing batch reactors (SBRs) Ren et al. (2018) Naphtalene (2 g/L) Pseudomonas putida ND6 pND6-1 and pND6-2 Yes Yes Aquous solutions: phosphate buffer, artificial lake, and oilfield-produced water Wang et al.…”

“…In more recent studies, Comamonas testosteroni , Escherichia coli , and Rhodococcus sp. were also applied ( Bathe et al., 2009 ; Tsutsui et al., 2010 ; Ren et al., 2018 ). Different MGEs were used, mainly plasmids.…”