A Newly Discovered Humic-Reducing Bacterium, Pseudomonas geniculata PQ01, Isolated From Paddy Soil Promotes Paraquat Anaerobic Transformation

Abstract

Due to toxicity and persistence of paraquat (a widely used herbicide), eco-friendly remediation approaches to its contamination and effective antidotes to its poisoning have been highly desired and raised increasing concerns. Paraquat degradation was lesser in aerobic soil in comparison with anaerobic soil, and humic-reducing microorganisms (HRMs) play a key role in paraquat anaerobic transformation process. However, the degradation pathways and related mechanisms remain poorly understood. In this study, we investigated the specific interaction mechanisms of the paraquat transformation processes mediated by a humic-reducing strain under anaerobic conditions. A strain of pure culture, designated as PQ01, was successfully isolated from paddy soil using anaerobic enrichment procedure, and identified as Pseudomonas geniculata using phenotypic and phylogenetic analysis. Sucrose, glucose, pyruvate, formic acid, and acetic acid were shown to be favorable electron donors for the reduction of anthrahydroquinone-2,6-disulfonate (AQDS) reduction by PQ01. The strain also had the ability of reducing Fe(III) (hydr)oxides in the presence of sucrose with efficiencies in the order of ferrihydrite > α-FeOOH/γ-FeOOH > γ-Fe 2 O 3 > α-Fe 2 O 3 . In the “PQ01 + paraquat + AQDS + sucrose” system, AQDS reduction and paraquat biotransformation by strain PQ01 occurred simultaneously, and the presence of sucrose significantly enhanced the biotransformation. Specific mechanisms of the electron transfer processes are promoted by both PQ01 and AQDS, and proceed in two aspects: (1) paraquat served as electron donor in the anaerobic reduction of AQDS by strain PQ01; (2) AQDS was reduced by PQ01 anaerobic metabolism to produce AH 2 QDS, which can directly react with paraquat under anaerobic conditions to generate a single crystal compound (molecular formula of the unit structure is C 2 6 H 2 0 N 2 O 8 S 2 ), causing the paraquat to decline dramatically. In conclusion, this main mechanism included the microbial reduction of AQDS to AH 2 QDS, followed by the abiotic reaction between AH 2 QDS and paraquat. This study reported the new characteristics of P. geniculata capable of reducing humics analogs, Fe(III) (hydr)oxides, and paraquat, and proposed a novel electron transformation mechanism of the HRMs’ mediated degradation of organic contaminants.

Pesticides Xenobiotics in Soil Ecosystem and Their Remediation Approaches

“…Similarly, excessive water content can lead to anoxic conditions that can affect microbial work as well. The results showed that anoxic conditions have an increased degradation process of pesticides as determined for HCH and DDT [63]. Temperature and pH are also important factors influencing the remediation or degradation process [9].…”

Profiling of Seawater Bacterial Diversity in Tanjung Mas Port Using 16S rRNA eDNA Metabarcoding and Next-Generation Sequencing (NGS)

“…P. geniculata, a recognized species, opens avenues for understanding its specific ecological roles and contributions to the overall microbial community dynamics (Wu et al, 2022). The prevalence of unidentified species suggests the potential for uncovering novel microbial diversity within Tanjung Mas seawater, highlighting the importance of advanced sequencing techniques for future taxonomic exploration (Wu et al, 2020). Future studies also need to incorporate multiple samples over time, allowing for a more thorough examination of microbial community dynamics.…”

Achromobacter sp. Strain BUKˍBCHˍTQ1: A Potential Paraquat-Degrading Bacterium Isolated from Pesticide Contaminated Agricultural Soil

“…Different genera of bacteria capable of Paraquat biodegradation were identified in many other studies. These include genera such as Sphingomicrobium marinum, Ferrovibrio xuzhouensis, Azospirillum lipoferum, Altererythrobacterinangensis, Xanthobacter.autotrophicus, Pseudomonas geniculata and Azospirillum amazonense (21,22). The diversity of Paraquat degrading bacteria may be attributed to the differences in the environmental conditions where these organisms were isolated as each organism may be well adapted and suited to a particular environmental condition.…”