Isolation of a bacterial consortium able to degrade the fungicide thiabendazole: the key role of a Sphingomonas phylotype

Abstract

Thiabendazole (TBZ) is a fungicide used in fruit-packaging plants. Its application leads to the production of wastewaters requiring detoxification. In the absence of efficient treatment methods, biological depuration of these effluents could be a viable alternative. However, nothing is known regarding the microbial degradation of the recalcitrant and toxic to aquatics TBZ. We report the isolation, via enrichment cultures from a polluted soil, of the first bacterial consortium able to rapidly degrade TBZ and use it as a carbon source. Repeated efforts using various culture-dependent approaches failed to isolate TBZ-degrading bacteria in axenic cultures. Denaturating gradient gel electrophoresis (DGGE) and cloning showed that the consortium was composed of α-, β- and γ-Proteobacteria. Culture-independent methods including antibiotics-driven selection with DNA/RNA-DGGE, q-PCR and stable isotope probing (SIP)-DGGE identified a Sphingomonas phylotype (B13) as the key degrading member. Cross-feeding studies with structurally related chemicals showed that ring substituents of the benzimidazole moiety (thiazole or furan rings) favoured the cleavage of the imidazole moiety. LC-MS/MS analysis verified that TBZ degradation proceeds via cleavage of the imidazole moiety releasing thiazole-4-carboxamidine, which was not further transformed, and the benzoyl moiety, possibly as catechol, which was eventually consumed by the bacterial consortium as suggested by SIP-DGGE.

Characterization of the biodegradation, bioremediation and detoxification capacity of a bacterial consortium able to degrade the fungicide thiabendazole

“…60% of the benzyl part of the benzimidazole moiety of TBZ. This is in agreement with the microbial metabolic pathway of TBZ proposed by Perruchon et al (2017) after cross-feeding studies with compounds of the same chemical group, feeding studies with 13 C-benzyl-ring labelled TBZ and LC-MS/MS analysis. They proposed that the biodegradation of TBZ proceeds via cleavage of the imidazole moiety releasing thiazole-4-carboxamidine and the ) and inoculated (closed square, solid line) or not inoculated (open square, dashed line) with the bacterial consortium.…”

“…The TBZ-degrading bacterial consortium recently isolated by Perruchon et al (2017) could be a useful tool for the bioremediation of TBZ-contaminated soils or for the biodepuration of TBZ-contaminated effluents. A prerequisite for its future exploitation in such applications is to verify its capacity to mineralize, detoxify and degrade TBZ in range of conditions (pollutant concentration, temperature and pH) which might encounter under practical conditions (Gavrilescu 2005; Magan et al 2010).…”

“…Analytical methods TBZ, OPP and DPA were extracted from liquid media as described before (Perruchon et al , 2017. For the extraction of TBZ from soil a two-step process was followed.…”

“…The consortium was stabilized upon prolonged enrichment and its major members belong to a-(Shinella, Oligotropha, Sphingomonas), b-(Methylobacillus, Methilibium, Hydrogenophaga), and c-proteobacteria (Pseudomonas, Hydrocarboniphaga), with a Sphingomonas strain identified as the key component driving the degradation of TBZ (Perruchon et al 2017). Other bacteria used in the current study were an OPP-degrading Sphingomonas haloaromaticamans strain ) and a DPA-degrading Pseudomonas putida strain .…”

“…We recently reported the isolation of the first microbial consortium able to rapidly degrade TBZ (Perruchon et al 2017). However little is still known about the optimum conditions for maximum biodegradation, bioremediation and detoxification performance of the consortium.…”