Biodegradation and decolorization of Congo red dye by metal-dependent hydrolase (MdeH) in Buttiauxella sp. S19-1

As one of the azo dyes, Congo red (CR) is widely used in the garment industry, posing significant environmental and health risks. In this study, Buttiauxella sp. S19-1 was selected for the efficient decolorization of CR. The optimal decolorization conditions were determined to be the anaerobic culture at 100 mg/L, with pH 5.0, and 27 °C for 30 h, achieving a decolorization efficiency of 89.6 %. Prokaryotic transcriptome analysis revealed a significantly up-regulated gene encoding a metal-dependent hydrolase in Buttiauxella sp. (BuMdeH) during biodegradation of CR, with zinc ions identified as the essential metal ion. The S19-1 mutant lacking the BuMdeH gene (S-∆M) showed a 1.42-fold decrease in decolorization efficiency compared to S19-1. In contrast, the Escherichia coli (E. coli) expressing BuMdeH (E-M) exhibited a 2.8-fold increase compared to E. coli. The recombinant BuMdeH protein (rBuMdeH) was purified, displaying a specific activity (with Zn^2 +) of 1.10 ± 0.02 μmol/min·mg. Gas chromatography-mass spectrometry (GC-MS) analysis identified [1,1'-biphenyl]-4-amine and 1-naphthylamine as the metabolites of CR, which significantly decreased the toxicity following degradation by rBuMdeH. The results implied that MdeH played a pivotal role in the catalytic degradation of CR by strain S19-1 through a novel pathway, which proposed a sustainable bioremediation strategy for CR-contaminated wastewater.