Shumei Fang,Xuejiao An,Hongyuan Liu,Yi Cheng,Ning Hou,Lu Feng,Xinning Huang,Chunyan Li
Nitriles are common environmental pollutants, and their removal has attracted increasing attention. Microbial degradation is considered to be the most acceptable method for removal. In this work, we investigated the biodegradation of three aliphatic nitriles (acetonitrile, acrylonitrile and crotononitrile) by Rhodococcus rhodochrous BX2 and the expression of their corresponding metabolic enzymes. This organism can utilize all three aliphatic nitriles as sole carbon and nitrogen sources, resulting in the complete degradation of these compounds. The degradation kinetics were described using a first-order model. The degradation efficiency was ranked according to t 1/2 as follows: acetonitrile > trans-crotononitrile > acrylonitrile > cis-crotononitrile. Only ammonia accumulated following the three nitriles degradation, while amides and carboxylic acids were transient and disappeared by the end of the assay. mRNA expression and enzyme activity indicated that the tested aliphatic nitriles were degraded via both the inducible NHase/amidase and the constitutive nitrilase pathways, with the former most likely preferred.
Qinghua Zhang,Lei Zhang,Zehua Li,Lixia Zhang,Daping Li
The degradation of fipronil was investigated in microbial fuel cells (MFCs). Almost 79% of 30 mg/L fipronil was rapidly degraded within 12 h by MFC biofilm. Based on the constructed quadratic polynomial model, a maximum fipronil degradation rate of 94.22% could be theoretically achieved at pH of 7.01, 33.39 °C, and the initial fipronil concentration 74 mg/L after incubation for 72 h. The high acute toxicity of fipronil toward zebrafish was largely eliminated after degradation by the MFC. In addition, the MFC biofilm showed catabolic versatility to 4-chloronitrobenzene, sulfanilamide, fluoroglycofen, and azoxystrobin. The microbial community analysis revealed that the functional bacteria Sphaerochaeta , Pseudomonas , Azospirillum , Azoarcus , and Chryseobacterium were major predominant bacteria in the anodic biofilm. Therefore, the MFC offers a promising approach in treating the environmental contaminants due to its abilities of energy capture from waste substances and catabolic versatility to different organic compounds.
The immobilization of organonitrile-degrading bacteria via the addition of biofilm-forming bacteria represents a promising technology for the treatment of organonitrile-containing wastewater, but biofilm-forming bacteria simply mixed with degrading bacteria may reduce the biodegradation efficiency. Nitrile hydratase and amidase genes, which play critical roles in organonitriles degradation, were cloned and transformed into the biofilm-forming bacterium Bacillus subtilis N4 to construct a recombinant bacterium B. subtilis N4/pHT nha - ami . Modified polyethylene carriers with positive charge was applied to promote bacterial adherence and biofilm formation. The immobilized B. subtilis N4/pHT nha - ami was resistant to organonitriles loading shocks and could remove organic cyanide ion with a initial concentration of 392.6 mg/L for 24 h in a moving bed biofilm reactor. The imputed quorum-sensing signal and the high-throughput sequencing analysis of the biofilm indicated that B. subtilis N4/pHT nha-ami was successfully immobilized and became dominant. The successful application of the immobilized recombinant bacterium offers a novel strategy for the biodegradation of recalcitrant compounds.
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