Biodegradation of the Neonicotinoid Insecticide Acetamiprid by Actinomycetes Streptomyces canus CGMCC 13662 and Characterization of the Novel Nitrile Hydratase Involved

Abstract

Neonicotinoid insecticide pollution in soil and water poses serious environmental risks. Microbial biodegradation is an important neonicotinoid insecticide degradation pathway in the environment. In this study, 70.0% of the acetamiprid in a 200 mg/L solution was degraded by actinomycetes Streptomyces canus CGMCC 13662 (isolated from soil) in 48 h, and the acetamiprid degradation half-life was 27.7 h. Acetamiprid was degraded to IM-1-2 ((E)-1-(1-(((6chloropyridin-3-yl)methyl)(methyl) amino)ethylidene)urea) through hydrolysis of the cyanoimine moiety. Gene cloning and overexpression indicated that a novel nitrile hydratase with three unusual subunits (AnhD, AnhE, and AnhA) without accessory protein mediated IM-1-2 formation. The purified nitrile hydratase responsible for degrading acetamiprid had a K m of 5.85 mmol/L and a V max of 15.99 U/mg. A homology model suggested that AnhD-Glu56 and AnhE-His21 play important roles in the catalytic efficiency of the nitrile hydratase. S. canus CGMCC 13662 could be used to remediate environments contaminated with acetamiprid.

Maturation Mechanism of Nitrile Hydratase From Streptomyces canus CGMCC 13662 and Its Structural Character

“…The features of self-subunit swapping can be summarized as follows: (i) The metallochaperone does not deliver cobalt to the Apo-AnhA, but enables AnhA to incorporate cobalt; (ii) cobalt first inserts into the AnhAM 2 complex; (iii) the Co-bounded AnhAM 2 complex named as holoprotein (Holo)-AnhAM 2 possess cysteine-oxidized AnhA; (iv) subunit swapping occurs between an unmodified AnhA and modified AnhA; and (v) selfsubunit swapping is a subunit-specific reaction. Importantly, in contrast to all previously reported NHases, structural genes of ScNHase have the order <anhD><anhE><anhA> (Figure 1), with anhD and anhE identified as β-subunit partial peptides (Guo et al, 2019). No anhC was recognized in the ScNHase genome, and ScNHase is similar to eukaryotic NHase (Guo et al, 2019).…”

“…Importantly, in contrast to all previously reported NHases, structural genes of ScNHase have the order <anhD><anhE><anhA> (Figure 1), with anhD and anhE identified as β-subunit partial peptides (Guo et al, 2019). No anhC was recognized in the ScNHase genome, and ScNHase is similar to eukaryotic NHase (Guo et al, 2019). Therefore, investigating the post-transitional maturation of ScNHase represents a meaningful and interesting study.…”

“…The enzyme activity was determined at the optimal temperature and pH. The enzyme reaction system and one unit (U) of NHase activity were the same as previously described (Guo et al, 2019).…”

Effects of Neonicotinoid Seed Treatments on Phyllosphere and Soil Bacterial Communities Over Time

“…Bacterial taxa that were favored by the pesticide treatment include several genera that are known to be potentially involved in neonicotinoid degradation (e.g. Hymenobacter [62], Mycobacterium [52], Pseudomonas [63], and Streptomyces [53]). In soils, there was a decline in the relative abundance of several ASVs from Proteobacteria and Gemmatimonadetes phyla and an increase in some ASVs from Chloroflexi and Actinobacteria, a result partially in accordance with a previous study that reported a decrease in the relative abundance of Gemmatimonadetes and OD1 phyla and an increase in the relative abundance of the Chloroflexi and Nitrospirae phyla in response to the neonicotinoid treatments [47].…”

“…In the phyllosphere, 22 ASVs (mainly Bacteroidetes) were more abundant, and 12 (mainly Proteobacteria) were less abundant in response to neonicotinoid seed treatment ( Table 4) in neonicotinoid degradation (e.g. Mycobacterium [52] and Streptomyces [53]) or other pesticides degradation (e.g. Arthrobacter [54]).…”