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Detoxification Esterase StrH Initiates Strobilurin Fungicide Degradation in Hyphomicrobium sp. Strain DY-1.

ABSTRACT: Strobilurin fungicides are widely used in agricultural production due to their broad-spectrum and fungal mitochondrial inhibitory activities. However, their massive application has restrained the growth of eukaryotic algae and increased collateral damage in freshwater systems, notably harmful cyanobacterial blooms (HCBs). In this study, a strobilurin fungicide-degrading strain, Hyphomicrobium sp. strain DY-1, was isolated and characterized successfully. Moreover, a novel esterase gene, strH, responsible for the de-esterification of strobilurin fungicides, was cloned, and the enzymatic properties of StrH were studied. For trifloxystrobin, StrH displayed maximum activity at 50°C and pH 7.0. The catalytic efficiencies (k _cat/K_m ) of StrH for different strobilurin fungicides were 196.32 ± 2.30 μM^-1 · s^-1 (trifloxystrobin), 4.64 ± 0.05 μM^-1 · s^-1 (picoxystrobin), 2.94 ± 0.02 μM^-1 · s^-1 (pyraclostrobin), and (2.41 ± 0.19)×10^-2μM^-1 · s^-1 (azoxystrobin). StrH catalyzed the de-esterification of a variety of strobilurin fungicides, generating the corresponding parent acid to achieve the detoxification of strobilurin fungicides and relieve strobilurin fungicide growth inhibition of Chlorella This research will provide insight into the microbial remediation of strobilurin fungicide-contaminated environments.IMPORTANCE Strobilurin fungicides have been widely acknowledged as an essential group of pesticides worldwide. So far, their residues and toxic effects on aquatic organisms have been reported in different parts of the world. Microbial degradation can eliminate xenobiotics from the environment. Therefore, the degradation of strobilurin fungicides by microorganisms has also been reported. However, little is known about the involvement of enzymes or genes in strobilurin fungicide degradation. In this study, a novel esterase gene responsible for the detoxification of strobilurin fungicides, strH, was cloned in the newly isolated strain Hyphomicrobium sp. DY-1. This degradation process detoxifies the strobilurin fungicides and relieves their growth inhibition of Chlorella.

SUBMITTER: Jiang W

PROVIDER: S-EPMC8208146 | biostudies-literature |

REPOSITORIES: biostudies-literature

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Project description:Witches' broom disease (WBD) is a major constraint for cacao production in the Americas. The severe socioeconomic impact of WBD encouraged the evaluation of different control strategies, including the use of strobilurin fungicides. These molecules inhibit mitochondrial respiration, thus impairing ATP generation and leading to oxidative stress. These chemicals, however, have proven ineffective against the WBD pathogen Moniliophthora perniciosa. Here, we demonstrate that M. perniciosa tolerates high concentrations of strobilurins under in vitro conditions and highlight a set of molecular alterations that correlate with strobilurin tolerance in this fungus. Short-term exposure of M. perniciosa to the commercial strobilurin azoxystrobin led to the up-regulation of genes encoding enzymes of the glyoxylate cycle, gluconeogenesis, and fatty acid and amino acid catabolism, indicating that the fungal metabolism is remodeled to compensate for reduced ATP production. Furthermore, cell division, ribosome biogenesis, and sterol metabolism were repressed, which agrees with the impaired mycelial growth on azoxystrobin. Genes associated with cellular detoxification and response to oxidative stress (e.g., cytochrome P450s, membrane transporters and glutathione s-transferases) were strongly induced by the drug and represent potential strategies used by the pathogen to mitigate the toxic effects of the fungicide. Remarkably, exposure of M. perniciosa to azoxystrobin resulted in the spontaneous generation of a mutant with increased resistance to strobilurin. Comparative genomics and transcriptomics revealed alterations that may explain the resistance phenotype, including a large deletion in a putative transcriptional regulator and significant changes in the mutant transcriptome. Overall, this work provides important advances towards a comprehensive understanding of the molecular basis of strobilurin resistance in a tropical fungal pathogen. This is a fundamental step to efficiently employ these fungicides in agriculture and to prevent the emergence of strobilurin resistance.

Project description:Since the original report that Halomonas sp. strain GFAJ-1 was capable of using arsenic instead of phosphorus to sustain growth, additional studies have been conducted, and GFAJ-1 is now considered a highly arsenic-resistant but phosphorus-dependent bacterium. However, the mechanisms supporting the extreme arsenic resistance of the GFAJ-1 strain remain unknown. In this study, we show that GFAJ-1 has multiple distinct arsenic resistance mechanisms. It lacks the genes to reduce arsenate, which is the essential step in the well-characterized resistance mechanism of arsenate reduction coupled to arsenite extrusion. Instead, GFAJ-1 has two arsenic resistance operons, arsH1-acr3-2-arsH2 and mfs1-mfs2-gapdh, enabling tolerance to high levels of arsenate. mfs2 and gapdh encode proteins homologous to Pseudomonas aeruginosa ArsJ and glyceraldehyde-3-phosphate dehydrogenase (GAPDH), respectively, which constitute the equivalent of an As(V) efflux system to catalyze the transformation of inorganic arsenate to pentavalent organoarsenical 1-arseno-3-phosphoglycerate and its subsequent extrusion. Surprisingly, the arsH1-acr3-2-arsH2 operon seems to consist of typical arsenite resistance genes, but this operon is sufficient to confer both arsenite and arsenate resistance on Escherichia coli AW3110 even in the absence of arsenate reductase, suggesting a novel pathway of arsenic detoxification. The simultaneous occurrence of these two unusual detoxification mechanisms enables the adaptation of strain GFAJ-1 to the particularly arsenic-rich environment of Mono Lake.IMPORTANCEHalomonas sp. strain GFAJ-1 was previously reported to use arsenic as a substitute for phosphorus to sustain life under phosphate-limited conditions. Although this claim was later undermined by several groups, how GFAJ-1 can thrive in environments with high arsenic concentrations remains unclear. Here, we determined that this ability can be attributed to the possession of two arsenic detoxification operons, arsH1-acr3-2-arsH2 and mfs1-mfs2-gapdhmfs2 and gapdh encode proteins homologous to ArsJ and GAPDH in Pseudomonas aeruginosa; these proteins create an arsenate efflux pathway to reduce cellular arsenate accumulation. Interestingly, the combination of acr3-2 with either arsH gene was sufficient to confer resistance to both arsenite and arsenate in E. coli AW3110, even in the absence of arsenate reductase, suggesting a new strategy for bacterial arsenic detoxification. This study concludes that the survival of GFAJ-1 in high arsenic concentrations is attributable to the cooccurrence of these two unusual arsenic detoxification mechanisms.

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Detoxification Esterase StrH Initiates Strobilurin Fungicide Degradation in Hyphomicrobium sp. Strain DY-1.

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