|Glenn, Anthony - Tony|
|DAVIS, BRITTON - Former ARS Employee|
|SNOOK, MAURICE - Former ARS Employee|
|GEO, MINGLU - University Of Georgia|
|STEWART, JANE - Colorado State University|
Submitted to: PLOS ONE
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/5/2016
Publication Date: 1/25/2016
Citation: Glenn, A.E., Davis, B.C., Snook, M.E., Mitchell, T.R., Gold, S.E., Geo, M., Proctor, R., Stewart, J. 2016. Two horizontally transferred xenobiotic resistance gene clusters associated with detoxification of benzoxazolinones by Fusarium species. PLoS One. 11(1):e0147486.
Interpretive Summary: As microbes such as bacteria and fungi grow and colonize various substrates in different environments, they often encounter a broad spectrum of chemical compounds that may reduce their growth or even kill them. Such compounds are referred to as xenobiotics. To counter these adverse effects, many microbes are able to enzymatically detoxify and alter these xenobiotics. Fusarium verticillioides is one such microbe. It is a common fungal pathogen of corn that is known for its production of fungal metabolites called fumonisins that are a food safety concern due to their negative effects on animals and potentially humans. This fungus possesses genes that are necessary for detoxification of xenobiotic chemical compounds produced by corn. We previously characterized some of these genes, and here we detail our evaluation of another set of genes involved in the detoxification of the xenobiotics. One of these genes, designated MBL1, encodes an enzyme classified as a metallo-ß-lactamase (MBL). Targeted deletion of MBL1 rendered F. verticillioides incapable of metabolizing the corn xenobiotic compound 2-benzoxazolinone (BOA). Deletion of the adjacent gene, DLH1, encoding a putative dienelactone hydrolase had no effect on BOA biotransformation when it was deleted from a standard wild-type strain, but DLH1 was necessary when examined in another strain having a different genetic background. The necessity of both MBL1 and DHL1 was also assessed for metabolism of a different compound, 2-oxindole. This lactam compound is structurally similar to BOA and was assessed since it could provide some details on the specificity of enzyme substrates. All wild-type and deletion strains were able to fully metabolize 2-oxindole, indicating MBL1 may have specificity for BOA. The fungus F. verticillioides has additional genes encoding for other MBLs that may be able to metabolize a diversity of lactam xenobiotics. To our knowledge this is the first report of a MBL from fungi involved in xenobiotic degradation.
Technical Abstract: Microbes encounter a broad spectrum of chemical compounds in their diverse environments. These xenobiotics may negatively impact growth or cause death. To counter such adverse effects, many microbes possess metabolic strategies to detoxify and biotransform xenobiotics. Fusarium verticillioides is a mycotoxigenic fungal pathogen of maize known for its production of fumonisin mycotoxins. This fungus possesses two loci, FDB1 and FDB2, which are necessary for detoxification of maize phytoprotectant compounds. We previously characterized the multigenic FDB2 locus, and here we detail our evaluation of the FDB1 locus. Microarray analysis of F. verticillioides transcription in response to exposure to one of the maize phytochemicals, 2-benzoxazolinone (BOA), indicated clear induction of the FDB1 and FDB2 gene clusters. One of the FDB1 genes encodes a putative metallo-ß-lactamase (MBL). Targeted deletion of this gene, designated MBL1, rendered F. verticillioides incapable of metabolizing BOA. Deletion of the adjacent gene, DLH1, encoding a putative dienelactone hydrolase had no effect on BOA biotransformation, but DLH1 was necessary for cosmid complementation of a BOA-sensitive lab strain known to lack the FDB1 locus. Differing genetic backgrounds and potential redundancy of function due to gene duplication may be the cause of such variation. The necessity of both MBL1 and DHL1 was also assessed for metabolism of 2-oxindole, a lactam-containing compound structurally similar to BOA. All wild-type and deletion strains were able to fully metabolize 2-oxindole, indicating MBL1 may have specificity for BOA. Other encoded MBLs may provide hydrolytic capabilities for diverse lactam xenobiotics. To our knowledge this is the first report of a hydrolytic MBL from fungi.