Characterization of diverse 2,4-dichlorophenoxyacetic acid-degradative plasmids isolated from soil by complementation

Area of Science:

• Environmental microbiology
• Molecular biology
• Biochemistry

Background:

• 2,4-dichlorophenoxyacetic acid (2,4-D) is a widely used herbicide.
• Understanding the microbial degradation of 2,4-D is crucial for environmental remediation.
• The diversity of genes and plasmids involved in 2,4-D degradation remains incompletely characterized.

Purpose of the Study:

• To investigate the diversity of 2,4-D degradative plasmids in agricultural soil microbial communities.
• To identify and characterize novel plasmids conferring 2,4-D degradation capabilities.
• To determine the genetic relatedness of these plasmids to known 2,4-D degradation gene clusters.

Main Methods:

• Complementation assay using Alcaligenes eutrophus recipient strains (JMP228 and JMP228/pBH501aE).
• Selection of transconjugants capable of utilizing 2,4-D as a sole carbon source.
• Plasmid isolation, EcoRI restriction digestion, and Southern hybridization with tfd gene probes (tfdA-tfdF).

Main Results:

• Transconjugants were obtained only from 2,4-D treated soil, indicating the presence of degradative plasmids.
• Seven distinct plasmids (pEMT1-pEMT7) were identified based on EcoRI restriction patterns.
• Most plasmids (pEMT2-pEMT7) belonged to the IncP1 group, while pEMT1 did not.
• All identified plasmids showed homology to the tfdA gene; varying degrees of homology to other tfd genes were observed.

Conclusions:

• Agricultural soil with a history of 2,4-D application harbors diverse 2,4-D degradative plasmids.
• The tfdA gene is a common element in these plasmids, suggesting its critical role in initial 2,4-D metabolism.
• The IncP1 group of plasmids is prevalent among 2,4-D degraders in this environment.