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Some evidences for the involvement of plasmid in diuron herbicide degradation
B A El-Deeb1, A M Ali, K A Ali
1Department of Botany, Faculty of Science, Sohag, Egypt.
Abstract:
Pseudomonas sp. strain Bk8 was isolated from field soil contaminated with different urea-herbicides. This strain is a plasmid (pBkB)-harbouring organism capable of complete degradation of diuron herbicide. Plasmid-cured strain Bk8M was obtained by treatment of Pseudomonas sp. Bk8 with Mitomycin C. This cured strain is capable of only partial degradation of diuron side chain and accumulated a phenolic compound in the medium during growing on diuron as a sole source of carbon and energy. Conjugation experiment was carried out using Bk8M as a recipient and Bk8 as a donor of pBk8 plasmid. The transconjugant was able to degrade a diuron without accumulation of phenolic compound. It was proposed that plasmid pBk8 is self-transmissible and involved in the degradation of diuron aromatic ring but it is not connected with the transformation of diuron into diuron phenol compound.
Insights
Pseudomonas sp. strain Bk8, which harbors plasmid pBkB, can fully degrade the herbicide diuron. This plasmid is essential for breaking down the diuron aromatic ring, as shown by experiments with a plasmid-cured strain.
Area of Science:
- Environmental microbiology
- Bioremediation of herbicides
- Bacterial genetics
Background:
- Soil contamination with urea-herbicides poses environmental risks.
- Pseudomonas sp. strain Bk8 degrades the herbicide diuron.
- Diuron degradation involves complex metabolic pathways.
Purpose of the Study:
- To investigate the role of plasmid pBkB in diuron degradation by Pseudomonas sp. strain Bk8.
- To elucidate the specific functions of the plasmid in breaking down the diuron molecule.
- To understand the genetic basis of diuron herbicide bioremediation.
Main Methods:
- Isolation of Pseudomonas sp. strain Bk8 from contaminated soil.
- Curing the strain of its plasmid (pBkB) using Mitomycin C to obtain strain Bk8M.
- Assessing diuron degradation capabilities of the wild-type, cured, and transconjugant strains.
- Performing conjugation experiments to transfer the plasmid back into the cured strain.
Main Results:
- Plasmid-cured strain Bk8M showed partial degradation of diuron, accumulating a phenolic compound.
- The transconjugant strain, possessing the pBkB plasmid, completely degraded diuron without phenolic accumulation.
- Plasmid pBkB was confirmed to be self-transmissible.
Conclusions:
- Plasmid pBkB is crucial for the complete degradation of diuron, specifically targeting the aromatic ring.
- The plasmid is not involved in the transformation of diuron into diuron phenol.
- The genetic elements on pBkB are essential for efficient diuron bioremediation by Pseudomonas sp.