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Updated: Jul 13, 2026
05:51
Direct Detection of the Acetate-forming Activity of the Enzyme Acetate Kinase
Published on: December 19, 2011
The distribution of acetohydroxyacid synthase in soil bacteria
Darryl R Nelson1, Trevor Duxbury
1School of Molecular and Microbial Biosciences, University of Sydney, Sydney, NSW, 2006, Australia. d.r.nelson@ncl.ac.uk;
Antonie Van Leeuwenhoek
|July 13, 2007
Summary
Most soil bacteria have acetohydroxyacid synthase (AHAS) enzymes sensitive to sulfonylurea herbicides. This study investigated AHAS distribution in soil bacteria, finding most isolates possess a single, herbicide-sensitive AHAS enzyme.
Area of Science:
- Microbiology
- Biochemistry
- Environmental Science
Background:
- Acetohydroxyacid synthase (AHAS) is crucial for branched-chain amino acid synthesis in bacteria.
- While enteric bacteria have multiple AHAS isozymes, their prevalence in soil bacteria is poorly understood.
- Sulfonylurea herbicides inhibit specific AHAS isozymes, impacting bacterial growth.
Purpose of the Study:
- To investigate the distribution and characteristics of acetohydroxyacid synthase (AHAS) enzymes in soil bacteria.
- To determine the sensitivity of soil bacterial AHAS to sulfonylurea herbicides and amino acid feedback inhibition.
- To analyze the genetic diversity of AHAS large subunit genes in an agricultural soil environment.
Main Methods:
- Growth experiments using Escherichia coli, Salmonella enterica, Enterobacter aerogenes, and soil isolates with valine and triasulfuron.
- Molecular analysis involving primer design targeting AHAS large subunit genes (ilvB, ilvG, ilvI).
- Amplification and cloning of AHAS gene fragments from soil DNA, followed by phylogenetic analysis.
Main Results:
- Escherichia coli, Salmonella enterica, and Enterobacter aerogenes exhibited isozymes allowing growth despite valine or triasulfuron presence.
- 21 out of 27 soil isolates were inhibited by triasulfuron, with 19 showing reversed inhibition upon isoleucine/valine addition.
- Phylogenetic analysis of 19 cloned AHAS sequences revealed significant variation but close relation to known AHAS sequences across Proteobacteria and Actinobacteria.
Conclusions:
- The majority of soil microorganisms possess a single acetohydroxyacid synthase (AHAS) enzyme that is sensitive to sulfonylurea herbicides.
- Understanding AHAS distribution is critical for predicting microbial responses to herbicide application in soil ecosystems.
- Genetic analysis confirms the presence of diverse AHAS genes in soil bacteria, primarily belonging to Proteobacteria and Actinobacteria phyla.
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