Anaeromyxobacter dehalogenans

A Microbial Biorealm page on the genus Anaeromyxobacter dehalogenans

Classification

Anaeromyxobacter dehalogenans is a Gram-negative rod-shaped, motile, spore-forming bacteria found in the soil.

Higher order taxa

Bacteria; Proteobacteria; delta/epsilon subdivisions; Deltaproteobacteria; Myxococcales; Cystobacterineae; Myxococcaceae; Anaeromyxobacter.

Species

NCBI: Taxonomy

The "Anaeromyxobacter dehalogenans" 2CP-C strain has been most studied and its complete genomic sequence has been determined. Species that fall under Anaeromyxobacter dehalogenans are Anaeromyxobacter sp. FAc12, Anaeromyxobacter sp. Fw109-5 and environmental samples such as uncultured Anaeromyxobacter sp.

Description and significance

Anaeromyxobacter dehalogenans is a slender Gram-negative rod-shaped spore-forming soil bacterium. It is capable of a gliding motility and forms a spore-like structure (Char/Desc). It was the first Myxobacterium that was found capable of anaerobic respiration, wherein it is able to grow by coupling the oxidation of both acetate or hydrogen, which is a distinguishing property of the organism from other reducing populations, to the reduction of ortho-substituted halophenols, ferric iron, nitrate, nitrite and fumarate (2). It was first isolated by enrichment and isolation of single plate-grown colonies obtained from uranium-contaminated sediment collected at the U.S. DOE Field Research Center near Oak Ridge, TN, which allowed for a 16s rRNA gene-based community analysis of the sample that suggested that the species helped in metal reduction (3). These metal-reducing microorganisms are widely distributed in the environment (2). It has been found in undisturbed and contaminated soils and sediments, and evidence shows they also exist in acidic subsurface sediments (4).

A. dehalogenans is an important model organism that exists as both as a productive dechlorinator and metal reducer. Sequencing this bacteria also provides information about the reductive dehalogenase genes and the organization of its operon, which will help to design nucleic acid-based tools to "detect, monitor and quantify functional genes involved in reductive dechlorination processes at contaminated sites" (5). By studying the potential interferences between the competing substrates in contaminated environments we can further understand bioremediation efforts (2).

Genome structure

The Joint Genome Institute has determined the complete genomic sequence of A. dehalogenans strain 2CP-C. Its replicon type is the chromosome. The genome of contains 5,013,479 bp, 4,346 genes and its predicted origin is at 3,425 kbp. It contains 58 RNA genes. It has a 75% GC content and a 25 % AT content. It is found as 90% coding. Its molecule is DNA.

A. dehalogenans has a circular chromosome topography. It does not have any plasmids.

Cell structure and metabolism

Anaeromyxobacter dehalogenans has anaerobic growth and lacks a fruiting body, which is uncharactaristic of the Myxococcus subgroup it belongs to, but it can be considered a Myxococcus due to other close resemblences (2). It is a member of the delta-proteobacteria group that exhibits anaerobic diversity like sulfate reduction, iron reduction, fermentation and dehalogenation (32 Char/Desc). The A. dehalogenan lifestyle allows halogenated compounds to be used as electron acceptors for growth (13 Char/Desc) and chlororespiration enables the organism to release energy for growth (10 Char/Desc).

A. dehalogenans has a great deal of metabolic diversity, such as "halorespiration of herbicides, ferric-ion reduction, ammoniafication, and N2O reduction" (6). It is able to grow under different redox conditions. It also has electron donor versatility and it uses oxidized metals like Uranium(VI) and Fe(III), phenols, oxygen, nitrite, nitrate and fumarate as terminal electron aceeptors (2). It is able to couple electron acceptor reduction with the oxidation of compounds such as formate, hydrogen, acetate, succinate, pyruvate and glucose (7).

Ecology

Anaerobic conditions have been found to possibly impact agrochemical fate, nutrient cycling, and plant/seed-microbe interactions and research has shown that A. dehalogenans are useful in charactarizing anaerobic agricultural soil processes in an observatory (6). Under environmentally relevant conditions this organism is robust and competitive as it acts as both a productive dechlorinator and a metal reducer. It is not affected by changing redox conditions and it is found to be active at a pH of 6-8.5 (2).

Pathology

Anaeromyxobacter dehalogenans is not a pathogen, nor does it cause disease.

Application to Biotechnology

Understanding the unique class of enzymes with novel catalytic proteins and the mechanisms involved in metal reduction can lead to biotechnological applications especially at sites that contain halogenated and chlorinated compounds, where biostimulation can occur by "supplying the populations of interest with reducing equivalents needed to reduce the contaminants"(5).

Current Research

1. Towards a More Complete Picture: Dissimillatory Metal Reduction by Anaeromyxobacter Species is a 3-year project lead by Frank Loeffler and Robert Sanford focusing on uranium reduction in the species. The research will look at the isolates of the bacteria and look at its physiological requirements. Molecular biology tools will be designed in order to detect and quantify samples in culture and in the environment with hopes to discover Anaeromyxobacter's distribution and abundance within the environment. Also, at in the Field Research Center they will attempt to isolate additional species.

2. Biomolecular Mechanisms Controlling Metal and Radionuclide Transformations in Anaeromyoxybacter dehalogenans is a research project whose goal is to find out the "molecular mechanisms of radionuclide biotransformation" and "assess the effects of relevant environmental factors on these transformation reactions" (GEO). By using targeted physiological and genetic analysis and a microarray-based comparitive genomics approach they aim to find out the mechanisms involved allowing us to become more capable of predicting processes involved transformation in subsurface environments in order to use for bioremidiation.

3. Fast Dechlorination of Chlorinated Phenols by Anaeromyxobacter dehalogenans Strain 2CP-C is a research study by R. A. Sanford and Q. He at the University of Illinois which focuses on the physiology and kinetics of the dechlorination that allows the organism to grow. Using halogenated phenolic compounds they determine its rates of growth and dechlorination, and furthermore aim to determine if the strain can be used for the bioremediation of chlorinated phenols.

References

2. Sanford, R. A., J. R. Cole, and J. M. Tiedje. 2002. Characterization and description of Anaeromyxobacter dehalogenans gen. nov., sp. nov., an aryl halorespiring facultative anaerobic myxobacterium. Appl. Environ. Microbiol. 68:893-900.

3. Petrie, L., N. N. North, S. L. Dollhopf, D. L. Balkwill, and L. E. Kostka. 2003. Enumeration and characterization of iron(III)-reducing microbial communities from acidic subsurface sediments contaminated with uranium. Appl. Environ. Microbiol. 69:7467-7479.

4. North, N. N., S. L. Dollhopf, L. Petrie, J. D. Istok, D. L. Balkwill, and J. E. Kostka. 2004. Change in bacterial community structure during in situ biostimulation of subsurface sediment cocontaminated with uranium and nitrate. Appl. Environ. Microbiol. 70:4911-4920.

5. Anaeromyxobacter dehalogenans 2CP-C IMG/Organism Details. Joint Genome Institute. 4 Jun 2007.

6. Chee Sanford, J.C., Sanford, R.A., Loffler, F.E., Thomas, S.H., Sims, G.K. 2006. Investigating anaerobic microbial processes in agricultural soils using Anaeromyxobacter dehalogenans as a cosmopolitan model.International Society for Microbial Ecology. 11:2025.

7. He, Q., and R. A. Sanford. 2003. Characterization of Fe(III) Reduction by Chlororespiring Anaeromxyobacter dehalogenans. Appl Environ Microbiol 69:2712-8.

Edited by student of Rachel Larsen and Kit Pogliano