Cometabolism

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Cometabolism is defined as the simultaneous degradation of two compounds, in which the degradation of the second compound (the secondary substrate) depends on the presence of the first compound (the primary substrate). [1] This is in contrast to simultaneous catabolism, where each substrate is catabolized concomitantly by different enzymes. [1] [2] Cometabolism occurs when an enzyme produced by an organism to catalyze the degradation of its growth-substrate to derive energy and carbon from it is also capable of degrading additional compounds. The fortuitous degradation of these additional compounds does not support the growth of the bacteria, and some of these compounds can even be toxic in certain concentrations to the bacteria. [3] [4]

The first report of this phenomenon was the degradation of ethane by the species Pseudomonas methanica. [4] These bacteria degrade their growth-substrate methane with the enzyme methane monooxygenase (MMO). MMO was discovered to be capable of degrading ethane and propane, although the bacteria were unable to use these compounds as energy and carbon sources to grow. [4]

Another example is Mycobacterium vaccae , which uses an alkane monooxygenase enzyme to oxidize propane. Accidentally, this enzyme also oxidizes, at no additional cost for M. vaccae, cyclohexane into cyclohexanol. Thus, cyclohexane is co-metabolized in the presence of propane. This allows for the commensal growth of Pseudomonas on cyclohexane. The latter can metabolize cyclohexanol, but not cyclohexane. [5] [6]

Cometabolism in Bioremediation

Some of the molecules that are cometabolically degraded by bacteria are xenobiotic, persistent compounds, such as PCE, TCE, and MTBE, that have harmful effects on several types of environments. Co-metabolism is thus used as an approach to biologically degrade hazardous solvents. [7] [4]

Cometabolism can be used for the biodegradation of methyl-tert-butyl ether (MTBE): an aquatic environment pollutant. Some Pseudomonas members were found to be able to fully degrade MTBE cometabolically with the enzymes they produce to oxidize n-alkanes (e.g. methane, propane). [7]

Additionally, a promising method of bioremediation of chlorinated solvents involves cometabolism of the contaminants by aerobic microorganisms in groundwater and soils. Several aerobic microorganisms have been demonstrated to be capable of doing this, including n-alkane, aromatic compound (e.g. toluene, phenol) and ammonium oxidizers. [4] [3] One example is Pseudomonas stutzeri OX1, which can degrade a hazardous, and water-soluble compound tetrachloroethylene (PCE). [6] PCE, one of the major underground water contaminants, was regarded as being undegradable under aerobic conditions and only degraded via reductive dehalogenation to be used as a growth-substrate by organisms. [6] Reductive dehalogenation often results in the partial dechlorination of the PCE, giving rise to toxic compounds such as TCE, DCE, and vinyl chloride. Pseudomonas st. OX1 can degrade PCE under aerobic conditions by using toluene-o-xylene monooxygenase (ToMO), an enzyme they produce to derive energy and carbon from toluene and several other aromatic compounds. This biological process could be utilized to remove PCE from aerobic polluted sites. [6]

However, the difficulties and high costs of maintaining the growth-substrates of the organisms capable of cometabolising these hazardous compounds and providing them an aerobic environment have led to the limited field-scale application of cometabolism for pollutant solvent degradation. Recently, this method of remediation has been proposed to be improved by the substitution of the synthetic aromatic growth-substrates (e.g. toluene) of these bacteria with cheap, non-toxic plant secondary metabolites. [8]

Related Research Articles

<span class="mw-page-title-main">Hydrocarbon</span> Organic compound consisting entirely of hydrogen and carbon

In organic chemistry, a hydrocarbon is an organic compound consisting entirely of hydrogen and carbon. Hydrocarbons are examples of group 14 hydrides. Hydrocarbons are generally colourless and hydrophobic, and their odors are usually weak or exemplified by the odors of gasoline and lighter fluid. They occur in a diverse range of molecular structures and phases: they can be gases, liquids, low melting solids or polymers.

<span class="mw-page-title-main">Bioremediation</span> Process used to treat contaminated media such as water and soil

Bioremediation broadly refers to any process wherein a biological system, living or dead, is employed for removing environmental pollutants from air, water, soil, flue gasses, industrial effluents etc., in natural or artificial settings. The natural ability of organisms to adsorb, accumulate, and degrade common and emerging pollutants has attracted the use of biological resources in treatment of contaminated environment. In comparison to conventional physicochemical treatment methods bioremediation may offer considerable advantages as it aims to be sustainable, eco-friendly, cheap, and scalable. Most bioremediation is inadvertent, involving native organisms. Research on bioremediation is heavily focused on stimulating the process by inoculation of a polluted site with organisms or supplying nutrients to promote the growth. In principle, bioremediation could be used to reduce the impact of byproducts created from anthropogenic activities, such as industrialization and agricultural processes. Bioremediation could prove less expensive and more sustainable than other remediation alternatives.

Biological augmentation is the addition of archaea or bacterial cultures required to speed up the rate of degradation of a contaminant. Organisms that originate from contaminated areas may already be able to break down waste, but perhaps inefficiently and slowly.

<span class="mw-page-title-main">Sulfate-reducing microorganism</span> Microorganisms which "breathe" sulfates

Sulfate-reducing microorganisms (SRM) or sulfate-reducing prokaryotes (SRP) are a group composed of sulfate-reducing bacteria (SRB) and sulfate-reducing archaea (SRA), both of which can perform anaerobic respiration utilizing sulfate (SO2−
4) as terminal electron acceptor, reducing it to hydrogen sulfide (H2S). Therefore, these sulfidogenic microorganisms "breathe" sulfate rather than molecular oxygen (O2), which is the terminal electron acceptor reduced to water (H2O) in aerobic respiration.

Methylotrophs are a diverse group of microorganisms that can use reduced one-carbon compounds, such as methanol or methane, as the carbon source for their growth; and multi-carbon compounds that contain no carbon-carbon bonds, such as dimethyl ether and dimethylamine. This group of microorganisms also includes those capable of assimilating reduced one-carbon compounds by way of carbon dioxide using the ribulose bisphosphate pathway. These organisms should not be confused with methanogens which on the contrary produce methane as a by-product from various one-carbon compounds such as carbon dioxide. Some methylotrophs can degrade the greenhouse gas methane, and in this case they are called methanotrophs. The abundance, purity, and low price of methanol compared to commonly used sugars make methylotrophs competent organisms for production of amino acids, vitamins, recombinant proteins, single-cell proteins, co-enzymes and cytochromes.

Halorespiration or dehalorespiration or organohalide respiration is the use of halogenated compounds as terminal electron acceptors in anaerobic respiration. Halorespiration can play a part in microbial biodegradation. The most common substrates are chlorinated aliphatics, chlorinated phenols and chloroform. Dehalorespiring bacteria are highly diverse. This trait is found in some Campylobacterota, Thermodesulfobacteriota, Chloroflexota, low G+C gram positive Clostridia, and ultramicrobacteria.

<span class="mw-page-title-main">Methane monooxygenase</span> Class of enzymes

Methane monooxygenase (MMO) is an enzyme capable of oxidizing the C-H bond in methane as well as other alkanes. Methane monooxygenase belongs to the class of oxidoreductase enzymes.

Microbial metabolism is the means by which a microbe obtains the energy and nutrients it needs to live and reproduce. Microbes use many different types of metabolic strategies and species can often be differentiated from each other based on metabolic characteristics. The specific metabolic properties of a microbe are the major factors in determining that microbe's ecological niche, and often allow for that microbe to be useful in industrial processes or responsible for biogeochemical cycles.

In biology, syntrophy, synthrophy, or cross-feeding is the phenomenon of one species feeding on the metabolic products of another species to cope up with the energy limitations by electron transfer. In this type of biological interaction, metabolite transfer happens between two or more metabolically diverse microbial species that live in close proximity to each other. The growth of one partner depends on the nutrients, growth factors, or substrates provided by the other partner. Thus, syntrophism can be considered as an obligatory interdependency and a mutualistic metabolism between two different bacterial species.

Dehalococcoides is a genus of bacteria within class Dehalococcoidia that obtain energy via the oxidation of hydrogen and subsequent reductive dehalogenation of halogenated organic compounds in a mode of anaerobic respiration called organohalide respiration. They are well known for their great potential to remediate halogenated ethenes and aromatics. They are the only bacteria known to transform highly chlorinated dioxins, PCBs. In addition, they are the only known bacteria to transform tetrachloroethene to ethene.

Desulfatibacillum alkenivorans AK-01 is a specific strain of Desulfatibacillum alkenivorans.

Thauera butanivorans is a species of Gram-negative bacteria capable of growth on alkanes C2-C9, but not methane, as well as other organic substrates such as lactate, acetate, succinate and citrate. To grow on alkanes, this bacterium expresses a soluble di-iron monooxygenase closely related to soluble methane monooxygenase from methanotrophs.

Methylobacillus flagellatus is a species of aerobic bacteria.

Microbial biodegradation is the use of bioremediation and biotransformation methods to harness the naturally occurring ability of microbial xenobiotic metabolism to degrade, transform or accumulate environmental pollutants, including hydrocarbons, polychlorinated biphenyls (PCBs), polyaromatic hydrocarbons (PAHs), heterocyclic compounds, pharmaceutical substances, radionuclides and metals.

<span class="mw-page-title-main">4-Hydroxyphenylacetate 3-monooxygenase</span>

4-hydroxyphenylacetate 3-monooxygenase (EC 1.14.14.9) is an enzyme that catalyzes the chemical reaction

<span class="mw-page-title-main">Lily Young</span>

Lily Young is a distinguished professor of environmental microbiology at Rutgers New Brunswick. She is also a member of the administrative council at Rutgers University. She is the provost of Rutgers New Brunswick. She is a member of the Biotechnology Center for Agriculture and the Environment and has her academic appointment in the Department of Environmental Sciences.

Petroleum microbiology is a branch of microbiology that deals with the study of microorganisms that can metabolize or alter crude or refined petroleum products. These microorganisms, also called hydrocarbonoclastic microorganisms, can degrade hydrocarbons and, include a wide distribution of bacteria, methanogenic archaea, and some fungi. Not all hydrocarbonoclasic microbes depend on hydrocarbons to survive, but instead may use petroleum products as alternative carbon and energy sources. Interest in this field is growing due to the increasing use of bioremediation of oil spills.

Adsorbable Organic Halides (AOX) is a measure of the organic halogen load at a sampling site such as soil from a land fill, water, or sewage waste. The procedure measures chlorine, bromine, and iodine as equivalent halogens, but does not measure fluorine levels in the sample.

<i>In situ</i> bioremediation

Bioremediation is the process of decontaminating polluted sites through the usage of either endogenous or external microorganism. In situ is a term utilized within a variety of fields meaning "on site" and refers to the location of an event. Within the context of bioremediation, in situ indicates that the location of the bioremediation has occurred at the site of contamination without the translocation of the polluted materials. Bioremediation is used to neutralize pollutants including Hydrocarbons, chlorinated compounds, nitrates, toxic metals and other pollutants through a variety of chemical mechanisms. Microorganism used in the process of bioremediation can either be implanted or cultivated within the site through the application of fertilizers and other nutrients. Common polluted sites targeted by bioremediation are groundwater/aquifers and polluted soils. Aquatic ecosystems affected by oil spills have also shown improvement through the application of bioremediation. The most notable cases being the Deepwater Horizon oil spill in 2010 and the Exxon Valdez oil spill in 1989. Two variations of bioremediation exist defined by the location where the process occurs. Ex situ bioremediation occurs at a location separate from the contaminated site and involves the translocation of the contaminated material. In situ occurs within the site of contamination In situ bioremediation can further be categorized by the metabolism occurring, aerobic and anaerobic, and by the level of human involvement.

Hydrocarbonoclastic bacteria are a heterogeneous group of prokaryotes which can degrade and utilize hydrocarbon compounds as source of carbon and energy. Despite being present in most of environments around the world, several of these specialized bacteria live in the sea and have been isolated from polluted seawater.

References

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  2. ↑ Gulvik, C. A.; Buchan, A. (2013). "Simultaneous catabolism of plant-derived aromatic compounds results in enhanced growth for members of the Roseobacter lineage". Appl Environ Microbiol. 79 (12): 3716–3723. Bibcode:2013ApEnM..79.3716G. doi:10.1128/AEM.00405-13. PMC   3675927 . PMID   23563956.
  3. 1 2 Qin, Ke; Struckhoff, Garrett C.; Agrawal, Abinash; Shelley, Michael L.; Dong, Hailiang (2015-01-01). "Natural attenuation potential of tricholoroethene in wetland plant roots: Role of native ammonium-oxidizing microorganisms". Chemosphere. 119 (Supplement C): 971–977. Bibcode:2015Chmsp.119..971Q. doi:10.1016/j.chemosphere.2014.09.040. PMID   25303656.
  4. 1 2 3 4 5 Nzila, Alexis (2013-07-01). "Update on the cometabolism of organic pollutants by bacteria". Environmental Pollution. 178 (Supplement C): 474–482. doi:10.1016/j.envpol.2013.03.042. PMID   23570949.
  5. ↑ Beam, H. W.; Perry, J. J. (1973-03-01). "Co-metabolism as a factor in microbial degradation of cycloparaffinic hydrocarbons". Archiv für Mikrobiologie. 91 (1): 87–90. doi:10.1007/BF00409542. ISSN   0003-9276. PMID   4711459. S2CID   22727106.
  6. 1 2 3 4 Ryoo, D.; Shim, H.; Canada, K.; Barbieri, P.; Wood, T. K. (July 2000). "Aerobic degradation of tetrachloroethylene by toluene-o-xylene monooxygenase of Pseudomonas stutzeri OX1". Nature Biotechnology. 18 (7): 775–778. doi:10.1038/77344. ISSN   1087-0156. PMID   10888848. S2CID   19633783.
  7. 1 2 Li, Shanshan; Wang, Shan; Yan, Wei (2016). "Biodegradation of Methyl tert-Butyl Ether by Co-Metabolism with a Pseudomonas sp. Strain". International Journal of Environmental Research and Public Health. 13 (9): 883. doi: 10.3390/ijerph13090883 . ISSN   1661-7827. PMC   5036716 . PMID   27608032.
  8. ↑ Fraraccio, Serena; Strejcek, Michal; Dolinova, Iva; Macek, Tomas; Uhlik, Ondrej (2017-08-16). "Secondary compound hypothesis revisited: Selected plant secondary metabolites promote bacterial degradation of cis-1,2-dichloroethylene (cDCE)". Scientific Reports. 7 (1): 8406. Bibcode:2017NatSR...7.8406F. doi:10.1038/s41598-017-07760-1. ISSN   2045-2322. PMC   5559444 . PMID   28814712.
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