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Phenazines, in particular, are heterotricyclic nitrogen-containing metabolites.<ref name="(Mavrodi et al., 2010)">Mavrodi DV, Peever TL, Mavrodi OV, Parejko JA, Raaijmakers JM, Lemanceau P, Mazurier S, Heide L, Blankenfeldt W, Weller DM, Thomashow LS. (2010). [[Diversity]] and evolution of the phenazine biosynthesis pathway. ''Applied and Environmental Microbiology'' 76:866–879. [https://doi.org/10.1128/AEM.02009-09 https://doi.org/10.1128/AEM.02009-09]</ref> They are produced by ''Actinobacteria'' and ''Proteobacteria'', including the genera ''Pseudomonas spp.'', ''Streptomyces spp.'', and ''Pantoea agglomerans''.<ref name="(Dahlstrom et al., 2020)"/><ref name="(Pierson & Pierson, 2010)">Pierson, Leland S.; Pierson, Elizabeth A. (2010). "Metabolism and function of phenazines in bacteria: impacts on the behavior of bacteria in the environment and biotechnological processes". ''Applied Microbiology and Biotechnology''. 86 (6): 1659–1670. [https://link.springer.com/article/10.1007/s00253-010-2509-3 doi:10.1007/s00253-010-2509-3]</ref> All producer genomes contain the core biosynthesis genes ''phzA/BCDEFG'' that synthesize one of the two main phenazines which are precursors for all other derivatives: phenazine-1-carboxylic acid (PCA) in pseudomonads and phenazine-1,6-dicarboxylic acid (PDC) in most other species.<ref name="(Mavrodi et al., 2010)"/><ref name="(Dar et al., 2020)">Dar D, Thomashow LS, Weller DM, Newman DK. (2020). Global landscape of phenazine biosynthesis and biodegradation reveals species-specific colonization patterns in agricultural soils and crop microbiomes. ''Elife'' 9:e59726 [https://elifesciences.org/articles/59726 doi: 10.7554/eLife.59726]</ref> Auxiliary genes modify the core structure of these parent compounds to create different daughter phenazines with varying redox potentials and solubilities, ultimately affecting their beneficial function and toxicity.<ref name="(Laursen & Nielson, 2004)">Laursen JB, Nielsen J. (2004). Phenazine natural products: biosynthesis, synthetic analogues, and biological activity. ''Chemical Reviews'' 104:1663–1686. [https://doi.org/10.1021/cr020473j https://doi.org/10.1021/cr020473j]</ref> The variety of functional groups gives rise to a full spectrum of colors as well. For instance, 5-methyl-7-amino-1-carboxyphenazinium betaine (aeruginosin A) is deep red, PCA is lemon yellow, 1-hydroxy-5-methylphenazine (pyocyanin, PYO) is bright blue, 2-hydroxyphenazine-1-carboxylic acid (2-OHPCA) is bright orange, and 1-hydroxyphenazine (1-OHPHZ) is bright green.<ref name="(Price-Whelan et al., 2006)">LPrice-Whelan, A., Dietrich, L. & Newman, D. Rethinking 'secondary' metabolism: physiological roles for phenazine antibiotics. ''Nat Chem Biol'' 2, 71–78 (2006).  [https://doi.org/10.1038/nchembio764 https://doi.org/10.1038/nchembio764]</ref>
Phenazines, in particular, are heterotricyclic nitrogen-containing metabolites.<ref name="(Mavrodi et al., 2010)">Mavrodi DV, Peever TL, Mavrodi OV, Parejko JA, Raaijmakers JM, Lemanceau P, Mazurier S, Heide L, Blankenfeldt W, Weller DM, Thomashow LS. (2010). [[Diversity]] and evolution of the phenazine biosynthesis pathway. ''Applied and Environmental Microbiology'' 76:866–879. [https://doi.org/10.1128/AEM.02009-09 https://doi.org/10.1128/AEM.02009-09]</ref> They are produced by ''Actinobacteria'' and ''Proteobacteria'', including the genera ''Pseudomonas spp.'', ''Streptomyces spp.'', and ''Pantoea agglomerans''.<ref name="(Dahlstrom et al., 2020)"/><ref name="(Pierson & Pierson, 2010)">Pierson, Leland S.; Pierson, Elizabeth A. (2010). "Metabolism and function of phenazines in bacteria: impacts on the behavior of bacteria in the environment and biotechnological processes". ''Applied Microbiology and Biotechnology''. 86 (6): 1659–1670. [https://link.springer.com/article/10.1007/s00253-010-2509-3 doi:10.1007/s00253-010-2509-3]</ref> All producer genomes contain the core biosynthesis genes ''phzA/BCDEFG'' that synthesize one of the two main phenazines which are precursors for all other derivatives: phenazine-1-carboxylic acid (PCA) in pseudomonads and phenazine-1,6-dicarboxylic acid (PDC) in most other species.<ref name="(Mavrodi et al., 2010)"/><ref name="(Dar et al., 2020)">Dar D, Thomashow LS, Weller DM, Newman DK. (2020). Global landscape of phenazine biosynthesis and biodegradation reveals species-specific colonization patterns in agricultural soils and crop microbiomes. ''Elife'' 9:e59726 [https://elifesciences.org/articles/59726 doi: 10.7554/eLife.59726]</ref> Auxiliary genes modify the core structure of these parent compounds to create different daughter phenazines with varying redox potentials and solubilities, ultimately affecting their beneficial function and toxicity.<ref name="(Laursen & Nielson, 2004)">Laursen JB, Nielsen J. (2004). Phenazine natural products: biosynthesis, synthetic analogues, and biological activity. ''Chemical Reviews'' 104:1663–1686. [https://doi.org/10.1021/cr020473j https://doi.org/10.1021/cr020473j]</ref> The variety of functional groups gives rise to a full spectrum of colors as well. For instance, 5-methyl-7-amino-1-carboxyphenazinium betaine (aeruginosin A) is deep red, PCA is lemon yellow, 1-hydroxy-5-methylphenazine (pyocyanin, PYO) is bright blue, 2-hydroxyphenazine-1-carboxylic acid (2-OHPCA) is bright orange, and 1-hydroxyphenazine (1-OHPHZ) is bright green.<ref name="(Price-Whelan et al., 2006)">LPrice-Whelan, A., Dietrich, L. & Newman, D. Rethinking 'secondary' metabolism: physiological roles for phenazine antibiotics. ''Nat Chem Biol'' 2, 71–78 (2006).  [https://doi.org/10.1038/nchembio764 https://doi.org/10.1038/nchembio764]</ref>


The chemistry and toxicity of phenazines is dictated by the chemical microenvironment in the soil, namely oxygen, pH, and moisture.<ref name="(Dahlstrom et al., 2020)"/> For instance, at low pH, PCA is uncharged and more cell permeable, ultimately making it more toxic.<ref name="(Dahlstrom et al., 2020)"/> At high oxygen levels, PCA reacts with oxygen to create toxic reactive oxygen species (ROS).<ref name="(Dahlstrom et al., 2020)"/> In anoxic environments, PCA reacts with ferric iron minerals and produces ferrous iron through the process of reductive dissolution which may help solubilize mineral-adsorbed phosphorous. <ref name="(Dahlstrom et al., 2020)"/>
The chemistry and toxicity of phenazines is dictated by the chemical microenvironment in the soil, namely oxygen, pH, and moisture.<ref name="(Dahlstrom et al., 2020)"/> For instance, at low pH, PCA is uncharged and more cell permeable, ultimately making it more toxic.<ref name="(Dahlstrom et al., 2020)"/> At high oxygen levels, PCA reacts with oxygen to create toxic reactive oxygen species (ROS).<ref name="(Dahlstrom et al., 2020)"/> In anoxic environments, PCA reacts with ferric iron minerals and produces ferrous iron through the process of reductive dissolution which may help solubilize mineral-adsorbed phosphorous.<ref name="(Dahlstrom et al., 2020)"/>
 
==Effect on Competitive Fitness of Producer Organisms==
 
The primary function of phenazines is for the competitive fitness of producer [[organisms]]. Phenazines allow their producers to survive under anoxic conditions, facilitate biofilm development, and aid acquisition of essential inorganic nutrients like iron and phosphorus.<ref name="(Dahlstrom et al., 2020)"><ref name="(Dar et al., 2020)"> Phenazine-producing strains have been shown to be better able to colonize the roots of wheat plants and persist in the rhizosphere than phenazine-lacking mutants.<ref name="(Mazzola et al., 1992)">Mazzola, M., Cook, R.J., Thomashow, L.S., Weller, D.M. & Pierson, L.S., III. Contribution of phenazine antibiotic biosynthesis to the ecological competence of fluorescent pseudomonads in soil habitats. ''Appl. Environ. Microbiol.'' 58, 2616–2624 (1992).</ref>
 
In the same way that pseudomonads use phenazines to colonize [[plant roots]] in the rhizosphere, the opportunistic pathogen ''Pseudomonas aeruginosa'' uses the phenazine pyocyanin to colonize the biofilms of the lungs of cystic fibrosis patients.<ref name="(Villavicencio, 1998)">Villavicencio, R.T. The history of blue pus. J. ''Am. Coll. Surg.'' 187, 212–216 (1998).</ref> Pyocyanin has also been shown to facilitate interspecies antibiotic resistance, such as aiding the pathogenic fungi ''Candida albicans'' and ''Aspergillus fumigatus'' to colonize the cystic fibrosis lung.<ref name="(Morales et al., 2013)">D.K. Morales, N. Grahl, C. Okegbe, L.E.P. Dietrich, N.J. Jacobs, D.A. Hogan. Control of Candida albicans metabolism and biofilm formation by ''Pseudomonas aeruginosa'' phenazines. ''mBio'', 4 (2013), pp. e00526-00512</ref><ref name="(Briard et al., 2015)">B. Briard, P. Bomme, B.E. Lechner, G.L.A. Mislin, V. Lair, M.-C. Prévost, J.-P. Latgé, H. Haas, A. Beauvais. ''Pseudomonas aeruginosa'' manipulates redox and iron homeostasis of its microbiota partner ''Aspergillus fumigatus'' via phenazines. ''Sci. Rep.'', 5 (2015), p. 8220</ref>
 
 
 




==References==  
==References==  
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Revision as of 14:14, 4 May 2022

Phenazines are redox-active metabolites that are produced by certain soil bacteria and play an important role in the chemistry and ecology of the pedosphere. The compounds have been found across habitats and are especially abundant in root zones. Their redox activity makes them very reactive, and although they are found in relatively low concentrations, they have a disproportionate impact on the microbial ecology of the rhizosphere. Producer bacteria use phenazines to effectively compete with other soil microbes and acquire inorganic nutrients, which are processes that could be harnessed for sustainable agricultural practices in the future.

Biosynthesis and Chemistry

Redox-active metabolites (RAMs) can be generally defined as ‘natural byproducts’ or ‘secondary metabolites’ of soil bacteria.[1] Although they are produced intracellularly and support cellular redox balancing, they are also secreted and may react extracellularly in the soil.[1] They accept and donate electrons to various soil constituents, hence why they are called ‘redox-active.'[1]

Phenazines, in particular, are heterotricyclic nitrogen-containing metabolites.[2] They are produced by Actinobacteria and Proteobacteria, including the genera Pseudomonas spp., Streptomyces spp., and Pantoea agglomerans.[1][3] All producer genomes contain the core biosynthesis genes phzA/BCDEFG that synthesize one of the two main phenazines which are precursors for all other derivatives: phenazine-1-carboxylic acid (PCA) in pseudomonads and phenazine-1,6-dicarboxylic acid (PDC) in most other species.[2][4] Auxiliary genes modify the core structure of these parent compounds to create different daughter phenazines with varying redox potentials and solubilities, ultimately affecting their beneficial function and toxicity.[5] The variety of functional groups gives rise to a full spectrum of colors as well. For instance, 5-methyl-7-amino-1-carboxyphenazinium betaine (aeruginosin A) is deep red, PCA is lemon yellow, 1-hydroxy-5-methylphenazine (pyocyanin, PYO) is bright blue, 2-hydroxyphenazine-1-carboxylic acid (2-OHPCA) is bright orange, and 1-hydroxyphenazine (1-OHPHZ) is bright green.[6]

The chemistry and toxicity of phenazines is dictated by the chemical microenvironment in the soil, namely oxygen, pH, and moisture.[1] For instance, at low pH, PCA is uncharged and more cell permeable, ultimately making it more toxic.[1] At high oxygen levels, PCA reacts with oxygen to create toxic reactive oxygen species (ROS).[1] In anoxic environments, PCA reacts with ferric iron minerals and produces ferrous iron through the process of reductive dissolution which may help solubilize mineral-adsorbed phosphorous.[1]

Effect on Competitive Fitness of Producer Organisms

The primary function of phenazines is for the competitive fitness of producer organisms. Phenazines allow their producers to survive under anoxic conditions, facilitate biofilm development, and aid acquisition of essential inorganic nutrients like iron and phosphorus.Cite error: Closing </ref> missing for <ref> tag

In the same way that pseudomonads use phenazines to colonize plant roots in the rhizosphere, the opportunistic pathogen Pseudomonas aeruginosa uses the phenazine pyocyanin to colonize the biofilms of the lungs of cystic fibrosis patients.[7] Pyocyanin has also been shown to facilitate interspecies antibiotic resistance, such as aiding the pathogenic fungi Candida albicans and Aspergillus fumigatus to colonize the cystic fibrosis lung.[8][9]



References

  1. ↑ 1.0 1.1 1.2 1.3 1.4 1.5 1.6 1.7 Dahlstrom, Kurt; McRose, Darcy L.; Newman, Dianne K. (2020). Keystone metabolites of crop rhizosphere microbiomes. Current Biology. Volume 30, Issue 19, Pages R1131-R1137, ISSN 0960-9822, https://doi.org/10.1016/j.cub.2020.08.005
  2. ↑ 2.0 2.1 Mavrodi DV, Peever TL, Mavrodi OV, Parejko JA, Raaijmakers JM, Lemanceau P, Mazurier S, Heide L, Blankenfeldt W, Weller DM, Thomashow LS. (2010). Diversity and evolution of the phenazine biosynthesis pathway. Applied and Environmental Microbiology 76:866–879. https://doi.org/10.1128/AEM.02009-09
  3. ↑ Pierson, Leland S.; Pierson, Elizabeth A. (2010). "Metabolism and function of phenazines in bacteria: impacts on the behavior of bacteria in the environment and biotechnological processes". Applied Microbiology and Biotechnology. 86 (6): 1659–1670. doi:10.1007/s00253-010-2509-3
  4. ↑ Dar D, Thomashow LS, Weller DM, Newman DK. (2020). Global landscape of phenazine biosynthesis and biodegradation reveals species-specific colonization patterns in agricultural soils and crop microbiomes. Elife 9:e59726 doi: 10.7554/eLife.59726
  5. ↑ Laursen JB, Nielsen J. (2004). Phenazine natural products: biosynthesis, synthetic analogues, and biological activity. Chemical Reviews 104:1663–1686. https://doi.org/10.1021/cr020473j
  6. ↑ LPrice-Whelan, A., Dietrich, L. & Newman, D. Rethinking 'secondary' metabolism: physiological roles for phenazine antibiotics. Nat Chem Biol 2, 71–78 (2006). https://doi.org/10.1038/nchembio764
  7. ↑ Villavicencio, R.T. The history of blue pus. J. Am. Coll. Surg. 187, 212–216 (1998).
  8. ↑ D.K. Morales, N. Grahl, C. Okegbe, L.E.P. Dietrich, N.J. Jacobs, D.A. Hogan. Control of Candida albicans metabolism and biofilm formation by Pseudomonas aeruginosa phenazines. mBio, 4 (2013), pp. e00526-00512
  9. ↑ B. Briard, P. Bomme, B.E. Lechner, G.L.A. Mislin, V. Lair, M.-C. Prévost, J.-P. Latgé, H. Haas, A. Beauvais. Pseudomonas aeruginosa manipulates redox and iron homeostasis of its microbiota partner Aspergillus fumigatus via phenazines. Sci. Rep., 5 (2015), p. 8220
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