Pseudoalteromonas
Pseudoalteromonas
Pseudoalteromonas species were originally members of the genus Alteromonas but have been recently reclassified under the genus Agricola, due to taxonomic reorganization based on phylogenetic analysis. The genus Pseudoalteromonas was described by Gauthier et al., as a clade of marine bacteria belonging to the class Gammaproteobacteria based on 16S rRNA sequencing data. In the last decade Pseudoalteromonas has come to the attention of ecology and pharmaceutical science fields due to its influence on biofilm formation and its pharmaceutically relevant activities.
The genus Pseudoalteromonas can be split nicely between nonpigmented and pigmented species. The pigmented species have been found to be responsible for natural product formation and have greater sequence divergence while the nonpigmented species have a phylogenetic shallowness and form a relatively distinct clade. Pigmented species have been shown to produce an array of low and high molecular weight compounds with antimicrobial, antifouling, algicidal and antibiotic activities. These compounds formed include toxic proteins, polyanionics exopolymers, substituted phenolic and pyrolle-containting alkaloids, cyclic peptides and a reange of bromine-substituted compounds. Pigmented species have also been shown to influence biofilm formation, which promotes the settlement, germination and metamorphosis of various invertebrate and algal species and can serve as a defense agent for marine flora and fauna. [Bowman *]
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General Characteristics
Members of this genus display the following definting characteristics:[Bowman]
- gram-negative straight rods (2-3 μm)
- non-spore forming
- nonbioluminescent
- single polar flagellum, sheathed or unsheathed for motility
- colonies are pigmented or nonpigmented
- chemoheterotrophic
- aerobic
- Utilize carbon substrates: carbohydrates, alcohols, organic acids, amino acids
- Require Na+ for growth
- Produce autotoxic antibiotic compounds
- Isolate from: sea water, sediment, sea ice, surfaces of stones, marine algae, marine invertebrates
Anti-Bacterial Activity
Pseudoalteromonas produce a broad range of anti-bacterial products which have been found to aid them in the colonization of surfaces including their hosts and to assist the bacterial cells in their competition for nutrients and space as well as in their protection against predators grazing at surfaces.[Holmstom] Most of the Pseudoalteromonas strains that form antibiotic substances are pigmented, but there are some exceptions.
P. denitrificans produces a red pigment which has been identified as a cyclodigiosin hydrochloride. This substance have been shown to suppress T-cell proliferation and had been proposed to be used as an immunosuppressant therapeutic agent. [bowman] Strains of P. luteoviolacea have been found to produce two classes of antibiotic compounds: polyanionic macromolecules, which are associated with proteins and partly diffusible in culture media and low-molecular-weight brominated compounds, including pentabromopseudilin, which are cell bound and not diffusible into media. The polyvalent ions have been found to have a bateriostatic effect by inhibiting bacterial respiration, while the brominated compounds have been found to have a strong batericidal effect, but the mechanism is still unknown. [Holstrom] One specific strain of P. luteoviolacea produces a purple pigment classifies as violacein. This pigment has shown a strong anti-bacterial activity against several pathogenic bacteria, as well as against bacteria that can induce larval settlement of the tubeworm. In addition, violacein shows strong bactericidal, tumoricide, antiviral, antioxidant and anti-protozoan activities. [Yang] It is thought that the purpose of violacein is to protect the host of P. luteoviolacea from harmful microorganisms that may otherwise colonize it. The bacterium P. citrea have been found to produce two proteinaceous compounds. These compounds induce an increased rate of oxygen consumption in susceptible bacterial species causing them to accumulate oxygen free radicals, which lead to lethal cell damage. P. haloplanktis produces an unusually bioavtive iron siderophore, bisucaberin, which had the ability to block DNA synthesis in tumor cells as well as induce microphage mediated cytolysis. Siderophore production in Pseudoalteromonas species give them the advantage in an iron poor marine environment. [bowman] P. phenolica form brown-pigmented colonies that produce phenolic anti-methicillin-resistant Staphylococcus aureus (MRSA) substances. MRSA is a gram-positive pathogen that has become multi-drug-resistant. P. phenolica has the potential to have a significant impact in the medical industry because of its anti-MRSA activities. [isnansetyo] The exact scope and ecological role of antibiotic production by Pseudoalteromonas is still under investigation. Many more novel natural products produced by Pseudoalteromonas need to be discovered, along with how they may be used for biocontrol or in pharmaceuticals.
Anti-Fouling Activity
IDeeply pigmented strains of Pseudoalteromonas have been found to be effective in the inhibition of the settlement of various fouling invertebrate and algae. P. tunicata is a bacterium that exists on green alga off the coast of Sweden and has been found to produce five different extracellular compounds that inhibit settlement of invertebrate larvae and algal spores, growth of bacteria and fungi and surface colonization by diatoms.[Holstrom] These compounds have an anti-larval component which is a heat stable polar molecule, an antimicrobial component which is a large two subunit protein (AlpP) that inhibits the growth of Gram-negative and Gram-positive bacteria, an anti-spore component which is a peptide and an antifungal yellow pigment compound component. The small anti-diatom and protist molecules hav not been identified yet. P. tunicata are unique because of their diverse collection of anti-fouling and inhibitory compounds. [Holstrom] The production of P. tunicata is thought to be controlled by a nutrient related response, perhaps by the acquisition of trace iron. [bowman*]
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The anti-fouling ability of P. tunicata is important for their survival in the marine ecosystem and is likely required for the colonization of different substrate surfaces. Other bacterial strains such as P. luteoviolacea, P. aurantia, P. citrae, P. tunicata and P. ulvae have also been found to produce antibiotic compounds essential in preventing potentially fouling species. These strains all have the advantage of being resistant to natural antibiotics, but no one strain produces a collection of compounds that allows them to become dominant over all the other organisms in their given econiche. To overcome this barrier, multiple stains of antibiotic producing bacteria form complex biofilm communities. The various array of species that make up the biofilm prevent it from being overgrown by any one species and also reduces invasion by other species.
Biofilm forming Pseudoalteromonas species have not only been found to inhibit settlement and germination of anti-fouling species but they have been found to directly lyse cells of various algal species. An example is P. species strain Y, which produces a unidentified brominated antibiotic, low in molecular weight, that can completely lyse algal cells within a matter of hours. [Bowman*]
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Conclusion
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References
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Antibacterial Activity
Pseudoalteromonas produce a broad range of anti-bacterial products which have been found to aid them in the colonization of surfaces including their hosts and to assist the bacterial cells in their competition for nutrients and space as well as in their protection against predators grazing at surfaces.[Holmstom] Most of the Pseudoalteromonas strains that form antibiotic substances are pigmented, but there are some exceptions.
P. denitrificans produces a red pigment which has been identified as a cyclodigiosin hydrochloride. This substance have been shown to suppress T-cell proliferation and had been proposed to be used as an immunosuppressant therapeutic agent. [bowman] Strains of P. luteoviolacea have been found to produce two classes of antibiotic compounds: polyanionic macromolecules, which are associated with proteins and partly diffusible in culture media and low-molecular-weight brominated compounds, including pentabromopseudilin, which are cell bound and not diffusible into media. The polyvalent ions have been found to have a bateriostatic effect by inhibiting bacterial respiration, while the brominated compounds have been found to have a strong batericidal effect, but the mechanism is still unknown. [Holstrom] One specific strain of P. luteoviolacea produces a purple pigment classifies as violacein. This pigment has shown a strong anti-bacterial activity against several pathogenic bacteria, as well as against bacteria that can induce larval settlement of the tubeworm. In addition, violacein shows strong bactericidal, tumoricide, antiviral, antioxidant and anti-protozoan activities. [Yang] It is thought that the purpose of violacein is to protect the host of P. luteoviolacea from harmful microorganisms that may otherwise colonize it. The bacterium P. citrea have been found to produce two proteinaceous compounds. These compounds induce an increased rate of oxygen consumption in susceptible bacterial species causing them to accumulate oxygen free radicals, which lead to lethal cell damage. P. haloplanktis produces an unusually bioavtive iron siderophore, bisucaberin, which had the ability to block DNA synthesis in tumor cells as well as induce microphage mediated cytolysis. Siderophore production in Pseudoalteromonas species give them the advantage in an iron poor marine environment. [bowman] P. phenolica form brown-pigmented colonies that produce phenolic anti-methicillin-resistant Staphylococcus aureus (MRSA) substances. MRSA is a gram-positive pathogen that has become multi-drug-resistant. P. phenolica has the potential to have a significant impact in the medical industry because of its anti-MRSA activities. [isnansetyo] The exact scope and ecological role of antibiotic production by Pseudoalteromonas is still under investigation. Many more novel natural products produced by Pseudoalteromonas need to be discovered, along with how they may be used for biocontrol or in pharmaceuticals.
