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 range 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 *]

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.