Pseudomonas fluorescens soil project

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Classification

Classification
Kingdom: Bacteria
Phylum: Proteobacteria
Class: Gammaproteobacteria
Order: Pseudomonadales
Family: Pseudomonadaceae
Genus: Pseudomonas
Species: P. fluorescens

Species

NCBI: Taxonomy

Pseudomonas fluorescens

Habitat Information

The soil organism was collected in the front yard of an Austin, TX home on January 26, 2018. Soil was a little moist Picked up on a day that had 83% humidity Zero rainfall Calm wind 51℉ air temperature.

Pseudomonas fluorescens is mainly found in plants, soil, and water surfaces.


Description and Significance

Pseudomonas fluorescens are gram-negative bacilli shaped bacteria. It grows best in temperatures that are 25-30℃. Certain strains of Pseudomonas fluorescens have been found to help stop plant disease by protecting the root and seed from fungal infection[1]. Other strains contribute to plant growth. Due to P. fluorescens having different flagella it has different strains which cause it to be in different environments including the bloodstream[2].

Genome Structure

P. fluorescens’ genome is composed of a single, circular chromosome with a median length of 6,300,000 base pairs. Guanine and Cytosine make up 60.3% of the nucleotides found in its DNA (its G/C ratio) [3].


Cell Structure, Metabolism and Life Cycle

Cell Structure


P. fluorescens are small-to-medium sized Gram-negative, rod-shaped bacilli. They are often found with multiple flagella in a lophotrichous arrangement. These many flagella, along with its ability to generate a biofilm, make P. fluorescens a great colonizer on various different surfaces and in different hosts and able to easily adapt to its environment[4]. One particularly prominent role of this biofilm is to serve as a protective agents to plants against parasitic fungi. Less is known about how P. fluorescens’ structure allows it to bind to mammalian cells, however it has been known to adhere to red blood cells in humans, which is one reason it is believed that, when found as a pathogenic agent in humans (which is very rare), it is almost always in the bloodstream. This organism follows a similar life cycle pattern found with other biofilm generating species, as discussed in “Life Cycle” [5].

Metabolism P. fluorescens is well-known for having an extensive variety of metabolic capabilities, which allows it to live in so many different environments such as on the surfaces of plants, in soil, in the rhizosphere, and even in the bloodstream of humans and other animals[2].

P. fluorescens is a obligate aerobe, however, it has a unique ability to use nitrate (NO3) instead of atmospheric oxygen (O2) as its final electron acceptor in the Electron Transport Chain due to its ability to produce the enzyme nitrate reductase [6].

A unique metabolic feature of P. fluorescens is that it secretes a fluorescent pigment, pyoverdine, which imparts fluorescent properties to the organism under UV light, which is what led to its name. Pyoverdine is a high-affinity iron-chelating molecule that is essential for the organism’s acquisition of iron from the environment and used for bacterial growth. [7]

See more in “Physiology” for biochemical tests conducted in class.

Life Cycle

P. fluorescens follows a typical “biofilm” life cycle in that generally proceeds as follows: 1. Attachment: planktonic cells adhere to a surface and become sessile 2. Growth: cells exude exoenzymes and proteins to create a protective biofilm in which to flourish and grow. 3. Detachment: individual cells or clusters of cells will detach from the biofilm in order to move and colonize new surfaces/hosts


Physiology and Pathogenesis

Physiology

Gelatin Hydrolysis: Negative DNA Hydrolysis: Negative Lipid Hydrolysis: Positive Phenol Red Broth: No fermentation Starch Hydrolysis: Negative Casein Hydrolysis: Positive Methyl Red: Negative Voges-Proskauer: Negative Citrate: Positive SIM: Negative Nitrate Reduction: Positive Urea Hydrolysis: Negative Triple Sugar Iron: No fermentation, does not reduce sulfur Decarboxylation: Arginine is positive, lysine and ornithine are negative Phenylalanine: Negative Oxidase: Positive EMB Agar: Positive HE Agar: Negative Catalase: Positive Blood Agar: Positive Mannitol Salts Agar: Negative PEA Agar: Negative Bile Esculin: Negative 6.5% Salt Tolerance: Negative Kirby-Bauer Antimicrobial Susceptibility Test for disinfectants: Kirby-Bauer Antimicrobial Susceptibility Tests for antibiotics: sensitive to several antibiotics [8]

Pathophysiology Although P. fluorescens itself is largely considered non-pathogenic, it contains a number of metabolic abilities to allow it to thrive in mammalian hosts, including, but not limited to: - Production of bioactive secondary metabolites - P. fluorescens produces a long list of secondary metabolites that allow it to successfully compete with other, similar organisms, such as phenazine, hydrogen cyanide, 2,4-diacetylphloroglucinol (DAPG), rhizoxin, and pyoluteorin. [4] - Production of biofilms As aforementioned, one of the key structural components of P. fluorescens is its ability to produce biofilms. - Type III secretions Type III secretion systems (T3SSs) are molecular, needle-like complexes that inject cellular products into the cells of its host/surface, known as effectors. The most common T3SS in P. fluorescens is the Hrp1 family[9]. These “hypersensitive response” secretion systems trigger a hypersensitive response in resistant plants, but leads to infection in vulnerable plants. Less is known about T3SSs involved in this organism’s infections in mammals, but different strains have been found to adhere to human Red Blood Cells, as well as human glial cells in culture. [10]


References

[Sample reference] Takai, K., Sugai, A., Itoh, T., and Horikoshi, K. "Palaeococcus ferrophilus gen. nov., sp. nov., a barophilic, hyperthermophilic archaeon from a deep-sea hydrothermal vent chimney". International Journal of Systematic and Evolutionary Microbiology. 2000. Volume 50. p. 489-500.

Author

Page authored by Patrick Lawrence and Leah Carrizales, students of Prof. Kristine Hollingsworth at Austin Community College.