IngredientsPseudomonas fluorescens is a species of Gram-negative, aerobic, non-spore-forming bacteria belonging to the genus Pseudomonas, family Pseudomonadaceae, class Gammaproteobacteria. It is a Gram-negative environmental bacterium often studied as a key contributor to plant and soil health. Pan-genome analysis suggests that P. fluorescens is not a single species, but is better described as a species complex — a set of closely related species that are very similar in appearance and traits — within which there are more than 50 species along with many unclassified isolates. This complex is highly diverse, both genetically and ecologically, with species inhabiting a variety of environments, including soil, water, plant tissues, and even dairy products.
P. fluorescens gained its name because it fluoresces under UV light due to production of a green, iron-scavenging siderophore called pyoverdine. The bacterium is a member of a wider P. fluorescens species complex (including Pseudomonas protegens, Pseudomonas chlororaphis, and many others) that have a broad habitat range and are commonly found in soil, water, on plant surfaces, and in the rhizosphere.
P. fluorescens cells are unicellular rods, with a long straight or curved axis, but not helical, exhibiting motility by one or more polar flagella; they are Gram-negative and non-spore-forming. P. fluorescens is represented by seven biotypes denoted by the letters A, B, C, D, E, F, and G. The microbe shows a wide choice of growth temperature. Pseudomonas fluorescens is an aerobic, Gram-negative, ubiquitous organism present in agricultural soils and well adapted to grow in the rhizosphere.
P. fluorescens grows rapidly in vitro and can be mass-produced. It rapidly utilizes seed and root exudates and colonizes and multiplies in the rhizosphere and spermosphere environments. In the plant rhizosphere, it produces a wide spectrum of bioactive metabolites — including antibiotics, siderophores, volatiles, and growth-promoting substances — competes aggressively with other microorganisms, and adapts to environmental stresses.
Pseudomonas fluorescens is also a common spoilage microorganism in proteinaceous raw foods stored under aerobic refrigerated conditions, such as dairy products, meat, and seafoods. While P. fluorescens is not generally considered a bacterial pathogen in humans, multiple culture-based and culture-independent studies have identified it at low levels in the indigenous microbiota of various body sites. With recent advances in comparative genomics, many isolates originally identified as the "species" P. fluorescens are now being reclassified as novel Pseudomonas species within the P. fluorescens "species complex."
Among PGPR with wide scope for commercialization, Pseudomonas fluorescens stands as one of the primary candidates. PGPR isolates are formulated using different organic and inorganic carriers either through solid or liquid fermentation technologies. They are delivered either through seed treatment, bio-priming, seedling dip, soil application, foliar spray, fruit spray, hive insert, and sucker treatment.
Earlier researchers standardized a process of mass production of Pseudomonas fluorescens using King's B broth with talc powder as a carrier. This process included only a liquid fermentation step and not solid fermentation. Commercial formulations are also produced using solid fermentation; one process involves inoculation in King's B broth at 30°C for 24–36 hours, followed by liquid fermentation in substrates such as pongamia cake aqueous extract, neem cake aqueous extract, sugarcane molasses, and King's B broth, followed by solid fermentation using sterile pongamia de-oiled cake, neem de-oiled cake, and wheat bran.
Formulations may be employed as wettable powders, granules, or dusts by mixing with various inert materials, such as inorganic minerals (phyllosilicates, carbonates, sulfates, phosphates) or botanical materials (powdered corncobs, rice hulls, walnut shells). The formulations may include spreader-sticker adjuvants, stabilizing agents, other pesticidal additives, or surfactants. Liquid formulations may be aqueous-based or non-aqueous and employed as foams, gels, suspensions, emulsifiable concentrates, or similar forms.
Pseudomonas fluorescens is not a substance with a classical ethnobotanical or traditional medicine history in the way that botanical extracts or herbal preparations typically are. As a bacterium present ubiquitously in soil and water, it has not been consciously isolated or used as a traditional preparation by ancient or pre-modern cultures. There is accordingly no documented history of its use in traditional Ayurvedic, Chinese, European, or Indigenous medicine systems.
Its scientific recognition began in the 19th century with early microbiology. Although most widely studied for its role in the soil and the rhizosphere, P. fluorescens has been found to possess a number of functional traits that provide it with the capability to grow and thrive in mammalian hosts. Formal applied use emerged from agricultural microbiology in the 20th century, when researchers recognized its capacity to protect crop plants from soilborne diseases — research that has progressively driven its development into commercial bioinoculant formulations.
Over time, a range of probiotic species from the bacterial genus Pseudomonas, among others, have been identified and applied to boost the growth and immune capabilities of various aquaculture species. This represents the closest analogy to a "traditional" application: the empirical use of environmental bacteria in agriculture and aquaculture well before their mechanisms of action were fully characterized. However, this history is limited to applied science rather than ethnomedicinal practice.
Pseudomonas species that are well-studied PGPRs secrete a battery of antimicrobial metabolites, including 2,4-diacetylphloroglucinol (2,4-DAPG), phenazines, pyoluteorin, pyrrolnitrin, hydrogen cyanide, and nonribosomal peptides. These compounds collectively underpin the biocontrol and plant growth-promotion activities attributed to the organism.
Among the secondary metabolites, 2,4-diacetylphloroglucinol (2,4-DAPG) has received special attention because of its broad-spectrum antimicrobial activity. The gene cluster involved in 2,4-DAPG biosynthesis comprises the phlACBD operon. Specifically, the phlD gene encodes a type III polyketide synthase, which catalyzes the formation of phloroglucinol (PG) from malonyl-CoA. Monoacetylphloroglucinol (MAPG) acetyltransferase, encoded by phlACBD, then acetylates PG to MAPG and ultimately to 2,4-DAPG.
Certain strains are capable of exerting a variety of mechanisms of plant growth promotion and protection, including the production of the natural antibiotics 2,4-diacetylphloroglucinol (2,4-DAPG) and derivatives of phenazine. These compounds are broadly active against plant pathogens and are produced by widely distributed, taxonomically diverse Pseudomonas spp. that inhabit the rhizosphere of cereal crops and render certain soils naturally suppressive to soilborne plant diseases. There is mounting evidence that the role of 2,4-DAPG and phenazines in the rhizosphere is not limited to antibiosis but also involves regulatory and signaling functions, induction of systemic resistance, and reduction of minerals in soil.
P. fluorescens produces a green, iron-scavenging siderophore called pyoverdine, which is responsible for the organism's characteristic fluorescence under UV light. Siderophores serve a dual function: they mobilize iron from the soil environment for use by the bacterium and the host plant, while simultaneously depleting iron available to competing plant pathogens. The mode of action of these bacteria in biocontrol is likely related to the production of siderophores — small compounds with high affinity binding for iron.
Phenazine compounds are nitrogen-containing heterocyclic secondary metabolites. Several Pseudomonas species significantly control the growth of different bacterial and fungal plant pathogens by the secretion of diffusible compounds including phenazine-1-carboxamide (PCN). Phenazines contribute to the redox activity and iron cycling in the rhizosphere in addition to their antimicrobial effects.
Pseudomonas fluorescens secondary control activity includes ACC deaminase, IAA synthesis, siderophore production, and antifungal compound synthesis, which collectively regulate its PGPR functions. Among the phytohormones produced by plant growth-promoting bacteria, auxins and indolyl-3-acetic acid (IAA) are the most studied. IAA production by P. fluorescens proceeds through tryptophan-dependent pathways and promotes root elongation, lateral root formation, and increased surface area for nutrient absorption.
Properties of Pseudomonas in providing disease resistance include induced systemic resistance (ISR), phenazine production, and antibiotic production. Hydrogen cyanide, a volatile metabolite produced by specific P. fluorescens strains, inhibits enzymes in competing organisms, contributing to pathogen suppression in the rhizosphere.
P. fluorescens suppresses the growth of pathogenic microorganisms by various mechanisms including the production of hydrolytic enzymes such as β-1,3-glucanase and chitinases. These enzymes degrade the cell walls of fungal pathogens and contribute to biocontrol activity.
Pseudomonas fluorescens produces the antibiotic obafluorin. Obafluorin is a β-lactone antibiotic with documented antibacterial properties, representing another secondary metabolite in the organism's wide chemical repertoire.
Selected strains of rhizosphere bacteria reduce disease by activating a resistance mechanism in the plant named rhizobacteria-mediated induced systemic resistance (ISR). ISR resembles pathogen-induced systemic acquired resistance (SAR) in that both types of induced resistance render uninfected plant parts more resistant towards a broad spectrum of plant pathogens. Some rhizobacteria trigger the salicylic acid (SA)-dependent SAR pathway by producing SA at the root surface. In other cases, rhizobacteria trigger a different signaling pathway that does not require SA.
ISR induced by Pseudomonas fluorescens WCS417r is independent of SA accumulation and pathogenesis-related (PR) gene activation but, instead, requires responsiveness to the plant hormones jasmonic acid (JA) and ethylene. ISR relies on priming faster and robust expression of marker genes for the salicylic acid (SA), jasmonic acid (JA), and ethylene (ET) signaling pathways upon pathogen challenge.
Pseudomonas fluorescens WCS374r has been shown to trigger ISR in rice (Oryza sativa) against the leaf blast pathogen Magnaporthe oryzae. This WCS374r-induced resistance is regulated by an SA-independent but jasmonic acid/ethylene-modulated signal transduction pathway. Bacterial mutant analysis uncovered a pseudobactin-type siderophore as the crucial determinant responsible for ISR elicitation in this system.
Inorganic phosphate solubilization is one of the major mechanisms of plant growth promotion by plant-associated bacteria. This involves bacteria releasing organic acids into the soil which solubilize phosphate complexes, converting them into ortho-phosphate, which is available for plant uptake and utilization. Studies have shown that endophytic P. fluorescens strains produce gluconic acid (GA) in significant quantities (14–169 mM) and have moderate to high phosphate solubilization capacities (~400–1300 mg L⁻¹). When inoculated into pea plants grown in soil under soluble phosphate-limiting conditions, the endophytes that produced medium-high levels of GA displayed beneficial plant growth promotion effects.
Through siderophore production, auxin synthesis, and biosurfactant activity, P. fluorescens supports robust root development, nutrient uptake, and plant resilience. The siderophore pyoverdine, in addition to supporting the bacterium's own iron nutrition, depletes the iron available to competing pathogens, suppressing their growth through iron starvation — a process known as siderophore-mediated competition.
Various biocontrol agents including Pseudomonas fluorescens exert their effects through antimicrobial compound production, competition, and activation of host defenses. Specifically, P. fluorescens enhances plant resistance by inducing defense-related enzymes. Its volatile organic compounds inhibit Ralstonia solanacearum growth and virulence by targeting essential metabolic pathways.
Mutations in the wsp regulatory pathway result in constitutive expression of the response regulator WspR, raising cyclic-di-GMP levels and promoting extracellular polysaccharide production. The resulting phenotype is a mutant with robust biofilm formation and wrinkled colonies; this gives the bacteria a competitive advantage at the air–liquid interface. Environmental strains that form cellulose-based biofilms in static microcosms have been isolated from natural habitats, suggesting that these mutations also provide a fitness advantage outside of laboratory settings.
Pseudomonas fluorescens 2P24 has demonstrated strong inhibitory activity against Ralstonia solanacearum, Fusarium oxysporum, and Rhizoctonia solani, and was isolated from wheat rhizosphere take-all decline soils in Shandong province, China.
Meta-analyses indicate significant reductions in disease incidence and severity, as well as increased plant growth and yield, particularly with Pseudomonas spp. compared to Bacillus spp. However, it is important to note that these findings are largely derived from controlled experimental conditions, and field-level consistency of biocontrol activity remains variable. While Pseudomonas fluorescens strains have demonstrated biocontrol efficacy, concerns remain regarding their ecological safety within the One Health framework. These include the production of antimicrobial compounds contributing to resistance gene dissemination, variable efficacy across environments and strains, and occasional adverse effects on plant immunity.
Evidence strength: Predominantly experimental (laboratory and greenhouse); meta-analyses provide moderate aggregate evidence for efficacy but with significant heterogeneity across strains and environments.
Research has shown that inoculation of wheat seeds with Pseudomonas fluorescens Ms-01 and Azospirillum brasilense DSM1690, which solubilize phosphates and secrete auxins, strongly increases root and shoot biomass compared to application of the strains separately.
Pseudomonas fluorescens has also been shown to improve peanut plant growth with an increased harvest of approximately 20% (dry weight of nodule, nitrogen content, and phosphorus content in the rhizosphere). One characterized endophytic strain, BsEB-1, possessed three growth-promoting activities — phosphate solubilizing, indoleacetic acid (IAA) production, and siderophore production — but had no nitrogen-fixing activity. This strain could rapidly attach to root hairs and endophytically colonize the roots, and significantly promoted rooting, transplant survival rate, and growth of the host plant.
Plant growth-promoting rhizobacteria (PGPR) such as P. fluorescens may trigger flavonoid biosynthesis as part of an induced systemic response (ISR), given the important role of this pathway in plant defence, causing increased levels of flavonoids in the fruit.
Evidence strength: Moderate — supported by numerous controlled agricultural studies and some field trials. Human clinical evidence is absent; applications are to plants, not to human physiology.
Previous studies have shown the usefulness of two Pseudomonas fluorescens isolates for the biocontrol of saprolegniosis in rainbow trout — a disease caused by a pseudo-fungus affecting freshwater fish — under experimental conditions when they are added to tank water. Investigated mechanisms of action include stimulation of the immune response, competition for binding sites or sources of nutrients, and the production of bioactive substances inhibitory to pathogenic agents.
The stimulation of the innate immune response and the production of siderophores and bioactive substances inhibiting Saprolegnia parasitica present in cells and supernatants of isolates LE89 and LE141 were studied. Regarding the immune response, the only noteworthy findings were an increase in phagocytic activity of macrophages and the concentration of serum proteins when LE141 was administered. Both bacteria produced siderophores.
Evidence strength: Preliminary and experimental (laboratory/aquaculture tank conditions). No controlled human trials exist. Evidence is limited to non-human organisms.
Pseudomonas fluorescens is a common spoilage microorganism in proteinaceous raw foods stored under aerobic refrigerated conditions, such as dairy products, meat, and seafoods. As a spoiler, P. fluorescens can produce ammonia, amine, ketones, aldehydes, esters, organic acids, and non-H₂S sulfides with spoilage off-odors and off-flavors. It also causes spoilage by producing heat-stable lipases and proteases, biofilms, biosurfactants, siderophores, pigments, and quorum-sensing signaling molecules.
Pseudomonas fluorescens is a primary spoilage bacterium in aquatic products. Due to its strong ability to adhere to surfaces and form persistent biofilm, it poses a persistent challenge to food safety.
Evidence strength: Well-established and consistent in the food microbiology literature. This is a safety-relevant finding rather than a therapeutic one.
Pseudomonas fluorescens is increasingly recognized for its bioremediation potential, particularly in the degradation of environmental pollutants such as hydrocarbons. Research into bioremediation applications is ongoing; this is an area distinct from dietary supplement use, and evidence pertains to environmental rather than human health applications.
It is essential to emphasize that Pseudomonas fluorescens is not an approved or established dietary supplement for human internal use by any major regulatory body (including the U.S. FDA, EFSA, or WHO). The associations with human body systems documented in the scientific literature are primarily in the context of opportunistic infection, food safety, or — at the level of preliminary research — potential microbiome relationships. Its use is principally as an agricultural bioinoculant.
Pseudomonas fluorescens is not generally considered a bacterial pathogen in humans; however, multiple culture-based and culture-independent studies have identified it at low levels in the indigenous microbiota of various body sites. While far less virulent than P. aeruginosa, P. fluorescens can cause acute opportunistic infections in humans and has been reported in clinical samples from the mouth, stomach, and lungs.
P. fluorescens can cause acute infections in humans and has been reported in clinical samples from the mouth, stomach, and lungs. The most common site of P. fluorescens infection is the bloodstream. Most reported cases have been iatrogenic, with bacteremia attributable either to transfusion of contaminated blood products or to use of contaminated equipment associated with intravenous infusions.
While not suspected of being an etiologic agent of pulmonary disease, P. fluorescens is routinely cultured at a low frequency from clinically indicated respiratory samples. The significance of this finding in terms of causation of respiratory disease remains under investigation.
P. putida and P. fluorescens are Gram-negative bacillus bacteria that are ubiquitous in soil and water but have been reported as opportunistic human pathogens capable of causing nosocomial infections, especially in immunocompromised patients. Pseudomonas fluorescens and Pseudomonas putida are uncommon causes of skin and soft tissue infections. They are rarely associated with bacteremia and fatality. When presenting with sepsis or shock, patients are usually immunocompromised.
Some strains of Pseudomonas fluorescens are reported to be opportunistic pathogens in fish under stress from transportation or those cultivated in commercial hatcheries. Conversely, specific isolates have been studied as beneficial probiotic agents in fish species in the context of biocontrol, as described in Section 5.3.
There are no established human dietary supplement dosages for Pseudomonas fluorescens in any peer-reviewed clinical pharmacology literature, and no regulatory body has established a recommended daily intake for humans. Dosage information documented in the scientific literature pertains exclusively to agricultural and aquaculture applications.
No controlled human clinical trials have been published that evaluate any form of P. fluorescens as a human probiotic or dietary supplement at any dose. The absence of such data means that no safe or effective human dosage range can be stated.
The species Pseudomonas fluorescens is considered to be an opportunistic pathogen, and some strains have been reported to infect humans with compromised immunity. Human outbreaks have been associated with contaminated medical devices and fluids. The key human health effects of concern are associated with contamination of blood products and medical devices with Pseudomonas fluorescens.
Pseudomonas fluorescens is a water-borne pathogen that has been associated with outbreaks from transfusion of contaminated blood products or medical equipment. In October 1980, two units of blood contaminated with Pseudomonas fluorescens caused septic transfusion reactions in two recipients at a Chicago hospital; one patient died. Both units had been purchased from the same blood center. From 2004 to 2006, an outbreak of P. fluorescens in the United States involved 80 patients in six states. The source of the infection was contaminated heparinized saline flushes being used with cancer patients.
Laboratory studies showed that prolonged storage was a risk factor associated with clustering of contamination cases. Small inocula of P. fluorescens proliferated in refrigerated fresh whole blood and reached 10⁶ to 10⁷ colony-forming units per milliliter seven days after incubation.
Pseudomonas fluorescens and related species have been reported to cause bloodstream, urinary, pulmonary, cerebrospinal, joint-fluid, skin, and soft-tissue infections. The Pseudomonas fluorescens complex consists of environmental and, in some cases, pathogenic opportunistic microorganisms.
Other members of the genus Pseudomonas might act as opportunistic pathogens, causing infections mainly in immunocompromised patients or individuals subjected to invasive medical procedures. Pseudomonas fluorescens and related species have been reported to cause bloodstream, urinary, pulmonary, cerebrospinal, joint-fluid, skin, and soft-tissue infections. Risk of infection is considerably elevated in individuals with cancer, HIV/AIDS, or those undergoing immunosuppressive therapy.
Pseudomonas spp. are ubiquitous microorganisms that exhibit intrinsic and acquired resistance to many antimicrobial agents. Pseudomonas aeruginosa is the most studied species of this genus due to its clinical importance. In contrast, the Pseudomonas fluorescens complex consists of environmental and, in some cases, pathogenic opportunistic microorganisms. Recent studies have reported P. fluorescens members that are resistant to clinically relevant antibiotics such as piperacillin, aztreonam, ceftazidime, carbapenems, and colistin.
However, Pseudomonas fluorescens strain ATCC 13525 is susceptible to several antibiotics. Susceptibility is highly strain-dependent, and resistance profiles vary considerably across environmental and clinical isolates.
While Pseudomonas fluorescens strains have demonstrated biocontrol efficacy, concerns remain regarding their ecological safety within the One Health framework. These include the production of antimicrobial compounds contributing to resistance gene dissemination, variable efficacy across environments and strains, and occasional adverse effects on plant immunity.
The advantages associated with industrial and environmental applications involving Pseudomonas species need to be balanced with the potential risk of human health effects. One aspect of this stewardship is timely hazard assessment of individual strains and oversight of their intended use in biotechnology applications to limit environmental and commercial dissemination of potentially pathogenic strains.
Based on available information, the risk to human health from Pseudomonas fluorescens strain ATCC 13525 is low, and there is low risk of harm to organisms and the broader integrity of the environment from this specific strain. However, this assessment applies to a single, well-characterized strain evaluated under the Canadian Environmental Protection Act framework and cannot be generalized to all strains or all applications. P. fluorescens does not hold GRAS (Generally Recognized As Safe) status from the U.S. FDA for human consumption, and it is not included among the approved probiotic microorganisms recognized by the European Food Safety Authority (EFSA) for use in food.
As a food spoilage agent, P. fluorescens produces ammonia, amines, ketones, aldehydes, esters, organic acids, and non-H₂S sulfides with spoilage off-odors and off-flavors, and also causes spoilage by producing heat-stable lipases and proteases, biofilms, biosurfactants, siderophores, pigments, and quorum-sensing signaling molecules. These heat-stable enzymes can persist even after pasteurization or cooking, contributing to off-flavor and shortened shelf life in dairy and meat products, a consideration with direct relevance to food safety.
Pseudomonas fluorescens occupies a well-established scientific position as a plant-growth-promoting rhizobacterium (PGPR) and agricultural biocontrol agent, with a substantial body of laboratory and field research supporting its roles in phosphate solubilization, siderophore-mediated iron competition, auxin production, and induced systemic resistance in crop plants. Its utility as an aquaculture probiotic in fish species has preliminary experimental support.
There is, however, a complete absence of human clinical trials evaluating P. fluorescens as a probiotic or dietary supplement for any human health indication. No dosage, safety profile, or therapeutic indication for human use has been established in peer-reviewed clinical pharmacology literature. The organism's classification as an opportunistic pathogen in immunocompromised humans — with documented fatal transfusion-related outbreaks and reported clinical infections across multiple organ systems — represents a significant safety concern that would need to be rigorously addressed before any human supplemental use could be scientifically or regulatorily justified.
Current research gaps include: the characterization of safe, non-pathogenic strains for any potential human microbiome applications; the development of strain-specific safety and efficacy data in human populations; and mechanistic studies on potential interactions with the human gut microbiome. The ecological dissemination of antibiotic resistance genes by P. fluorescens in agricultural settings is an area of ongoing public health concern.
Health conditions that Pseudomonas fluorescens may help support.
Body systems that Pseudomonas fluorescens may help support.
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