IngredientsScientific name: Azotobacter chroococcum Beijerinck 1901. The genus name derives from the Greek azote (nitrogen) and bacter (rod/staff), reflecting its defining role as a nitrogen-fixing bacterium. The species epithet chroococcum refers to its coccoid-to-rod morphology and the brown pigment it characteristically produces.
Taxonomic placement: Azotobacter belongs to the family Pseudomonadaceae/Azotobacteraceae and class Gammaproteobacteria. Members of the genus are Gram-negative, free-living, aerobic, soil-dwelling, oval or spherical bacteria that form thick-walled cysts as a means of asexual reproduction under favorable conditions; there are seven known species in the genus.
Morphology and ecology: Azotobacter chroococcum is a microaerophilic plant growth-promoting rhizobacterium (PGPR), which is bacillus in shape and Gram-negative. As a mesophile, this bacterium grows best in moderate-temperature soils and requires a neutral pH environment. It can be found in alkaline to neutral soils, and in arable soils, A. chroococcum is the most commonly occurring species.
Pigment production: It forms a dark-brown, water-soluble pigment melanin at high levels of metabolism during the fixation of nitrogen, which is thought to protect the nitrogenase system from oxygen.
Natural source and habitat: Azotobacter chroococcum is a widespread free-living soil bacterium within the genus Azotobacter, known for assimilation of atmospheric nitrogen and subsequent conversion into nitrogenous compounds, which henceforth enrich the nitrogen content of soils. The species has been isolated from soils and the rhizosphere of various plants.
Common forms and preparations in use: A. chroococcum is commercially available in several agricultural formulations. Owing to their ability to fix molecular nitrogen and therefore increase soil fertility and stimulate plant growth, Azotobacter species are widely used in agriculture, particularly in nitrogen biofertilizers such as azotobacterin. They are also used in production of alginic acid, which is applied in medicine as an antacid, in the food industry as an additive to ice cream, puddings, and creams. The bacterium itself is sold primarily as a powder, liquid inoculant, or carrier-based granular preparation for agricultural application. Laboratory reference strains held by depositories such as ATCC are designated as intended for laboratory research use only and not for any human or animal therapeutic use or any human or animal consumption.
The genus Azotobacter was discovered in 1901 by Dutch microbiologist and botanist Martinus Beijerinck, who was one of the founders of environmental microbiology; he selected and described the species Azotobacter chroococcum — the first aerobic, free-living nitrogen fixer.
The genus Azotobacter has been used as a biofertilizer since more than a century, dating to Gerlach and Vogel (1902). Gerlach and Vogel (1902) initiated work on artificial inoculation of seeds with A. chroococcum and reported an increase of dry matter in buckwheat by 42 percent. Kostychev et al. (1926) recommended the use of Azotobacter to improve the growth of agricultural plants and soil properties.
Azotobacters are the previously discovered and studied free-living, obligately aerobic diazotrophs, which have been used as nitrogen fixation fertilizer for more than a century. Their application in Soviet and Eastern European agriculture, under the trade name "azotobacterin," represented one of the earliest large-scale deployments of a live bacterial agricultural supplement. A. chroococcum and A. vinelandii have long been used as soil and seed inoculants.
In the Indian subcontinent, A. chroococcum has been extensively integrated into agricultural practice for decades. The possibility of using Azotobacter chroococcum in research experiments as a microbial inoculant through production of growth substances and their effects on plants has markedly enhanced crop production in agriculture. The Azotobacter genus was discovered in 1901 by Dutch microbiologist and botanist Beijerinck et al., the founder of environmental microbiology. The traditional use of A. chroococcum across multiple cultures has been fundamentally agricultural and soil-fertility-focused rather than medicinal or dietary.
There is no documented tradition of A. chroococcum being used in human medicine, phytotherapy, or as a dietary supplement in any culture prior to the modern biotechnology era. Its historical use is confined to agronomic applications — principally as a seed inoculant and soil amendment to reduce dependence on synthetic nitrogen fertilizers.
A. chroococcum produces a diverse array of bioactive metabolites. These are primarily characterized in the context of plant growth promotion and soil biology, though several classes of compounds have broader biochemical relevance.
Biological nitrogen fixation (BNF) is a microbial-mediated process based upon an enzymatic "nitrogenase" conversion of atmospheric nitrogen (N₂) into ammonium readily absorbable by roots. For Azotobacter nitrogen fixation, previous evidence suggested that nif-A acted as an activator of nitrogenase expression, while nif-L acted as an anti-activator; with the presence of oxygen or ammonium, nif-L interacts with nif-A and blocks its function. The isolated culture of Azotobacter fixes about 10 mg N per g of carbon source in vitro.
Azotobacter species stimulate plant growth through phytohormone synthesis, including indole acetic acid, cytokinins, and gibberellins.
B-group vitamins such as pantothenic acid, biotin, niacin, and riboflavin are produced by A. chroococcum strain H23 (CECT 4435). Phytohormone synthesis in Azotobacter is also associated with the production of extracellular compounds such as riboflavin, vitamin B12, biotin, thiamine, pyridoxine, cyanocobalamin, folic acid, and pantothenic acid.
Cyanocobalamin (Vitamin B12): A strain of Azotobacter chroococcum was found to produce a considerable amount of cyanocobalamine, especially when cultivated in a medium enriched with 0.3% ammonium chloride; maximal production of the vitamin was achieved after six days of incubation in static cultures. The genus Azotobacter is listed among reported cobalamin-producing natural bacterial genera.
At diazotrophic conditions in glucose-supplemented culture media, Azotobacter species produce different amino acids such as tryptophan, lysine, glutamic acid, and methionine. A. vinelandii and A. chroococcum are recognized for the production of aspartic acid, serine, glutamic acid, glycine, histidine, threonine, arginine, alanine, proline, cysteine, valine, lysine, isoleucine, phenylalanine, tyrosine, methionine, and leucine.
Alginate is a linear anionic heteropolysaccharide with a chemical structure consisting of 1,4-linked subunits of β-D-mannuronic acid (M) and its C-5 epimer α-L-guluronic acid (G); the monomer composition and molecular weight of alginates affect their properties and influence their use in the food and pharmaceutical industries. Bacteria produce alginate as an exopolysaccharide in response to certain physiological processes such as surface/cell adhesion, resistance to cytotoxic compounds, and dormant cell differentiation.
The nitrogen-fixing bacterium A. chroococcum is capable of producing siderophores and positively affecting the growth of various crops under different soil types and climatic conditions. Azotobacter produces antifungal antibiotic compounds (2,3-dihydroxybenzoic acid, aminochelin, azotochelin, protochelin, and azotobactin), which inhibit the growth of plant pathogenic fungi, viz., Aspergillus, Fusarium, Curvularia, Alternaria, and Helminthosporium.
A novel glycoside hydrolase family 70 enzyme (GtfD) has been described from the nitrogen-fixing Gram-negative bacterium Azotobacter chroococcum. This enzyme converts starch into a reuteran-like α-glucan polymer regarded as a health-promoting food ingredient. This finding remains at the preclinical, enzymatic-characterization stage.
The secondary metabolites of Azotobacter include poly-hydroxybutyrate (PHB), produced for large-scale production of alginic acid, along with auxins, vitamins, amino acids, and provision of iron to plants via siderophores. PHB is a biodegradable biopolymer with applications in biomaterials research, though no human dietary or clinical evidence has been established for the PHB fraction derived from A. chroococcum specifically.
Biological nitrogen fixation refers to a microbial-mediated process based upon an enzymatic nitrogenase conversion of atmospheric nitrogen (N₂) into ammonium readily absorbable by roots; N₂-fixing microorganisms collectively termed diazotrophs are able to fix biologically N₂ in association with plant roots. A. chroococcum is the first described aerobic free-living nitrogen fixer; these bacteria utilize atmospheric nitrogen gas for their cell protein synthesis. This cell protein is then mineralized in soil after the death of Azotobacter cells, thereby contributing to the nitrogen availability of crop plants.
Azotobacter spp. are non-symbiotic heterotrophic bacteria capable of fixing an average 20 kg N/ha/per year; bacterization helps to improve plant growth and to increase soil nitrogen through nitrogen fixation by utilizing carbon for its metabolism.
Being soil bacteria, the Azotobacteria genus synthesizes auxins, cytokinins, and GA-like substances, and these growth materials are primary substances controlling enhanced growth; these hormonal substances, which originate from the rhizosphere or root surface, affect the growth of closely associated higher plants. In vitro experiments have confirmed that A. chroococcum produces phytohormones (auxin and gibberellic acid), fixes nitrogen efficiently, forms biofilms, and stimulates early wheat seedling development.
Strains of A. chroococcum are capable of fixing nitrogen, solubilizing phosphorus, synthesizing indole compounds, and producing hydrolytic enzymes. Seeds inoculated with Azotobacter help in uptake of N and P along with micronutrients like Fe and Zn; in wheat, these strains can potentially be used to improve wheat nutrition.
A. chroococcum forms a dark-brown, water-soluble pigment melanin which occurs at high levels of metabolism during biological nitrogen fixation; this process is thought to protect the nitrogenase system from oxygen. Melanin produced by this bacterium can also bind to heavy metals, subsequently protecting A. chroococcum, which may be useful for removing heavy metals from polluted soils.
In Adhatoda vasica leaf discs, multiple Azotobacter chroococcum and Pseudomonas putida strains were shown to increase the accumulation of pyrroloquizoline alkaloids, including vasicine, vasicinone, vasicine acetate, and related compounds, which are the most bioactive phytochemicals in A. vasica with anti-inflammatory and antimicrobial activities. This represents an indirect mechanism by which A. chroococcum inoculation may enhance the pharmacological content of medicinal plant material, though this finding is limited to in vitro/biotization studies and has not been translated to human clinical outcomes.
The overwhelming body of peer-reviewed evidence for A. chroococcum concerns its role in soil biology and crop production. In published reviews, the importance of Azotobacter species has been highlighted as both important free-living N₂-fixing bacteria and potential bacterial biofertilizer with proven efficacy for plant nutrition and biological soil fertility.
Research has evaluated whether application of plant growth-promoting (rhizo)bacteria might reduce nitrogen fertilization doses in cotton, using strains Azotobacter chroococcum AC1 and AC10 for their proven ability to promote seed germination and cotton growth; these microorganisms were characterized by their plant growth-promoting activities, and a glasshouse study was conducted to evaluate the plant growth-promoting ability of these strains with reduced doses of urea fertilization. After 12 weeks, the glasshouse experiment showed that cotton growth was positively influenced due to bacterial inoculation with respect to chemical fertilization; microbial inoculation further influenced plant biomass (p<0.05) more than nitrogen content; similar results without significant statistical differences were observed among bacterial co-inoculation plus 50% urea and 100% fertilization; findings suggest that co-inoculation of A. chroococcum strains allows for a reduction of nitrogen fertilization doses up to 50% on cotton growth.
As a biostimulant, the rhizobacteria Azotobacter chroococcum along with other Azotobacter species is well studied and proved for their ability to enhance growth and tolerance to drought stress; research on A. chroococcum on crop productivity has clearly demonstrated its value in improving plant nutrition and amelioration of soil fertility; in a study with sweet potatoes, application of A. chroococcum enabled nitrogen fertilization levels to be reduced by 25%; however, a study with wheat clearly demonstrated that whilst Azotobacter species may enhance growth and stress tolerance, nutrient availability, soil, and environmental conditions heavily influence these responses.
Evidence strength (agricultural): Strong and consistent for nitrogen fixation and biofertilizer effects across multiple controlled glasshouse and field studies. Results vary considerably by strain, crop species, soil type, and environmental conditions. This body of evidence is robust within the agricultural sciences but is not directly applicable to human health.
A 2024 study published in Polymers (Basel) investigated alginate extracted from Azotobacter sp. loaded into selenium nanoparticles. The work aimed to extract alginate from Azotobacter sp., fabricate selenium nanoparticles using ascorbic acid as a reducing agent (As/Se-NPs), and load the extracted alginate with selenium nanoparticles (Alg-Se-NCMs); the compounds were characterized by TEM, EDX, UV–Vis spectrophotometry, FT-IR, and zeta potential; antifungal activities were investigated against human pathogen fungi that cause skin infection such as Aspergillus niger, Aspergillus fumigatus, Cryptococcus neoformans, Candida albicans, and Penicillium marneffei. The anticancer activities were also determined in this in vitro study.
An earlier study on A. chroococcum strain 92 reported that it produces an antibiotic active against phytopathogenic fungi. The strain was obtained as a result of natural selection and produces an antibiotic active against phytopathogenic fungi; the antibiotic was isolated from the bacterial mass of the culture with ethanol extraction followed by column and thin-layer chromatography on silica gel; the pure antibiotic is a viscous oily substance of a yellowish colour, readily soluble in the majority of organic solvents, not soluble in water, and readily oxidized by air oxygen.
Evidence strength (anticancer/antifungal): Entirely preclinical; limited to in vitro and nanoparticle-based experiments. No human or animal clinical trials exist evaluating A. chroococcum or its extracts for cancer treatment or prevention. These findings cannot be extrapolated to clinical utility in humans.
Multiple Azotobacter chroococcum strains were shown to increase the accumulation of pyrroloquizoline alkaloids in Adhatoda vasica hairy roots; the bacteria-enhanced production of pyrroloquizoline alkaloids was attributed to the increased activity of anthranilate synthase, which functions as a rate-limiting factor for biosynthesis.
Evidence strength: This mechanism is limited to in vitro biotization studies of hairy-root cultures. It does not establish any direct human health outcome from consuming A. chroococcum and is mentioned here as a laboratory-level area of scientific inquiry only.
Azotobacter chroococcum is also a possible asset for bioremediation; melanin produced by this bacterium can bind to heavy metals, subsequently protecting A. chroococcum, which may be useful for removing heavy metals from polluted soils; since this bacterium promotes plant growth through nitrogen fixation, it can also reduce the amount of nitrogen that has to be added to fields, which can reduce the amount of nitrogen runoff.
Evidence strength: Laboratory and field-level evidence. No human clinical evidence exists. This application is environmental in nature.
It is critical to note at the outset that A. chroococcum does not have a documented, evidence-supported role as a human dietary supplement in any clinical or regulatory sense. The body-system associations described below reflect areas of basic or preclinical scientific interest rather than established human health indications.
There is no established or approved human therapeutic dosage for A. chroococcum as a dietary supplement. The following information reflects dosages and formulations reported in peer-reviewed agricultural literature only.
No human clinical trials have established safe or effective doses of A. chroococcum for any health purpose. No official body — including the NIH Office of Dietary Supplements, NCCIH, WHO, EMA, or EFSA — has issued a monograph or recommended intake for A. chroococcum as a dietary supplement or therapeutic agent.
Laboratory reference culture collections such as ATCC explicitly state that Azotobacter chroococcum products are intended for laboratory research use only and are not intended for any animal or human therapeutic use, any human or animal consumption, or any diagnostic use. A. chroococcum is not listed on the FDA's GRAS (Generally Recognized as Safe) registry as a food ingredient for human consumption, nor does it appear in any approved pharmacopoeial monograph (USP, European Pharmacopoeia, WHO Monographs) for human medicinal use.
A. chroococcum is a Gram-negative bacterium. Gram-negative bacterial cell walls contain lipopolysaccharide (LPS), also known as endotoxin, which is a potent immunostimulatory and potentially pyrogenic compound in mammalian systems. Any preparation of A. chroococcum for potential human use would require rigorous testing for endotoxin content, though no such human-facing safety data have been published in peer-reviewed sources.
All tested isolates of A. chroococcum were sensitive to the β-lactam antibiotic meropenem; however, high intraspecies differentiation was observed concerning resistance to other antibiotics. This indicates that antibiotic sensitivity profiles differ markedly between strains, a factor relevant to any discussion of safety in clinical or supplemental contexts.
All tested strains of A. chroococcum were resistant to Pb²⁺, whereas other metals (Cd²⁺, Cu²⁺, Fe³⁺, Mn²⁺, Zn²⁺) caused growth inhibition of the analyzed strains. The metal-resistance profile of a given strain may influence its behavior in different soil environments; this is not a direct human safety concern but is relevant to agricultural use near food crops.
The herbicide linuron did not inhibit the growth of A. chroococcum in any of the concentrations tested; all other tested pesticides caused growth inhibition only in concentrated forms. This finding has implications for the viability of A. chroococcum biofertilizer applications in conventionally managed agricultural systems.
A systematic search of PubMed and PMC finds no published human clinical trials, randomized controlled trials, systematic reviews, or safety studies evaluating A. chroococcum as a dietary supplement in humans. No adverse event reports or pharmacovigilance data pertaining to human ingestion of this organism are available in peer-reviewed form. The absence of such data represents a significant knowledge gap and means that no evidence-based statement can be made about the safety, tolerability, or appropriate dose of A. chroococcum for human consumption.
The evidence base for Azotobacter chroococcum as a soil bacterium and agricultural biofertilizer is extensive, peer-reviewed, and well-established over more than a century of research. Evidence for any direct human health benefit — whether from ingestion as a probiotic, dietary supplement, or pharmaceutical preparation — is entirely absent at the level of human clinical research. The few laboratory studies exploring anticancer or antifungal activities of A. chroococcum-derived compounds involve nanoparticle drug-delivery constructs or in vitro cell assays, and cannot be used to support health claims for the live organism or whole-cell preparations. All phytohormone and vitamin production data are microbiological findings obtained under laboratory fermentation conditions, with no direct translation to human dietary supplementation established in peer-reviewed literature.
Any representation of A. chroococcum as a human dietary supplement should be distinguished clearly from its well-characterized role as an agricultural microorganism, and any health claims would currently lack the evidentiary foundation required by regulatory authorities in the United States, European Union, or internationally.
Health conditions that Azotobacter chroococcum may help support.
Body systems that Azotobacter chroococcum may help support.
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