Pseudomonas fluorescens

The microorganism that works for you.

What is Pseudomonas fluorescens?

Pseudomonas fluorescens is a common colonizer of soil, plants, and water. This nonpathogenic saprophytic bacteria is gram-negative and easily identified under a microscope by its rod shape. It has multiple flagella and an extremely versatile metabolism. The flagella on this microorganism allow for mobility in soil and water. Some strains of P. fluorescens can use nitrate instead of oxygen during cellular respiration; however, most are obligate aerobes, meaning this organism requires oxygen for cellular respiration.

P. fluorescens prefer temperatures between 25-30 degrees celsius. They are non-fermenters that produce heat-stable lipases and proteases, which break down phosphoproteins like the proteins found in mammalian milk. This enzymatic breakdown causes slime and protein coagulation, leading to milk spoilage.

How Does P. fluorescens Affect Seed Development?

Seeds pre-treated with P. fluorescens and S. marcescens have repeatedly reduced symptom development and viral infection in many crop plants, including tomatoes and cucumbers. Seeds have remained resistant up to 30 days after inoculation with P. fluorescens.

Some organic farmers utilized seed inoculation practices with legumes to ensure proper nitrogen fixation.

How Does P. fluorescens Manage Crop Pests?

Research shows a 60% reduction in the adult emergence of larval corn worms when managed by P. fluorescens. The overall influence on bacteria-infected larvae growth and development results in smaller adults. The metabolic rates of crop pests are significantly reduced, which leads to decreased overall pathogen population.

How Does P. fluorescens Affect Plant Growth?

P. fluorescens is a common biocontrol agent used to prevent seed and soil-borne pathogens from damaging crops. Biocontrol agents or microbial antagonists are used for protection against the infection of host plants by harmful pathogens. In both field and laboratory trials, studies showed positive results when P. fluorescens was used to control bacterial wilt and blight on potatoes. Successful pathogen resistance was also seen in other plants such as tobacco, radish, cucumber, pearl millet, rice, eucalyptus, and chili. Furthermore, P. fluorescens positively affected seed quality and the reduction of bacterial spot disease.

Photo of P. fluorescens growing on agar, courtesy of Ninjatacoshell, CC BY-SA 3.0, via Wikimedia Commons.

P. fluorescens promotes plant growth while reducing insect and pathogen damage to roots. As they colonize plant roots, plants experience direct and indirect beneficial effects. The root colonizers can solubilize phosphate, thereby increasing phosphate ion availability in the rhizosphere for ease of uptake by the plant. The rhizosphere is the area surrounding the plant roots and is inhabited by a unique population of microorganisms.

Some P. fluorescens species are known siderophore producers, low-molecular-weight molecules that chelate iron. As P. fluorescens releases siderophores, it increases iron availability for itself, other microbes, as well as for plants. The siderophores produced are crucial in stimulating plant growth while combating various plant diseases.

Further Reading

Bong, C. F. J., & Sikorowski, P. P. (1991). Effects of cytoplasmic polyhedrosis virus and bacterial contamination on growth and development of the corn earworm, Helicoverpa Zea (Lepidoptera: Noctuidae). Journal of Invertebrate Pathology, 57(3), 406–412. https://doi.org/10.1016/0022-2011(91)90145-g

Ciampi-Panno, L., Fernandez, C., Bustamante, P., Andrade, N., Ojeda, S., & Contreras, A. (1989). Biological control of bacterial wilt of potatoes caused By Pseudomonas solanacearum. American Potato Journal, 66(5), 315–332. https://doi.org/10.1007/bf02854019

Das, A., Prasad, R., Srivastava, A., Giang, P. H., Bhatnagar, K., & Varma, A. (n.d.). Fungal siderophores: Structure, functions and regulation. Soil Biology, 1–42. https://doi.org/10.1007/978-3-540-71160-5_1

David, B. V., Chandrasehar, G., & Selvam, P. N. (2018). Pseudomonas fluorescens: A plant-growth-promoting Rhizobacterium (PGPR) with potential role in biocontrol of pests of crops. Crop Improvement Through Microbial Biotechnology, 221–243. https://doi.org/10.1016/b978-0-444-63987-5.00010-4

Ganeshan, G., & Manoj Kumar, A. (2005). Pseudomonas fluorescens, a potential bacterial antagonist to control plant diseases. Journal of Plant Interactions, 1(3), 123–134. https://doi.org/10.1080/17429140600907043

Lavakush, Yadav, J., Verma, J. P., Jaiswal, D. K., & Kumar, A. (2014). Evaluation of PGPR and different concentration of phosphorus level on plant growth, yield and nutrient content of rice (Oryza sativa). Ecological Engineering, 62, 123–128. https://doi.org/10.1016/j.ecoleng.2013.10.013

Maurhofer, M. (1994). Induction of systemic resistance of tobacco to tobacco necrosis virus by the root-colonizing Pseudomonas fluorescens strain cha0: Influence of thegacagene and of pyoverdine production. Phytopathology, 84(2), 139. https://doi.org/10.1094/phyto-84-139

Maurhofer, M., Reimmann, C., Schmidli-Sacherer, P., Heeb, S., Haas, D., & Défago, G. (1998). Salicylic acid biosynthetic genes expressed in Pseudomonas fluorescens strain P3 improve the induction of systemic resistance in tobacco against tobacco necrosis virus. Phytopathology®, 88(7), 678–684. https://doi.org/10.1094/phyto.1998.88.7.678

Prasad, R., Kumar, M., & Varma, A. (2014). Role of PGPR in soil fertility and Plant Health. Soil Biology, 247–260. https://doi.org/10.1007/978-3-319-13401-7_12

Raupach, G. S. (1996). Induced systemic resistance in cucumber and tomato against Cucumber Mosaic cucumovirus using plant growth-promoting rhizobacteria (PGPR). Plant Disease, 80(8), 891. https://doi.org/10.1094/pd-80-0891

Stock, C. A., McLoughlin, T. J., Klein, J. A., & Adang, M. J. (1990). Expression of a Bacillus thuringiensis crystal protein gene in Pseudomonas cepacia 526. Canadian Journal of Microbiology, 36(12), 879–884. https://doi.org/10.1139/m90-152

Vanitha, S. C., Niranjana, S. R., Mortensen, C. N., & Umesha, S. (2009). Bacterial wilt of tomato in Karnataka and its management by Pseudomonas fluorescens. BioControl, 54(5), 685–695. https://doi.org/10.1007/s10526-009-9217-x

Vidhyasekaran, P., Kamala, N., Ramanathan, A., Rajappan, K., Paranidharan, V., & Velazhahan, R. (2001). Induction of Systemic Resistance By Pseudomonas fluorescens pf1 Againstxanthomonas oryzae pv.oryzae in Rice leaves. Phytoparasitica, 29(2), 155–166. https://doi.org/10.1007/bf02983959

Zehnder, G., Kloepper, J., Yao, C., & Wei, G. (1997). Induction of systemic resistance in cucumber against cucumber beetles (Coleoptera: Chrysomelidae) by Plant Growth-promoting rhizobacteria. Journal of Economic Entomology, 90(2), 391–396. https://doi.org/10.1093/jee/90.2.391