28/08/2026
The Microbe of the Month is a project presented by The UPLB Microbiological Society. Its goal is to introduce the interesting members of the microbial community. We hope you learn something from our monthly posts and be encouraged to join the conversation about science. This August, letโs get to know ๐ผ๐ฏ๐ค๐จ๐ฅ๐๐ง๐๐ก๐ก๐ช๐ข ๐๐ง๐๐จ๐๐ก๐๐ฃ๐จ๐.
๐ง ๐๐๐๐ญ ๐ญ๐ก๐ ๐๐ข๐๐ซ๐จ๐๐: ๐๐ก๐ ๐๐๐ ๐ข๐๐ข๐๐ง ๐จ๐ ๐ญ๐ก๐ ๐๐จ๐ข๐ฅ!
๐ผ๐ฏ๐ค๐จ๐ฅ๐๐ง๐๐ก๐ก๐ช๐ข ๐๐ง๐๐จ๐๐ก๐๐ฃ๐จ๐ is a free-living, Gram-negative, soil bacterium that colonizes root systems to promote plant growth and development through various mechanisms. While usually found alongside grains such as corn, wheat, and rice, its tricks work on a variety of crop plants. Abra is known for nitrogen-fixation โ converting atmospheric nitrogen (N2) into ammonia for plants to use. Under the microscope, it appears as motile, vibrioid to straight rod-shaped cells. It can grow in both aerobic and anaerobic conditions, but performs nitrogen fixation specifically in microaerophilic (low-oxygen) environments [1].
๐ ๐๐๐ซ๐โ๐ฌ ๐๐ซ๐ข๐ ๐ข๐ง ๐๐ญ๐จ๐ซ๐ฒ
First isolated from Dutch soils in 1925 as ๐๐ฅ๐๐ง๐๐ก๐ก๐ช๐ข ๐ก๐๐ฅ๐ค๐๐๐ง๐ช๐ข, Abra was later rediscovered in Brazilian tropical grasses in 1976. Its unique physiological traits and dynamic nitrogenase activity prompted Tarrand, Krieg, and Dรถbereiner (1978) to reassign it to the ๐ผ๐ฏ๐ค๐จ๐ฅ๐๐ง๐๐ก๐ก๐ช๐ข genus [2]. Since then, Abra has been thoroughly studied and now stands as one of the safest bioinoculants in modern agriculture, with zero pathogenic strains ever recorded.
๐๐๐ง๐ฅ๐จ๐๐ค๐ข๐ง๐ ๐ญ๐ก๐ ๐๐๐๐ซ๐๐ญ ๐๐ฉ๐๐ฅ๐ฅ ๐๐จ๐ซ ๐๐จ๐จ๐ญ ๐๐ซ๐จ๐ฐ๐ญ๐ก!
While famous for its nitrogen-fixing ability, Abraโs true magic lies in its multiple-mechanism approach for plant growth promotion. By producing plant hormones like auxins (IAA), it signals the plant to expand its root surface area with branching root hairs [3,4]. Furthermore, it secretes organic acids and iron-binding molecules (siderophores) to unlock bound soil nutrients like phosphorus and iron [5]. Beyond providing access to nutrients, Abra confers increased tolerance to harsh environmental stresses such as drought and high soil salinity [4].
๐ช๐๐ก๐๐ฉ๐ข๐ง๐ ๐ญ๐ก๐ ๐
๐ฎ๐ญ๐ฎ๐ซ๐ ๐จ๐ ๐
๐๐ซ๐ฆ๐ข๐ง๐
Today, Abra is widely used as a commercial biofertilizer and seed inoculant with strains Ab-V5 and Ab-V6 officially registered in Brazil for application across a variety of crops [4]. Its performance generally depends on inoculum concentration, environmental conditions, and the crop species [3]. That being said, there is still more to discover! Researchers continue to optimize co-inoculation formulas, encapsulation techniques, and genetic stability to maximize Abraโs efficiency in diverse soils [4,6].
Literature Cited
[1] D. Dasgupta, K. Kumar, R. Miglani, R. Mishra, A. K. Panda, and S. S. Bisht, โChapter 1 - Microbial biofertilizers: Recent trends and future outlook,โ in Recent Advancement in Microbial Biotechnology, S. De Mandal and A. K. Passari, Eds., Elsevier, 2021.
[2] J. J. Tarrand, N. R. Krieg, and J. Dรถbereiner, โA Taxonomic Study of the Spirillum Lipoferum Group, With Descriptions of a New Genus, Azospirillum Gen. Nov. And Two Species, Azospirillum Lipoferum (Beijerinck) Comb. Nov. And Azospirillum Brasilense Sp. Nov.,โ Canadian Journal of Microbiology, vol. 24, no. 8, pp. 967โ980, Aug. 1978, doi: 10.1139/m78-160.
[3] M. A. German, S. Burdman, Y. Okon, and J. Kigel, โEffects of Azospirillum Brasilense on Root Morphology of Common Bean ( Phaseolus Vulgaris L.) Under Different Water Regimes,โ Biology and Fertility of Soils, vol. 32, no. 3, pp. 259โ264, Nov. 2000, doi: 10.1007/s003740000245.
[4] R. Pelagio-Flores, G. Ravelo-Ortega, E. Garcรญa-Pineda, and J. Lรณpez-Bucio, โA Century of Azospirillum: Plant Growth Promotion and Agricultural Promise,โ Plant Signaling & Behavior, vol. 20, no. 1, Aug. 2025, doi: 10.1080/15592324.2025.2551609.
[5 ]B. R. Giri, S. Chattaraj, S. Rath, M. M. Pattnaik, D. Mitra, and H. Thatoi, โUnveiling the Molecular Mechanism of Azospirillum in Plant Growth Promotion,โ Bacteria, vol. 4, no. 3, p. 36, Jul. 2025, doi: 10.3390/bacteria4030036.
[6]M. Vincekoviฤ, K. Gaลกpariฤ, N. Jalลกenjak, and N. Hulak, โEncapsulation of Plant Growth-Promoting and Biocontrol Microorganisms: Advances in Formulation Strategies and Future Perspectives for Multifunctional Microbial Consortia,โ Agronomy, vol. 16, no. 16, p. 1597, Aug. 2026, doi: 10.3390/agronomy16161597.
Pub/Design by: Althea Eclipse
Research and Content by: Zaira Rendon
