Auxin production of the filamentous cyanobacterial Planktothricoides strain isolated from a polluted river in Vietnam

Cyanobacteria are photosynthetic microorganisms with widespread diversity and extensive global distribution. They produce a wide variety of bioactive substances (e.g., lipopeptides, fatty acids, toxins, carotenoids, vitamins and plant growth regulators) that are released into culture media. In this study, the capability of a cyanobacterial strain of Planktothricoides raciborskii to produce intra- and extracellular auxins was investigated. The filamentous cyanobacterial P. raciborskii strain was isolated from a river in Vietnam, and it was cultivated in the laboratory under the optimum conditions of the BG11 culture medium and a pH of 7.0. The auxins were identified and quantified by the Salkowski colorimetric method and high-performance liquid chromatography coupled with mass spectrometry (HPLC–MS). Colorimetric analysis revealed that P. raciborskii produces extracellular indole-3-acetic acid (IAA) in the absence and presence of l-tryptophan. The maximum extracellular IAA concentration of the culture reached 118 ± 2 μg mL−1, which was supplemented with 900 μg mL−1 of l-tryptophan. HPLC–MS analysis revealed that the isolated cyanobacteria accumulate other plant-growth-promoting hormones besides IAA, such as indole-3-carboxylic acid (ICA), indole-3 butyric acid (IBA) and indole propionic acid (IPA). This is the first report on the production of auxins in an isolated strain of cyanobacteria Planktothricoides from a polluted river. The capability of producing auxins makes the P. raciborskii strain an appropriate candidate for the formulation of a biofertilizer. [Display omitted] •Planktothricoides raciborskii was isolated from a polluted river in Vietnam and cultured in BG 11 medium.•Four Auxins (IBA, IPA, ICA, IAA) were found in the isolated P. raciborskii strain by HPLC-ESI-MS/MS analysis.•Increased levels of IAA was observed in P. raciborskii strain under supplementation of l-tryptophan.