Exogenous Indole-3-Acetic Acid Production and Phosphate Solubilization by Chlorella vulgaris Beijerinck in Heterotrophic Conditions

The role of soil-borne microalgae in the edaphic ecosystem is barely known, especially concerning their plant-growth-promoting traits, although they are used as biofertilizers. In this study, a microalgal strain isolated from soil cultivated with maize was evaluated as an exogenous producer of indole-3-acetic acid (IAA) in potato dextrose broth-PD-and sugarcane molasses, with or without tryptophan, and phosphate solubilizer (in 'National Botanical Research Institute's phosphate'-NBRIP-medium with tricalcium phosphate)with plant-growth-promoting traits, under heterotrophic conditions. The species of microalga was identified, by sequencing the ITS region in the rDNA and the morphological characteristics, as Chlorella vulgaris. Its growth was significantly higher in the PD medium, with slower growth in molasses. The addition of tryptophan did not influence the growth of C. vulgaris in either medium, but it increased the production of IAA, mainly in the PD medium, to 265 mu g mL(-1). The microalga grew in the medium with insoluble phosphate, releasing phosphorus into the medium (30 mg L-1 after 72 h). This is the first study on the application of C. vulgaris as a phosphate solubilizer. More studies should be performed on C. vulgaris as a prospective plant-growth-promoting microorganism, besides its ability to produce exogenous IAA, and further investigations should be conducted on developing inexpensive culture media.