The Isolation, Identification, and Analysis of Nutritional Potential of Microalga Spirulina subsalsa and its Cultivation in a Low-Cost Medium

Spirulina, a multicellular filamentous blue-green alga, exhibits a wide range of biological activities and is nutritionally significant. This study aimed to isolate, identify, mass-cultivate, perform nutrient analysis, and formulate a cost-effective medium using waste materials for a less-exploited Spirulina strain in Sri Lanka. The organism was isolated from a pond in Jaffna, Sri Lanka. Zarrouk’s culture medium was used for the isolation and subculturing of Spirulina sp. Mass culturing was carried out in a 15 L tank with half-strength medium concentration under greenhouse conditions. Carbohydrate, lipid, protein, mineral content, and sugars were measured by standard methods. Total Mycrocystin and Cylindrospermopsin content was measured by the ELISA technique. Various media formulations containing cow dung ash, paddy husk ash, and banana pseudo-stem extract were tested for their cultivation. The strain was identified as Spirulina subsalsa at the molecular level using 16S rRNA sequencing. Among the media tested, paddy husk ash medium yielded comparable biomass to that of Zarrouk’s medium. The total carbohydrate, protein, and lipid content of Spirulina biomass were 7.26%, 52.13%, and 12.03%, respectively. Arabinose, Galactose, and Mannose were the main sugars found in the strain. Of the 14 minerals tested, the strain was rich in K (949.99 g kg^-1), Mg (434.88 g kg^-1), and Fe (293.33 g kg^-1).  This study identifies a low-cost medium for cultivating Spirulina subsalsa, highlighting its potential as an alternative nutrient source and biofertilizer.