Effect of salinity and biopesticide on Arthrospira platensis mass culture growth, metabolites, and bacterial diversity

Arthrospira platensis mass culture contamination is a recurring concern. Salinity alteration appears to be a promising approach, given that A. platensis can withstand various salinities. In addition, biopesticide is also expected to eliminate the bacteria. Therefore, it is critical to investigate the effects of salinity and biopesticide on the growth, nutritional value, and bacterial diversity of A. platensis mass culture. A completely randomized design was used, with five salinity treatment levels: 5 ppt (S5B), 10 ppt (S10B), 15 ppt (S15B), 20 ppt (S20B), and 25 ppt (S25B), with 0.5 ml/L of biopesticide Azadirachta indica applied on days 2 and 4. The growth rate was calculated using daily density and biomass, and on day 7, carbohydrates, proteins, lipids, and pigments were determined. Furthermore, the contamination test and bacterial diversity were determined using Total Plate Count and Next-Generation Sequencing, respectively. The results showed that the S15B had the fastest growth rate and the largest carbohydrate content. However, S5B produced the best results in terms of protein, chlorophyll, and phycocyanin content, while S25B produced the most carotene and lipids. Proteobacteria were the most abundant in all NGS samples. The number of OTU treatments obtained for A (NCD7), B (NCD0), and C (S15BD7) were 646, 636, and 286, respectively. Moreover, C (S15BD7) was the most effective treatment to reduce bacterial diversity contamination, in which several bacterial diversity, including Acidobacteriota, Chloroflexi, Gemmatimonadota, Myxococcota, and Desulfobacterota, were eliminated completely. As a result of the salinity adjustment and the use of biopesticides, the mass culture of A. platensis was able to grow more quickly and contain more nutrients while having less bacterial diversity.